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   16908篇
  免费   43篇
林业   3659篇
农学   1304篇
基础科学   141篇
  2848篇
综合类   716篇
农作物   2138篇
水产渔业   1832篇
畜牧兽医   1255篇
园艺   1123篇
植物保护   1935篇
  2024年   1篇
  2023年   4篇
  2022年   9篇
  2021年   29篇
  2020年   26篇
  2019年   21篇
  2018年   2758篇
  2017年   2714篇
  2016年   1199篇
  2015年   87篇
  2014年   42篇
  2013年   46篇
  2012年   832篇
  2011年   2168篇
  2010年   2124篇
  2009年   1268篇
  2008年   1353篇
  2007年   1618篇
  2006年   54篇
  2005年   121篇
  2004年   117篇
  2003年   162篇
  2002年   69篇
  2001年   14篇
  2000年   42篇
  1999年   8篇
  1998年   7篇
  1996年   3篇
  1995年   1篇
  1994年   1篇
  1993年   13篇
  1992年   7篇
  1991年   1篇
  1990年   1篇
  1989年   5篇
  1988年   11篇
  1987年   2篇
  1986年   1篇
  1984年   1篇
  1977年   4篇
  1972年   1篇
  1969年   1篇
  1968年   4篇
  1967年   1篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
A longitudinal study was done to monitor incidence of livestock diseases in ranch and pastoral herds around Lake Mburo National Park, in South-western Uganda with a high level of wildlife (impala and zebra) and livestock (cattle and goats) interactions. East Coast Fever (ECF), abortions, helminthosis and starvation due to drought were major livestock disease problems encountered. ECF was a major disease affecting mainly calves, causing mortality both in ranch (8.5%) and pastoral (8.2%) herds. Meanwhile, drought was a more serious in pastoral than ranch herds (p < 0.05), killing 28.5 % and 5.8% of adult female cattle in respective production systems. Other endemic diseases found and controlled by vaccination were FMD, CBPP and blackquarter. In both cattle and goats helminthosis was causing mortalities, 3.3% and 0.8% among calves in pastoral and ranches respectively; and 4.8% and 6.9% among kids and sub-adult goats respectively. Many cases of abortions occurred among pastoral herds. In conclusion, the disease incidence among livestock was the same or relatively low as compared to other areas without wildlife.  相似文献   
82.
Responding to the challenges posed by global warming, peak oil and biofuels will require a paradigm shift in the practice of agriculture and in the role of live stock within the farming system. Farming systems should aim at maximizing plant biomass production from locally available diversified resources, processing of the biomass on farm to provide food, feed and energy and recycling of all waste materials. The approach that is the subject of this paper is that the generation of electricity can be a by-product of food/feed production. The concept is the fractionation of biomass into inedible cell wall material that can be converted to an inflammable gas by gasification, the gas in turn being the source of fuel for internal combustion engines driving electrical generators. The cell contents and related structures such as tree leaves are used as human food or animal feed. As well as providing food and feed the model is highly appropriate for decentralized small scale production of electricity in rural areas. It also offers opportunities for sequestration of carbon in the form of biochar the solid residue remaining after gasification of the biomass.  相似文献   
83.
We analyzed ostriches from an equipped farm located in the Brazilian southeast region for the presence of Salmonella spp. This bacterium was investigated in 80 samples of ostrich droppings, 90 eggs, 30 samples of feed and 30 samples of droppings from rodents. Additionally, at slaughter-house this bacterium was investigated in droppings, caecal content, spleen, liver and carcasses from 90 slaughtered ostriches from the studied farm. Also, blood serum of those animals were harvested and submitted to serum plate agglutination using commercial Salmonella Pullorum antigen. No Salmonella spp. was detected in any eggs, caecal content, liver, spleen, carcass and droppings from ostriches and rodents. However, Salmonella Javiana and Salmonella enterica subsp. enterica 4, 12: i:- were isolated from some samples of feed. The serologic test was negative for all samples. Good sanitary farming management and the application of HACCP principles and GMP during the slaughtering process could explain the absence of Salmonella spp. in the tested samples.  相似文献   
84.

