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   109591篇
  免费   5766篇
  国内免费   44篇
林业   7526篇
农学   4839篇
基础科学   794篇
  15119篇
综合类   15139篇
农作物   5491篇
水产渔业   6811篇
畜牧兽医   49725篇
园艺   2237篇
植物保护   7720篇
  2020年   764篇
  2019年   973篇
  2018年   4424篇
  2017年   4706篇
  2016年   2905篇
  2015年   1504篇
  2014年   1763篇
  2013年   3798篇
  2012年   3845篇
  2011年   5991篇
  2010年   4715篇
  2009年   3963篇
  2008年   5076篇
  2007年   5258篇
  2006年   3243篇
  2005年   2858篇
  2004年   2772篇
  2003年   2849篇
  2002年   2513篇
  2001年   3437篇
  2000年   3395篇
  1999年   2581篇
  1998年   999篇
  1997年   1074篇
  1996年   901篇
  1995年   1034篇
  1994年   907篇
  1993年   937篇
  1992年   1896篇
  1991年   1932篇
  1990年   1876篇
  1989年   1914篇
  1988年   1650篇
  1987年   1622篇
  1986年   1653篇
  1985年   1546篇
  1984年   1246篇
  1983年   1050篇
  1982年   725篇
  1979年   1078篇
  1978年   832篇
  1975年   824篇
  1974年   913篇
  1973年   889篇
  1972年   829篇
  1971年   809篇
  1970年   818篇
  1969年   796篇
  1968年   737篇
  1967年   749篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
53.
54.
55.
56.
57.
58.
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   
59.
60.
Estrogen and progesterone receptors (ER, PR) were measured in cytosol fractions from 18 primary canine mammary carcinomas by use of biochemical assays. One or both receptors were detected (> 10 fmol/mg of cytosol protein) in 11 tumors: 5 ER and PR; 2 ER only; 4 PR only. Mean cytoplasmic receptor concentrations (fmol/mg of cytosol protein) were 22.8 +/- 2.9 (SEM) for ER and 51.0 +/- 10.3 for PR in tumors containing ER and PR, 28.8 +/- 12.1 for ER in tumors containing only ER and 13.2 +/- 1.5 for PR in tumors containing only PR. Estrogen or progesterone receptors or both were identified in 6 of 9 tubular adenocarcinomas, 4 of 5 papillary adenocarcinomas, and 1 of 1 squamous cell carcinoma. These receptors were not identified in solid carcinomas (n = 2) or a single spindle cell carcinoma. Although the number of cases was limited, survival times of dogs tended to be longest in those with tumors containing ER alone or in combination with PR, intermediate in those with tumors containing only PR, and shortest in those with tumors without ER or PR. A correlation was not apparent between receptor status and age, presence of ovaries, tumor size, or histologic classification of the tumor. In the analysis of this series, the extent of surgery (mastectomy of the involved gland vs unilateral or bilateral mastectomy) did not appear to influence the outcome of the disease, and metastasis to regional lymph nodes did not appear to be a reliable prognostic indicator.  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