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   202585篇
  免费   1474篇
  国内免费   421篇
化学   104496篇
晶体学   3384篇
力学   10270篇
综合类   10篇
数学   21826篇
物理学   64494篇
  2021年   1966篇
  2020年   2008篇
  2019年   2566篇
  2018年   3658篇
  2017年   3667篇
  2016年   4807篇
  2015年   2343篇
  2014年   4295篇
  2013年   8580篇
  2012年   6835篇
  2011年   8042篇
  2010年   6456篇
  2009年   6639篇
  2008年   7632篇
  2007年   7595篇
  2006年   6691篇
  2005年   5921篇
  2004年   5642篇
  2003年   5161篇
  2002年   5153篇
  2001年   5604篇
  2000年   4135篇
  1999年   3132篇
  1998年   2698篇
  1997年   2757篇
  1996年   2540篇
  1995年   2209篇
  1994年   2328篇
  1993年   2225篇
  1992年   2523篇
  1991年   2644篇
  1990年   2552篇
  1989年   2623篇
  1988年   2532篇
  1987年   2550篇
  1986年   2411篇
  1985年   3032篇
  1984年   3101篇
  1983年   2596篇
  1982年   2562篇
  1981年   2527篇
  1980年   2338篇
  1979年   2710篇
  1978年   2672篇
  1977年   2871篇
  1976年   2873篇
  1975年   2664篇
  1974年   2602篇
  1973年   2711篇
  1972年   2085篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
891.
A methodology is developed to analyse present and future crisis and conflict potentials of small or large geopolitical regions. A set of criteria is used to describe the present economic, social, political and military conditions of a country and the future criteria trends. A multi-criteria decision analysis model is invoked to compute the crisis and conflict potentials under simultaneous consideration of all other countries in that region. The methodology is demonstrated in the crisis and conflict potentials analysis of the former Soviet republics including bordering countries.  相似文献   
892.
893.
A potential of mean torque is derived for a solute at infinite dilution in a uniaxial liquid crystal solvent, which contains terms originating from the dispersion interaction, and the electrostatic interaction between quadrupole moments on both molecules. It is shown that the electrostatic term is non-zero only if the solute-solvent vectors are distributed with lower than spherical symmetry. If this distribution has cylindrical symmetry then both the electrostatic and dispersion terms in the potential of mean torque are shown to depend on order parameters for the orientational distribution of the solute-solvent vectors, as well as on the order parameters of the solvent molecules.  相似文献   
894.
Summary Epitaxial films of YBa2Cu3O7−x were depositedin situ on LaAlO3 substrates using single-target 90° off-axis sputtering. The films were characterized by magnetization measurements (M vs. T, H), applying the field parallel toc-axis. The observed differences in theT c andJ c values are attributed to the different oxygen content in the superconducting films. Paper presented at the ?VII Congresso SATT?, Torino, 4–7 October 1994.  相似文献   
895.
An all-fibre optical system for optical interrogation and detection of the vibrations of a silicon microresonator is reported. Metal-coated silicon microresonators are excited by intensity modulated laser light delivered through an optical fibre, while the vibration of the resonators is detected by an optical fibre interferometer. Measurements have shown that an average optical power of 10 μW is sufficient to maintain the flexural vibration of the resonator. When the resonator is used as a pressure sensor, its resonant frequency changes from 62 kHz to 130 kHz as the pressure varies from -0°6 bar to 1 bar (gauge). A silicon resonator with 700 nm aluminium coating functions as a temperature sensor, showing a frequency shift from 262 kHz to 251 kHz when the temperature changes from 25 °C to 80 °C.  相似文献   
896.
897.
898.
899.
The angular dependence of the muon Knight shift,K μ, and the muon relaxation rate in Bi at 11 K were measured in external magnetic fields up to 1 T. BothK μ and the second moment,M 2, are field dependent and involveP 4 0(cos θ) andP 4 3(cos θ) terms in the angular dependence. The Knight shift behaviour is discussed in terms of the dipole-dipole interaction and the de Haas-van Alphen effect, a consistent interpretation was not achieved in either case. The field dependence ofM 2 is in complete contrast to the second moment calculations and points to a field dependent redistribution of the charge distribution around the interstitial site.  相似文献   
900.
Pseudo-billiards     
A new class of Hamiltonian dynamical systems with two degrees of freedom and kinetic energy of the form T = c1|p1| + c2|p2| (called “pseudo-billiards”) is studied. For any kind of interaction, the canonical equations can always be integrated on sequential time intervals; i.e. in principle all the trajectories can be found explicitly.

Depending on the potential, a dynamical system of this class can either be completely integrable or behave just as a usual non-integrable Hamiltonian system with two degrees of freedom: in its phase space there exist invariant tori, stochastic layers, domains of global chaos, etc. Pseudo-billiard models of both the types are considered.

If a potential of a pseudo-billiard system has critical points (equilibria), then trajectories close to these points (“loops”) can exist; they can be treated as images of self-localized objects with finite duration. Such a model (with quartic potential) is also studied.  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