全文获取类型
收费全文 | 1656篇 |
免费 | 69篇 |
国内免费 | 1篇 |
专业分类
林业 | 109篇 |
农学 | 53篇 |
基础科学 | 18篇 |
282篇 | |
综合类 | 232篇 |
农作物 | 44篇 |
水产渔业 | 122篇 |
畜牧兽医 | 711篇 |
园艺 | 41篇 |
植物保护 | 114篇 |
出版年
2023年 | 11篇 |
2022年 | 15篇 |
2021年 | 24篇 |
2020年 | 40篇 |
2019年 | 46篇 |
2018年 | 39篇 |
2017年 | 33篇 |
2016年 | 43篇 |
2015年 | 27篇 |
2014年 | 32篇 |
2013年 | 62篇 |
2012年 | 96篇 |
2011年 | 105篇 |
2010年 | 55篇 |
2009年 | 63篇 |
2008年 | 125篇 |
2007年 | 107篇 |
2006年 | 101篇 |
2005年 | 81篇 |
2004年 | 101篇 |
2003年 | 91篇 |
2002年 | 82篇 |
2001年 | 16篇 |
2000年 | 16篇 |
1999年 | 26篇 |
1998年 | 13篇 |
1997年 | 17篇 |
1996年 | 18篇 |
1995年 | 17篇 |
1994年 | 9篇 |
1993年 | 11篇 |
1992年 | 8篇 |
1991年 | 10篇 |
1990年 | 11篇 |
1989年 | 9篇 |
1988年 | 7篇 |
1987年 | 8篇 |
1985年 | 9篇 |
1984年 | 8篇 |
1983年 | 9篇 |
1982年 | 8篇 |
1980年 | 10篇 |
1979年 | 8篇 |
1978年 | 8篇 |
1976年 | 6篇 |
1974年 | 6篇 |
1971年 | 5篇 |
1968年 | 7篇 |
1966年 | 7篇 |
1926年 | 5篇 |
排序方式: 共有1726条查询结果,搜索用时 15 毫秒
51.
China holds the greatest proportion of the snow leopard's (Panthera uncia) global range and is central to their conservation. The country is also undergoing unprecedented economic growth, which increases both the threats to the snow leopard and the opportunities for its conservation. In this paper we aim to review published literature (from 1950 to 2014) in English and Mandarin on snow leopard ecology and conservation in China in order to identify thematic and geographic research gaps and propose research priorities. We first retrieved all published items that considered snow leopards in China (n = 106). We extracted from these papers 274 reports of snow leopard presence in China. We then reviewed a subset of papers (n = 33) of this literature, which specifically focused on snow leopard ecology and conservation within China. We introduced a thematic framework that allows a structured and comprehensive assessment of findings. This framework recognizes 4 critical and interrelated topics underpinning snow leopard ecology and conservation: habitat (distribution and protected area coverage); prey (distribution and abundance, predator–prey relationships); human interactions (hunting and trade, livestock interactions and conflicts); and the underlying policy context. Significant gains in knowledge as well as research gaps and priorities are discussed with reference to our framework. The modest quantity and limited scope of published research on the snow leopard in China calls for a continued and intensified effort to inform and support national conservation policies. 相似文献
52.
The objective of the study was to identify risk factors for reintroduction of Actinobacillus pleuopneumoniae and Mycoplasma hyopneumoniae (enzootic pneumonia) onto pig farms in areas in Switzerland that were involved in an eradication programme from 1996 to 1999 and to assess the role of dealers in relation to these reinfections. The study was based on the comparison of pig farms that were reinfected in the year 2000 (cases) and pig farms that remained uninfected in the same area (controls). Additionally, data were collected from Swiss pig dealers and transport companies. Out of a total of 3983 farms, 107 farms were reinfected in the year 2000. The incidences were 0.1% for Actinobacillus pleuopneumoniae and 2.6% for Mycoplasma hyopneumoniae (enzootic pneumonia). Compared to reinfection rates prior to the eradication programme, this is a considerable reduction. Statistically significant risk factors for the reinfection were 'finishing farm', 'large mixed breeding-finishing farm', 'reinfected neighbour' and 'parking site for pig transport vehicles close to the farm'. Pig farmers that purchased pigs from only one supplier per batch had a lower risk of reintroducing infection (protective factor). As long as infected and uninfected regions co-exist in Switzerland, direct and indirect contact between farms, pig herds and slaughter sites via transport vehicles are a major pathway of disease spread. Risk management measures linked to these contacts are therefore of key importance. The survey of dealers indicated various areas for improvement such as strategic planning of pick-up routes or cleaning and disinfecting of trucks. 相似文献
53.
