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   77022篇
  免费   3670篇
  国内免费   53篇
林业   3275篇
农学   2135篇
基础科学   534篇
  8400篇
综合类   16814篇
农作物   3176篇
水产渔业   3195篇
畜牧兽医   38173篇
园艺   829篇
植物保护   4214篇
  2018年   808篇
  2017年   897篇
  2016年   782篇
  2014年   823篇
  2013年   2465篇
  2012年   1650篇
  2011年   2001篇
  2010年   1306篇
  2009年   1263篇
  2008年   1973篇
  2007年   1888篇
  2006年   1838篇
  2005年   1784篇
  2004年   1690篇
  2003年   1783篇
  2002年   1670篇
  2001年   1924篇
  2000年   1874篇
  1999年   1532篇
  1997年   692篇
  1995年   769篇
  1994年   705篇
  1993年   698篇
  1992年   1526篇
  1991年   1665篇
  1990年   1714篇
  1989年   1767篇
  1988年   1657篇
  1987年   1570篇
  1986年   1657篇
  1985年   1583篇
  1984年   1325篇
  1983年   1187篇
  1982年   840篇
  1981年   812篇
  1980年   762篇
  1979年   1340篇
  1978年   1056篇
  1977年   945篇
  1976年   883篇
  1975年   1006篇
  1974年   1325篇
  1973年   1244篇
  1972年   1329篇
  1971年   1270篇
  1970年   1185篇
  1969年   1030篇
  1968年   842篇
  1967年   971篇
  1966年   832篇
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
61.
62.
63.
64.
Ohne Zusammenfassung Hoewel dit artikel ook reeds in eenige bladen is gepubliceerd, meenen wij het, in verband met het groote belang, dat aan een ruime bekendmaking van het gebruik van Derris bij de thripsbestrijding in vlas verbonden is, ook in ons Tijdschrift te kunnen opnemen, mede als aanvulling van wat daarin over dit onderwerp reeds verschenen is. Red.  相似文献   
65.
COPYRIGHT     
  相似文献   
66.
Ohne Zusammenfassung Mit 2 Abbildungen  相似文献   
67.
68.
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   
69.
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   
70.
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