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   53194篇
  免费   2454篇
  国内免费   2097篇
化学   26162篇
晶体学   831篇
力学   2079篇
综合类   112篇
数学   4760篇
物理学   16038篇
无线电   7763篇
  2022年   631篇
  2021年   678篇
  2020年   664篇
  2019年   794篇
  2018年   910篇
  2017年   887篇
  2016年   1293篇
  2015年   1120篇
  2014年   1561篇
  2013年   2676篇
  2012年   2714篇
  2011年   3066篇
  2010年   2355篇
  2009年   2486篇
  2008年   2706篇
  2007年   2721篇
  2006年   2427篇
  2005年   2145篇
  2004年   1979篇
  2003年   1648篇
  2002年   1633篇
  2001年   1948篇
  2000年   1447篇
  1999年   1172篇
  1998年   911篇
  1997年   843篇
  1996年   734篇
  1995年   656篇
  1994年   635篇
  1993年   597篇
  1992年   629篇
  1991年   621篇
  1990年   587篇
  1989年   508篇
  1988年   517篇
  1987年   470篇
  1986年   416篇
  1985年   472篇
  1984年   497篇
  1983年   362篇
  1982年   395篇
  1981年   387篇
  1980年   334篇
  1979年   408篇
  1978年   382篇
  1977年   412篇
  1976年   400篇
  1975年   350篇
  1974年   330篇
  1973年   343篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
131.
In this paper, a model of a linear multilevel programming problem with dominated objective functions (LMPPD(l)) is proposed, where multiple reactions of the lower levels do not lead to any uncertainty in the upper-level decision making. Under the assumption that the constrained set is nonempty and bounded, a necessary optimality condition is obtained. Two types of geometric properties of the solution sets are studied. It is demonstrated that the feasible set of LMPPD(l) is neither necessarily composed of faces of the constrained set nor necessarily connected. These properties are different from the existing theoretical results for linear multilevel programming problems.  相似文献   
132.
133.
In this paper, we prove convergence rates for spherical spline Hermite interpolation on the sphere Sd−1 via an error estimate given in a technical report by Luo and Levesley. The functionals in the Hermite interpolation are either point evaluations of pseudodifferential operators or rotational differential operators, the desirable feature of these operators being that they map polynomials to polynomials. Convergence rates for certain derivatives are given in terms of maximum point separation.  相似文献   
134.
Channel-optimized vector quantization (COVQ) has proven to be an effective joint source-channel coding technique that makes the underlying quantizer robust to channel noise. Unfortunately, COVQ retains the high encoding complexity of the standard vector quantizer (VQ) for medium-to-high quantization dimensions and moderate-to-good channel conditions. A technique called sample adaptive product quantization (SAPQ) was recently introduced by Kim and Shroff to reduce the complexity of the VQ while achieving comparable distortions. In this letter, we generalize the design of SAPQ for the case of memoryless noisy channels by optimizing the quantizer with respect to both source and channel statistics. Numerical results demonstrate that the channel-optimized SAPQ (COSAPQ) achieves comparable performance to the COVQ (within 0.2 dB), while maintaining considerably lower encoding complexity (up to half of that of COVQ) and storage requirements. Robustness of the COSAPQ system against channel mismatch is also examined.  相似文献   
135.
136.
We study condensation of ethanol-hexanol vapour by numerical solution of kinetic equations. The number of droplets formed in unit volume is computed within self-consistent classical model. It is shown that formation of ethanol-rich droplets prevails at the initial stage of nucleation process, but in the stationary state formation of droplets near the saddle point (on cluster formation energy surface) plays the dominant role. Presented at the 6th Joint Seminar “Development of Materials Science in Research and Education”, Karlštejn, Czech Republic, 17–19 September 1996. This work was supported by Grant No. A1010615 of the Grant Agency of the Academy of Sciences of the Czech Republic.  相似文献   
137.
将在时间和空间上为高斯型的超短脉冲分解成不同时间频率的高斯光束.详细地分析了其远场由于时空耦合引起的光谱频移、波前弯曲等复杂的时空特征。  相似文献   
138.
139.
The purpose of this paper is to give the Reid ``Roundabout Theorem' for quadratic functionals with general boundary conditions. In particular, we describe the so-called coupled point and regularity condition introduced in [16] in terms of Riccati equation solutions. Accepted 27 February 1996  相似文献   
140.
By active-passive-decomposition synchronisation, the application of the one-way coupled ring map lattice hyperchaotic system in secure digital speech communication is demonstrated. Synchronisation guarantees strong security and recovery without error  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