Major outer membrane proteins of Brucella spp.: past,present and future 总被引:16,自引:0,他引:16
The major outer membrane proteins (OMPs) of Brucella spp. were initially identified in the early 1980s and characterised as potential immunogenic and protective antigens. They were classified according to their apparent molecular mass as 36–38 kDa OMPs or group 2 porin proteins and 31–34 and 25–27 kDa OMPs which belong to the group 3 proteins. The genes encoding the group 2 porin proteins were identified in the late 1980s and consist of two genes, omp2a and omp2b, which are closely linked in the Brucella genome, and which share a great degree of identity (>85%). In the 1990s, two genes were identified coding for the group 3 proteins and were named omp25 and omp31. The predicted amino acid sequences of omp25 and omp31 share 34% identity. The recent release of the genome sequence of B. melitensis 16 M has revealed the presence of five additional gene products homologous to Omp25 and Omp31. The use of recombinant protein technology and monoclonal antibodies (MAbs) has shown that the major OMPs appear to be of little relevance as antigens in smooth (S) B. abortus or B. melitensis infections i.e. low or no protective activity in the mouse model of infection and low or no immunogenicity during host infection. However, group 3 proteins, in particular Omp31, appear as immunodominant antigen in the course of rough (R) B. ovis infection in rams and as important protective antigen in the B. ovis mouse model of infection. The major OMP genes display diversity and specific markers have been identified for Brucella species, biovars, and strains, including the recent marine mammal Brucella isolates for which new species names have been proposed. Recently, Omp25 has been shown to be involved in virulence of B. melitensis, B. abortus and B. ovis. Mutants lacking Omp25 are indeed attenuated in animal models of infection, and moreover provide levels of protection similar or better than currently used attenuated vaccine strain B. melitensis Rev.1. Therefore, these mutant strains appear interesting vaccine candidates for the future. The other group 3 proteins identified in the genome merit also further investigation related to the development of new vaccines. 相似文献
54.
Zur G Ihrke PJ White SD Kass PH 《Veterinary therapeutics : research in applied veterinary medicine》2002,3(1):88-96
Antihistamines were prescribed for 178 of 271 dogs with a diagnosis of atopic dermatitis at the Veterinary Medical Teaching Hospital of the University of California, Davis from 1992 to 1998. Fifty-four percent of 166 dogs given antihistamines responded favorably to these treatments, with 27% of the responses rated as good and 27% rated as moderate. Diphenhydramine and hydroxyzine were the most commonly used antihistamines and were the most frequently effective. Chlorpheniramine and clemastine were administered less frequently and had much lower positive response rates. Responses to antihistamines as a group were significantly better in dogs having onset of clinical signs at younger ages (odds ratios for 1-year increase in age = 0.72, 95% confidence interval = 0.57 to 0.91, P =.005). 相似文献
55.
人工驯养野生动物是获取野生动物产品的重要手段,但是非法盗猎的野生动物产品以人工饲养的名义进入市场,就会对野生动物的保护形成挑战。因此,准确鉴别市场上的动物产品是来自养殖场还是野外,是保护野外种群,维持养殖业正常秩序的关键。本研究以北美水貂(Neovison vison)为例,基于颧骨内侧空间(ZAS)、颧宽(ZAA和ZBA)、颅基长(BSL)、下颌长(MDL)、眶后收缩(POC)和最大面部宽度(GFB)等量度,建立了9个头骨形态计量学指标:POC/GFB、POC/BSL、POC/MDL、ZAS SQRT/BSL、ZA SSQRT/MDL、ZBA×BSL/2ZAS、ZBA×MDL/2ZAS、ZBB×BSL/2ZAS和ZBB×MDL/2ZAS。野生组(n=32,9雄23雌)和饲养组(n=45,35雄10雌)的比较表明,除POC/GFB外,所有指标对于在两组样品之间均有显著差异,整体判别正确率为73.2%—85.5%。在性别已知的情况下,雄性的整体正确率为82.4%—93.8%,雌性为41.7%—85.7%。为此,应针对不同性别、不同来源的动物建立相应的参考数据,利用似然比进行鉴别。本研究的结果不仅可用于北美水貂的鉴别,也为其他小型食肉动物的鉴别提供经验。 相似文献
56.
