全文获取类型
收费全文 | 22280篇 |
免费 | 2118篇 |
国内免费 | 2295篇 |
专业分类
化学 | 3112篇 |
晶体学 | 51篇 |
力学 | 1440篇 |
综合类 | 531篇 |
数学 | 16721篇 |
物理学 | 4838篇 |
出版年
2024年 | 36篇 |
2023年 | 238篇 |
2022年 | 278篇 |
2021年 | 412篇 |
2020年 | 499篇 |
2019年 | 568篇 |
2018年 | 524篇 |
2017年 | 618篇 |
2016年 | 728篇 |
2015年 | 527篇 |
2014年 | 1028篇 |
2013年 | 1767篇 |
2012年 | 943篇 |
2011年 | 1316篇 |
2010年 | 1194篇 |
2009年 | 1466篇 |
2008年 | 1571篇 |
2007年 | 1647篇 |
2006年 | 1370篇 |
2005年 | 1286篇 |
2004年 | 1022篇 |
2003年 | 1091篇 |
2002年 | 979篇 |
2001年 | 778篇 |
2000年 | 797篇 |
1999年 | 699篇 |
1998年 | 650篇 |
1997年 | 510篇 |
1996年 | 410篇 |
1995年 | 267篇 |
1994年 | 239篇 |
1993年 | 175篇 |
1992年 | 144篇 |
1991年 | 137篇 |
1990年 | 85篇 |
1989年 | 76篇 |
1988年 | 75篇 |
1987年 | 46篇 |
1986年 | 48篇 |
1985年 | 70篇 |
1984年 | 64篇 |
1983年 | 31篇 |
1982年 | 47篇 |
1981年 | 35篇 |
1980年 | 40篇 |
1979年 | 39篇 |
1978年 | 27篇 |
1977年 | 30篇 |
1976年 | 18篇 |
1973年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
31.
定义了一类相空间中的准几率分布函数系,这个准几率分布函数系直接建立在具有更加广泛意义的量子相空间Schr?dinger方程解的基础之上,其中定义α=αp-i?q和α=(1-α)q+i?p.发现了两个有趣的关系.(1)建立的量子相空间Schr?dinger方程的解实际上是对函数φ(λ)exp[i(1-α)qp]做窗口Fourier变换.(2)这个窗口函数g(λ)起着选择窗口形式的作用,而且不同的窗口对应着不同的分布函数.当g(λ)是一个代表Gauss窗的Gauss函数的时候,准几率分布函数就是一个类似于Husimi的分布函数fHLα(q,p);当g(λ)是一个表示椭圆的复函数时,准几率分布函数就是一个椭圆分布函数fEα(q,p);再在g(λ)为复函数的基础上附加α=0,就可得到标准序分布函数fS(q,p)、反标准序分布函数fAS(q,p)和Wigner分布函数fW(q,p),此时g(λ)表示高度为1/12π?而长度为λ的矩形窗.
关键词:
窗口Fourier变换
相空间
Wigner分布函数 相似文献
32.
33.
34.
35.
We consider some Sobolev-type spaces and obtain a necessary and sufficient condition for their embedding in a Lebesgue space. 相似文献
36.
Several new families of c‐Bhaskar Rao designs with block size 4 are constructed. The necessary conditions for the existence of a c‐BRD (υ,4,λ) are that: (1)λmin=?λ/3 ≤ c ≤ λ and (2a) c≡λ (mod 2), if υ > 4 or (2b) c≡ λ (mod 4), if υ = 4 or (2c) c≠ λ ? 2, if υ = 5. It is proved that these conditions are necessary, and are sufficient for most pairs of c and λ; in particular, they are sufficient whenever λ?c ≠ 2 for c > 0 and whenever c ? λmin≠ 2 for c < 0. For c < 0, the necessary conditions are sufficient for υ> 101; for the classic Bhaskar Rao designs, i.e., c = 0, we show the necessary conditions are sufficient with the possible exception of 0‐BRD (υ,4,2)'s for υ≡ 4 (mod 6). © 2002 Wiley Periodicals, Inc. J Combin Designs 10: 361–386, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/jcd.10009 相似文献
37.
This paper gives some global and uniform convergence estimates for a class of subspace correction (based on space decomposition) iterative methods applied to some unconstrained convex optimization problems. Some multigrid and domain decomposition methods are also discussed as special examples for solving some nonlinear elliptic boundary value problems.
38.
本文给出了一个关联图为圈的非负、半正定矩阵A为完全正的一个充要条件.我们还证明了这样的矩阵A(当A为完全正时)的分解指数即为A的阶数. 相似文献
39.
This paper investigates the large scale travelling ionospheric disturbances (LSTIDs) using the observation data of an HF Doppler array located in Central China. The data observed in a high solar activity year (year 1989) are analyzed to obtain the main propagation parameters of LSTIDs such as period, horizontal phase velocity and propagating direction. Results are outlined as follows: Most of the LSTIDs propagate southward; others tend to propagate northward, mostly in summer; dispersion of most LSTIDs is matched with that of Lamb pseudomode, while others have the dispersion of long period gravity wave mode. The horizontal phase velocities of these two modes are about 220 and 450 m/s respectively. The analysis shows that LSTIDs are strongly pertinent to solar activity and space magnetic storms; thus the results presented here are significant for the research of ionospheric weather in mid-low latitude region. 相似文献
40.
Dalila B. M. M. Fontes Eleni Hadjiconstantinou Nicos Christofides 《Journal of Global Optimization》2006,34(1):97-125
In this paper we obtain Lower Bounds (LBs) to concave cost network flow problems. The LBs are derived from state space relaxations
of a dynamic programming formulation, which involve the use of non-injective mapping functions guaranteing a reduction on
the cardinality of the state space. The general state space relaxation procedure is extended to address problems involving
transitions that go across several stages, as is the case of network flow problems. Applications for these LBs include: estimation
of the quality of heuristic solutions; local search methods that use information of the LB solution structure to find initial
solutions to restart the search (Fontes et al., 2003, Networks, 41, 221–228); and branch-and-bound (BB) methods having as
a bounding procedure a modified version of the LB algorithm developed here, (see Fontes et al., 2005a). These LBs are iteratively
improved by penalizing, in a Lagrangian fashion, customers not exactly satisfied or by performing state space modifications.
Both the penalties and the state space are updated by using the subgradient method. Additional constraints are developed to
improve further the LBs by reducing the searchable space. The computational results provided show that very good bounds can
be obtained for concave cost network flow problems, particularly for fixed-charge problems. 相似文献