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   285809篇
  免费   16277篇
  国内免费   1263篇
林业   23940篇
农学   14401篇
基础科学   3208篇
  44853篇
综合类   37600篇
农作物   17358篇
水产渔业   17139篇
畜牧兽医   113656篇
园艺   6629篇
植物保护   24565篇
  2020年   3056篇
  2019年   3825篇
  2018年   4149篇
  2017年   4626篇
  2016年   4925篇
  2015年   4550篇
  2014年   5860篇
  2013年   16511篇
  2012年   7206篇
  2011年   9282篇
  2010年   7893篇
  2009年   8297篇
  2008年   8444篇
  2007年   7598篇
  2006年   8058篇
  2005年   7403篇
  2004年   7053篇
  2003年   6900篇
  2002年   6254篇
  2001年   6585篇
  2000年   6409篇
  1999年   5787篇
  1998年   4218篇
  1997年   4238篇
  1996年   3998篇
  1995年   4521篇
  1994年   3984篇
  1993年   3700篇
  1992年   4891篇
  1991年   5188篇
  1990年   4937篇
  1989年   4911篇
  1988年   4447篇
  1987年   4481篇
  1986年   4413篇
  1985年   4585篇
  1984年   4220篇
  1983年   3896篇
  1982年   3157篇
  1981年   3040篇
  1980年   2987篇
  1979年   3754篇
  1978年   3323篇
  1977年   3011篇
  1976年   2925篇
  1975年   2823篇
  1974年   3250篇
  1973年   3138篇
  1972年   2994篇
  1971年   2904篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
171.
172.
173.
174.
175.
Ohne Zusammenfassung Mit 2 Abbildungen  相似文献   
176.
177.
Observations on transplacental infection with bluetongue virus in sheep   总被引:1,自引:0,他引:1  
Twenty-four ewes were inoculated with 1 of 2 strains of bluetongue virus type 4 at 40, 60, or 80 days of gestation. Two ewes aborted, 2 ewes died, and 1 was killed during the experiment, but their fetuses were recovered. At term, 2 mummified fetuses, 4 dead lambs, and 17 clinically healthy lambs were produced by 12 sheep, and the remaining 7 sheep were barren. Porencephaly and cerebellar dysgenesis were found in term lambs born to sheep inoculated at 40 and 60 days of gestation. Radiographic examination of 12 fetuses showed developmental ages far less than their chronologic age; 8 fetuses had skeletal growth-retardation lines, which were also observed in the dead lambs. A systemic lymphoreticular hyperplasia was observed in the dead lambs and in all lambs at 12 weeks of age; in 4 of the latter, granulomatous reactions were present in the liver and kidney. Lungs of the full-term lambs were reduced in weight and showed poor alveolar development and mononuclear cell infiltration, which persisted in the 12-week-old lambs. It was concluded that bluetongue virus is capable of causing not only gross abnormalities of the CNS, but also generalized growth retardation and fetal lymphoreticular hyperplasia.  相似文献   
178.
179.
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   
180.
Isolated dog neutrophils exposed to known chemotactic factors assumed a bipolar configuration in suspension. This response was initiated within 2 minutes with a gradual return to spherical shape. The rate of return to sphere was positively correlated with the dose of stimulant. Dog neutrophils exposed to N-formylmethionyl-leucyl-phenylalanine (fMLP) did not adapt to bipolar conformation and did not bind radiolabeled fMLP. These findings are consistent with other species (pig and cow) that also did not respond to fMLP.  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