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   103202篇
  免费   4965篇
  国内免费   3715篇
化学   42793篇
晶体学   1200篇
力学   8244篇
综合类   252篇
数学   34422篇
物理学   24971篇
  2024年   106篇
  2023年   665篇
  2022年   1030篇
  2021年   1061篇
  2020年   1177篇
  2019年   1128篇
  2018年   11165篇
  2017年   10926篇
  2016年   7204篇
  2015年   2168篇
  2014年   1761篇
  2013年   2195篇
  2012年   6146篇
  2011年   12741篇
  2010年   7119篇
  2009年   7417篇
  2008年   8187篇
  2007年   10267篇
  2006年   1631篇
  2005年   2549篇
  2004年   2390篇
  2003年   2732篇
  2002年   1741篇
  2001年   824篇
  2000年   832篇
  1999年   735篇
  1998年   625篇
  1997年   584篇
  1996年   589篇
  1995年   473篇
  1994年   426篇
  1993年   383篇
  1992年   286篇
  1991年   286篇
  1990年   255篇
  1989年   189篇
  1988年   158篇
  1987年   158篇
  1986年   129篇
  1985年   101篇
  1984年   95篇
  1983年   74篇
  1982年   71篇
  1981年   58篇
  1980年   61篇
  1979年   48篇
  1914年   45篇
  1912年   40篇
  1909年   41篇
  1908年   40篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
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   
3.
论述两类岸基光电探测系统;岸基光电跟踪仪和岸基红外监视系统。阐述其典型实例、特点及发展方向。  相似文献   
4.
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   
5.
Data Envelopment Analysis (DEA) offers a piece-wise linear approximation of the production frontier. The approximation tends to be poor if the true frontier is not concave, eg in case of economies of scale or of specialisation. To improve the flexibility of the DEA frontier and to gain in empirical fit, we propose to extend DEA towards a more general piece-wise quadratic approximation, called Quadratic Data Envelopment Analysis (QDEA). We show that QDEA gives statistically consistent estimates for all production frontiers with bounded Hessian eigenvalues. Our Monte-Carlo simulations suggest that QDEA can substantially improve efficiency estimation in finite samples relative to standard DEA models.  相似文献   
6.
7.
Courses which teach discrete-event simulation are based on many different simulation languages. The requirements for a language to support teaching simulation are discussed. In particular, it is recommended that such languages separate into distinct modules those aspects of simulation which are taught as separate topics. Implementation of the separation is discussed. The SEESIM language, developed as a teaching aid, is described, and examples of its use are given. Straightforward use of SEESIM can be learned quickly, yet the language provides facilities for a staged introduction to advanced concepts of simulation.  相似文献   
8.
9.
We consider complete ideals supported on finite sequences of infinitely near points, in regular local rings with dimensions greater than two. We study properties of factorizations in Lipman special *-simple complete ideals. We relate it to a type of proximity, linear proximity, of the points, and give conditions in order to have unique factorization. Several examples are presented. Received: 2 February 2000 / in final form: 14 March 2001 / Published online: 18 January 2002  相似文献   
10.
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