全文获取类型
收费全文 | 19835篇 |
免费 | 193篇 |
国内免费 | 1篇 |
专业分类
林业 | 3897篇 |
农学 | 1707篇 |
基础科学 | 189篇 |
3496篇 | |
综合类 | 863篇 |
农作物 | 2334篇 |
水产渔业 | 2095篇 |
畜牧兽医 | 2086篇 |
园艺 | 1227篇 |
植物保护 | 2135篇 |
出版年
2023年 | 39篇 |
2022年 | 85篇 |
2021年 | 108篇 |
2020年 | 125篇 |
2019年 | 137篇 |
2018年 | 2874篇 |
2017年 | 2839篇 |
2016年 | 1323篇 |
2015年 | 176篇 |
2014年 | 164篇 |
2013年 | 325篇 |
2012年 | 990篇 |
2011年 | 2296篇 |
2010年 | 2230篇 |
2009年 | 1362篇 |
2008年 | 1451篇 |
2007年 | 1695篇 |
2006年 | 145篇 |
2005年 | 192篇 |
2004年 | 180篇 |
2003年 | 226篇 |
2002年 | 127篇 |
2001年 | 68篇 |
2000年 | 95篇 |
1999年 | 53篇 |
1998年 | 30篇 |
1997年 | 24篇 |
1996年 | 23篇 |
1995年 | 18篇 |
1994年 | 17篇 |
1993年 | 30篇 |
1992年 | 36篇 |
1991年 | 34篇 |
1990年 | 43篇 |
1989年 | 36篇 |
1988年 | 35篇 |
1987年 | 33篇 |
1986年 | 24篇 |
1985年 | 23篇 |
1984年 | 18篇 |
1983年 | 20篇 |
1982年 | 18篇 |
1981年 | 26篇 |
1980年 | 18篇 |
1979年 | 34篇 |
1978年 | 19篇 |
1977年 | 17篇 |
1971年 | 15篇 |
1969年 | 21篇 |
1968年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Danilo T. Stipp Aline F. Barry Alice F. Alfieri Elisabete Takiuchi Alexandre M. Amude Amauri A. Alfieri 《Tropical animal health and production》2009,41(7):1563-1567
Bovine coronavirus (BCoV) is one of the main causes of neonatal calf diarrhoea. Several diagnostic assays have been employed
to detect the presence of the virus in stool samples from calves. Despite this, the frequency of BCoV infection among Brazilian
and even South American cattle herds has yet to be well characterised. This study describes the occurrence of BCoV infection
among calves from dairy and beef herds in four Brazilian states. A total of 282 stool samples from 1 to 60-day-old calves
were evaluated for the presence of BCoV by a semi-nested (SN) PCR assay. The animals were from herds (n = 23) located in three geographical regions in Brazil (south, southeast, and center-west). The specific BCoV amplicon was
detected in 15.6% (44/282) of the faecal specimens examined, of which 95.4% (42/44) were from diarrhoeic and 4.6% (2/44) from
asymptomatic calves. The specificity of the SN-PCR amplicons was evaluated by restriction fragment length polymorphism (RFLP)
analysis. The results show that the BCoV is widespread, mainly among calves from 16 to 30-days-old (p = 0.0023), and verify the association between BCoV infection and clinical signs of diarrhoea (p = 0.005). These findings emphasise the importance of this virus in enteric infections of Brazilian cattle herds. 相似文献
42.
