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   346037篇
  免费   3856篇
  国内免费   1684篇
化学   189638篇
晶体学   4862篇
力学   14686篇
综合类   66篇
数学   38332篇
物理学   103993篇
  2020年   2675篇
  2019年   2875篇
  2018年   3678篇
  2017年   3722篇
  2016年   5672篇
  2015年   3696篇
  2014年   5518篇
  2013年   14216篇
  2012年   11638篇
  2011年   14353篇
  2010年   9993篇
  2009年   9896篇
  2008年   13335篇
  2007年   13475篇
  2006年   12759篇
  2005年   11697篇
  2004年   10357篇
  2003年   9167篇
  2002年   9096篇
  2001年   10059篇
  2000年   7716篇
  1999年   5783篇
  1998年   4893篇
  1997年   4856篇
  1996年   4655篇
  1995年   4213篇
  1994年   4258篇
  1993年   4044篇
  1992年   4468篇
  1991年   4633篇
  1990年   4294篇
  1989年   4182篇
  1988年   4088篇
  1987年   3976篇
  1986年   3916篇
  1985年   5129篇
  1984年   5301篇
  1983年   4416篇
  1982年   4771篇
  1981年   4462篇
  1980年   4207篇
  1979年   4507篇
  1978年   4832篇
  1977年   4759篇
  1976年   4850篇
  1975年   4497篇
  1974年   4638篇
  1973年   4685篇
  1972年   3481篇
  1971年   2859篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
We analyze diffusion from a periodic array of hemispherical droplets through a membrane. We find that the multiple sources do not interact strongly, even when the droplets are closely spaced, so that the flux through the membrane appears nearly additive.  相似文献   
63.
Nienhaus  G. U.  Hartmann  H.  Parak  F.  Heinzl  J.  Huenges  E. 《Hyperfine Interactions》1989,47(1-4):299-310

RSMR experiments with57Fe radiation were performed on myoglobin. An areasensitive detector was employed for simultaneous angular dependent collection of the scattered quanta up to a maximum angle 2θ of 17‡. Experimental data of polycrystalline and lyophilized myoglobin are compared with computer calculations of the scattering which are based on the atomic coordinates determined by X-ray structure analysis. Special attention has been paid to the influence of coherence effects from collectively moving parts of the protein. A simple model is introduced in order to take into account these segmental motions. Our first results indicate that the sizes of collectively moving segments are comparable with spheres of about 6 å in diameter in dry myoglobin. In myoglobin crystals, where the molecules are surrounded by large hydration shells, the movements appear to be correlated in segments with sizes comparable to helices.

  相似文献   
64.
65.
66.
The general structure of the pureSU(2) gauge potentials is calculated in detail. It is shown that the expansion of the gauge potentials about nonvanishing pure gauge potentials gives rise to new effects with confinement character.  相似文献   
67.
68.
Theoretical and experimental investigations on the performance of micro-perforated -panel absorbers are reviewed in this paper. By reviewing recent research work, this paper reveals a relationship between the maximum absorption coefficient and the limit of the absorption frequency bandwidth. It has been demonstrated that the absorption frequency bandwidth can be extended up to 3 or 4 octaves as the diameters of the micro-holes decrease. This has become possible with the development of the technologies for manufacturing micro-perforated panels, such as laser drilling, powder metallurgy, welded meshing and electro-etching to form micrometer order holes. In this paper, absorption characteristics of such absorbers in random fields and in high sound intensity are discussed both theoretically and experimentally. A new absorbing structure based on micro-perforated-panel absorbers demonstrate experimentally high sound absorption capability. This review shows that the micro-perforated-panel absorber has potentials to be one of ideal absorbing materials in the 21st century.  相似文献   
69.
On Quantum Team Games   总被引:2,自引:0,他引:2  
Recently Liu and Simaan (2004) convex static multi-team classical games have been introduced. Here they are generalized to both nonconvex, dynamic and quantum games. Puu's incomplete information dynamical systems are modified and applied to Cournot team game. The replicator dynamics of the quantum prisoner's dilemma game is also studied.  相似文献   
70.
The influence of processing parameters on the electrical characteristics of RuO2/LaAlO3/Si metal-oxide-semiconductor structures was investigated. In particular, the sputtering regime during deposition of LaAlO3 on Si and the atmosphere used in the post-deposition annealing step were addressed by determining capacitance-voltage and gate current-voltage characteristics. These results were correlated with compositional information obtained by Rutherford backscattering spectrometry and nuclear reaction analysis. A post-deposition annealing step in oxygen at 600 °C resulted in better electrical characteristics of the final structure as compared to the same treatment performed in nitrogen. This result is explained by oxygen ability to heal oxygen vacancies in the LaAlO3 film, especially at the dielectric/semiconductor interface region. A thermalized sputtering regime during deposition of LaAlO3 on Si leads to capacitors with electrical characteristics superior to those deposited in ballistic regime. PACS 77.84.Dy; 81.15.Cd; 81.40.Gh; 73.40.Qv; 82.80.Yc  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