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   1389313篇
  免费   26277篇
  国内免费   7791篇
化学   694935篇
晶体学   20575篇
力学   75681篇
综合类   108篇
数学   250254篇
物理学   381828篇
  2021年   13872篇
  2020年   16274篇
  2019年   16484篇
  2018年   14639篇
  2017年   13008篇
  2016年   29518篇
  2015年   21680篇
  2014年   31284篇
  2013年   76198篇
  2012年   40995篇
  2011年   39284篇
  2010年   39131篇
  2009年   41277篇
  2008年   37610篇
  2007年   33708篇
  2006年   38120篇
  2005年   30992篇
  2004年   31703篇
  2003年   29554篇
  2002年   30391篇
  2001年   29781篇
  2000年   25659篇
  1999年   23014篇
  1998年   21354篇
  1997年   21316篇
  1996年   21444篇
  1995年   19411篇
  1994年   18925篇
  1993年   18476篇
  1992年   18561篇
  1991年   18719篇
  1990年   17934篇
  1989年   17935篇
  1988年   17482篇
  1987年   17449篇
  1986年   16414篇
  1985年   22824篇
  1984年   24028篇
  1983年   20160篇
  1982年   21819篇
  1981年   21020篇
  1980年   20367篇
  1979年   20593篇
  1978年   21822篇
  1977年   21416篇
  1976年   21134篇
  1975年   19783篇
  1974年   19419篇
  1973年   19874篇
  1972年   14346篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
In this paper we generalize recent theoretical results on the local continuation of parameter-dependent non-linear variational inequalities. The variational inequalities are rather general and describe, for example, the buckling of beams, plates or shells subject to obstacles. Under a technical hypothesis that is satisfied by the simply supported beam, we obtain the existence of a continuation of both the solution and the eigenvalue with respect to a local parameter. A numerical continuation method is presented that easily overcomes turning points. Numerical results are presented for the non-linear beam.  相似文献   
992.
本文提出从高分辨电子显微像中,利用光学、全息和部分相干等方法,提取传递函数,制作相位和振幅滤波器,实现解卷,提高高分辨电子显微像的分辨率.  相似文献   
993.
In recent years there has been tremendous progress in lithium niobate-based photonic switches. The various switch configurations proposed and implemented, and their characteristics, are reviewed. A summary of the device technology is given. Performance analysis based on different architecture and the size of arrays that can be relalized are discussed.Indian Institute of Science, Bangalore, India  相似文献   
994.
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 32, No. 9, pp. 1132–1136, September, 1989.  相似文献   
995.
Conclusions The sets (3) and (4) of condensates have been compared using the QCD sum rules (2) with indefinite weight functions. A bad matching between both sets of condensates and experimental data has been obtained. The standard values (3) appear to be closer to data but some increase ofQ is necessary to improve the agreement. Only higher values ofm 0 2 could change the results of this analysis. It is interesting that negative values ofm 0 2 considerably improve the agreement with data; note that this quantity cannot be determined with a sufficient accuracy. We conclude that the QCD sum rules (2) cannot definitely determine a privileged set of condensates.Dedicated to Academician Václav Votruba on the occasion of his eightieth birthday.  相似文献   
996.
997.
998.
This paper proposes and analyzes a GaAs traveling-wave optical modulator which uses a modulated coplanar strip electrode with periodic cross-tie overlay. This slow-wave structure can be designed to satisfy phase velocity and impedance matching conditions simultaneously. The dominant conductor loss in the slow-wave structure is reduced using the modulated coplanar strip electrode. The calculated 3-dB modulation bandwidth (100 GHz) is much wider than the bandwidth limit (30 GHz) of conventional electrode structures that are limited by phase velocity mismatch.This work was supported by the U.S. Army Research Office under contract DAAL-03-88-K-0005 and the Texas Advanced Technology Program.  相似文献   
999.
Time structure of iodine laser pulse in the free running mode of operation was studied using the power amplifier of laser system PERUN as the laser oscillator. Two characteristic shapes of laser pulse correspond to different regimes of laser operation, the existence of which is ascribed to the critical concentration of I2 molecules. Simultaneously an additional chemical pumping was proved at least in the initial phase of photodissociation and in a late-time lasing after the end of flashlamps pumping light.  相似文献   
1000.
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