首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   658篇
  免费   52篇
林业   98篇
农学   25篇
基础科学   4篇
  86篇
综合类   25篇
农作物   31篇
水产渔业   66篇
畜牧兽医   323篇
园艺   6篇
植物保护   46篇
  2023年   6篇
  2022年   11篇
  2021年   19篇
  2020年   36篇
  2019年   32篇
  2018年   31篇
  2017年   22篇
  2016年   33篇
  2015年   21篇
  2014年   30篇
  2013年   51篇
  2012年   41篇
  2011年   31篇
  2010年   23篇
  2009年   20篇
  2008年   31篇
  2007年   37篇
  2006年   31篇
  2005年   23篇
  2004年   17篇
  2003年   11篇
  2002年   16篇
  2001年   16篇
  2000年   12篇
  1999年   7篇
  1998年   4篇
  1997年   14篇
  1996年   3篇
  1995年   5篇
  1994年   4篇
  1993年   5篇
  1992年   11篇
  1991年   11篇
  1990年   6篇
  1989年   7篇
  1988年   3篇
  1987年   3篇
  1986年   4篇
  1985年   4篇
  1983年   1篇
  1981年   2篇
  1980年   1篇
  1979年   2篇
  1978年   5篇
  1977年   1篇
  1976年   2篇
  1974年   1篇
  1969年   1篇
  1968年   2篇
排序方式: 共有710条查询结果,搜索用时 265 毫秒
71.
This study aimed to evaluate the potential of Moringa oleifera fresh leaves (MOL) as feed supplement on the performance and egg quality of Rhode Island Red (RIR) hens under the tropical conditions of Yucatan, Mexico. Forty-eight RIR hens were allocated in 12 floor pen replicates each with four birds. Thereafter, the replicates were divided into three groups which were corresponded to ad libitum feed (control), ad libitum feed supplemented with MOL T1 (AL + MOL) and restricted feed amount (20% lower than control) with MOL T2 (RCD + MOL), respectively. T1 (AL + MOL) had higher egg laying rate (71.4% versus 66.6%), higher daily egg mass production (45.4 versus 41.9 g/day), lower feed intake (121.3 versus 127.5 g/day) and better feed conversion ratio (2.8 versus 3.2 g feed:g egg) versus control. T2 / (RCD + MOL) had lower values of body weight, egg laying rate, egg weight and egg mass, and recorded better feed conversion ratio than the control group. The control group recorded a higher percentage of pecked eggs versus T1 and T2 (6.5% versus 1.2% and 2.0 %). Similar intake of MOL (3.1 and 3.4 g DM/day) was recorded in T1 (AL + MOL) and T2 (RCD + MOL). Yolk color was improved significantly in T1 (AL + MOL) than both control and T2 (RCD + MOL), while T2 (RCD + MOL) had eggs with lower yolk and higher albumen percentages than the other two ad libitum groups. The results suggest that MOL could be used successfully as sustainable tropical feed resource for RIR hens.  相似文献   
72.
Equine motor neuron disease (EMND) is a neurodegenerative disorder of unknown etiology affecting horses worldwide. Trans-Active Response DNA Binding Protein of 43?kDa (TDP-43) has been reported in the central nervous system (CNS) of several neurodegenerative conditions in humans including Amyotrophic Lateral Sclerosis (ALS) and assumed to play role in the disease. We examined whether horses afflicted with EMND express the TDP-43 in CNS. Ten horses with EMND and 6 controls of different ages and breed we enrolled. Detection of presence of TDP-43 protein in the CNS was analyzed by immunohistochemical staining using rabbit anti-human TARDBP (TDP-43) polyclonal antibody. Formalin fixed neuronal tissues from medulla, cervical, and lumbar spinal cord were harvested from EMND and from control horses. Sections were assigned randomly to TDP-43 treated or rabbit anti-IgG as control. Nuclear staining of TDP-43 was detected in one of the neural tissues of 75?% of EMND-positive and 0 of 0?% of control horses in the central nervous system (medulla, and/or cervical spinal cord and/or lumbar spinal cord). TDP-43 antibody was detected in the nucleus of EMND horses and no cytoplasmic staining was noted. As in ALS, there was no pattern of age clustering associated with the detection of TDP-43. This is the first report on the staining of TDP-43 in neuronal tissues of horses and suggests that TDP-43 may play a role in the pathogenesis of EMND. Further studies are needed to elucidate the etiologic role of this protein in the diseases.  相似文献   
73.
