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   172057篇
  免费   9416篇
  国内免费   121篇
林业   7781篇
农学   5821篇
基础科学   1082篇
  22324篇
综合类   26095篇
农作物   6798篇
水产渔业   8870篇
畜牧兽医   89265篇
园艺   2347篇
植物保护   11211篇
  2019年   1686篇
  2018年   2595篇
  2017年   2949篇
  2016年   2722篇
  2015年   2294篇
  2014年   2843篇
  2013年   6849篇
  2012年   5208篇
  2011年   6421篇
  2010年   4183篇
  2009年   4246篇
  2008年   6219篇
  2007年   5915篇
  2006年   5580篇
  2005年   5226篇
  2004年   4914篇
  2003年   5055篇
  2002年   4538篇
  2001年   5592篇
  2000年   5633篇
  1999年   4485篇
  1998年   1917篇
  1997年   1817篇
  1996年   1714篇
  1995年   1995篇
  1994年   1769篇
  1993年   1636篇
  1992年   3438篇
  1991年   3650篇
  1990年   3610篇
  1989年   3526篇
  1988年   3225篇
  1987年   3216篇
  1986年   3225篇
  1985年   3122篇
  1984年   2564篇
  1983年   2216篇
  1982年   1526篇
  1979年   2332篇
  1978年   1870篇
  1977年   1505篇
  1976年   1592篇
  1975年   1649篇
  1974年   1984篇
  1973年   1977篇
  1972年   1872篇
  1971年   1774篇
  1970年   1689篇
  1969年   1693篇
  1967年   1522篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
102.
103.
104.
105.
106.
107.
108.
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   
109.
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   
110.
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   
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