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   51561篇
  免费   256篇
  国内免费   542篇
系统科学   1229篇
丛书文集   99篇
教育与普及   283篇
理论与方法论   527篇
现状及发展   30870篇
研究方法   633篇
综合类   16528篇
自然研究   2190篇
  2013年   805篇
  2012年   575篇
  2011年   2558篇
  2010年   416篇
  2009年   604篇
  2008年   745篇
  2007年   830篇
  2006年   934篇
  2005年   1105篇
  2004年   2193篇
  2003年   1807篇
  2002年   1519篇
  2001年   1289篇
  2000年   825篇
  1999年   916篇
  1998年   642篇
  1997年   775篇
  1996年   510篇
  1994年   683篇
  1993年   691篇
  1992年   833篇
  1991年   730篇
  1990年   795篇
  1989年   608篇
  1988年   602篇
  1987年   608篇
  1986年   664篇
  1985年   803篇
  1984年   727篇
  1983年   622篇
  1982年   774篇
  1981年   811篇
  1980年   865篇
  1979年   1288篇
  1978年   1165篇
  1977年   1129篇
  1976年   1062篇
  1975年   1015篇
  1974年   792篇
  1973年   1062篇
  1972年   1137篇
  1971年   1145篇
  1970年   1178篇
  1969年   1048篇
  1968年   1069篇
  1967年   922篇
  1966年   764篇
  1965年   625篇
  1964年   492篇
  1958年   450篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
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   
82.
83.
通过对“洋务运动博物馆”东立面形象的反思 ,讨论了建筑形态设计中隐喻手法的运用 ;就此引申 ,探讨传统问题 ,指出正确理解传统与创新的四个方面。  相似文献   
84.
Summary Hydrochlorothiazide, acutely injected in rats, has a weak analgesic activity per se and potentiates and prolongs the antinociceptive effect of morphine.This work was supported in part by grants from Consiglio Nazionale delle Ricerche, and by Ministero della Pubblica Istruzione, Roma.  相似文献   
85.
Targeted inhibition of Livin resensitizes renal cancer cells towards apoptosis   总被引:10,自引:0,他引:10  
Cancer cells are typically characterized by apoptosis deficiency. In order to investigate a possible role for the anti-apoptotic livin gene in renal cell cancer (RCC), we analyzed its expression in tumor tissue samples and in RCC-derived cell lines. In addition, we studied the contribution of livin to the apoptotic resistance of RCC cells by RNA interference (RNAi). Livin gene expression was detected in a significant portion of RCC tumor tissue specimens (13/14, 92.9%) and tumor-derived cell lines (12/15, 80.0%). Moreover, targeted inhibition of livin by RNAi markedly sensitized RCC cells towards proapoptotic stimuli, such as UV irradiation or the chemotherapeutic drugs etoposide, 5-fluorouracil, and vinblastine. These effects were specific for livin expressing tumor cells. We conclude that livin can contribute significantly to the apoptosis resistance of RCC cells. Targeted inhibition of livin could represent a novel therapeutic strategy to increase the sensitivity of renal cancers towards pro-apoptotic agents. Received 30 November 2006; received after revision 22 February 2007; accepted 20 March 2007  相似文献   
86.
87.
88.
89.
Summary Traces of nor-adrenaline restore the vascular action of adrenaline altered in epinephrectomized dogs to the reaction of the normal animal. Therefore it is claimed that the adrenals discharge one or several substances into the blood stream, which are necessary for the usual peripheral vascular action of adrenaline. Further investigations are in progress.  相似文献   
90.
The visual field is topographically mapped onto the primary visual cortex (V1), forming a retinotopic map which is far more detailed for the foveal regions than for the periphery. We found that receptive field (RF) size in monkey V1 increases with eccentricity, and that a 1—2 m2 V1 region contains roughly a complete set of machinery necessary to analyze a visual-field area whose size is about that of the RFs of the cells. This allows V1 to be anatomically uniform, and is in sharp contrast with the retina.  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