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   11577篇
  免费   653篇
  国内免费   951篇
林业   878篇
农学   751篇
基础科学   482篇
  1691篇
综合类   4554篇
农作物   681篇
水产渔业   647篇
畜牧兽医   2034篇
园艺   789篇
植物保护   674篇
  2024年   77篇
  2023年   254篇
  2022年   524篇
  2021年   618篇
  2020年   586篇
  2019年   569篇
  2018年   446篇
  2017年   550篇
  2016年   472篇
  2015年   617篇
  2014年   610篇
  2013年   816篇
  2012年   1066篇
  2011年   1056篇
  2010年   908篇
  2009年   780篇
  2008年   730篇
  2007年   665篇
  2006年   538篇
  2005年   402篇
  2004年   248篇
  2003年   175篇
  2002年   157篇
  2001年   70篇
  2000年   95篇
  1999年   37篇
  1998年   22篇
  1997年   11篇
  1996年   16篇
  1995年   6篇
  1994年   9篇
  1993年   5篇
  1992年   9篇
  1991年   8篇
  1990年   3篇
  1989年   3篇
  1988年   3篇
  1987年   3篇
  1986年   4篇
  1985年   2篇
  1984年   2篇
  1982年   2篇
  1981年   1篇
  1978年   1篇
  1962年   1篇
  1956年   2篇
  1955年   2篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
The impact of an efflux pump-related interaction between ivermectin and danofloxacin on their intestinal transport (ex vivo) and disposition kinetics (in vivo) was assessed. Eighteen male Corriedale sheep were randomly assigned to one of three groups. Animals in Group A received 0.2mg/kg ivermectin by SC injection, those in Group B were given 6 mg/kg danofloxacin SC on two occasions 48 h apart and those in Group C were treated with both compounds at the same rates. Plasma concentrations of ivermectin and danofloxacin were measured by HPLC using fluorescence detection. Ex vivo intestinal drug transport activity was measured by the use of the Ussing chamber technique. Plasma concentrations of ivermectin in the first 6 days after injection tended to be higher in Group C than Group A. Contemporaneous treatment with ivermectin significantly increased systemic exposure to danofloxacin (AUC values were 32-35% higher) and prolonged the elimination half-life of danofloxacin (40-52% longer). Ex vivo, incubation with ivermectin significantly decreased the efflux transport of rhodamine 123, a P-glycoprotein substrate, in sheep intestine, but no significant effect of danofloxacin on transport activity was observed. Evaluation of the interaction of danofloxacin with the breast cancer resistance protein (BCRP) showed that pantoprazole and ivermectin significantly decreased danofloxacin secretion in the rat intestine. Thus, the ivermectin-induced reduction of danofloxacin efflux transport observed in this study may involve BCRP activity but the involvement of P-glycoprotein cannot be ruled out.  相似文献   
22.
Salmonella and Yersinia are important enteropathogens in poultry and can affect birds of all ages, including embryos. These food-borne zoonotic enteropathogens are of great economic and medical concern worldwide and are intensely studied in poultry. Information regarding the prevalence of these bacteria in wild birds is scarce and biased toward avian species ecologically linked to humans, which have often been incriminated as both reservoirs and disseminators of these enteropathogens. The prevalence of Salmonella and Yersinia recovered from both the feces and eggs in a population of female pied flycatchers (Ficedula hypoleuca) breeding in nest-boxes in central Spain was evaluated. Salmonella arizonae was recovered from the feces of one female but was not recovered from eggs. Yersinia was not detected in either the feces or eggs. These results may suggest that Salmonella and Yersinia may be uncommon in this population studied and may indicate that these birds are unlikely reservoirs of Salmonella and Yersinia.  相似文献   
23.
本文通过对狼犬、鞑子犬、青龙犬、大丹犬、英卡犬、沙皮犬、藏鳌、拿波伦犬等8个品种192只犬繁殖性能研究。发现这八种犬的发情季节多集中在3月份和10~11月份,发情持续时间一般为14d,交配最佳时间为11d。配种次数与窝产仔数间不存在相关。  相似文献   
24.
