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   122527篇
  免费   1885篇
  国内免费   424篇
化学   51857篇
晶体学   1011篇
力学   7399篇
综合类   1篇
数学   39838篇
物理学   24730篇
  2023年   335篇
  2022年   313篇
  2021年   530篇
  2020年   718篇
  2019年   644篇
  2018年   11011篇
  2017年   10778篇
  2016年   7548篇
  2015年   2198篇
  2014年   1662篇
  2013年   3391篇
  2012年   6538篇
  2011年   12853篇
  2010年   7239篇
  2009年   7358篇
  2008年   8797篇
  2007年   10683篇
  2006年   2226篇
  2005年   3261篇
  2004年   3214篇
  2003年   3370篇
  2002年   2269篇
  2001年   1213篇
  2000年   1265篇
  1999年   842篇
  1998年   714篇
  1997年   601篇
  1996年   798篇
  1995年   548篇
  1994年   569篇
  1993年   547篇
  1992年   530篇
  1991年   468篇
  1990年   501篇
  1989年   423篇
  1988年   435篇
  1987年   396篇
  1986年   384篇
  1985年   499篇
  1984年   458篇
  1983年   364篇
  1982年   369篇
  1981年   383篇
  1980年   327篇
  1979年   326篇
  1978年   309篇
  1977年   281篇
  1976年   295篇
  1974年   263篇
  1973年   287篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
63.
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   
64.
65.
Parallel preconditioners are presented for the solution of general linear systems of equations. The computation of these preconditioners is achieved by orthogonal projections related to the Frobenius inner product. So, minM∈??AM?IF and matrix M0∈?? corresponding to this minimum (?? being any vectorial subspace of ??n(?)) are explicitly computed using accumulative formulae in order to reduce computational cost when subspace ?? is extended to another one containing it. Every step, the computation is carried out taking advantage of the previous one, what considerably reduces the amount of work. These general results are illustrated with the subspace of matrices M such that AM is symmetric. The main application is developed for the subspace of matrices with a given sparsity pattern which may be constructed iteratively by augmenting the set of non‐zero entries in each column. Finally, the effectiveness of the sparse preconditioners is illustrated with some numerical experiments. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   
66.
In this Note we give a necessary and sufficient condition for the spectral controllability from one simple node of a general network of strings that undergoes transversal vibrations in a sufficiently large time. This condition asserts that no eigenfunction vanishes identically on the string that contains the controlled node. The proof combines the Beurling–Malliavin's theorem and an asymptotic formula for the eigenvalues of the network. The optimal control time may be characterized as twice the sum of the lengths of all the strings of the network. To cite this article: R. Dáger, E. Zuazua, C. R. Acad. Sci. Paris, Ser. I 334 (2002) 545–550.  相似文献   
67.
68.
The capability of gated saturable absorbers for single-pulse selection is studied theoretically using the classical space-time-dependent rate-equation model. The dynamics of operation is followed experimentally by the well-known pump—probe technique. Comparing the theoretical and experimental results, it is found that gated saturable absorbers can efficiently be used for pulse forming and pulse selection of pulses longer than picosecond.  相似文献   
69.
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   
70.
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