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   398724篇
  免费   4074篇
  国内免费   1912篇
化学   219005篇
晶体学   5826篇
力学   16268篇
综合类   67篇
数学   45796篇
物理学   117748篇
  2020年   3411篇
  2019年   3774篇
  2018年   5086篇
  2017年   5044篇
  2016年   7180篇
  2015年   4440篇
  2014年   6768篇
  2013年   16771篇
  2012年   13343篇
  2011年   16267篇
  2010年   11602篇
  2009年   11331篇
  2008年   15394篇
  2007年   15582篇
  2006年   14585篇
  2005年   13294篇
  2004年   11868篇
  2003年   10613篇
  2002年   10425篇
  2001年   11297篇
  2000年   8835篇
  1999年   6507篇
  1998年   5485篇
  1997年   5515篇
  1996年   5342篇
  1995年   4554篇
  1994年   4717篇
  1993年   4595篇
  1992年   4985篇
  1991年   5068篇
  1990年   4811篇
  1989年   4728篇
  1988年   4590篇
  1987年   4520篇
  1986年   4487篇
  1985年   5839篇
  1984年   6038篇
  1983年   4939篇
  1982年   5382篇
  1981年   5093篇
  1980年   4718篇
  1979年   5089篇
  1978年   5355篇
  1977年   5404篇
  1976年   5421篇
  1975年   5022篇
  1974年   5161篇
  1973年   5303篇
  1972年   3900篇
  1967年   3224篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
We establish soliton-like asymptotics for finite energy solutions to the Schrödinger equation coupled to a nonrelativistic classical particle. Any solution with initial state close to the solitary manifold converges to a sum of a travelling wave and an outgoing free wave. The convergence holds in global energy norm. The proof uses spectral theory and the symplectic projection onto the solitary manifold in the Hilbert phase space.  相似文献   
52.
53.
The spatial structure of Bragg angles and the transfer functions of an acousto-optic cell are calculated for the cases of isotropic and anisotropic light diffraction in a uniaxial crystal. Their change with ultrasound frequency is traced. The possibility of image processing by acousto-optic filtration of the spatial spectrum of an image is considered. The results of experimental visualization of the transfer functions of a calcium molybdate crystal cell are presented.  相似文献   
54.
The satellite structure of 1s2p 1,3 P 1-1s 21 S 0 lines of the He-like argon ion in plasma produced by a 45-fs laser pulse in a gas-jet cluster target is measured with a high spectral resolution. Radiation transitions 2p → 1s from autoionizing states (AISs) are detected for ions ranging from Li-like to F-like. The spectrum observed is theoretically simulated with the use of the spectroscopic data for the AISs of multicharged ions obtained within the multiconfiguration relativistic Hartree-Fock method. Good agreement with experimental data is obtained when the main population channels of these states are taken into account for typical values of cluster-target plasma parameters.  相似文献   
55.
Effective magnetic properties of a composite meta-material consisting of periodically arranged circular conductive elements are studied theoretically. A general expression for the effective bulk permeability is obtained with mutual effects and lattice ordering being taken into account. The resonance frequency of the permeability is found to be strongly dependent on the size and shape of the unit cell. Frequency dispersion of the permeability is studied with special attention paid to the frequency range, where negative values of the permeability are possible. Corresponding recommendations for optimisation of the meta-materials with negative permeability are made. The results are confirmed by numerical simulations of the finite structure behaviour in an external magnetic field. Received 19 April 2002 Published online 31 July 2002  相似文献   
56.
An overview of theoretical and experimental studies of the coherent type-B e + e-pair production by photons in aligned crystals performed at Nuclear Physics Institute at Tomsk Polytechnic University is given.  相似文献   
57.
The EPR spectra evolution of Cs2Zn1?x Cux(ZrF6)2 · 6H2O (x=0.01, 0.6, 0.8, and 1.0) in the temperature range 4.2–330 K and the x-ray structure analysis of the compound with x=1.0 in the range 150–327 K show that the Jahn-Teller (JT) complex Cu(H2O)6 coordination sphere undergoes a plastic deformation. The observed effect is due to the combined influence of small lattice strains existing in the paraphase and a new one appearing as a result of a ferroelastic phase transition and increasing with decreasing temperature below T c . It is proved that both cooperative interactions between JT complexes and ferroelastic strain stabilize a certain JT configuration. The problem of instability of a JT configuration compressed at T ~ 265 K is discussed.  相似文献   
58.
Analytical formulas are derived that describe the dependences of the transition probabilities in vibrational-rotational spectra of XY3-type molecules with C 3v symmetry on the rotational quantum numbers.  相似文献   
59.
A detailed analysis is made within perturbative QCD of the decays into gluon jets of P-wave and S-wave quarkonia (JPC = 0++, 1++, 2++, 1+? and 0?+, 1??). For all those states we compute to leading non-trivial order in αs the conventional fraction f(?, δ) of the jet-like hadronic final states, characterized by the back-to-back cone of half angle δ, in which all but a small fraction ? of the total energy is emitted. To the same order we give also the average values of thrust momenta and spherocity distributions.  相似文献   
60.
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