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   302560篇
  免费   3396篇
  国内免费   982篇
化学   142453篇
晶体学   3613篇
力学   16285篇
综合类   5篇
数学   56721篇
物理学   87861篇
  2021年   2003篇
  2020年   2259篇
  2019年   2436篇
  2018年   13223篇
  2017年   12925篇
  2016年   10608篇
  2015年   3948篇
  2014年   4745篇
  2013年   11158篇
  2012年   12737篇
  2011年   20641篇
  2010年   12518篇
  2009年   12577篇
  2008年   15853篇
  2007年   18014篇
  2006年   9401篇
  2005年   9466篇
  2004年   8959篇
  2003年   8332篇
  2002年   7219篇
  2001年   7176篇
  2000年   5660篇
  1999年   4287篇
  1998年   3469篇
  1997年   3319篇
  1996年   3051篇
  1995年   2860篇
  1994年   2666篇
  1993年   2588篇
  1992年   2885篇
  1991年   2797篇
  1990年   2696篇
  1989年   2488篇
  1988年   2546篇
  1987年   2550篇
  1986年   2378篇
  1985年   3113篇
  1984年   3339篇
  1983年   2728篇
  1982年   2890篇
  1981年   2840篇
  1980年   2705篇
  1979年   2816篇
  1978年   2890篇
  1977年   2889篇
  1976年   2949篇
  1975年   2727篇
  1974年   2687篇
  1973年   2855篇
  1972年   1798篇
排序方式: 共有10000条查询结果,搜索用时 843 毫秒
991.
992.
Comprehensive self-consistent simulations of the positive column plasma of a dc oxygen discharge are performed with the help of commercial CFDRC software (), which enables one to carry out computations in an arbitrary 3D geometry using fluid equations for heavy components and a kinetic equation for electrons. The main scaling laws for the spatial distributions of charged particles are determined. These scaling laws are found to be quite different in the parameter ranges that are dominated by different physical processes. At low pressures, both the electrons and negative ions in the inner discharge region obey a Boltzmann distribution; as a result, a flat profile of the electron density and a parabolic profile of the ion density are established there. In the ion balance, transport processes prevail, so that ion heating in an electric field dramatically affects the spatial distribution of the charged particles. At elevated pressures, the volume processes prevail in the balance of negative ions and the profiles of the charged particle densities in the inner region turn out to be similar to each other.  相似文献   
993.
Problem-structuring techniques are an integral aspect of ‘Soft-OR’. SSM, SAST, Strategic Choice, and JOURNEY Making, all depend for their success on a group developing a shared view of a problem through some form of explicit modelling. The negotiated problem structure becomes the basis for problem resolution. Implicit to this process is an assumption that members of the group share and build their knowledge about the problem domain. This paper explores the extent to which this assumption is reasonable. The research is based on detailed records from the use of JOURNEY Making, where it has used special purpose Group Support software to aid the group problem structuring. This software continuously tracks the contributions of each member of the group and thus the extent to which they appear to be ‘connecting’ and augmenting their own knowledge with that of other members of the group. Software records of problem resolution in real organisational settings are used to explore the sharing of knowledge among senior managers. These explorations suggest a typology of knowledge sharing. The implications of this typology for problem structuring and an agenda for future research are considered.  相似文献   
994.
§ 1 IntroductionInthispaperwediscusstheglobalclassicalsolutionofamultidimensionalquasistationaryproblem .Theproblemcomesfromthediscussionofagrowthmodelofselfmaintainingprotocell(see [1— 3])inmultidimensionalcase .Theprotocellcanbevisualizedashavingaporousst…  相似文献   
995.
A set of new, air‐stable, RhI‐based heterogeneous asymmetric hydrogenation catalysts have been synthesised, characterised, and tested. Individual members of this new family all exhibit good enantioselectivity.  相似文献   
996.
 The inner radius of univalence of a domain D with Poincaré density ρ D is the possible largest number σ such that the condition ∥ S f D  = sup w∈ D ρ D (w) −2S f (z) ∥ ≤ σ implies univalence of f for a nonconstant meromorphic function f on D, where S f is the Schwarzian derivative of f. In this note, we give a lower bound of the inner radius of univalence for strongly starlike domains of order α in terms of the order α. The author was partially supported by the Ministry of Education, Grant-in-Aid for Encouragement of Young Scientists, 11740088. A part of this work was carried out during his visit to the University of Helsinki under the exchange programme of scientists between the Academy of Finland and the JSPS. Received November 26, 2001; in revised form September 24, 2002 Published online May 9, 2003  相似文献   
997.
998.
The catalytic properties of cluster magnesium derivatives were studied using the self-hydrogenation reaction of unsaturated compounds as an example. In the presence of a cluster magnesium–anthracene adduct at 150–298 K, the self-hydrogenation of anthracene occurred with yields of up to 40 molecules per atom of magnesium.  相似文献   
999.
1000.
We present kinetic inductance measurements in current driven Josephson junction arrays. Measurements performed with circular coils indicate that this technique is very sensitive to the vortex mobility. Results obtained with anisotropic detection coils provide experimental evidence for the anisotropic response of a driven vortex lattice. Anisotropic behavior is obtained when rising the temperature or the mean vortex velocity as indicated by the loss of the superconducting shielding capability, first in the direction of vortex motion and then in the perpendicular direction.  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