Background

The authors report the first case of feline gastric actinomycosis associated with infection by Actinomyces hordeovulneris.

Case presentation

A 4-year-old, neutered male, semi-feral European cat, with a 1 year history of chronic vomiting, was referred to the clinic. Abdominal ultrasound examination identified a hypoechoic focal transmural thickening with loss of normal wall layering and hyperechoic speckles at the gastric body. Initial gastroscopic examination showed a tumour-like gastric mass with an ulcerated depression at the level of the greater curvature. Histologic examination of endoscopic biopsy specimens was consistent with a severe lymphoplasmacytic gastritis. After 2 months, due to persistence of abdominal discomfort, surgical exploration and intraoperative sampling of gross abnormalities was recommended. Full thickness gastric wall biopsies, and fine needle aspiration of the gastric thickening and gastric lymph node, were performed. Histopathological examination identified a transmural pyogranulomatous gastritis. Aspirate samples of the gastric wall cultured positive, with colony morphology, biochemical testing and PCR of the 16 s rRNA gene compatible with Actinomyces hordeovulneris. After 4 months of treatment with cefovecin (8 mg/kg subcutaneously every 14 days), the vomiting completely resolved, as well as the ultrasonographic gastric alteration.

Conclusion

This case report of feline gastric actinomycosis, caused by Actinomyces hordeovulneris, suggests that gastric bacterial infection should be considered in cases of focal gastric wall thickening associated with chronic vomiting in the cat, which may otherwise closely resemble neoplastic disease. Once a diagnosis of actinomycosis was obtained, a correct treatment with antibiotic therapy can resolve it.
  相似文献   
85.
Probiotics of Lactobacillus acidophilus, Saccharomyces cerevisiae, and Aspergillus niger and three commercial exogenous fibrolytic enzymes (EFE) were tested in vitro to select best source and optimum dose followed by in vivo studies on male buffalo calves. Bacterial (P < 0.001) and protozoal population were increased significantly (P < 0.001) with probiotics and EFE. In vitro dry matter digestibility was more (P < 0.001) on L. acidophilus and then on S. cerevisiae. Dose required for L. acidophilus and S. cerevisiae probiotics was 1 × 109 and 3 × 109 cfu/flask, respectively. Cellulase and xylanase were effective at 4,000 and 12,500 IU/kg DM. In vitro cell wall digestibility was increased (P < 0.001) when probiotics and EFE were used together. Best source and optimum dose of probiotics and EFE were fed to 18 male buffalo calves with concentrate supplement (CS). Calves were randomly divided into three groups either without probiotics and EFE (CG) or with probiotics (EG1) or probiotics combined with EFE (EG2) on wheat straw diet. Organic matter, neutral detergent fiber, and acid detergent fiber digestibility was improved significantly. Average daily weight gain (ADG) and feed efficiency were significantly higher (P < 0.001) in EG2 than EG1 or CG. Final body weight was 4% and 12% and feed efficiency was 2.6% or 1.6% more (P < 0.001) in EG2 compared to CG or EG1, respectively. Fortification of CS with probiotics and EFE together had more impact on FE and ADG in buffalo calves.  相似文献   
86.
87.
A cross-sectional survey was conducted in Sudan to determine sero-prevalence and risk factors associated with Neospora caninum infection in non-vaccinated dairy herds and to assess importance of the disease. Blood samples were collected from a total of 262 animals from 25 herds. Sera were tested for antibodies against N. caninum using ELISA test. The prevalence rates of N. caninum antibodies in cattle were high both at herd level (44%) and at individual animal level (10.7%). Herd level infection rates were similar in Khartoum State (43.7%) and at Gazira States (44.4%). The overall prevalence rates were higher (16.1%) in Gazira State than in Khartoum State (9%) but with no significant variation. The sero-prevalence at individual animal level was significantly higher (p < 0.05) in animals with history of abortion (12.8%) than in apparently healthy animal (11.3%), animal with history of infertility (8.1%), or neonatal death of calves (4.3%). In addition, significantly higher (P < 0.05) sero-prevalence was observed in samples collected during the rainy season (6.87%) than winter (3.05%) or summer (0.76%). However, no significant differences in sero-prevalence due to locality, animal breed, sex, and age were observed (p > 0.05). This preliminary study reveals for the first time the existence of natural N. caninum infection in Sudan. Also, the findings of the present study indicated that this disease is highly prevalent in two major areas of dairy production in the country, and this calls for control strategy to be implemented.  相似文献   