The morpho-physiological quality of seedlings is negatively affected by the wide scale use of forest soils as substrates in developing countries. With the objective of finding long-term sustainable supply of growing media, compost was produced from shredded branches of three fast growing species (Acacia cyanophylla (AA), Acacia cyclops (AS) and Eucalyptus gomphocephala (EG). The composting process covered three different periods over the course of a year. Pile temperatures were monitored daily and the composts were routinely sampled and analyzed for 19 chemical variables. Although composting is feasible year-round in arid climates, compost produced in the humid cool conditions of autumn, winter and early spring reaches the maturation phase more quickly than compost produced under hot, dry summer conditions. It also requires less turning and water. The evolution of the composting process and quality of the final product can be assessed using three chemical variables (C/N, pH, EC). Seed germination rates in the three types of compost were similar to that in a peat:vermiculite substrate and vigorous high quality seedlings were produced in the two acacia composts. However, compost-grown seedlings had significantly smaller shoots and root systems than those produced in peat substrate. Principal components analyses showed that the quality of a compost-based substrate is reproducible and that its final chemical composition can be predicted from its raw organic materials. The EG composts had higher pH than the acacia composts, whereas the AA and EG composts were higher in mineral salts than the AS.  相似文献   
74.
The seroprevalence of Toxoplasma gondii, Dirofilaria immitis (heartworm), feline immunodeficiency virus (FIV) and feline leukemia virus (FeLV) infections was examined using serum or plasma samples from 746 pet cats collected between May and July 2009 from clinics and hospitals located in and around Bangkok, Thailand. The samples were tested for heartworm, FIV, and FeLV using a commercial ELISA. Of the 746 samples, 4.6% (34/746) were positive for heartworm antigen, 24.5% (183/746) had circulating FeLV antigen, and 20.1% (150/746) had antibodies against FIV. In addition, the first 348 submitted samples were tested for T. gondii antibodies using a modified agglutination test (MAT, cut off 1:25); 10.1% (35/348) were seropositive. Of the 348 cats sampled for all four pathogens, 11, 10, and 1 were positive for T. gondii antibodies and FIV antibodies, FeLV antigen, or D. immitis antigen, respectively. Of the 35 T. gondii-seropositive cats, 42.9% (15/35) were co-infected with at least one of the other three pathogens. The presence of antibodies to FIV was significantly associated with both age and gender, while FeLV antigen presence was only associated with age. In the case of FIV, males were twice as likely to be infected as females, and cats over 10 years of age were 13.5 times more likely to be infected than cats less than 1 year of age. FeLV antigen was more common in younger cats, with cats over 10 years of age being 10 times less likely to be FeLV positive than cats under 1 year of age. This is the first survey for these four pathogens affecting feline health in Thailand.  相似文献   
75.
A longitudinal herd-level study was carried out to determine the cumulative incidence of Giardia duodenalis infections in dairy cattle in the New York City Watershed. We also sought to assess the changes in infection pattern of animals diagnosed as shedding Giardia over time, determine risk factors that may be associated with G. duodenalis infections, and identify potentially zoonotic infections. A total of 2109 fecal samples were randomly collected from dairy cattle at 34 farms in the New York City Watershed on a seasonal basis. A total of 504 Giardia-positive samples were identified by zinc sulfate flotation. The overall cumulative incidence of G. duodenalis based on flotation results was 23.9% with 73.8% of all infections occurring in animals under 180 days of age (372/504). The intensity of infection ranged from 2 to 563,200 cysts/gram of feces. Cattle shedding Cryptosporidium spp. oocysts were twice as likely to shed G. duodenalis cysts in comparison to the animals that did not shed oocysts (1.81 95% CI 1.26-2.60 p=0.0012). In the multivariate analysis, only the age of the animal and the presence of dogs on the farm were significantly associated with the likelihood of shedding G. duodenalis. DNA was extracted from positive samples and analyzed by polymerase chain reaction (PCR) of the beta-giardin and triosephosphate isomerase genes of Giardia spp. 304 samples were analyzed by PCR of which 131 were sequenced. 22.1% of sequenced samples were identified as assemblage A and 77.9% were identified as assemblage E. Interestingly, 100% of specimens identified as assemblage A were from calves under 84 days of age indicating that younger cattle are important reservoirs for potentially zoonotic assemblages of G. duodenalis.  相似文献   
76.
