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   41139篇
  免费   67篇
  国内免费   114篇
系统科学   209篇
丛书文集   852篇
教育与普及   108篇
理论与方法论   256篇
现状及发展   17994篇
研究方法   1634篇
综合类   19659篇
自然研究   608篇
  2013年   258篇
  2012年   570篇
  2011年   1213篇
  2010年   254篇
  2008年   744篇
  2007年   732篇
  2006年   769篇
  2005年   787篇
  2004年   737篇
  2003年   732篇
  2002年   729篇
  2001年   1181篇
  2000年   1086篇
  1999年   751篇
  1992年   714篇
  1991年   571篇
  1990年   610篇
  1989年   609篇
  1988年   605篇
  1987年   606篇
  1986年   613篇
  1985年   775篇
  1984年   630篇
  1983年   493篇
  1982年   455篇
  1981年   429篇
  1980年   550篇
  1979年   1237篇
  1978年   1053篇
  1977年   1036篇
  1976年   768篇
  1975年   850篇
  1974年   1183篇
  1973年   1054篇
  1972年   1092篇
  1971年   1312篇
  1970年   1685篇
  1969年   1317篇
  1968年   1272篇
  1967年   1289篇
  1966年   1110篇
  1965年   816篇
  1964年   221篇
  1959年   505篇
  1958年   765篇
  1957年   587篇
  1956年   508篇
  1955年   433篇
  1954年   500篇
  1948年   304篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
Blinking     
CLARK RE  LAWSON RW 《Nature》1948,162(4129):970
  相似文献   
142.
143.
The association of variants in complement factors H and B with age-related macular degeneration has led to more intense genetic and functional analysis of the complement pathway. We identify a nonsynonymous coding change in complement factor 3 that is strongly associated with risk of age-related macular degeneration in a large case-control sample.  相似文献   
144.
145.
Rhinoviruses, which cause common cold, belong to the Picornaviridae family, small non-enveloped viruses (diameter 15-30 nm) containing a single-stranded RNA genome (about 7 kb). Over 100 different rhinoviral serotypes have been identified thus far, establishing rhinoviruses as the most diverse group of Picornaviridae. Based on receptor binding properties, rhinoviruses are divided into two classes: the major group binding to intracellular adhesion molecule-1 and the minor group binding to the very low density lipoprotein receptors. Interactions between virus and the receptor molecules cause a conformational change in the capsid, which is a prerequisite for viral uptake. Rhinoviruses trigger a chemokine response upon infection that may lead to exacerbation of the symptoms of common cold, i.e. asthma and inflammation. The following review aims to summarize the knowledge about rhinoviral infections and discusses therapeutical approaches against this almost perfectly adapted pathogen.  相似文献   
146.
It is well known that considering a non-Euclidean Minkowski metric in Multidimensional Scaling, either for the distance model or for the loss function, increases the computational problem of local minima considerably. In this paper, we propose an algorithm in which both the loss function and the composition rule can be considered in any Minkowski metric, using a multivariate randomly alternating Simulated Annealing procedure with permutation and translation phases. The algorithm has been implemented in Fortran and tested over classical and simulated data matrices with sizes up to 200 objects. A study has been carried out with some of the common loss functions to determine the most suitable values for the main parameters. The experimental results confirm the theoretical expectation that Simulated Annealing is a suitable strategy to deal by itself with the optimization problems in Multidimensional Scaling, in particular for City-Block, Euclidean and Infinity metrics.  相似文献   
147.
148.
Protein-protein interaction analyses have uncovered a ciliary and basal body protein network that, when disrupted, can result in nephronophthisis (NPHP), Leber congenital amaurosis, Senior-L?ken syndrome (SLSN) or Joubert syndrome (JBTS). However, details of the molecular mechanisms underlying these disorders remain poorly understood. RPGRIP1-like protein (RPGRIP1L) is a homolog of RPGRIP1 (RPGR-interacting protein 1), a ciliary protein defective in Leber congenital amaurosis. We show that RPGRIP1L interacts with nephrocystin-4 and that mutations in the gene encoding nephrocystin-4 (NPHP4) that are known to cause SLSN disrupt this interaction. RPGRIP1L is ubiquitously expressed, and its protein product localizes to basal bodies. Therefore, we analyzed RPGRIP1L as a candidate gene for JBTS and identified loss-of-function mutations in three families with typical JBTS, including the characteristic mid-hindbrain malformation. This work identifies RPGRIP1L as a gene responsible for JBTS and establishes a central role for cilia and basal bodies in the pathophysiology of this disorder.  相似文献   
149.
150.
Summary Chalcone, flavanone, flavone, and its derivatives had a certain bacteriostatic effect onSt. aureus. Flavonol has no activity and morin, a derivative of flavonol, showed only a weak inhibition of the bacterial growth.Cystein did not have any antagonistic effect.Extracts of drugs, which contain natural flavanones, flavones, isoflavones and flavonols, are more or less bacteriostatic.  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