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   273481篇
  免费   15799篇
  国内免费   678篇
林业   23752篇
农学   14053篇
基础科学   2972篇
  43598篇
综合类   32852篇
农作物   17286篇
水产渔业   17083篇
畜牧兽医   107558篇
园艺   6414篇
植物保护   24390篇
  2020年   2887篇
  2019年   3694篇
  2018年   4060篇
  2017年   4394篇
  2016年   4838篇
  2015年   4351篇
  2014年   5735篇
  2013年   16379篇
  2012年   6507篇
  2011年   8452篇
  2010年   7448篇
  2009年   7996篇
  2008年   7767篇
  2007年   6889篇
  2006年   7575篇
  2005年   6795篇
  2004年   6644篇
  2003年   6496篇
  2002年   5853篇
  2001年   6209篇
  2000年   5880篇
  1999年   5527篇
  1998年   4195篇
  1997年   4243篇
  1996年   3995篇
  1995年   4566篇
  1994年   3973篇
  1993年   3688篇
  1992年   4672篇
  1991年   4931篇
  1990年   4662篇
  1989年   4698篇
  1988年   4226篇
  1987年   4219篇
  1986年   4145篇
  1985年   4521篇
  1984年   4055篇
  1983年   3820篇
  1982年   3078篇
  1981年   2992篇
  1980年   2948篇
  1979年   3657篇
  1978年   3225篇
  1977年   2974篇
  1976年   2833篇
  1975年   2750篇
  1974年   3111篇
  1973年   2985篇
  1972年   2852篇
  1971年   2744篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
73.
74.
75.
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   
76.
77.
Over 54,600 ha of table grapes (Vitis vinifera), mainly cvs. ‘Thompson Seedless’, ‘Flame Seedless’ and ‘Redglobe’, are planted in Chile. Almost the entire production is exported to the USA, Europe, Asia, or one of several Latin American countries, which typically requires 15–40 d of maritime transportation. During this period, several physical, physiological, and pathological factors cause table grape deterioration. Because berry size is the main quality factor in international markets, farmers often overuse the growth regulators, gibberellic acid (GA3) and forchlorfenuron (CPPU), in an effort to increase berry size. We examined the effect of preharvest growth regulators on seedless (‘Thompson Seedless’, and ‘Ruby Seedless’) and seeded (‘Redglobe’) table grape cultivars during cold (0 °C) storage plus a shelf life period of 3 d at 20 °C. The overuse of GA3, eight instead of two GA3 applications on Thompson Seedless, and the use of one GA3 application on Redglobe and ‘Ruby Seedless’, increased berry pedicel thickness and lowered cuticle content but induced shatter and predisposed grapes to gray mold caused by Botrytis cinerea. In contrast, CPPU increased berry pedicel thickness and cuticle content but did not increase shatter or gray mold incidence. Clusters that were subjected to overuse of combined GA3 and CPPU were highly sensitive to shatter, had the thickest pedicel, and developed a high gray mold incidence during cold storage. Hairline, a fine cracking developed during cold storage, was induced on ‘Thompson Seedless’ and ‘Ruby Seedless’ by growth regulators, but no hairline occurred on ‘Redglobe’ table grapes. Therefore, berry quality during cold storage is greatly influenced by growth regulator management in the vineyard.  相似文献   
78.
Disseminated Aspergillus terreus infection was diagnosed in ten previously healthy adult dogs--nine German shepherds and one dalmatian. The disease was characterized by the presence of multiple granulomas and infarcts in a wide range of organs. The kidney, spleen, and skeletal system were most commonly and severely affected. Fungal hyphae were demonstrated in large numbers within granulomas and thrombi, and A. terreus was readily isolated by culture. This disseminated mycosis appears unique; in this series of cases there was no apparent predisposing factor, portal of entry, or primary focus for dissemination of the infection.  相似文献   
79.
80.
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