Rattan, an important non-timber forest product, is a flexible palm used in weaving baskets or furniture. Rattan is light yet sturdy, making it suitable for furniture that can be moved often. Bangladesh has a large number of rattan-based enterprises. This paper reports a case study carried out in Sylhet City Corporation of north-eastern Bangladesh, exploring the production, financial profitability and marketing of rattan-based products, and the problems and priorities of rattan-based enterprises as well as their potential contribution to employment opportunity. A sample survey was conducted of 58 randomly selected rattan-based enterprises with entrepreneurs personally interviewed using a semi-structured questionnaire. Based on the total investment, the enterprises were divided into large, medium and small categories. Three origins of rattan (Local, Myanmar and Indonesia) and five species were used by the enterprises to produce 29 rattan-based product types. Rattan products were divided into three basic categories, viz. domestic utensils, domestic decorative articles and others for which uses are not specific. Among the three rattan origins, processing cost of local and Myanmar rattan species products was less and more articles were sold than for Indonesia rattan species. Financial analysis indicated that rattan-based enterprises are a profitable and attractive option for local socio-economic development. Entrepreneurs’ views on major problems and issues in rattan-based product trading and suggested measures to improve the condition of rattan-based enterprises also collected. Rattan-based enterprises will generate more domestic revenue, foreign exchange and employment if policies are adopted to provide the enterprises with a reliable source of raw materials and technical and financial assistance from Government to NGOs to sell the products, and expand market facilities in both local and international markets.  相似文献   
77.
ABSTRACT: BACKGROUND: Phloem-feeding insects are among the most devastating pests worldwide. They not only cause damage by feeding from the phloem, thereby depleting the plant from photo-assimilates, but also by vectoring viruses. Until now, the main way to prevent such problems is the frequent use of insecticides. Applying resistant varieties would be a more environmental friendly and sustainable solution. For this, resistant sources need to be identified first. Up to now there were no methods suitable for high throughput phenotyping of plant germplasm to identify sources of resistance towards phloem-feeding insects. RESULTS: In this paper we present a high throughput screening system to identify plants with an increased resistance against aphids. Its versatility is demonstrated using an Arabidopsis thaliana activation tag mutant line collection. This system consists of the green peach aphid Myzus persicae (Sulzer) and the circulative virus Turnip yellows virus (TuYV). In an initial screening, with one plant representing one mutant line, 13 virus-free mutant lines were identified by ELISA. Using seeds produced from these lines, the putative candidates were re-evaluated and characterized, resulting in nine lines with increased resistance towards the aphid. CONCLUSIONS: This M. persicae-TuYV screening system is an efficient, reliable and quick procedure to identify among thousands of mutated lines those resistant to aphids. In our study, nine mutant lines with increased resistance against the aphid were selected among 5160 mutant lines in just 5 months by one person. The system can be extended to other phloem-feeding insects and circulative viruses to identify insect resistant sources from several collections, including for example genebanks and artificially prepared mutant collections.  相似文献   
78.
Objective To evaluate the pre‐emptive analgesic effect of pre‐incisional epidural ketamine. Study Design A blinded, randomized experimental study. Animals Sixteen mixed breed mares, 7.6 ± 2.8 years old, weighing 352 ± 32 kg. Methods In a pilot study, an incision was made on one lateral thigh using a lidocaine block and no further analgesics, and it was verified that the nociceptive threshold was lower on the incised side than nonincised side (p ≤ 0.05), and that von Frey filaments evoked a pain response. The 16 animals were divided into group A (ketamine, n = 9) and B (saline, n = 7). An epidural catheter was inserted 24 hours before the trials. The thigh was shaved bilaterally, and the right side was blocked (incised side) using lidocaine. Twenty‐five minutes later, ketamine (A) or saline (B) was administered epidurally. Five minutes later, a 10‐cm skin incision was made on the right side, and then sutured. Nociceptive threshold was determined with von Frey filaments at 1, 3, and 5 cm around the incision at 15‐minute intervals for 2 hours, then at 4, 6, and 8 hours. Behavioral alterations, heart and respiratory rates were recorded. Nociceptive thresholds from these points were averaged to obtain mean values at each time, converted to a logarithmic scale, and submitted to a nonparametric analysis (Mann–Whitney and one‐way repeated measures anova test, p ≤ 0.05). Results After 8 hours, the global range score revealed reduced hyperalgesia (p < 0.01) around the incision in 92% (4.65–4.27) of evaluated intervals in group A (ketamine). There were no significant changes in behavior, heart and respiratory rates. Conclusions It was concluded that pre‐emptive epidural ketamine reduced post‐incisional pain in the horse, and that von Frey filaments were able to quantify cutaneous sensitivity after tissue damage. Clinical relevance Epidural ketamine injection can reduce post‐incisional sensitivity in the horse.  相似文献   
79.
