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   7890篇
  免费   820篇
  国内免费   6篇
  8716篇
  2023年   37篇
  2022年   66篇
  2021年   128篇
  2020年   76篇
  2019年   121篇
  2018年   109篇
  2017年   116篇
  2016年   180篇
  2015年   337篇
  2014年   373篇
  2013年   414篇
  2012年   541篇
  2011年   503篇
  2010年   321篇
  2009年   316篇
  2008年   428篇
  2007年   463篇
  2006年   432篇
  2005年   435篇
  2004年   392篇
  2003年   370篇
  2002年   373篇
  2001年   141篇
  2000年   97篇
  1999年   122篇
  1998年   91篇
  1997年   77篇
  1996年   64篇
  1995年   77篇
  1994年   72篇
  1993年   64篇
  1992年   73篇
  1991年   71篇
  1990年   68篇
  1989年   69篇
  1988年   64篇
  1987年   74篇
  1986年   69篇
  1985年   65篇
  1984年   83篇
  1983年   50篇
  1982年   61篇
  1981年   48篇
  1980年   42篇
  1979年   40篇
  1978年   48篇
  1976年   44篇
  1974年   32篇
  1973年   45篇
  1972年   39篇
排序方式: 共有8716条查询结果,搜索用时 19 毫秒
1.
2.
3.
4.
From experience in the Northampton/Kettering area 9 to 10% of all patients in a general hospital requiring care in an intensive therapy unit were aged 12 years or under. Fifty-nine children were admitted to the intensive therapy unit of Northampton General Hospital between May 1967 and August 1969. Of these, 22 had been injured in road traffic accidents, five were surgical emergencies, five had meningitis, four status epilepticus, and four respiratory infections.All of the 30 families interviewed were in favour of their child being admitted to the unit, and none considered that the experience had had any lasting adverse psychological effect on the child. It is suggested that certain carefully selected child patients do benefit from the facilities of an intensive therapy unit, and for this reason such units must be designed, equipped, and staffed with this in mind.  相似文献   
5.
Summary The physicochemical properties of the interactions of RNA polymerase (RPase) with promoter and nonspecific DNA sequences have been investigated. These show that nonspecific binding is principally an ionic interaction and that promoter binding is more complex, involving nonionic interactions. Nonspecific binding has been shown to be very important in the promoter search, and one-dimensional diffusion can account for the rate at which RPase finds the promoter. Significant differences have been reported in the binding process for various promoters and in the effects of regulatory proteins. Further investigation of these differences will lead to a better understanding of the selectivity and regulation of the initiation process.The pathways of the initiation process have been outlined, by recent studies and considerable progress has been made in determining the rates of interconversion of the intermediate states. A number of questions remain about the detail of initiation and the effects of various parameters on the reactions. Of particular importance is the identification of the point at which the enzyme becomes truly processive. In addition, the step which is rate limiting has not been identified in either the productive or nonproductive process. The mechanistic features of the steps after bond formation are just beginning to yield to investigation.Use of substrate analogs with RPase has led to a picture of the polymerization site according to the ability of the enzyme to incorporate analogs. Base specificity appears to be determined primarily by interaction with the template rather than the enzyme, but the ribose moiety must interact with the site quite specifically. The orientation of the phosphate residues has been determined by NMR, which has also proved to be a valuable probe of the initiation site. At this site base specificity is resident in the enzyme and expressed through the interaction of the base and intrinsic metal, as shown by studies with the Cobalt substituted enzyme. In both initiation and polymerization, the reaction has been shown to proceed by inversion of configuration. Techniques similar to those used for initiation will probably be applied to the polymerization reaction as well, which has not recently received as much attention with respect to mechanism. Functional phenomena such as pausing make the polymerization process particularly promising for producing insight into RPase reactions.  相似文献   
6.
Andrew C. Harper 《CMAJ》1980,123(5):400-401
  相似文献   
7.
8.
9.
10.
Leaves and roots of 19 species and six subspecies of Hawaiian Bidens were examined for polyacetylenes. Eleven C13 hydrocarbons, aromatic and thiophenyl derivatives, one C14 tetrahydropyran and three C17 hydrocarbons were isolated all identified. All can be derived from a common precursor, oleic acid. Polyacetylenes were not detected in the leaves of 13 taxa although they are found in the roots of all. The occurrence of 2-[2-phenyl-ethyne-1-yl]-5 acetoxymethyl thiopene in Bidens has not been previously reported. Its ubiquitous presence is consistent with other evidence that the Hawaiian species are all derived from a single ancestral immigrant to the islands. Most taxa could be distinguished by their complement of polyacetylenes in roots and leaves. No variation was found to occur within taxa except in B. torta, in which each population had a unique array of polyacetylenes. Above the species level there appeared to be no taxonomically significant pattern to the distribution of polyacetylenes in this group.  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