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   11456篇
  免费   1550篇
  国内免费   4篇
  13010篇
  2021年   123篇
  2018年   140篇
  2017年   118篇
  2016年   202篇
  2015年   343篇
  2014年   332篇
  2013年   432篇
  2012年   498篇
  2011年   479篇
  2010年   297篇
  2009年   312篇
  2008年   411篇
  2007年   479篇
  2006年   419篇
  2005年   406篇
  2004年   378篇
  2003年   354篇
  2002年   318篇
  2001年   298篇
  2000年   315篇
  1999年   321篇
  1998年   152篇
  1997年   124篇
  1996年   139篇
  1995年   129篇
  1994年   135篇
  1993年   142篇
  1992年   245篇
  1991年   235篇
  1990年   216篇
  1989年   214篇
  1988年   224篇
  1987年   212篇
  1986年   205篇
  1985年   226篇
  1984年   202篇
  1983年   152篇
  1982年   143篇
  1981年   121篇
  1980年   116篇
  1979年   187篇
  1978年   152篇
  1977年   130篇
  1976年   152篇
  1975年   146篇
  1974年   118篇
  1973年   151篇
  1972年   144篇
  1971年   120篇
  1970年   136篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
Grey seals on the West Hoyle Bank feed on a variety of fish and have a high incidence of dermal lesions, often associated with emaciation and nematode parasite infection. Corynebacterium phocae has been isolated from an active lesion. The significance of large numbers of seals in the Dee Estuary bearing lesions is discussed and the occurrence of seals with lesions elsewhere in British waters is reviewed. No evidence was found to associate the dermal lesions with any environmental factor and it is probable that lesions develop as a result of infection of minor wounds.  相似文献   
62.
63.
64.
65.
Optimum conditions for the extraction and assay by ATP-pyrophosphate exchange of the aminoacyl-sRNA synthetases of the various tissues of french bean (Phaseolus vulgaris) seeds and seedlings are described. Extracts of plumules, after passage through Sephadex G-25, were assayed for synthetase activity using an amino acid mixture as substrate, when a 30 to 100-fold stimulation of exchange above the endogenous level was obtained. This marked enhancement of exchange by added amino acids is largely attributed to the use of dilute extracts.  相似文献   
66.
67.
Summary The techniques of light and electron microscopy have been employed in a study of the protective coverings of the egg of Drosophila melanogaster. Data obtained during this investigation suggest the involvement of the follicle cells, in the production of one of these coverings and justify its classification as a secondary coat. The secondary coat of D. melanogaster is highly organized and has been divided into three Zones (I, II, IIII). The follicle cells enveloping the oocyte exhibit two phases of secretory activity each involving hypertrophy of the Golgi complex and rough endoplasmic reticulum, and the production of protein and polysaccharide components. The first phase concerns the elaboration of the material which gives rise to the homogeneous lamina referred to as Zone I. The second results in the release of an electron dense component which becomes organized into two laminae separated by struts or pillars; this construction is referred to as Zone II. At the completion of this secretory phase, the follicle cells assume a squamous morphology and a third Zone, composed of a homogeneous substance, appears between the follicle cells and Zone II.This investigation was supported by grant GM-08776 to one of us (EA) from the National Institutes of Health, United States Public Health Service.  相似文献   
68.
69.
Three cases of xylene poisoning occurred after prolonged inhalation of paint fumes. Analysis showed that xylene comprised more than 90% of the solvent in the paint, the total solvent comprising 34% of the paint by weight. One patient was dead on admission, while the other two recovered after at least 15 hours'' loss of consciousness. Both patients had transient liver cell damage, and one temporary impairment of renal function.  相似文献   
70.
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