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   38096篇
  免费   66篇
  国内免费   100篇
系统科学   175篇
丛书文集   757篇
教育与普及   102篇
理论与方法论   221篇
现状及发展   16542篇
研究方法   1569篇
综合类   18386篇
自然研究   510篇
  2013年   200篇
  2012年   501篇
  2011年   1048篇
  2010年   211篇
  2008年   641篇
  2007年   667篇
  2006年   697篇
  2005年   707篇
  2004年   652篇
  2003年   680篇
  2002年   689篇
  2001年   1193篇
  2000年   1112篇
  1999年   755篇
  1994年   340篇
  1992年   720篇
  1991年   572篇
  1990年   624篇
  1989年   598篇
  1988年   584篇
  1987年   621篇
  1986年   629篇
  1985年   774篇
  1984年   620篇
  1983年   510篇
  1982年   445篇
  1981年   450篇
  1980年   551篇
  1979年   1224篇
  1978年   1046篇
  1977年   992篇
  1976年   720篇
  1975年   771篇
  1974年   1069篇
  1973年   914篇
  1972年   966篇
  1971年   1195篇
  1970年   1538篇
  1969年   1168篇
  1968年   1116篇
  1967年   1135篇
  1966年   982篇
  1965年   721篇
  1959年   417篇
  1958年   621篇
  1957年   500篇
  1956年   412篇
  1955年   355篇
  1954年   403篇
  1948年   236篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
32.
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   
33.
S J Weintraub  C A Prater  D C Dean 《Nature》1992,358(6383):259-261
  相似文献   
34.
35.
36.
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   
37.
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   
38.
This paper assesses the information content of two survey indicators for consumption developments in the near future for eight European countries in the period 1985–1998. Empirical work on this topic typically focuses on consumer confidence, the perceptions of buyers of consumption goods. This paper examines whether perceptions of sellers of consumption goods, measured by retail trade surveys, may also improve short‐term monitoring of consumption. We find that both consumer confidence and retailer confidence embody valuable information, when analysed in isolation. For France, Italy and Spain we conclude that adding retail confidence does not improve the indicator model once consumer confidence has been included. For the UK the reverse case is obtained. For the remaining four countries we show that combining consumer sentiment and retail trade confidence into a composite indicator leads to optimal results. Our results suggest that incorporating information from retail trade surveys may offer significant benefits for the analysis of short‐term prospects of consumption. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   
39.
40.
A linear regression model with random walk coefficients is extended to allow for linear restrictions between the coefficients to be satisfied at each point in time. Estimation in this model is shown to be no more involved than estimation in the standard model. It is also demonstrated how, after a slight modification to the testing problem, classical test procedures may be applied to the problem of testing for such restrictions. The performance of the Lagrange Multiplier test for a variety of different restrictions is then investigated via simulation. An empirical application involving testing for homogeneity in a random walk coefficient version of the AIDS model is given.  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