Raghavendra G Amachawadi Wesley A Tom Michael P Hays Samodha C Fernando Philip R Hardwidge T G Nagaraja 《Journal of animal science》2021,99(4)
Liver abscesses in feedlot cattle are polymicrobial infections. Culture-based studies have identified Fusobacterium necrophorum as the primary causative agent, but a number of other bacterial species are frequently isolated. The incidence of liver abscesses is highly variable and is affected by a number of factors, including cattle type. Holstein steers raised for beef production have a higher incidence than crossbred feedlot cattle. Tylosin is the commonly used antimicrobial feed additive to reduce the incidence of liver abscesses. The objective of this study was to utilize 16S ribosomal RNA amplicon sequence analyses to analyze the bacterial community composition of purulent material of liver abscesses of crossbred cattle (n = 24) and Holstein steers (n = 24), each fed finishing diet with or without tylosin. DNA was extracted and the V3 and V4 regions of the 16S rRNA gene were amplified, sequenced, and analyzed. The minimum, mean, and maximum sequence reads per sample were 996, 177,070, and 877,770, respectively, across all the liver abscess samples. Sequence analyses identified 5 phyla, 14 families, 98 genera, and 102 amplicon sequence variants (ASV) in the 4 treatment groups. The dominant phyla identified were Fusobacteria (52% of total reads) and Proteobacteria (33%). Of the top 25 genera identified, 17 genera were Gram negative and 8 were Gram positive. The top 3 genera, which accounted for 75% of the total reads, in the order of abundance, were Fusobacterium, Pseudomonas, and Bacteroides. The relative abundance, expressed as percent of total reads, of phyla, family, and genera did not differ (P > 0.05) between the 4 treatment groups. Generic richness and evenness, determined by Shannon–Weiner and Simpson’s diversity indices, respectively, did not differ between the groups. The UniFrac distance matrices data revealed no clustering of the ASV indicating variance between the samples within each treatment group. Co-occurrence network analysis at the genus level indicated a strong association of Fusobacterium with 15 other genera, and not all of them have been previously isolated from liver abscesses. In conclusion, the culture-independent method identified the bacterial composition of liver abscesses as predominantly Gram negative and Fusobacterium as the dominant genus, followed by Pseudomonas. The bacterial community composition did not differ between crossbred and Holstein steers fed finishing diets with or without tylosin. 相似文献
57.
