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   45190篇
  免费   1512篇
  国内免费   165篇
化学   29466篇
晶体学   356篇
力学   795篇
综合类   4篇
数学   7785篇
物理学   8461篇
  2023年   300篇
  2022年   505篇
  2021年   678篇
  2020年   691篇
  2019年   729篇
  2018年   847篇
  2017年   769篇
  2016年   1563篇
  2015年   1268篇
  2014年   1324篇
  2013年   2790篇
  2012年   2740篇
  2011年   2965篇
  2010年   1811篇
  2009年   1707篇
  2008年   2669篇
  2007年   2587篇
  2006年   2362篇
  2005年   2166篇
  2004年   1810篇
  2003年   1521篇
  2002年   1314篇
  2001年   1006篇
  2000年   906篇
  1999年   684篇
  1998年   515篇
  1997年   497篇
  1996年   617篇
  1995年   451篇
  1994年   473篇
  1993年   457篇
  1992年   425篇
  1991年   366篇
  1990年   337篇
  1989年   284篇
  1988年   269篇
  1987年   264篇
  1986年   266篇
  1985年   368篇
  1984年   370篇
  1983年   248篇
  1982年   267篇
  1981年   260篇
  1980年   248篇
  1979年   172篇
  1978年   181篇
  1977年   176篇
  1976年   150篇
  1975年   143篇
  1973年   134篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
121.
The Gaussian property of the Brownian bridge is characterized as an application of Ramachandran's theorem in terms of the independence of the random variables that appear in the Karhunen-Loéve expansion of the process. A reference about the construction of the Brownian bridge by means of functional transformations is also included.  相似文献   
122.
We give a criterion to compare the physical content of different mathematical structures derived from a preparation-question structure. Then this criterion is used in order to compare the physical content of the (Jauch-Piron's) property lattice with the physical content of the poset of testable properties. We prove that for complete preparation-question structures these two structures carry the same physical content; moreover the set of testable properties has the algebraic structure of the Brouwer-Zadeh lattice. For more general preparation-question structures the physical content of the poset of testable property can be larger than that of the property lattice. Physically relevant examples of the possible cases are given.  相似文献   
123.
Ultraviolet-visible spectra of 4-oxo 1 and 4-imino 2 quinolizines or their monocyclic tautomers 3, 4 have been studied in neutral, acidic and basic ethanolic solution as well as in dimethyl sulfoxide and chloroform. Ring B of 4-oxo and 6-unsubstituted 4-imino compounds can be cleaved by sodium ethanolate more or less easily. Ring B of 6-methyl-4-iminoquinolizines is very unstable and they are present mainly in the monocyclic form which are partly dissociated in ethanol and dimethyl sulfoxide especially in higher dilution or in the presence of sodium ethanolate. In dilute acidic ethanol or chloroform, the dissociation is suppressed and in the latter solvent and in some cases, absorption bands can be observed due to a small amount of the 4-imino-6-methylquinolizines. In acidic solution of compounds 3B=C, 3D, 4E, 4F=G having simultaneously cyano and ethoxycarbonyl groups in 1 and 3 position, not simple reprotonation occurs but irreversible changes can be observed.  相似文献   
124.
We present two different approaches to detect and quantify phase synchronization in the case of coupled non-phase coherent oscillators. The first one is based on the general idea of curvature of an arbitrary curve. The second one is based on recurrences of the trajectory in phase space. We illustrate both methods in the paradigmatic example of the R?ssler system in the funnel regime. We show that the second method is applicable even in the case of noisy data. Furthermore, we extend the second approach to the application of chains of coupled systems, which allows us to detect easily clusters of synchronized oscillators. In order to illustrate the applicability of this approach, we show the results of the algorithm applied to experimental data from a population of 64 electrochemical oscillators.  相似文献   
125.
126.
The tunneling of single electrons in small capacitance tunnel junctions is influenced by charging effects and by the fluctuations of the elecromagnetic environment. We study the effect of an external circuit with arbitrary impedance on the tunneling of quasiparticles and Cooper pairs in voltage driven Josephson junctions. We present results at finite temperatures and also consider an acdriven system.  相似文献   
127.
In this paper we present photoionization cross sections of the Cu and Al dimers and tetramers. The local spin density method is applied to calculate the electronic structure and the ground state potential. The cross sections are calculated using the continuum multiple scattering method, and a basic analysis of the photoionization process is given within the independent particle picture.  相似文献   
128.
Ferric ferrocyanides synthesized from different sources of ferric cations and ferrocyanide anions and those derived from ferrous ferricyanide, ferrous ferrocyanide and ferric ferricyanide have been studied using Mössbauer and XRD techniques. Structural information of the effect of the provenance on the properties of the final compound is obtained. Significant correlations between isomer shift and quadrupole splitting of inner and outer iron cations have been observed.  相似文献   
129.
130.
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