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   21556篇
  免费   42篇
  国内免费   74篇
系统科学   74篇
丛书文集   279篇
教育与普及   68篇
理论与方法论   90篇
现状及发展   9798篇
研究方法   935篇
综合类   10151篇
自然研究   277篇
  2013年   173篇
  2012年   317篇
  2011年   584篇
  2010年   142篇
  2008年   358篇
  2007年   408篇
  2006年   376篇
  2005年   405篇
  2004年   376篇
  2003年   362篇
  2002年   362篇
  2001年   597篇
  2000年   590篇
  1999年   408篇
  1992年   382篇
  1991年   303篇
  1990年   335篇
  1989年   333篇
  1988年   335篇
  1987年   328篇
  1986年   308篇
  1985年   436篇
  1984年   295篇
  1983年   266篇
  1982年   254篇
  1981年   239篇
  1980年   307篇
  1979年   716篇
  1978年   549篇
  1977年   564篇
  1976年   437篇
  1975年   481篇
  1974年   618篇
  1973年   551篇
  1972年   613篇
  1971年   622篇
  1970年   814篇
  1969年   694篇
  1968年   714篇
  1967年   650篇
  1966年   590篇
  1965年   403篇
  1964年   115篇
  1959年   216篇
  1958年   390篇
  1957年   299篇
  1956年   270篇
  1955年   222篇
  1954年   203篇
  1948年   177篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Retrograde transport of endocytosed Shiga toxin to the endoplasmic reticulum.   总被引:39,自引:0,他引:39  
K Sandvig  O Garred  K Prydz  J V Kozlov  S H Hansen  B van Deurs 《Nature》1992,358(6386):510-512
Shiga toxin and some other protein toxins that act on targets in the cytosol have previously been shown to enter the trans-Golgi network. Transport by this route may be necessary for translocation of the toxin to the cytosol and for intoxication, but it is not known whether the enzymatically active part of the toxins actually enters the cytosol from the trans-Golgi network. It has been suggested that such toxins are transported in a retrograde manner to the endoplasmic reticulum and that translocation occurs in this organelle, but retrograde transport of endocytosed material beyond the trans-Golgi network has never been demonstrated. Here we show that in butyric acid-treated A431 cells endocytosed Shiga toxin is not only transported to the trans-Golgi network, but also to all Golgi stacks, to the endoplasmic reticulum and to the nuclear envelope. Furthermore, butyric acid sensitizes the cells to Shiga toxin, which is consistent with the possibility that retrograde transport is required for translocation of the toxin to the cytosol.  相似文献   
22.
1 Results The development of the concepts of nanotechnology has given an important impact on the design of new polymer based materials which are in most cases characterized by a multiphase morphology. When at least one phase has nanometric dimension(s) the system can be considered as a nanocomposite where the interface is not only determining for the adhesion but also may play a role in some bulk properties. Indeed in nanostructured multiphase solids the interface is significant as a bulk component. The...  相似文献   
23.
1 Results Pyrimidinones (PMs) are a class of important heterocycles which have been well documented throughout the literature due to their biological importance. They exhibit a wide range of pharmaceutical and therapeutic properties[1].A rapid and efficient one-pot method for the synthesis of 4,6-diarylpyrimidin-2(1H)- ones and related heterocycles is described.The condensation of acetophenone derivatives,aldehydes and urea in the presence of sulfamic acid was employed to synthesize a variety of pyrimid...  相似文献   
24.
Summary The application of diphenylilacetic acid has shown favorable effects on the growth of tobacco plants. Solutions containing 10 p.p.m. and 20 p.p.m. produce, in weight, an almost double growth in treated plants in comparison with the controls. Diphenylilacetic acid can be considered as a growth-promoting substance. The data are not definite.  相似文献   
25.
1 Introduction   Nanoscale science and technology have attracted greatattention since the novel properties become dominant for well-known materials as their sizes reduced to some critical dimension. These properties frequently originate in lattice distortions, structure transformations etc[1]. The variations of size and structure ofnanocrystals lead to the change of their electronic structures. Very recently, nanoscale materials with different electronic structures were utilized in fabricating nanoscale junctions[2].   ……  相似文献   
26.
27.
The characteristic circular dichroism of bilirubin bound to human serum albumin undergoes a remarkable sign inversion on addition of halothane, chloroform and other volatile anesthetics. This sign inversion, which is completely reversed by removal of the anesthetic, reflects a pronounced conformational change of the bound ligand; probably a complete inversion of chirality. The observation suggests that association of volatile anesthetics with proteins can markedly alter the internal topography of receptor sites and potentially influence the stereoselectivity of ligand binding.  相似文献   
28.
29.
DNA fingerprinting transforms the art of cell authentication.   总被引:4,自引:0,他引:4  
G N Stacey  B J Bolton  A Doyle 《Nature》1992,357(6375):261-262
The increasing diversity of new cell cultures is seriously stretching the capabilities of traditional methods of identification. DNA fingerprinting is set to play an important role in increasing confidence in the authenticity of cultures in research and industry.  相似文献   
30.
Thyroid cancer after Chernobyl.   总被引:17,自引:0,他引:17  
  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