Philip R. Fox Mark A. Oyama Caryn Reynolds John E. Rush Terri C. DeFrancesco Bruce W. Keene Clark E. Atkins Kristin A. MacDonald Karsten E. Schober John D. Bonagura Rebecca L. Stepien Heidi B. Kellihan Thaibinh P. Nguyenba Linda B. Lehmkuhl Bonnie K. Lefbom N. Sydney Moise Daniel F. Hogan 《Journal of Veterinary Cardiology》2009
BackgroundCirculating plasma N-terminal pro-brain natriuretic peptide (NT-proBNP) concentration facilitates emergency diagnosis of congestive heart failure (CHF) in people. Its utility to discriminate between dyspneic cats with CHF vs. primary respiratory disease requires further assessment. Our objectives were to determine if NT-proBNP (1) differentiates dyspneic cats with CHF vs. primary respiratory disease; (2) increases with renal insufficiency; (3) correlates with left atrial dimension, radiographic cardiomegaly, and estimated left ventricular filling pressure (E/Ea).MethodsNT-proBNP was measured in 167 dyspneic cats (66 primary respiratory disease, 101 CHF) to evaluate (1) relationship with clinical parameters; (2) ability to distinguish CHF from primary respiratory disease; (3) optimal cut-off values using receiver operating characteristic (ROC) curve analysis.ResultsNT-proBNP (1) was higher (median and inter-quartile [25th–75th] percentile) in CHF (754 pmol/L; 437, 1035 pmol/L) vs. primary respiratory disease (76.5 pmol/L; 24, 180 pmol/L) cohorts (P < 0.001); (2) positively correlated in CHF cats with increased inter-ventricular septal end-diastolic thickness (ρ = 0.266; P = 0.007) and LV free wall thickness (ρ = 0.218; P = 0.027), but not with radiographic heart size, left atrial size, left ventricular dimensions, E/Ea ratio, BUN, creatinine, or thyroxine; (3) distinguished dyspneic CHF cats from primary respiratory disease at 265 pmol/L cut-off value with 90.2% sensitivity, 87.9% specificity, 92% positive predictive value, and 85.3% negative predictive value (area under ROC curve, 0.94).ConclusionsNT-proBNP accurately discriminated CHF from respiratory disease causes of dyspnea. 相似文献
58.
Estimates of forest biomass in the Brazilian Amazon: New allometric equations and adjustments to biomass from wood-volume inventories 总被引:1,自引:0,他引:1
Euler Melo Nogueira Philip Martin Fearnside Bruce Walker Nelson Reinaldo Imbrozio Barbosa Edwin Willem Hermanus Keizer 《Forest Ecology and Management》2008
Uncertainties in biomass estimates in Amazonian forests result in a broad range of possible magnitude for the emissions of carbon from deforestation and other land-use changes. This paper presents biomass equations developed from trees directly weighed in open forest on fertile soils in the southern Amazon (SA) and allometric equations for bole-volume estimates of trees in both dense and open forests. The equations were used to improve the commonly used biomass models based on large-scale wood-volume inventories carried out in Amazonian forest. The biomass estimates from the SA allometric equation indicate that equations developed in forests on infertile soils in central Amazonia (CA) result in overestimates if applied to trees in the open forests of SA. All aboveground components of 267 trees in open forests of SA were cut and weighed, and the proportion of the biomass stored in the crowns of trees in open forest was found to be higher than in dense forest. In the case of inventoried wood volume, corrections were applied for indentations and hollow trunks and it was determined that no adjustment is needed for the form factor used in the RadamBrasil volume formula. New values are suggested for use in models to convert wood volume to biomass estimates. A biomass map for Brazilian Amazonia was produced from 2702 plots inventoried by the RadamBrasil Project incorporating all corrections for wood density and wood volume and in factors used to add the bole volume of small trees and the crown biomass. Considering all adjustments, the biomass map indicates total biomass of 123.1 Gt (1 Gt = 1 billion tons) dry weight (aboveground + belowground) for originally forested areas in 1976 in the Brazilian Legal Amazon as a whole (102.3 Gt for aboveground only) at the time of the RadamBrasil inventories, which were carried out before intensive deforestation had occurred in the region. Excluded from this estimate are 529,000 km2 of forest lacking sufficient RadamBrasil inventory data. After forest losses of 676,000 km2 by 2006 – not counting 175,000 km2 of this deforested area lacking RadamBrasil data – the estimated dry biomass stock was reduced to 105.4 and 87.6 Gt (aboveground + belowground and only above-ground). Thus, in 2006 the carbon storage in forested areas in Brazilian Amazonia as a whole will be around 51.1 Gt (assuming 1 Mg dry biomass = 0.485 Mg C). Biomass estimates by forest type (aggregated into 12 vegetation classes) are provided for each state in the Brazilian Legal Amazon. 相似文献
59.
Elizabeth A. Giuliano Ian MacDonald† Dudley L. McCaw‡ Thomas J. Dougherty† Gia Klauss§ Juri Ota Jacqueline W. Pearce Philip J. Johnson 《Veterinary ophthalmology》2008,11(S1):27-34
Objective Local photodynamic therapy (PDT) is a novel cancer therapy in veterinary ophthalmology. A prospective pilot study seeking to demonstrate proof of principle and safety for the treatment of equine periocular squamous cell carcinoma (PSCC) was therefore conducted. We hypothesized that surgical excision with adjunctive local PDT is an effective and safe treatment for equine PSCC.