Khanyisile Mdladla Edgar Farai Dzomba Farai Catherine Muchadeyi 《Tropical animal health and production》2017,49(3):515-527
Expansion of goat improvement programs requires exploration of the factors that influence the production system and breeding initiatives. Characterization of goat breeds or populations is crucial in providing information on prevalent goat types and their attributes and may suffice as a guideline on conservation, development, and selection for improved productivity. This study investigated the existing village goat production system and phenotypic diversity of the different village populations from four South African provinces. The study further investigated the use of phenotypic attributes to classify goats to breeds or populations. Data was collected from 142 households in 26 villages of the Eastern Cape (n?=?2 villages), KwaZulu-Natal (n?=?6 villages), Limpopo (n?=?13 villages), and North West (n?=?5 villages) provinces through a survey. Individual interviews and focus group discussions revealed that the mean goat herd size per household was least in Limpopo at 13.2?±?12.40 and highest in Eastern Cape (34.18?±?28.36). Flocks had more (p?<?0.05) adults than kids, and the distribution of breeding animals was biased towards does and less bucks. Goats were kept mainly for meat, for selling, and for ritual ceremonies. The goat production system was mainly scavenging. Goat health was a major challenge across households and villages. Qualitative traits such coat, horn, ears, and wattle characteristics were recorded for populations of village goats (n?=?319) and a feral Tankwa breed (n?=?50). The dominant coat pattern was plain (74.53%) with black as the most common coat color (31.98%). Across breeds, a majority (88.08%) of the goats had horns, and 7.59% had wattles while 56.64% had beard. Adult goats (<3 years; n?=?398) were further analyzed for five quantitative traits of chest girth, height, length, and pin bone and there were significant (p?<?0.05) breed differences in all. A stepwise discriminatory procedure was used to rank the quantitative traits according to their discriminatory power to separate breeds or populations. Significant traits were then subjected to canonical discriminant analysis for principle component analysis. Based on the quantitative traits, the Tankwa, Xhosa, and Tswana goats formed their own cluster separated from commercial meat type breeds and the Venda and Zulu ecotypes. The discriminant function analysis correctly classified 90.41% of the Zulu goats and 82.93% of the Xhosa village populations. None of the Savanna goats were correctly classified. The study demonstrated diversity in village goat populations and production systems, which would allow for within population selection in genetic improvement programs. The heterogeneity in the phenotypic traits in the village goats is reflective of the role of village production systems in the maintenance of animal diversity in local populations. 相似文献
43.
Awareness of animal influenza and its prevention and control is important for ensuring livestock health, production and welfare. In China, a country stereotyped as a major source of emerging zoonotic infectious diseases, research on the public understanding of animal influenza is limited to the Han, the main ethnic group. The present qualitative study in Southwest China investigated awareness of animal influenza among the Dai, an ethnic minority. The participants (15 men and 10 women, ages 18–83) were smallholder farmers of pigs and poultry in rural areas of Jinghong, Xishuangbanna, Yunnan Province. A mixture of interviews and group discussions took place in homes and villages. The participants were asked about their knowledge of avian influenza (H7N9), swine influenza (H1N1), precautions taken to protect against influenza, procedures when animals were sick and perceived risk of animal influenza. The data were analysed following coding and thematic analysis. The findings demonstrated a limited understanding of animal health and welfare among participants. Specifically, they were largely unaware of animal influenza (H7N9, H1N1) including its causes, symptoms, prevention and treatment. The farmers were also uninformed of the risks they faced and unknowingly engaged in behaviours which increased direct or indirect exposure to infected animals, a risk factor for human infection. They also reported poor usage of veterinary services. In order to guarantee the health, welfare and production of their livestock, immediate action is needed to enable Dai smallholder farmers to prevent and respond to animal influenza effectively and timely. 相似文献
44.
Identification of avian strains of Pasteurella multocida in India by conventional and PCR assays 总被引:1,自引:0,他引:1
Shivachandra SB Kumar AA Gautam R Singh VP Saxena MK Srivastava SK 《Veterinary journal (London, England : 1997)》2006,172(3):561-564
The prevalence of capsular and somatic serotypes were studied among 123 Pasteurella multocida strains isolated from chickens (n = 94), ducks (22), quails (4), turkeys (2) and geese (1) from different geographical regions of India. All strains exhibited similar cultural and morphological characteristics. Ninety-two of the isolates belonged to serotype A:1, the most prevalent serotype, with serotypes A:3, A:1,3, D:3 and F:3 having two isolates each. Only one isolate was positive for serotypes A:4 and D:1. Twenty isolates were untyped. A multiplex capsular PCR assay generated amplicons of sizes 460, 1044, 657 and 854 bp in 106 isolates identified as capsular serotype-A, 15 in serotype D and two in serotype F. Capsular types B and E were not detected in any of the avian isolates studied. The present findings suggest that a multiplex capsular PCR assay may be suitable for the rapid initial identification serotypes P. multocida during epidemiological studies of fowl cholera. 相似文献
45.
Interaction of bovine neutrophils in Pasteurella haemolytica mediated damage to pulmonary endothelial cells 总被引:3,自引:0,他引:3
The purpose of these studies was to determine mechanisms of pulmonary tissue damage mediated by Pasteurella haemolytica and interaction with bovine neutrophils. Bovine pulmonary artery endothelial cell monolayers were treated with various combinations of P. haemolytica factors including bacterial culture supernatant (CS) and purified LPS, with and without bovine neutrophils. Damage to endothelial cells was monitored by 51Cr release, cell detachment rate, and morphological changes. At 5 h post-treatment (PT) bacterial factors produced very little toxic change in cells, however, by 22 h PT both crude leukotoxin and LPS caused high levels of cytotoxicity and detachment. Neutrophils did not augment toxicity mediated by LPS, but actually protected endothelial cells from low levels of LPS. When the LPS component of CS was neutralized with polymyxin B, leukotoxin mediated neutrophil killing resulted in extensive endothelial cell damage. These results suggest that LPS may directly injure endothelial cells and this toxic effect may be reduced by neutrophils. However, neutrophil killing by leukotoxin may also contribute to endothelial cell damage in the absence of LPS. 相似文献
46.
