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   681271篇
  免费   4958篇
  国内免费   1848篇
化学   328216篇
晶体学   9390篇
力学   37753篇
综合类   24篇
数学   111685篇
物理学   201009篇
  2021年   5644篇
  2020年   6102篇
  2019年   6969篇
  2018年   19127篇
  2017年   18996篇
  2016年   18635篇
  2015年   7697篇
  2014年   12028篇
  2013年   26833篇
  2012年   24032篇
  2011年   34173篇
  2010年   23775篇
  2009年   24210篇
  2008年   29352篇
  2007年   31083篇
  2006年   21218篇
  2005年   19934篇
  2004年   18970篇
  2003年   17718篇
  2002年   16790篇
  2001年   17292篇
  2000年   13378篇
  1999年   10260篇
  1998年   8983篇
  1997年   8771篇
  1996年   8236篇
  1995年   7401篇
  1994年   7319篇
  1993年   7146篇
  1992年   7483篇
  1991年   8088篇
  1990年   7706篇
  1989年   7681篇
  1988年   7445篇
  1987年   7257篇
  1986年   6942篇
  1985年   8841篇
  1984年   9150篇
  1983年   7751篇
  1982年   8040篇
  1981年   7548篇
  1980年   7117篇
  1979年   7774篇
  1978年   8076篇
  1977年   7988篇
  1976年   7974篇
  1975年   7649篇
  1974年   7438篇
  1973年   7809篇
  1972年   5822篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
171.
We study the probabilistic consequences of the choice of the basic number field in the quantum formalism. We demonstrate that by choosing a number field for a linear space representation of quantum model it is possible to describe various interference phenomena. We analyse interference of probabilistic alternatives induced by real, complex, hyperbolic (Clifford) and p‐adic representations.  相似文献   
172.
The European Physical Journal E - The temperature-induced microphase separation of the binary liquid system iso-butyric acid+heavy water (iBA + D2O) in a mesoporous silica glass (CPG-10-75) of...  相似文献   
173.
Mutual–temporal coherence of the supercontinuum (SC) generation has been experimentally investigated using a diffraction grating based interferometer. A broadband SC generation was produced in a pyrex glass plate with a 1.6-μm coherence length at 550-nm center wavelength. The degree of mutual coherence of 0.34 was measured for a wavefront shift for zero and first diffraction orders of half of the beam diameter. A design of SC source with the capability of manipulating the amplitudes and phases of optical frequency components within the SC pulse is presented for coherence applications.  相似文献   
174.
We have analyzed the methyl fluoride RQ(J,0)Q branch lines located near 1475 cm−1 using a simultaneous multi-spectrum fitting technique. In this analysis we have used previously recorded diode-laser data in which we collected many data points covering only one or two Q branch lines in a particular run. The analysis consists of simultaneously fitting 57 spectra collected with numerous pressure and path length conditions for all absorption lines. The data are concatenated to create one continuous spectrum of the Q branch. We have determined the intensity and self-broadened widths at 296 K for 23 RQ(J,0) lines.  相似文献   
175.
The conditions for obtaining a high efficiency of energy exchange upon two-wave interactions in dynamic holograms are found by analysis and numerical simulation of a system of nonlinear equations. Use of an asymmetric scheme of beam interaction in a medium with two nonlinearities, one of which determines the amplitude and relaxation time of a grating and the other of which provides phase modulation of the interacting beams, is proposed. It is shown that such a scheme in combination with the specific properties of a medium makes it possible to radically reduce the requirements for the nonlinearity of a medium and the intensity of a light flux in limiting systems, as well as to significantly decrease the time of the transition process. As a result, it becomes possible to attain an efficiency of energy transfer higher than 90% and to increase the corresponding attenuation of a high-power beam by almost two orders of magnitude, which is of interest for optical limiting of intense light fluxes.  相似文献   
176.
Frank  A. I.  Nosov  V. G. 《JETP Letters》2004,79(7):313-315
JETP Letters - The problem of storing ultracold neutrons over a plane magnetic mirror in the presence of gravity is considered. For neutrons with a definite polarization, the sum of the magnetic...  相似文献   
177.
A mathematical method is presented for solving the Schr?dinger equation for a system of identical body forces. The N-body forces are more easily introduced and treated within the hyperspherical harmonics. The problem of the N-body potential has been used at the level of both classical and quantum mechanics. The hypercentral interacting potential is assumed to depend on the hyperradius x = (ξ12 + ξ22 + ⋯ + ξN−12)1/2 only, where ξ12,…,ξN−1 are Jacobi relative coordinates which are functions of N-particle relative positions r12,r23,…,rN1. The problem of the harmonic oscillator and the Coulomb-type potential has been widely studied in different contexts. Using the N-body potential V(x) = ax2 + bx − (c/x) as an example, and assuming an ansatz for the eigenfunction, an exact analytical solution of the Schr?dinger equation for an N-body system in three dimensions is obtained. This method is also applicable to some other types of potentials for N-identical interacting particles.  相似文献   
178.
The results of experimental investigations on thermal nonequilibrium ionization in CO2: N2: He mixtures are presented. Measurements of electron density, ne, in vibrationally excited nitrogen were made in a supersonic flow with different CO2 contents as well as in a CO2: N2: He = 1 : 5 : 4 mixture laser gas. The mixtures were heated in a shock tube and expanded through a supersonic nozzle. Furthermore, supersonic mixing of N2 and CO2 + He was used in some experiments. The measured values of ne in the plenum chamber and in the supersonic nozzle are reported, and the processes responsible for nonequilibrium ionization in a laser-active medium are discussed.  相似文献   
179.
180.
Different versions of the Darboux–Weinstein theorem guarantee the existence of action–angle-type variables and the harmonic-oscillator variables in a neighborhood of isotropic tori in the phase space. The procedure for constructing these variables is reduced to solving a rather complicated system of partial differential equations. We show that this system can be integrated in quadratures, which permits reducing the problem of constructing these variables to solving a system of quadratic equations. We discuss several applications of this purely geometric fact in problems of classical and quantum mechanics.  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