Procedures Nine horses (10 eyes) with PSCC were treated with surgical resection, local infiltration of resulting wound beds with 2-[1-hexyloxyethyl]-2-devinylpyropheophorbide-a (HPPH) and irradiation with 665-nm wavelength diode laser. Regular follow-up ophthalmic examinations were performed.
Results Surgical resection and PDT yielded disease-free intervals of 25–68 months in our study horses as of January, 2008. These results were obtained following a single treatment in seven horses and two treatments in one horse. In one horse, carcinoma in situ developed 2.5 months after partial surgical excision and PDT, requiring local excision under standing sedation.
Conclusions Preliminary results suggest that surgical resection and adjunctive local PDT is a safe and effective novel treatment for PSCC in horses. More research is needed before PDT for the treatment of equine PSCC can be adequately compared with other current modalities. Important to future investigations regarding PDT, tumor recurrence rate, length of hospitalization, number of treatment episodes required to effect tumor remission, and total treatment costs should be examined in a controlled manner. Our present results and experiences suggest that this treatment may be useful in the treatment of equine PSCC. 相似文献
Procedures Nine horses (10 eyes) with PSCC were treated with surgical resection, local infiltration of resulting wound beds with 2-[1-hexyloxyethyl]-2-devinylpyropheophorbide-a (HPPH) and irradiation with 665-nm wavelength diode laser. Regular follow-up ophthalmic examinations were performed.
Results Surgical resection and PDT yielded disease-free intervals of 25–68 months in our study horses as of January, 2008. These results were obtained following a single treatment in seven horses and two treatments in one horse. In one horse, carcinoma in situ developed 2.5 months after partial surgical excision and PDT, requiring local excision under standing sedation.
Conclusions Preliminary results suggest that surgical resection and adjunctive local PDT is a safe and effective novel treatment for PSCC in horses. More research is needed before PDT for the treatment of equine PSCC can be adequately compared with other current modalities. Important to future investigations regarding PDT, tumor recurrence rate, length of hospitalization, number of treatment episodes required to effect tumor remission, and total treatment costs should be examined in a controlled manner. Our present results and experiences suggest that this treatment may be useful in the treatment of equine PSCC. 相似文献
60.
Domestic animals belonging to seven different species (cattle, sheep, dogs, cats, pigs, chicken and goats) were investigated as natural reservoirs for attaching and effacing Escherichia coli (AEEC). For this, 2165 E. coli strains from faeces of 803 animals were examined for the presence of the intimin -(eae) gene as a characteristic of AEEC strains. Ten percent of the animals were found to excrete AEEC, most frequently found in sheep (19.2%) and pigs (17.6), followed by cattle (10.4%), dogs (7.2%), cats (6.5%) and poultry (2.3%). The 97 AEEC strains from animals were grouped into 44 serotypes. Only four E. coli serotypes (O2:H8, O26:[H11], O109:[H25] and O145:[H28] were found in more than one animal host species. AEEC O26:[H11] strains were most frequently isolated (13.4%) being present in cattle, poultry, pigs and sheep. A search for virulence markers associated with enterohemorrhagic E. coli (EHEC) revealed Shiga-toxin genes in three (3.1%) AEEC strains from sheep. Bundle forming pili genes as a trait of typical enteropathogenic E. coli (EPEC) were detected in four (4.1%) strains from dogs and cats. The remaining 90 AEEC strains were classified as atypical EPEC. Typing of intimin genes revealed intimin beta being present in 51.5% of the strains, followed by intimins theta (23.7%), epsilon (6.2%), kappa (5.2%), zeta (5.2%), alpha, eta and iota (each 1.0%). Our data indicate that domestic animals and pets constitute an important natural reservoir of AEEC strains, and some of these (O26:[H11], O103:H2, O128:H2, O145:[H28] and O177:[H11]) are known to occur as pathogens in humans. 相似文献