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   145572篇
  免费   8126篇
  国内免费   85篇
林业   5380篇
农学   4353篇
基础科学   1029篇
  16817篇
综合类   25419篇
农作物   5402篇
水产渔业   7307篇
畜牧兽医   75981篇
园艺   1768篇
植物保护   10327篇
  2018年   1791篇
  2017年   1977篇
  2016年   1857篇
  2015年   1624篇
  2014年   1982篇
  2013年   5397篇
  2012年   3799篇
  2011年   4773篇
  2010年   2949篇
  2009年   2988篇
  2008年   4702篇
  2007年   4484篇
  2006年   4352篇
  2005年   4051篇
  2004年   3949篇
  2003年   3948篇
  2002年   3874篇
  2001年   4690篇
  2000年   4538篇
  1999年   3691篇
  1998年   1463篇
  1997年   1488篇
  1996年   1393篇
  1995年   1744篇
  1994年   1577篇
  1993年   1503篇
  1992年   3150篇
  1991年   3279篇
  1990年   3323篇
  1989年   3321篇
  1988年   3050篇
  1987年   3132篇
  1986年   3222篇
  1985年   3087篇
  1984年   2606篇
  1983年   2309篇
  1982年   1574篇
  1981年   1471篇
  1980年   1427篇
  1979年   2316篇
  1978年   1909篇
  1977年   1623篇
  1976年   1441篇
  1975年   1540篇
  1974年   2074篇
  1973年   2086篇
  1972年   2053篇
  1971年   1816篇
  1970年   1712篇
  1969年   1571篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
191.
192.
In 15 horses with acute abdominal disease, a diagnosis of incarceration of small intestine through the epiploic foramen was made, either at the time of exploratory celiotomy or at necropsy.  相似文献   
193.
194.
Sheep affected by broken mouth periodontal disease (P.D.) were examined over a twelve month period for different clinical parameters. It is suggested that P.D. in sheep is an episodic phenomenon similar to human P.D., and that only a few animals with signs of P.D. may undergo clinically significant destruction over a yearly period. No single parameter could reliably predict future deterioration in other parameters.  相似文献   
195.
Analysis of whole blood samples from 174 cattle and, 174 sheep from 3 geographical regions of New Zealand over a 10 month period showed a mean (range) thiamine level of 122 nmol/l (71-237 nmol/l) for cattle and 118 nmol/l (67-227 nmol/l) for sheep. Regional and seasonal differences were noted with levels tending to rise over the summer period. A reference range of 75-185 nmol/l is proposed for both cattle and sheep to cover these variations. Levels below 50 nmol/l are considered indicative of deficiency.  相似文献   
196.
The detection of Mycobacterium paratuberculosis organisms in bovine faeces by isolation was compared with that by the microscopical examination of Ziehl-Neelsen stained faecal smears for the presence of clumps of acid-fast M. paratuberculosis organisms. Faeces were obtained from cattle naturally or experimentally infected with M. paratuberculosis as well as from uninfected cattle. Microscopical examination was an unreliable method for the detection of M. paratuberculosis organisms, since the organisms were only detected in 99 (=55.9%) of 177 culturally positive faecal samples. 1111 addition, clumps of acid-fast organisms indistinguishable from M. paratuberculosis were also observed iin three of 18 samples from cattle free from Johne's disease and in 18 of 37 culturally negative samples from paratuberculous cattle. When M. paratuberculosis organisms were added to faeces from an uninfected cow, results showed that isolation attempts should be positive when 15 or more M. paratuberculosis organisms per gram of faeces are present.  相似文献   
197.
Equine polymorphonuclear (PMN) and mononuclear (MN) leucocytes were separated on Percoll gradients and used to study the chemoattractant properties of the polar ether-linked phospholipid, platelet activating factor (PAF). Six concentrations of PAF ranging from 1 ng/ml to 100 g/ml were studied in each of two in vitro assay systems, the agarose microdroplet and a microfilter technique. Very significant (p<0.01) increases in the movement of both PMN and MN cells were obtained with most concentrations of PAF. In two instances there was no apparent concentration-response relationship, although the action of PAF was approximately bell-shaped in two others. The possible significance of these findings for equine inflammatory conditions is discussed.  相似文献   
198.
Pulmonary lesions associated with Corynebacterium ovis were analyzed with an indirect immunoperoxidase staining technique using monoclonal antibodies. The predominant cells in abscess walls and surrounding lung parenchyma were large macrophages which expressed major histocompatibility complex (MHC) class II molecules on their surfaces. T lymphocytes were prominent in the same sites in the naturally occurring lesions, and SBU-T4-positive ("helper/inducer") cells were the major subset of lymphocytes (mean T4/T8 ratio = 3.5). B lymphocytes and granulocytes comprised minor populations of infiltrating cells. These results implicate activated macrophages and MHC class II-restricted T lymphocytes in the pathogenesis of established C. ovis infections in sheep.  相似文献   
199.
200.
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