Keles I Sharma AK Woldehiwet Z Murray RD 《Comparative immunology, microbiology and infectious diseases》1999,22(1):1-13
In the present study peripheral blod mononuclear cells (MNC) obtained from normal uninfected lambs were used to study the possible effects of bovine respiratory syncytial virus (BRSV) on lymphocyte responses to the mitogens, phytohaemagglutinin (PHA), concanavalin A (Con A) and pokeweed mitogen (PWM) in vitro. Live BRSV had a depressive effect on the proliferative responses of normal MNC to PHA, Con A and PWM. Inactivated BRSV and a commercial preparation of prostaglandin E2 were also found to depress the proliferative responses of normal ovine MNC to PHA but recombinant tumour necrosis factor-alpha (TNF-alpha) had no such effect. Serum samples obtained from BRSV-infected lambs contained substances inhibitory to PHA-driven lymphocyte blastogenesis. Memory blastogenic responses to border disease virus (BDV) of lymyphocytes obtained from lambs previously primed with BDV were significantly reduced when lymphocytes were exposed to infectious BRSV. 相似文献
47.
Ezenduka EV Oboegbulem SI Nwanta JA Onunkwo JI 《Tropical animal health and production》2011,43(3):557-559
The use of antimicrobial agents in poultry production results in their accumulation in the body tissues and products such
as milk and egg. The subsequent accumulation of these drugs and their metabolites in body cells is known as drug residue.
This study was designed to determine the prevalence of antimicrobial residues in eggs from poultry farms and retail outlets
in Enugu State, Nigeria. Eggs from 25 selected commercial farms and ten retail outlets were screened for the prevalence of
antimicrobial residue. Also, structured questionnaires were administered to 25 commercial farms in the state to determine
the management practices and the most widely used antimicrobial drugs in farms and possible association between the management
practices and the occurrence of antimicrobial residues in eggs from these farms. All the 25 farms surveyed use oxytetracycline.
Eggs from nine of the surveyed farms tested positive for antimicrobial residue and three of the ten surveyed farms also tested
positive for antimicrobial residue. No association was observed (p 0.05; Fisher’s exact test) between the occurrence of antibiotic residues in eggs and farm size, feed source and housing systems.
This study was able to demonstrate the presence of antimicrobial residues in eggs destined for human consumption. Drugs like
nitrofurans which has been banned for use in food animals are still very much in use in Enugu State, Nigeria. Antibiotics
given as feed additives may give rise to drug residues in food animals. 相似文献
48.
49.
50.
K Ashley S Wilson JR Young HP Chan S Vitou S Suon PA Windsor RD Bush 《Tropical animal health and production》2018,50(1):63-73
Forage technology has been successfully introduced into smallholder cattle systems in Cambodia as an alternative feed source to the traditional rice straw and native pastures, improving animal nutrition and reducing labour requirements of feeding cattle. Previous research has highlighted the positive impacts of forage technology including improved growth rates of cattle and household time savings. However, further research is required to understand the drivers, challenges and opportunities of forage technology for smallholder cattle households in Cambodia to facilitate widespread adoption and identify areas for further improvement. A survey of forage-growing households (n = 40) in July–September 2016 examined forage technology adoption experiences, including reasons for forage establishment, use of inputs and labour requirements of forage plot maintenance and use of forages (feeding, fattening, sale of grass or seedlings and silage). Time savings was reported as the main driver of forage adoption with household members spending approximately 1 h per day maintaining forages and feeding it to cattle. Water availability was reported as the main challenge to this activity. A small number of households also reported lack of labour, lack of fencing, competition from natural grasses, cost of irrigation and lack of experience as challenges to forage growing. Cattle fattening and sale of cut forage grass and seedlings was not found to be a widespread activity by interviewed households, with 25 and 10% of households reporting use of forages for these activities, respectively. Currently, opportunities exist for these households to better utilise forages through expansion of forage plots and cattle activities, although assistance is required to support these households in addressing current constraints, particularly availability of water, if the sustainability of this feed technology for smallholder cattle household is to be established in Cambodia. 相似文献