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   84149篇
  免费   5265篇
  国内免费   768篇
林业   3243篇
农学   2534篇
基础科学   683篇
  10023篇
综合类   16793篇
农作物   3090篇
水产渔业   3812篇
畜牧兽医   43823篇
园艺   1158篇
植物保护   5023篇
  2021年   740篇
  2020年   828篇
  2019年   1004篇
  2018年   1383篇
  2017年   1589篇
  2016年   1405篇
  2015年   1348篇
  2014年   1537篇
  2013年   2986篇
  2012年   2932篇
  2011年   3538篇
  2010年   2340篇
  2009年   2207篇
  2008年   3158篇
  2007年   3035篇
  2006年   2730篇
  2005年   2660篇
  2004年   2382篇
  2003年   2443篇
  2002年   2279篇
  2001年   2530篇
  2000年   2586篇
  1999年   1989篇
  1998年   817篇
  1997年   721篇
  1995年   756篇
  1992年   1571篇
  1991年   1767篇
  1990年   1680篇
  1989年   1627篇
  1988年   1516篇
  1987年   1568篇
  1986年   1612篇
  1985年   1440篇
  1984年   1227篇
  1983年   1044篇
  1982年   697篇
  1979年   1086篇
  1978年   857篇
  1977年   699篇
  1976年   729篇
  1975年   764篇
  1974年   1027篇
  1973年   1017篇
  1972年   978篇
  1971年   903篇
  1970年   878篇
  1969年   842篇
  1967年   718篇
  1966年   685篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
51.
52.
53.
54.
55.
56.
57.
Antigens in the extracellular protein (ECP) complexes of Bacteroides nodosus, isolated from sheep with either benign or virulent footrot, were studied by immunoelectrophoresis (IEP). Rabbit antisera against ECP from virulent and benign strains, were used in homologous and heterologous crossed IEP. Four precipitin peaks unique to the virulent strain, and five peaks unique to the benign strain were identified. In an attempt to characterize the different antigens in ECP, rabbit antisera were raised against an outer membrane protein (OMP, mol. wt. 35 000 daltons), pili and various proteases of virulent and benign strains of B. nodosus. No precipitin band was observed when ECP from both B. nodosus strains were reacted against anti-OMP and anti-pilus antisera. However, single precipitin bands unique to one protease from the benign strain and one protease from the virulent strain were identified. The results suggest that specific antigens other than proteases or pili are important in determining whether a B. nodosus isolate is virulent or benign.  相似文献   
58.
A brief discussion of those aspects of neonatal physiology that pertain to anesthetic risk and selection of anesthetic techniques is followed by discussion of suggested techniques for anesthetic management in healthy foals. Preoperative preparation and management of foals with selected serious surgical conditions are also considered.  相似文献   
59.
Crystalluria results from oversaturation of urine with crystallogenic substance. However, oversaturation may occur as a result of in vitro as well as in vivo events. The microscopic appearance of crystals only represents a tentative identification of their composition because variable conditions associated with their formation, growth, and dissolution may alter their appearance. Definitive identification is dependent on physical methods such as optical crystallography, x-ray diffraction, and electron microscopic analysis.  相似文献   
60.
A steam-dryer, designed and manufactured in Sweden, was evaluated for destroying Bursaphelenchus xylophilus in pine chips from southern USA. In a trial, pine chips were treated at different temperature and pressure regimes for 5 or 10min. The lowest time/temperature/pressure combination was to increase the vessel temperature from 85 to 104°C in 5 min at low pressure. Samples of pine chips were assayed for nematodes in laboratories in USA, Sweden, and Finland. No nematodes of any species were recovered from any of the treated pine-chip samples. Large and heterogeneous pieces of wood in the treated samples were also nematode-free. The apparatus was a prototype capable of handling about 400 kg h-1. The final version would have to be able to process 100-200 th-1.  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