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   691839篇
  免费   6677篇
  国内免费   2103篇
化学   352521篇
晶体学   9942篇
力学   34257篇
综合类   20篇
数学   104013篇
物理学   199866篇
  2021年   4851篇
  2020年   5532篇
  2019年   6007篇
  2018年   17399篇
  2017年   17089篇
  2016年   17342篇
  2015年   8135篇
  2014年   11609篇
  2013年   27919篇
  2012年   24294篇
  2011年   35006篇
  2010年   23240篇
  2009年   23300篇
  2008年   29682篇
  2007年   31525篇
  2006年   22281篇
  2005年   21008篇
  2004年   19735篇
  2003年   18167篇
  2002年   17094篇
  2001年   18120篇
  2000年   14034篇
  1999年   10952篇
  1998年   9308篇
  1997年   9052篇
  1996年   8770篇
  1995年   7915篇
  1994年   7877篇
  1993年   7525篇
  1992年   8493篇
  1991年   8518篇
  1990年   8202篇
  1989年   7875篇
  1988年   8056篇
  1987年   7834篇
  1986年   7436篇
  1985年   9664篇
  1984年   9981篇
  1983年   8171篇
  1982年   8313篇
  1981年   8221篇
  1980年   7871篇
  1979年   8202篇
  1978年   8584篇
  1977年   8394篇
  1976年   8420篇
  1975年   7714篇
  1974年   7830篇
  1973年   7984篇
  1972年   5642篇
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
71.
72.
One obtains a formula for the transformation of a vector with a given covariance matrix. The sum of the squares of the components of the transformed vector is equal to a chi-square type quadratic form, constructed with the aid of the initial vector. Taking into account this property, one finds the components of the Pearson statistic, Pearson-Fisher statistic, etc.Translated from Veroyatnostnye Raspredeleniya i Matematicheskaya Statistika, pp. 337–350, 1986.  相似文献   
73.
74.
Transport as a consequence of state-dependent diffusion   总被引:1,自引:0,他引:1  
Overdamped particles subject to a drift in a force field with sinusoidal space dependence and also a sinusoidally modulated space-dependent diffusion, with the same period as the drift, experience a net driving force. The resulting current depends on the amplitude of the modulation of the diffusion and is a periodic function of the phase difference between the sinusoidal drift and the sinusoidal modulation of the diffusion. For small modulation amplitudes a particle subject to state-dependent noise behaves the same way as a particle subject to thermal noise but with a drift which, in addition to the sinusoidal term, contains a net force term.Dedicated to Professor Harry Thomas on the occasion of his 60th birthday  相似文献   
75.
76.
77.
Dielectric properties of polymer-liquid crystal mixture, having constituent polymer, poly-butyl methacrylate (PBMA) and liquid crystal, cholesteryl nonanoate, are reported as a function of frequency and temperature. The measurement has been done in a temperature range of 300-375 K and frequency range of 100 Hz-10 MHz. The dielectric permittivity and dielectric loss shows significant changes with the addition of polymer molecules in liquid crystal. The significant feature of composite formation is that the pure liquid crystal and polymer do not show dielectric relaxation in the frequency range covered, while the composite shows relaxation peak at a particular frequency. The optical transmittance of pure liquid crystal and composite has also been measured and compared.  相似文献   
78.
We report morphologic changes of metallic surfaces at the onset of ablation, starting from gentle ablation to the emergence of ablation craters. The evolution of both observed melting zones and of ablation craters therein are investigated in dependence of the ablation laser fluence for nanosecond ultraviolet laser pulses. Further, consequences of crater formation for cluster synthesis within the released atomic vapor are pointed out. PACS 52.38.Mf; 79.20.Ds; 65.40.De  相似文献   
79.
Space-time directional Lyapunov exponents are introduced. They describe the maximal velocity of propagation to the right or to the left of fronts of perturbations in a frame moving with a given velocity. The continuity of these exponents as function of the velocity and an inequality relating them to the directional entropy is proved.  相似文献   
80.
We give sufficient conditions for Sobolev and Lipschitz functions in terms of their lower scaled-oscillation. The sharpness of these conditions is shown by examples. Our examples also show that a Stepanov-type differentiability theorem does not hold under the boundedness assumption of the lower scaled-oscillation.

  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