88.
Bovine anaplasmosis, caused by the tick-borne rickettsia Anaplasma marginale, is endemic in South Africa and results in considerable economic loss to the cattle industry. This study was designed to characterize strains of A. marginale at the molecular level from cattle raised in communal and commercial farms in the north-eastern and south-western regions of the Free State Province, South Africa, that varied in rainfall and vegetation. Seroprevalence to A. marginale was determined in 755 cattle by an Anaplasma spp. competitive enzyme-linked immunosorbent assay and ranged from 44% to 98% and was similar in both regions. While Anaplasma centrale was not targeted in this study, A. marginale infections were identified by species-specific msp1alpha polymerase chain reaction in 129 of 215 of the samples studied. Similar genetic diversity of A. marginale strains was found in both the north-eastern and south-western regions. The sequences of 29 A. marginalemsp1alpha amplicons from South African strains revealed considerable genetic diversity providing 14 new repeat sequences. However, 42% of MSP1a repeat sequences were not unique to this region. These results indicated the presence of common genotypes between South African, American and European strains of A. marginale. Cattle movement between different parts of South Africa was suggested by the presence of identical A. marginale MSP1a genotypes in north-eastern and south-western regions of the Free State Province. Control strategies for anaplasmosis in South Africa should therefore be designed to be protective against genetically heterogeneous strains of A. marginale.  相似文献   
89.
West Nile Virus (WNV) was first detected in the Texas equine population during June 2002. Infection has since spread rapidly across the state and become endemic in the equine population. Environmental risk factors associated with equine WNV attack rates in Texas counties during the period 2002 to 2004 were investigated. Equine WNV attack rates were smoothed using an empirical Bayesian model, because of the variability among county equine populations (range 46−9,517). Risk factors investigated included hydrological features (lakes, rivers, swamps, canals and river basins), land cover (tree, mosaic, shrub, herbaceous, cultivated and artificial), elevation, climate (rainfall and temperature), and reports of WNV-positive mosquito and wild bird samples. Estimated county equine WNV attack rate was best described by the number of lakes, presence of broadleaf deciduous forest, presence of cultivated areas, location within the Brazos River watershed, WNV-positive mosquito status and average temperature. An understanding of environmental factors that increase equine WNV disease risk can be used to design and target disease control programs.  相似文献   
90.
Toxoplasmosis, caused by Toxoplasma gondii, is a significant disease in livestock and humans. In Iran, studies shows that T. gondii infection in humans is relatively high and prevalence is associated mainly with consumption of undercooked meat or meat products. We have examined 450 serum samples from female cattle distributed over all Ahvaz, the center of Khouzestan province, south-west of Iran. IgG antibodies to T. gondii were assayed by the modified agglutination test using whole tachyzoites of T. gondii, and found in 71 (15.77%) of 450 cattle with titers of 1:25 in 38, 1:50 in 18, 1:100 in 11, 1:200 in three and 1:400 in one. Titers of antibodies were decreased in cattle over 2 years old. These results indicate that T. gondii infection in cattle of Khouzestan is relatively considerable, but not very high and consumption of beef may be a source of infection for humans in south-west of Iran.  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