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   329529篇
  免费   17719篇
  国内免费   684篇
林业   24757篇
农学   14255篇
基础科学   3012篇
  47196篇
综合类   47673篇
农作物   17578篇
水产渔业   18289篇
畜牧兽医   142524篇
园艺   6562篇
植物保护   26086篇
  2019年   3753篇
  2018年   4334篇
  2017年   4765篇
  2016年   5047篇
  2015年   4526篇
  2014年   5877篇
  2013年   16614篇
  2012年   8129篇
  2011年   10507篇
  2010年   8064篇
  2009年   8433篇
  2008年   9807篇
  2007年   8932篇
  2006年   9387篇
  2005年   8633篇
  2004年   8455篇
  2003年   8169篇
  2002年   7647篇
  2001年   8851篇
  2000年   8517篇
  1999年   7309篇
  1998年   4420篇
  1997年   4476篇
  1996年   4221篇
  1995年   4943篇
  1994年   4427篇
  1993年   4094篇
  1992年   6220篇
  1991年   6595篇
  1990年   6394篇
  1989年   6313篇
  1988年   5755篇
  1987年   5865篇
  1986年   5947篇
  1985年   5953篇
  1984年   5245篇
  1983年   4824篇
  1982年   3669篇
  1981年   3470篇
  1980年   3396篇
  1979年   4655篇
  1978年   4060篇
  1977年   3547篇
  1976年   3316篇
  1975年   3311篇
  1974年   4037篇
  1973年   4074篇
  1972年   3823篇
  1971年   3629篇
  1970年   3488篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
994.
995.
996.
On a property in the Nelson District, blood and urine samples were taken from red deer (Cervus elaphus) from which low (<1:100) antibody titres to serovar copenhageni and suspected leptospiral abortions had previously been reported. A total of 27 hinds were sampled. Microscopic agglutination test (MAT) titres in sera ranging from 1:32 to 1:128 were found in six animals. Thirteen leptospiral isolations were made from nine of the 27 urine samples. Four of these were typed as copenhageni and nine as hardjo. Two cultures were prepared from each urine sample and hardjo and copenhageni were both isolated from single urine samples from two animals. None of the 27 deer had serum MAT titres at 1:32 or above to copenhageni.  相似文献   
997.
Of 32 calves given an unknown amount of a pluronic bloat mixture with their milk, 28 died in convulsions over 24 hours. Supportive therapy was unsuccessful. Concentrations of pluronic present in abomasal and rumenal contents supported a diagnosis of pluronic poisoning.  相似文献   
998.
999.
Twelve isolates of bovine rotavirus, originating from eight dairy herds in Quebec known to have frequent epizootics of diarrhea in young calves in the last five years, were successfully propagated in cell cultures. The 12 isolates produced clear-cut plaques in BSC-1 cells and, except for one isolate, agglutinated human group "O" erythrocytes to an higher titer than bovine erythrocytes. Antisera to each isolate were produced in rabbits and used to study their antigenic relationships. All the isolates shared the group-specific immunofluorescent antigen and were antigenically related as demonstrated by the seroneutralization and hemagglutination-inhibition tests. However, the relationships to the Nebraska rotavirus was quite weak in cases of two Quebec isolates. When the genomes of the various isolates were compared by polyacrylamide gel electrophoresis, at least three different reproducible fractionation patterns could be identified.  相似文献   
1000.
Four infectious agents were isolated from the ticks Ixodes ricinus (L.) collected in the recreational area and park-forest of Prague. On the basis of cultivation, staining, biochemical, serologic properties, pathogenicity for animals and histological tests they were identified as Francisella tularensis with the following features: they are short, gram-negative rods of approximate dimensions of 0.3 X 0.8 micron, growing in enriched media after 3-4 day incubation at 37 degrees C. They form small circular, at first transparent, later greyish turbid colonies with regular rims. They are little active biochemically. They are susceptible to streptomycin and some broad spectrum antibiotics. They react positively with tularemic serum, but in lower titres than those in which this serum reacts with standard antigen. The microbes are highly pathogenic for mice, guinea-pigs, young rats, in which a massive bacteriemia occurs before death, but they do not kill rabbits. They multiply well in chick embryo, but do not grow in cell or tissue cultures. The most important histologic changes were observed in liver and spleen of mice. No pathologic changes were found in brain, lungs, heart, kidneys. Necroses were found in liver and in their marginal zones the microbes were present. Conspicuous were changes in numerous hepatocytes which became enlarged due to microbial multiplication and finally transformed into "sacs" packed with microbes. Histological and electronoptical examination showed that these are intracellular parasites fringed with a light lytic zone. Discussed is the problem to what extent the properties of the isolated strains are typical of F. tularensis as well as the importance of their detection from the aspect of epidemiology and differential diagnostics.  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