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   576932篇
  免费   8122篇
  国内免费   1977篇
化学   310742篇
晶体学   8169篇
力学   25129篇
综合类   23篇
数学   69577篇
物理学   173391篇
  2021年   4664篇
  2020年   5294篇
  2019年   5580篇
  2018年   7026篇
  2017年   6891篇
  2016年   11104篇
  2015年   7451篇
  2014年   10858篇
  2013年   26972篇
  2012年   20978篇
  2011年   25741篇
  2010年   17589篇
  2009年   17366篇
  2008年   23425篇
  2007年   23370篇
  2006年   21818篇
  2005年   19701篇
  2004年   18152篇
  2003年   15900篇
  2002年   15566篇
  2001年   17342篇
  2000年   13205篇
  1999年   10340篇
  1998年   8478篇
  1997年   8239篇
  1996年   8130篇
  1995年   7288篇
  1994年   7129篇
  1993年   6888篇
  1992年   7728篇
  1991年   7671篇
  1990年   7280篇
  1989年   7071篇
  1988年   7081篇
  1987年   6931篇
  1986年   6600篇
  1985年   8807篇
  1984年   8967篇
  1983年   7158篇
  1982年   7404篇
  1981年   7292篇
  1980年   6850篇
  1979年   7248篇
  1978年   7420篇
  1977年   7292篇
  1976年   7230篇
  1975年   6820篇
  1974年   6707篇
  1973年   6720篇
  1972年   4527篇
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
231.
Formalization for problems of multicriteria decision making under uncertainty is constructed in terms of guaranteed and weak estimates. A relevant definition of the vector maximinimax value is given. Parameterization and approximation of maximum, minimax, and maximinimax values based on the inverse logical convolution are suggested. An application for multicommodity networks is considered. Received: December 13, 2000 / Accepted: August 21, 2001?Published online May 8, 2002  相似文献   
232.
The Wheeler–DeWitt equation of arbitrary Hartle–Hawking factor ordering for several minisuperspace universe models, such as the pure gravity Friedmann–Robertson–Walker and Taub ones, is mapped onto the dynamics of corresponding classical oscillators. The latter ones are studied by the classical Ermakov invariant method, which is a natural approach in this context. For the more realistic case of a minimally coupled massive scalar field, one can study, within the same type of approach, the corresponding squeezing features as a possible means of describing cosmological evolution. Finally, we comment on the analogy with the accelerator physics.  相似文献   
233.
In this paper a new state called odd-excited binomial state (OEBS) is introduced. It interpolates between the odd number state and the odd-excited coherent state. We discuss some statistical properties, such as the Glauber second-order correlation function and squeezing phenomenon (normal and amplitude-squared squeezing) for this state. The quasiprobability distribution functions (Husimi Q-function and Wigner W-function) are also examined.  相似文献   
234.
235.
N-Terminal tripeptide analogs of fibrin alpha-chain were synthesized and their inhibitory effect on fibrinogen/thrombin clotting was examined. A new water-soluble active ester, 3-pyridinium ester, was used for the synthesis. Among the synthetic peptides, H-Gly-Pro-Arg-hexamethyleneimine exhibited the highest inhibitory effect on fibrinogen-thrombin clotting.  相似文献   
236.
Hilbert重级数定理的一个改进   总被引:15,自引:3,他引:12       下载免费PDF全文
The object of this note is to prove the followingTheorem Let{a_n}and{b_n}be sequences of real numbers such that0<∑∑a_n~2<+∞and0<∑b_n~2<+∞.Then we have the inequalitysum from m=1 to∞sum from n=1 to∞a_mb_n/m+n<{sum from n=1 to∞(π-θ/n~(1/2)a_n~2}~1/2{sum from n=1 to∞(π-θ/n~(1/2)b_n~2}~1/2 (1)whereθ=3/2~(1/2)-1=1.121320343.  相似文献   
237.
238.
A digital watermark is a visible, or preferably invisible, identification code that is permanently embedded in digital media, to prove owner authentication and provide protection for documents. Given the interest in watermark generation using chaotic functions a detailed study of one chaotic function for this purpose is performed. In this paper, we present an approach for the generation of watermarks using the logistic map. Using this function, in conjunction with seed management, it is possible to generate chaotic sequences that may be used to create highpass or lowpass digital watermarks. In this paper we provide a detailed study on the generation of optically detectable watermarks and we provide some guidelines on successful chaotic watermark generation using the logistic map, and show using a recently published scheme, how care must be taken in the selection of the function seed.  相似文献   
239.
The paper is concerned with the study of plasticity models described by differential equations with stop and play operators. We suggest sufficient conditions for the global stability of a unique periodic solution for the scalar models and for the vector models with biaxial inputs of a particular form, namely the sum of a uniaxial function and a constant term. For another class of simple biaxial inputs, we present an example of the existence of unstable periodic solutions. The paper was written during the research stay of D. Rachinskii at the Technical University Munich supported by the research fellowship from the Alexander von Humboldt Foundation. His work was partially supported by the Russian Science Support Foundation, Russian Foundation for Basic Research (Grant No. 01-01-00146, 03-01-00258), and the Grants of the President of Russia (Grant No. MD-87.2003.01, NS-1532.2003.1). The support is gratefully acknowledged.  相似文献   
240.
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