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   267730篇
  免费   2051篇
  国内免费   623篇
化学   141991篇
晶体学   4162篇
力学   11922篇
综合类   9篇
数学   29485篇
物理学   82835篇
  2019年   2289篇
  2018年   3114篇
  2017年   3110篇
  2016年   4482篇
  2015年   2656篇
  2014年   4279篇
  2013年   10672篇
  2012年   8069篇
  2011年   9894篇
  2010年   7082篇
  2009年   6874篇
  2008年   9308篇
  2007年   9510篇
  2006年   8879篇
  2005年   8069篇
  2004年   7421篇
  2003年   6732篇
  2002年   6660篇
  2001年   7325篇
  2000年   5659篇
  1999年   4360篇
  1998年   3859篇
  1997年   3844篇
  1996年   3583篇
  1995年   3332篇
  1994年   3490篇
  1993年   3189篇
  1992年   3663篇
  1991年   3666篇
  1990年   3599篇
  1989年   3457篇
  1988年   3568篇
  1987年   3463篇
  1986年   3285篇
  1985年   4360篇
  1984年   4631篇
  1983年   3872篇
  1982年   4005篇
  1981年   3931篇
  1980年   3908篇
  1979年   3876篇
  1978年   4190篇
  1977年   4107篇
  1976年   4173篇
  1975年   3850篇
  1974年   3893篇
  1973年   4050篇
  1972年   2851篇
  1971年   2378篇
  1970年   2177篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
The fine-structure parameters of a series of configurations of the first ion of indium and the gyromagnetic ratios in intermediate coupling are calculated by a semiempirical method in the single-configuration approximation.  相似文献   
112.
113.
The ultraviolet band systemsA 1Π-X 1Σ+ of P14N and P15N were excited in an electrodeless tube containing traces of phosphorus specpure nitrogen and neon using a microwave discharge (2450 MHz). Bands of the isotopic species, P15N, were obtained using15N2 enriched to 95.5%. Rotational analyses of eleven bands of P14N and sixteen bands of P15N were carried out. Three perturbing statese 3Σ,d 3Δ andb 3Π, arising from the lower valence configurations were identified from the observed perturbations in thev′=0–4 levels of theA 1Π state. Deperturbation studies led to the determination of molecular constants of the perturbing states. Vibrational assignments of the perturbing states were made from isotope shift studies.  相似文献   
114.
It is observed experimentally that a periodic array of resistively coupled LC-oscillators with ans-shaped nonlinearity exhibits stable non-uniform voltage and current distributions. The dependence of the resulting structure on the coupling resistance and the boundary conditions is investigated. The structure is rather insensitive to variations of the boundary values. The experiments are well described by a two-variable reaction-diffusion equation.  相似文献   
115.
The {1/2, 0, 1/2} nuclear superstructure in an La0.93Sr0.07MnO3 manganite orthorhombic crystal is revealed using thermal-neutron diffraction. It is demonstrated that this superlattice belongs to the class of distortion-type structures and is directly associated with a 1/16-type ordering of Mn4+ and Mn3+ ions in a collinear ferromagnetic phase of the La0.93Sr0.07MnO3 manganite.  相似文献   
116.
117.
118.
We present a practical polynomial-time algorithm for computing the zeta function of a Kummer curve over a finite field of small characteristic. Such algorithms have recently been obtained using a method of Kedlaya based upon Monsky–Washnitzer cohomology, and are of interest in cryptography. We take a different approach. The problem is reduced to that of computing the L-function of a multiplicative character sum. This latter task is achieved via a cohomological formula based upon the work of Dwork and Reich. We show, however, that our method and that of Kedlaya are very closely related.Dedicated to the memory of Gian-Carlo Rota  相似文献   
119.
The influence of external uniaxial stress on the different indium-donor complexes in silicon has been studied using the perturbed γγ angular correlation (PAC) method. Such effect of an applied stress is detected by means of the probe atoms situated at different complexes in the sample. The current results showed that the responses of the probes in an extrinsic silicon samples are found to be dissimilar for the same value of stress. Such change in the local environments of the probe atoms could be associated with the various strain field created by the implantations of varied size of impurities. The phosphorous implantation in silicon has even lead to the complete absence of observable effect of the applied stress suggesting significant lose of the elasticity of the sample.  相似文献   
120.
The concept and application of phase-space reconstructions are reviewed. Fractional derivatives are then proposed for the purpose of reconstructing dynamics from a single observed time history. A procedure is presented in which the fractional derivatives of time series data are obtained in the frequency domain. The method is applied to the Lorenz system. The ability of the method to unfold the data is assessed by the method of global false nearest neighbors. The reconstructed data is used to compute recurrences and correlation dimensions. The reconstruction is compared to the commonly used method of delays in order to assess the choice of reconstruction parameters, and also the quality of results.  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