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   436179篇
  免费   4854篇
  国内免费   1234篇
化学   233804篇
晶体学   6536篇
力学   18781篇
综合类   13篇
数学   49952篇
物理学   133181篇
  2021年   3769篇
  2020年   4199篇
  2019年   4518篇
  2018年   5854篇
  2017年   5745篇
  2016年   8831篇
  2015年   5561篇
  2014年   8543篇
  2013年   20189篇
  2012年   15652篇
  2011年   19261篇
  2010年   13497篇
  2009年   13351篇
  2008年   17648篇
  2007年   17541篇
  2006年   16253篇
  2005年   14550篇
  2004年   13525篇
  2003年   11896篇
  2002年   11728篇
  2001年   13429篇
  2000年   10086篇
  1999年   7918篇
  1998年   6569篇
  1997年   6314篇
  1996年   6081篇
  1995年   5471篇
  1994年   5393篇
  1993年   5199篇
  1992年   5831篇
  1991年   5927篇
  1990年   5664篇
  1989年   5474篇
  1988年   5494篇
  1987年   5376篇
  1986年   5092篇
  1985年   6561篇
  1984年   6695篇
  1983年   5301篇
  1982年   5387篇
  1981年   5368篇
  1980年   4957篇
  1979年   5353篇
  1978年   5492篇
  1977年   5389篇
  1976年   5331篇
  1975年   4916篇
  1974年   4888篇
  1973年   4884篇
  1972年   3458篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Off-the-shell anomalous factors of the two-body Coulomb transition matrices appear in the integral form of the Faddeev second-order nuclear-electronic amplitude, for proton-hydrogen charge transfer scattering in a typical nlmnlm′ transition. A symmetric-impulse approximation (SIA) is applied to eliminate these factors and an induction method is proposed to analytically calculate the remaining integrals. The nuclear-electronic amplitude is derived for the general case, and for totally symmetric collisions, in terms of generalized hypergeometric functions of two variables, F 4, and of one variable, 3 F 2, respectively. The angular distribution of the second-order nuclear-electronic charge transfer amplitude shows the Thomas mechanism as a peak or a hump for symmetric and asymmetric collisions. There also exists a peak in the forward angular distribution of the second-order nuclear-electronic amplitude, which partly cancels the kinematic peak in the angular distribution of the charge transfer differential cross sections.  相似文献   
72.
73.
74.
The thermal and dielectric behaviors of poly(vinylidene fluoride-trifluoroethylene) copolymers near the ferroelectric-to-paraelectric phase transition are investigated for samples with 20, 25, 30, and 40 mol% trifluoroethylene (TrFE). The data suggest that the transition becomes continuous for a particular composition near 50 mol% TrFE. Experimental data are sensitive to thermal history (kinetics of crystallization, and kinetics and cycling over the structural transition). It is found that several anomalies are present at the structural change, and in particular the 30 mol% TrFE sample shows the most marked anomalies. These phenomena can be attributed to defects, but another possibility would be the existence of an intemediate supplementary phase. Both hypotheses are discussed.  相似文献   
75.
In recent years there has emerged significant interest in low pressure radio frequency (rf) glow discharges which are used widely particulary in IC fabrication. Various parameters of the rf glow discharge have been found to be useful for its electrical characterization; however, there is no uniformity and agreement. Extensive experimental investigations on various discharge systems have shown, that the self-bias on the rf driven electrode, the complex conductivity and the breakdown characteristic are preferable parameters of rf discharges. Advantageously the self-bias and the complex conductivity should be presented in dependence on the pressure and the applied rf voltage. The discharge current cannot be measured quite accurately due to currents via leaky capacitors and the deviations from a sinusoidal form of the current due to nonlinearities.  相似文献   
76.
77.
The electro-optic response of ferroelectric smectic C* liquid crystals has been studied. Anomalous switching behaviour of such materials which possess a negative dielectric anisotropy has been reported. These materials show a minimum in response time at a sufficiently high field. We present results showing the dependency of this minimum upon spontaneous polarisation and the effect of AC bias. Calculations based upon the equation of motion of the director around the cone are presented which describe this effect and its dependence on the relative magnitudes of the spontaneous polarization and dielectric anisotropy of the material. Good agreement with the experimental results is found.  相似文献   
78.
79.
A method for suppressing self-modulation in backward-wave tubes is proposed. Additional delay is introduced into the feedback circuit, owing to which the output signal amplitude affects the electron beam current that enters into the interaction space. Numerical simulations demonstrate that the operating current in the single-frequency oscillation mode may be increased roughly twofold.  相似文献   
80.
The luminescence and scintillation properties of poly(methyl methacrylate) containing 1,1,3-trimethyl-3-phenylindan were 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