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   18857篇
  免费   3343篇
  国内免费   2277篇
化学   13232篇
晶体学   173篇
力学   1099篇
综合类   118篇
数学   2718篇
物理学   7137篇
  2024年   18篇
  2023年   414篇
  2022年   388篇
  2021年   585篇
  2020年   852篇
  2019年   759篇
  2018年   672篇
  2017年   630篇
  2016年   960篇
  2015年   901篇
  2014年   1054篇
  2013年   1427篇
  2012年   1666篇
  2011年   1756篇
  2010年   1231篇
  2009年   1102篇
  2008年   1249篇
  2007年   1101篇
  2006年   977篇
  2005年   882篇
  2004年   705篇
  2003年   620篇
  2002年   683篇
  2001年   529篇
  2000年   415篇
  1999年   410篇
  1998年   329篇
  1997年   303篇
  1996年   318篇
  1995年   291篇
  1994年   232篇
  1993年   162篇
  1992年   165篇
  1991年   157篇
  1990年   118篇
  1989年   93篇
  1988年   53篇
  1987年   55篇
  1986年   71篇
  1985年   47篇
  1984年   31篇
  1983年   26篇
  1982年   15篇
  1981年   11篇
  1980年   4篇
  1976年   1篇
  1975年   2篇
  1974年   1篇
  1969年   1篇
  1957年   4篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
Schloegl’s second model for autocatalysis on a hypercubic lattice of dimension d≥2 involves: (i) spontaneous annihilation of particles at lattice sites with rate p; and (ii) autocatalytic creation of particles at vacant sites at a rate proportional to the number of diagonal pairs of particles on neighboring sites. Kinetic Monte Carlo simulations for a d=3 cubic lattice reveal a discontinuous transition from a populated state to a vacuum state as p increases above p=p e . However, stationary points, p=p eq (≤p e ), for planar interfaces separating these states depend on interface orientation. Our focus is on analysis of interface dynamics via discrete reaction-diffusion equations (dRDE’s) obtained from mean-field type approximations to the exact master equations for spatially inhomogeneous states. These dRDE can display propagation failure absent due to fluctuations in the stochastic model. However, accounting for this anomaly, dRDE analysis elucidates exact behavior with quantitative accuracy for higher-level approximations.  相似文献   
992.
By expanding the Debye theory into the tight focusing of partially coherent field, the intensity and spatial correlation properties of partially coherent radially polarized vortex beams are studied. Expressions are derived for the intensity distribution and the spectral degree of coherence in the focal region. It is found that the intensity and the transverse and longitudinal coherence degrees in the focal region change with the variation of the topological charge and coherence length of the vortex beam. In addition, the degree of coherence is shown to exhibit phase singularities.  相似文献   
993.
Based on the overlapping‐domain decomposition and parallel subspace correction method, a new parallel algorithm is established for solving time‐dependent convection–diffusion problem with characteristic finite element scheme. The algorithm is fully parallel. We analyze the convergence of this algorithm, and study the dependence of the convergent rate on the spacial mesh size, time increment, iteration times and sub‐domains overlapping degree. Both theoretical analysis and numerical results suggest that only one or two iterations are needed to reach to optimal accuracy at each time step. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   
994.
In this paper, we show the following result: Let K i be a knot in a closed orientable 3-manifold M i such that (M i ,K i ) is not homeomorphic to (S 2 ×S 1, x 0 ×S 1), i = 1, 2. Suppose that the Euler Characteristic of any meridional essential surface in each knot complement E(K i ) is less than the difference of one and twice of the tunnel number of K i . Then the tunnel number of their connected sum will not go down. If in addition that the distance of any minimal Heegaard splitting of each knot complement is strictly more than 2, then the tunnel number of their connected sum is super additive.  相似文献   
995.
We investigate the Morita context and graded cases for weak group corings and derive some equivalent conditions for μ to be surjective. Furthermore, we develop Galois theory for weak group corings. As an application, we give Galois theory for comodulelike algebras over a weak Hopf group coalgebra.  相似文献   
996.
We give new generalizations of some q-series identities of Dilcher and Prodinger related to divisor functions. Some interesting special cases are also deduced, including an identity related to overpartitions studied by Corteel and Lovejoy.  相似文献   
997.
In this paper,we characterize all generalized low pass filters and MRA Parseval frame wavelets in L 2 (R n ) with matrix dilations of the form (Df)(x) =√ 2f(Ax),where A is an arbitrary expanding n × n matrix with integer coefficients,such that |det A| = 2.We study the pseudo-scaling functions,generalized low pass filters and MRA Parseval frame wavelets and give some important characterizations about them.Furthermore,we give a characterization of the semiorthogonal MRA Parseval frame wavelets and provide several examples to verify our results.  相似文献   
998.
In this work, characteristics of microcavity top-emitting red organic light-emitting device (TEROLED) having metallic electrodes had been examined. The TEOLED shows the higher efficiency in comparison with that of the bottom OLED. However, color variation with the increasing view angles is also observed. For the purpose of diminishing the blue-shift of resonant wavelength (RW) in the device with increasing view angle, the effect of out-coupling layer on the emission properties of the TEOLED is discussed in detail. Finally, the out-coupling layer was introduced in theory without sacrificing the efficiency through precise optical simulation.  相似文献   
999.
Ruipeng Guo 《Optik》2011,122(21):1890-1894
An experimental investigation of a modified Beckmann-Kirchhoff scattering theory applied in an in-process optical measurement of surface quality is described. The proposed theory describes the scattered light intensity distribution from a surface with the additional layers, and can be employed to analyze the surface characteristics in in-process measurement. Based on light scattering principle and machine vision method, the surface roughness is extracted to testify the correction of the modified Beckmann-Kirchhoff scattering theory. The experimental apparatus consists of a collimated laser diode, a beam splitter, a screen, a measuring lens and a camera. Test specimens with different surface roughness are studied. The results obtained demonstrate the feasibility of in-process optical measurement of surface quality using the modified model.  相似文献   
1000.
Ag-mediated charge transfer from electron-doped SrTiO3 to molecules CO and NO has been studied through the first-principles calculations based on density functional theory (DFT). Evaluation of Fukui functions indicates that Ag atom on SrTiO3 (001) surface is presented as an active reduction and oxidation site. It shows that Ag prefers to mediate the charge transfer from electronically excited SrTiO3 to target species. It illustrates that electron initially transfers from electron-doped SrTiO3 to Ag, i.e., Ag is negatively charged. Interfacial charge transfer induces dipole moment and changes the surface work function. SrO-termination of SrTiO3 (001) surface has weak activity to CO and NO while CO and NO can be strongly adsorbed on the negatively charged Ag atom. Negatively charged Ag donates its charge to the molecules. Charge occupies the molecule π2p* orbital, which is responsible for the activation of the molecular bonds. Evidence that deposited metals on photocatalyst surface can efficiently separate the photogenerated electron-hole pairs has been addressed in this study.  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