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   1321647篇
  免费   29513篇
  国内免费   7721篇
化学   656359篇
晶体学   20219篇
力学   74439篇
综合类   102篇
数学   240187篇
物理学   367575篇
  2021年   13490篇
  2020年   15915篇
  2019年   16037篇
  2018年   12282篇
  2016年   27712篇
  2015年   20698篇
  2014年   30390篇
  2013年   74295篇
  2012年   36915篇
  2011年   33161篇
  2010年   36733篇
  2009年   39238篇
  2008年   32820篇
  2007年   28223篇
  2006年   34966篇
  2005年   27351篇
  2004年   28902篇
  2003年   27439篇
  2002年   28590篇
  2001年   27528篇
  2000年   24236篇
  1999年   22281篇
  1998年   20921篇
  1997年   20941篇
  1996年   21087篇
  1995年   19194篇
  1994年   18610篇
  1993年   18164篇
  1992年   17971篇
  1991年   18335篇
  1990年   17494篇
  1989年   17541篇
  1988年   17060篇
  1987年   17083篇
  1986年   15973篇
  1985年   22432篇
  1984年   23696篇
  1983年   19905篇
  1982年   21619篇
  1981年   20847篇
  1980年   20173篇
  1979年   20319篇
  1978年   21630篇
  1977年   21218篇
  1976年   20939篇
  1975年   19609篇
  1974年   19243篇
  1973年   19730篇
  1972年   14247篇
  1967年   12454篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
951.
It is shown that any finite dimensionalC 0 manifold (connected and Hausdorff but otherwise unrestricted) has an atlas of cardinality not greater than that of the continuum; while if it has a Hölder continuous pseudo-Riemannian metric then there is a countable atlas.  相似文献   
952.
The adsorption of hydrogen on a clean Cu10%/Ni90% (110) alloy single crystal was studied using flash desorption spectroscopy (FDS), Auger electron spectroscopy (AES), and work function measurements. Surface compositions were varied from 100% Ni to 35% Ni. The hydrogen chemisorption on a-surface of 100% nickel revealed strong attractive interactions between the hydrogen atoms in accordance with previous work on Ni(100). Three desorption states (β1, β2 and α) appeared in the desorption spectra. The highest temperature (α) state was occupied only after the initial population of the β2-state. As the amount of copper was increased in the nickel substrate, desorption from the higher energy binding α-state was reduced, indicating a decrease in the attractive interactions among hydrogen atoms. The hydrogen coverage at saturation was not affected by the addition of copper to the nickel substrate until the copper concentration was greater than 25% at which a sharp reduction in saturation coverage occurred. This phenomenon was apparently due to the adsorption of hydrogen on Ni atoms followed by occupation of NiNi and CuNi bridged adsorption sites, while occupation of CuCu sites was restricted due to an energy barrier to migration.  相似文献   
953.
Translated fromProblemy Ustoichivosti Stokhasticheskikh Modelei. Trudy Seminara, 1988, pp. 115–120.  相似文献   
954.
We study properties of some linear and nonlinear operators which occur in the theory of stochastic differential and integral equations.Translated from Statisticheskie Metody Otsenivaniya i Proverki Gipotez, pp. 148–154, 1988.  相似文献   
955.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 55, No. 3, pp. 478–484, September, 1991.  相似文献   
956.
A fast-frequency modulated (FM) diode laser has been optically narrowed using the technique of resonant optical feedback, to provide linewidths in each FM mode of ≈ 200 kHz peak-to-peak. With a drive frequency of 50 MHz and modulation index of 0.2, the FM laser has been used for the first time to obtain Doppler-free FM spectra of the Rb D1 line at 795 nm. The potential use of this system for laser frequency stabilisation is discussed.  相似文献   
957.
Translated from Itogi Nauki i Tekhniki, Seriya Matematicheskii Analiz, Vol. 27, pp. 3–146, 1989.  相似文献   
958.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 55, No. 4, pp. 624–629, October, 1991.  相似文献   
959.
Summary Considered here are model equations for weakly nonlinear and dispersive long waves, which feature general forms of dispersion and pure power nonlinearity. Two variants of such equations are introduced, one of Korteweg-de Vries type and one of regularized long-wave type. It is proven that solutions of the pure initial-value problem for these two types of model equations are the same, to within the order of accuracy attributable to either, on the long time scale during which nonlinear and dispersive effects may accumulate to make an order-one relative difference to the wave profiles.This research was supported in part by the National Science Foundation. A considerable portion of the project was completed while the first author was resident at the Institute for Mathematics and Its Applications, University of Minnesota.  相似文献   
960.
Diffraction by a semitransparent screen is considered in the framework of the nonlinear Schrödinger equation. The case of a defocusing medium is investigated. The method used represents a synthesis of the method of Riemann's matrix problem and the technique of Whitham's deformations of spectral curves.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova, Vol. 179, pp. 23–31, 1989.  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