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   104135篇
  免费   4802篇
  国内免费   3982篇
化学   43532篇
晶体学   1151篇
力学   8199篇
综合类   256篇
数学   34816篇
物理学   24965篇
  2024年   104篇
  2023年   489篇
  2022年   940篇
  2021年   972篇
  2020年   999篇
  2019年   1080篇
  2018年   11139篇
  2017年   10958篇
  2016年   7194篇
  2015年   2110篇
  2014年   1908篇
  2013年   2406篇
  2012年   6159篇
  2011年   12993篇
  2010年   7389篇
  2009年   7798篇
  2008年   8460篇
  2007年   10426篇
  2006年   1758篇
  2005年   2540篇
  2004年   2520篇
  2003年   2741篇
  2002年   1808篇
  2001年   915篇
  2000年   915篇
  1999年   661篇
  1998年   597篇
  1997年   479篇
  1996年   580篇
  1995年   432篇
  1994年   334篇
  1993年   315篇
  1992年   253篇
  1991年   238篇
  1990年   202篇
  1989年   198篇
  1988年   141篇
  1987年   138篇
  1986年   131篇
  1985年   110篇
  1984年   90篇
  1983年   74篇
  1982年   61篇
  1981年   57篇
  1980年   57篇
  1979年   59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.
A new procedure for the selective oxidation of alcohols to the corresponding aldehydes and ketones with potassium permanganate supported on aluminum silicate at room temperature under solvent-free conditions and shaking is reported.  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.
In this paper, the authors studied certain properties of the estimate of Liang and Krishnaiah (1985, J. Multivariate Anal. 16, 162–172) for multivariate binary density. An alternative shrinkage estimate is also obtained. The above results are generalized to general orthonormal systems.  相似文献   
6.
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   
7.
8.
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   
9.
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