从临床病料中分离鉴定出1株无血凝性的致病性兔出血症病毒(RHDV),命名为Yaan-1。HA试验测得该毒株原代及经兔体传3代后的肝毒在25℃、37℃和4℃时均无血凝性;但在琼脂扩散试验和对流免疫电泳中均可见分离株与常规RHDV高免血清形成清晰的沉淀线;电镜观察可见30nm左右的病毒粒子。采用RT-PCR方法将Yaan-1株的衣壳蛋白VP60基因进行了克隆测序,序列分析表明VP60基因序列全长1740bp,编码579个氨基酸,测序结果提交GenBank(注册号为DQ069280),并与世界各国的常规RHDV分离株进行比较,结果表明核苷酸同源性为90.0%~98.0%,氨基酸同源性为94.1%~99.0%,氨基酸变异多发生在衣壳蛋白C、E区;同时对Yaan-1株的分子量、等电点、疏水性、跨膜区等分子结构特征进行了分析。本研究首次报道了无血凝性RHDV中国分离株,丰富了地方毒株资源,为明确我国地方株的分子流行病学,以及对VP60蛋白分子特征研究提供了新材料。  相似文献   
25.
26.
浅谈二噁英的检验技术   总被引:2,自引:0,他引:2  
1 检测二口恶英的技术难度食品和饲料中二口恶英及其类似物的检验属于超痕量级检验,通常以ng/kg和pg/kg表示。它比其他污染物含量低千倍到亿倍以上,检测难度很大,其多组分即同系物、异构体的化学前处理技术几乎包罗近代最先进的手段,涉及分离、富集、提取、净化、清洗和浓缩装置,还包含自动凝胶色谱(AutomatedGelPermeationChromatography)、反相HPLC、玻璃色谱柱等。检测过程需要尖端大型分析仪器的支持,定量分析依靠HRGC/HRMS,对仪器的灵敏度、选择性和特异性要求极高,是现今分…  相似文献   
27.
文章对鸡球虫耐药性的产生机制、检测方法及其延缓措施的研究进展进行了概述。  相似文献   
28.
Four hundred male chickens were selected to study the effects of pyruvate (Pyr), creatine pyruvate (CrPyr) and creatine (Cr) on the expression of hepatic mitochondrial and cytoplasm proteins associated with lipid and protein metabolism. Mitochondrial purification was accomplished using the two-step differential centrifugation and density gradient method, and the activities of organelle-specific marker enzymes were determined to assess the purity of the mitochondria. Proteins were extracted and fractionated by two-dimensional electrophoresis and the differential protein spots were assessed by matrix-assisted laser desorption/ionization-time of flight mass spectrometry. CrPyr reduced fatty acid accumulation by down-regulating adipose differentiation-related protein, inhibited ATP synthase expression, and reduced cholesteryl ester transfer protein (CETP) expression, thus reducing the levels of high density lipoprotein and triglycerol (TG) levels (thereby lowering fat and cholesterol deposition). CrPyr increased the expression of eukaryotic translation initiation factor (eIF) 2B, calreticulin (CRT) and eIF3a, thus promoting protein synthesis. CrPyr up-regulated the expression of fatty acid-binding proteins, CETP and apolipoprotein A-IV in cytoplasmic extracts, and these proteins accelerated the decomposition of fatty acids and TG, thus reducing fat deposition. In conclusion, CrPyr plays an important role in lipolysis and protein synthesis, and this effect was more pronounced than was the effect of Pyr and Cr.  相似文献   
29.
为了提高葡萄园资源利用率和综合效益,构建了牧草-鹅-鲜食葡萄循环生态种养体系。实践表明,在设施葡萄园推广套种牧草养鹅、鹅粪生产有机肥料、有机肥料种植葡萄和牧草等高效配套技术,取得了良好的经济效益、生态效益和社会效益。实施牧草-鹅-鲜食葡萄循环生态种养是江苏沿海地区发展现代农业的一种有效生产模式。  相似文献   
30.
A seven-year-old female Indian python (Python molurus) weighing about 35kg was euthanased after several clinical episodes of stomatitis, pneumonia, ophthalmitis and dystocia over a period of four years. The animal had been maintained in a terrarium in a circus truck at an adequate temperature. During shows, however, the snake was considered to be exposed to stressful conditions for several hours at a time at low temperatures and with noise and bright lights. A post-mortem examination indicated ulcerative stomatitis, osteomyelitis, severe pneumonia and numerous granulomata and multifocal necrosis in stomach and spleen. Corynebacterium macginleyi was isolated in pure culture from the ulcerative stomatitis, and mixed with Stenotrophomonas maltophilia from the lungs and spleen. The findings indicated that the snake had died from a septicaemic process caused by C. macginleyi, probably originating from the stomatitis. The role of S. maltophilia as a secondary agent is discussed. The stress of the circus show and poor husbandry may have predisposed the animal to infection and septicaemia. This is the first report of C. macginleyi causing disease in a snake.  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