The aim of this study was to determine whether glucocorticoid production could be monitored non-invasively in dromedary camels by measuring faecal cortisol metabolites (FCMs). Five Sudanese dromedaries, two males and three females, were injected with a synthetic adrenocorticotropic hormone (ACTH) analogue. Blood samples were collected pre- and post-ACTH injection. Faeces were sampled after spontaneous defecation for five consecutive days (2 days before and 3 days after ACTH injection). Baseline plasma cortisol values ranged from 0.6 to 10.8 ng/ml in males and from 1.1 to 16.6 ng/ml in females, while peak values after ACTH injection were 10.9–41.9 in males and 10–42.2 ng/ml in females. Peak blood cortisol values were reached between 1.5 and 2.0 h after ACTH injection. The concentration of FCMs increased after ACTH injection in the faeces of both sexes, although steroid levels peaked earlier in males [24 h; (286.7–2,559.7 ng/g faeces)] than in females [36–48 h; (1,182.6–5,169.1 ng/g faeces)], reflecting increases of 3.1–8.3- and 4.3–8-fold above baseline levels. To detect chromatographic patterns of immunoreactive FCMs, faecal samples with high FCM concentrations from both sexes were pooled and subjected to reverse phase high performance liquid chromatography (RP-HPLC). RP-HPLC analysis revealed sex differences in the polarity of FCMs, with females showing more polar FCMs than males. We concluded that stimulation of adrenocortical activity by ACTH injection resulted in a measurable increase in blood cortisol that was reliably paralleled by increases in FCM levels. Thus, measurement of FCMs is a powerful tool for monitoring the adrenocortical responses of dromedaries to stressors in field conditions.  相似文献   
80.
The aim of this study was to determine whether postpartum variations of plasma IGF‐1 and IGFBP concentrations, oocyte production and quality were related to parity and subsequent conception rate in Holstein dairy cows. Holstein dairy cows [10 primiparous (PP) and 22 multiparous (MP)] were allotted in six batches and sampled once weekly between calving and oestrous synchronization treatment started at 71.2 ± 2.0 days postpartum. During the 3 weeks before treatment, ovum pick‐up (OPU) was performed twice weekly. Oocytes were scored on a 4‐point scale, and oocytes from OPU1, 3 and 5 were fertilized in vitro. Seventeen cows became pregnant after first and second AI and were considered as fertile (F), while the others were considered to be subfertile (SF). Logistic regression was carried out to investigate the relationships between repeated measurements and fertility including parity and batch effects in the models. Likelihood of fertility significantly increased when plasma urea and IGFBP‐3 concentrations decreased and was higher in PP compared with MP cows. There was a trend for fertility to increase when plasma IGF‐1 concentrations increased (p = 0.07). In vitro cleavage and development rates were similar between SF and F cows (46.4% and 28.3% in SF vs 55.0% and 22.1% in F). Parity had an effect on plasma IGF‐1 concentrations (PP: 61.65 ± 2.67 vs MP: 41.63 ± 5.81 ng/ml, p < 0.001), mean number of follicles aspirated per session (PP: 5.7 ± 1.3 vs MP: 9.5 ± 0.8, p < 0.05) and fertility (PP: 8/10 = 80% vs MP: 9/22 = 41%, p < 0.05) but not on the number of oocytes recovered per session nor their quality. In conclusion, postpartum plasma urea and IGFBP‐3 concentrations, but not oocyte production and quality before breeding, were related to subsequent conception rate in our experimental design. Parity had a significant effect on energy status, follicular growth and fertility and needs to be considered when investigating relationships between nutrition and reproduction.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号