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   382654篇
  免费   6079篇
  国内免费   3203篇
化学   192876篇
晶体学   6259篇
力学   18828篇
综合类   164篇
数学   43664篇
物理学   130145篇
  2022年   3189篇
  2021年   3980篇
  2020年   4262篇
  2019年   4637篇
  2018年   6119篇
  2017年   6255篇
  2016年   8676篇
  2015年   5267篇
  2014年   8492篇
  2013年   18663篇
  2012年   15185篇
  2011年   18086篇
  2010年   13366篇
  2009年   13288篇
  2008年   16027篇
  2007年   15723篇
  2006年   14422篇
  2005年   12492篇
  2004年   11546篇
  2003年   10187篇
  2002年   10112篇
  2001年   12562篇
  2000年   9324篇
  1999年   7202篇
  1998年   5851篇
  1997年   5677篇
  1996年   5200篇
  1995年   4496篇
  1994年   4431篇
  1993年   4209篇
  1992年   4827篇
  1991年   5010篇
  1990年   4746篇
  1989年   4569篇
  1988年   4327篇
  1987年   4499篇
  1986年   4149篇
  1985年   5286篇
  1984年   5295篇
  1983年   4314篇
  1982年   4408篇
  1981年   4113篇
  1980年   4027篇
  1979年   4358篇
  1978年   4385篇
  1977年   4421篇
  1976年   4324篇
  1975年   4044篇
  1974年   4000篇
  1973年   3977篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
952.
Observables on hypergraphs are described by event-valued measures. We first distinguish between finitely additive observables and countably additive ones. We then study the spectrum, compatibility, and functions of observables. Next a relationship between observables and certain functionals on the set of measures M(H) of a hypergraph H is established. We characterize hypergraphs for which every linear functional on M(H) is determined by an observable. We define the concept of an effect and show that observables are related to effect-valued measures. Finally, we define operational transformations from M(H) to itself and show that they can be described as a certain combination of effects.On leave from University of Berne, Institute of Mathematical Statistics, Sidlerstrasse 5, CH-3012 Berne, Switzerland.  相似文献   
953.
Complete integrability of the supersymmetric, two-dimensional sine-Gordon model of field theory within the framework of the Hamiltonian interpretation of the method of the inverse problem is proved. The classical r-matrix of the model is computed, and its equivalence to the r-matrix the Grassmann Thirring model is established. Variables of creation-annihilation type are constructed, and the spectrum of elementary excitations of the system is obtained.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova AN SSSR, Vol. 120, pp. 122–135, 1982.  相似文献   
954.
A two-stage nonlinear cochlear model possesses automatic gain control   总被引:1,自引:0,他引:1  
A model of the cochlea is explored using as stimuli two simultaneously presented sinusoids of equal amplitude. The model consists of two stages: a linear bandpass filter, followed by a reservoir-type representation of the hair-cell/nerve-fiber complex. Fast Fourier transforms of the model's output were computed. While the amplitudes of the individual response components were strongly nonlinear functions of intensity, the ratio of the magnitudes of the response components at the frequencies of the two stimulating sinusoids was found to be nearly equal, over a wide intensity range, to the ratio of the amplitudes which those stimulating sinusoids possessed at the output of the filter. Thus the reservoir stage exerts "automatic gain control".  相似文献   
955.
The results are presented of an investigation of the electrical characteristics of avalanche S-diodes based on a new type of structure (+---n), which is obtained by diffusing iron in GaAs with n = 1.1017 cm–3. The diodes have regions of S-type negative differential resistance (NDR), for both bias polarities and have a number of other features by comparison with diodes based on the --n structures with fused contacts. We discuss the mechanism for the formation of the NDR region of the voltage-current characteristics of the diode.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 54–58, April, 1986.  相似文献   
956.
This paper shows the separation and determination of eight compounds containing the OH group (ethanol, pentanol, 3-methyl-1-butanol, hexanol, phenol, benzyl-alcohol, phenylethanol and geraniol) in synthetic wine by gas chromatography using UV-Vis molecular absorption spectrometry as detection system. All the parameters affecting the separation and determination were optimised using some methods of experiment design. The analytical characteristics of each compound were calculated and detection limits ranging from 2.3 to 74 mg l(-1) have been obtained.  相似文献   
957.
Current ideas of soliton switching as a possible route towards molecular electronics are reviewed. The relation between photoinduced dipole moments in dye molecules and soliton motion is pointed out. Derivates of -carotene are presented as candidates for components of molecular electronic devices.Dedicated to K. Dransfeld on the occasion of his 60th birthday  相似文献   
958.
959.
The reduction of some dihydrothiazolobenzothiazolium salts with sodium borohydride may take place in two directions: with the formation of thiazolidino[2, 3-b]benzathiazolines and with the cleavage of the C-S bond to give N-(-mercaptoethyl)benzothiazolines. The behavior of thiazolidino[2, 3-b]benzothiazoline under the conditions of acid and alkaline hydrolysis has been studied.For communication VI, see [1].  相似文献   
960.
2.6 Foods     

Abstracts2 Particular products and fields of application

2.6 Foods  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