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   1313317篇
  免费   25789篇
  国内免费   7698篇
化学   651554篇
晶体学   20027篇
力学   74138篇
综合类   103篇
数学   239130篇
物理学   361852篇
  2021年   13488篇
  2020年   15890篇
  2019年   16023篇
  2016年   27290篇
  2015年   20570篇
  2014年   30330篇
  2013年   74244篇
  2012年   36111篇
  2011年   31325篇
  2010年   35592篇
  2009年   38221篇
  2008年   31220篇
  2007年   26491篇
  2006年   34299篇
  2005年   25772篇
  2004年   27895篇
  2003年   26735篇
  2002年   28157篇
  2001年   27580篇
  2000年   24233篇
  1999年   22252篇
  1998年   20935篇
  1997年   20920篇
  1996年   21032篇
  1995年   19130篇
  1994年   18567篇
  1993年   18106篇
  1992年   18116篇
  1991年   18356篇
  1990年   17652篇
  1989年   17689篇
  1988年   17240篇
  1987年   17253篇
  1986年   16153篇
  1985年   22598篇
  1984年   23796篇
  1983年   19973篇
  1982年   21628篇
  1981年   20881篇
  1980年   20202篇
  1979年   20443篇
  1978年   21698篇
  1977年   21344篇
  1976年   21030篇
  1975年   19737篇
  1974年   19381篇
  1973年   19851篇
  1972年   14341篇
  1968年   12255篇
  1967年   12606篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
961.
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   
962.
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   
963.
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   
964.
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 32, No. 9, pp. 1132–1136, September, 1989.  相似文献   
965.
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   
966.
967.
968.
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   
969.
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   
970.
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