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   124294篇
  免费   8677篇
  国内免费   7085篇
化学   58790篇
晶体学   1352篇
力学   9341篇
综合类   594篇
数学   37311篇
物理学   32668篇
  2024年   145篇
  2023年   934篇
  2022年   1694篇
  2021年   1737篇
  2020年   2038篇
  2019年   2079篇
  2018年   11750篇
  2017年   11427篇
  2016年   8169篇
  2015年   3217篇
  2014年   3172篇
  2013年   3865篇
  2012年   7945篇
  2011年   14560篇
  2010年   8615篇
  2009年   8817篇
  2008年   9715篇
  2007年   11501篇
  2006年   2901篇
  2005年   3650篇
  2004年   3407篇
  2003年   3585篇
  2002年   2804篇
  2001年   1825篇
  2000年   1397篇
  1999年   1162篇
  1998年   957篇
  1997年   851篇
  1996年   854篇
  1995年   682篇
  1994年   567篇
  1993年   489篇
  1992年   379篇
  1991年   396篇
  1990年   314篇
  1989年   267篇
  1988年   228篇
  1987年   177篇
  1986年   155篇
  1985年   142篇
  1984年   133篇
  1983年   93篇
  1982年   90篇
  1981年   71篇
  1980年   76篇
  1979年   54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.
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   
2.
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   
3.
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   
4.
激光除冰研究   总被引:7,自引:0,他引:7  
刘磊  朱晓 《光散射学报》2006,18(4):379-385
架空输送电线路因覆冰而导致的事故危害性很大,本文总结了目前国内外输电线路导线覆冰的现状。统计国内外探索出来的各种预防,融化,除冰等很多解决方案。通过研究和探讨,分析导线覆冰的传热和能量,运用了多种激光器进行激光熔(除)冰实验,比较研究二氧化碳激光器的除冰情况。以及提出激光熔冰的方法、研究方向和前景。  相似文献   
5.
6.
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   
7.
8.
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   
9.
10.
The principal physics goals of the Compact Muon Solenoid experiment under construction at the Large Hadron Collider at CERN in Geneva are reviewed. Procedures to search for the Standard Model Higgs boson, supersymmetric Higgses and other supersymmetric particles are described.  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