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   9958篇
  免费   660篇
  国内免费   893篇
化学   2660篇
晶体学   28篇
力学   1322篇
综合类   174篇
数学   4897篇
物理学   2430篇
  2023年   114篇
  2022年   174篇
  2021年   251篇
  2020年   250篇
  2019年   267篇
  2018年   238篇
  2017年   308篇
  2016年   366篇
  2015年   265篇
  2014年   389篇
  2013年   915篇
  2012年   430篇
  2011年   498篇
  2010年   407篇
  2009年   579篇
  2008年   600篇
  2007年   522篇
  2006年   523篇
  2005年   427篇
  2004年   385篇
  2003年   366篇
  2002年   363篇
  2001年   281篇
  2000年   260篇
  1999年   245篇
  1998年   236篇
  1997年   227篇
  1996年   162篇
  1995年   135篇
  1994年   116篇
  1993年   88篇
  1992年   89篇
  1991年   68篇
  1990年   56篇
  1989年   39篇
  1988年   56篇
  1987年   49篇
  1986年   29篇
  1985年   94篇
  1984年   104篇
  1983年   46篇
  1982年   92篇
  1981年   92篇
  1980年   59篇
  1979年   57篇
  1978年   59篇
  1977年   35篇
  1976年   22篇
  1974年   20篇
  1973年   21篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
Chenguang Ma 《中国物理 B》2021,30(12):120504-120504
A new five-dimensional fractional-order laser chaotic system (FOLCS) is constructed by incorporating complex variables and fractional calculus into a Lorentz-Haken-type laser system. Dynamical behavior of the system, circuit realization and application in pseudorandom number generators are studied. Many types of multi-stable states are discovered in the system. Interestingly, there are two types of state transition phenomena in the system, one is the chaotic state degenerates to a periodical state, and the other is the intermittent chaotic oscillation. In addition, the complexity of the system when two parameters change simultaneously is measured by the spectral entropy algorithm. Moreover, a digital circuit is design and the chaotic oscillation behaviors of the system are verified on this circuit. Finally, a pseudo-random sequence generator is designed using the FOLCS, and the statistical characteristics of the generated pseudo-random sequence are tested with the NIST-800-22. This study enriches the research on the dynamics and applications of FOLCS.  相似文献   
2.
We solve a combinatorial question concerning eigenvalues of the universal intertwining endomorphism of a subset representation.  相似文献   
3.
主要给出了偏缠绕模的Frobenius性质,推广了缠绕模相应的性质。  相似文献   
4.
5.
An innovative volatolomic approach employs the detection of biomarkers present in cerumen (earwax) to identify cattle intoxication by Stryphnodendron rotundifolium Mart., Fabaceae (popularly known as barbatimão). S. rotundifolium is a poisonous plant with the toxic compound undefined and widely distributed throughout the Brazilian territory. Cerumen samples from cattle of two local Brazilian breeds (‘Curraleiro Pé-Duro’ and ‘Pantaneiro’) were collected during an experimental intoxication protocol and analyzed using headspace (HS)/GC–MS followed by multivariate analysis (genetic algorithm for a partial least squares, cluster analysis, and classification and regression trees). A total of 106 volatile organic metabolites were identified in the cerumen samples of bovines. The intoxication by S. rotundifolium influenced the cerumen volatolomic profile of the bovines throughout the intoxication protocol. In this way, it was possible to detect biomarkers for cattle intoxication. Among the biomarkers, 2-octyldecanol and 9-tetradecen-1-ol were able to discriminate all samples between intoxicated and nonintoxicated bovines. The cattle intoxication diagnosis by S. rotundifolium was accomplished by applying the cerumen analysis using HS/GC–MS, in an easy, accurate, and noninvasive way. Thus, the proposed bioanalytical chromatography protocol is a useful tool in veterinary applications to determine this kind of intoxication.  相似文献   
6.
《Discrete Mathematics》2019,342(2):339-343
A strong edge-coloring of a graph G=(V,E) is a partition of its edge set E into induced matchings. Let G be a connected planar graph with girth k26 and maximum degree Δ. We show that either G is isomorphic to a subgraph of a very special Δ-regular graph with girth k, or G has a strong edge-coloring using at most 2Δ+12(Δ2)k colors.  相似文献   
7.
8.
The paper introduces a special system calibration technology in s-parameters measurement of microwave and millimeter wave devices. The 8-term errors module is built by analyzing the signals flowing in the measurement system. Then the calibration technology using non-standard kits is designed on the base. Finally, the experiment using the calibration technology is introduced.  相似文献   
9.
The Hahn–Banach Theorem for partially ordered totally convex modules [3] and a necessary and sufficient condition for the existence of an extension of a morphism from a submodule C 0 of a partially ordered totally convex module C (with the ordered unit ball of the reals as codomain) to C, are proved. Moreover, the categories of partially ordered positively convex and superconvex modules are introduced and for both categories the Hahn–Banach Theorem is proved.  相似文献   
10.
托卡马克工程试验混合堆等离子体性能的等值线图分析   总被引:3,自引:3,他引:0  
本文简要叙述托卡马克工程试验混合堆等离子体概念设计的物理基础,对等离子体性能进行了等值线图(Plasma Operation Contour)分析。根据工程试验混合堆的要求,得出一组等离子体参数。  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