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   109689篇
  免费   1419篇
  国内免费   633篇
化学   46384篇
晶体学   1001篇
力学   7413篇
数学   36933篇
物理学   20010篇
  2022年   285篇
  2021年   421篇
  2020年   516篇
  2019年   488篇
  2018年   10674篇
  2017年   10506篇
  2016年   6792篇
  2015年   1564篇
  2014年   1084篇
  2013年   2042篇
  2012年   5581篇
  2011年   12655篇
  2010年   6690篇
  2009年   6949篇
  2008年   8496篇
  2007年   10590篇
  2006年   2207篇
  2005年   3154篇
  2004年   3098篇
  2003年   3327篇
  2002年   2289篇
  2001年   652篇
  2000年   685篇
  1999年   517篇
  1998年   529篇
  1997年   505篇
  1996年   692篇
  1995年   472篇
  1994年   391篇
  1993年   391篇
  1992年   343篇
  1991年   307篇
  1990年   260篇
  1989年   273篇
  1988年   302篇
  1987年   261篇
  1986年   244篇
  1985年   406篇
  1984年   384篇
  1983年   280篇
  1982年   356篇
  1981年   362篇
  1980年   355篇
  1979年   330篇
  1978年   297篇
  1977年   250篇
  1976年   237篇
  1975年   234篇
  1974年   226篇
  1973年   247篇
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
31.
32.
33.
34.
The structure, chemical composition, and magnetic properties of electrochemically deposited nanocrystalline Co-Ni-Fe films were investigated using a number of techniques. A high saturation magnetic induction up to B s = 21 kG was attained. An enhancement of the saturation magnetization compared to the ideal anticipated one was revealed, which correlated with the nonlinear behavior of the structural phase composition and lattice parameters with the change of the composition. The text was submitted by the authors in English.  相似文献   
35.
36.
37.
The evaluation of second derivatives of the electronic energy for nonvariational wave functions using an energy functional is discussed. It is shown that, in certain cases, the formation of the first-order relaxed density matrix leads to an efficient algorithm for the calculation of second-order response properties. Detailed formulas are given for second-order Møller–Plesset perturbation theory. © 1994 John Wiley & Sons, Inc.  相似文献   
38.
A method using capillary gel electrophoresis with laser-induced fluorescence detection is described which permits complete sequence determination of antisense DNA analogues of unknown sequence. This method, originally created as a tool to confirm the sequence of antisense oligonucleotides being developed as therapeutic drugs, utilizes data collected under a range of experimental conditions described by the Ogston model as applied to gel electrophoresis. A linear relationship independent of experimental conditions between the relative electrophoretic migration time and the oligonucleotide base number was observed and is shown to be consistent with a simplified version of this model and can be used to facilitate the sequence determination.  相似文献   
39.
A forecasting model is developed for the number of daily applications for loans at a financial services telephone call centre. The purpose of the forecasts and the associated prediction intervals is to provide effective staffing policies within the call centre. The model building process is constrained by the availability of only 2 years and 7 months of data. The distinctive feature of the data is that demand is driven in the main by advertising. The analysis given focuses on applications stimulated by press advertising. Unlike previous analyses of broadly similar data, where ARIMA models were used, a model with a dynamic level, multiplicative calendar effects and a multiplicative advertising response is developed and shown to be effective.  相似文献   
40.
This paper describes three case studies which investigated issues relating to the implementation and management of advanced information technology. The benefits derived from information technology were found to vary from one organization to another. These studies provide further evidence to support earlier research findings that senior management has an important role to play in the effective exploitation of information technology, and that the investment approach taken by an organization has a significant effect on the development of computer-based information systems. The effectiveness of a system depends not only on applying the appropriate technology, but also on how successfully technical and behavioural issues are resolved.  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