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   113053篇
  免费   1855篇
  国内免费   867篇
化学   49404篇
晶体学   1054篇
力学   7391篇
综合类   5篇
数学   37746篇
物理学   20175篇
  2023年   208篇
  2022年   349篇
  2021年   509篇
  2020年   709篇
  2019年   671篇
  2018年   10755篇
  2017年   10567篇
  2016年   6986篇
  2015年   1732篇
  2014年   1369篇
  2013年   2136篇
  2012年   6035篇
  2011年   12913篇
  2010年   6913篇
  2009年   7199篇
  2008年   8835篇
  2007年   10751篇
  2006年   2403篇
  2005年   3318篇
  2004年   3228篇
  2003年   3343篇
  2002年   2359篇
  2001年   768篇
  2000年   797篇
  1999年   593篇
  1998年   611篇
  1997年   587篇
  1996年   681篇
  1995年   459篇
  1994年   474篇
  1993年   456篇
  1992年   378篇
  1991年   373篇
  1990年   318篇
  1989年   281篇
  1988年   281篇
  1987年   289篇
  1986年   244篇
  1985年   430篇
  1984年   384篇
  1983年   319篇
  1982年   391篇
  1981年   320篇
  1980年   337篇
  1979年   289篇
  1978年   260篇
  1977年   237篇
  1976年   222篇
  1975年   204篇
  1974年   171篇
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
31.
32.
33.
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   
34.
35.
36.
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   
37.
38.
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   
39.
40.
In this paper, an MILP formulation is proposed for the design of a reverse logistics network based on a warehouse location–allocation model, which optimizes, simultaneously, the forward and reverse networks. A single product model with unlimited capacity is first defined. Subsequently, the model is extended to a multi-product capacitated recovery network model, where capacity limitations and a multi-product system can be considered. The proposed model is compared to published work in the field, where different model assumptions have been proposed. Two cases are described so as to gain a better insight into the model and allow a comparative analysis.  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