全文获取类型
收费全文 | 8674篇 |
免费 | 1441篇 |
国内免费 | 1029篇 |
专业分类
化学 | 6154篇 |
晶体学 | 126篇 |
力学 | 495篇 |
综合类 | 60篇 |
数学 | 1223篇 |
物理学 | 3086篇 |
出版年
2024年 | 30篇 |
2023年 | 191篇 |
2022年 | 334篇 |
2021年 | 301篇 |
2020年 | 338篇 |
2019年 | 332篇 |
2018年 | 285篇 |
2017年 | 287篇 |
2016年 | 463篇 |
2015年 | 451篇 |
2014年 | 597篇 |
2013年 | 631篇 |
2012年 | 825篇 |
2011年 | 824篇 |
2010年 | 533篇 |
2009年 | 489篇 |
2008年 | 549篇 |
2007年 | 449篇 |
2006年 | 437篇 |
2005年 | 399篇 |
2004年 | 341篇 |
2003年 | 252篇 |
2002年 | 231篇 |
2001年 | 198篇 |
2000年 | 137篇 |
1999年 | 200篇 |
1998年 | 133篇 |
1997年 | 104篇 |
1996年 | 117篇 |
1995年 | 117篇 |
1994年 | 96篇 |
1993年 | 62篇 |
1992年 | 65篇 |
1991年 | 61篇 |
1990年 | 70篇 |
1989年 | 47篇 |
1988年 | 32篇 |
1987年 | 22篇 |
1986年 | 31篇 |
1985年 | 15篇 |
1984年 | 14篇 |
1983年 | 14篇 |
1982年 | 8篇 |
1981年 | 10篇 |
1979年 | 3篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1928年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Canonical correlation analysis based on information theory 总被引:2,自引:0,他引:2
In this article, we propose a new canonical correlation method based on information theory. This method examines potential nonlinear relationships between p×1 vector Y-set and q×1 vector X-set. It finds canonical coefficient vectors a and b by maximizing a more general measure, the mutual information, between aTX and bTY. We use a permutation test to determine the pairs of the new canonical correlation variates, which requires no specific distributions for X and Y as long as one can estimate the densities of aTX and bTY nonparametrically. Examples illustrating the new method are presented. 相似文献
42.
43.
多目标半定规划的互补弱鞍点和G-鞍点最优性条件 总被引:1,自引:0,他引:1
对于含矩阵函数半定约束和多个目标函数的多目标半定规划问题,给出Lagrange函数在弱有效意义下的互补弱鞍点和Geofrrion恰当有效意义下的G-鞍点的定义及其等价定义.然后,在较弱的凸性条件下,利用含矩阵和向量约束的择一性定理,建立多目标半定规划的互补弱鞍点和G-鞍点充分必要条件. 相似文献
44.
进一步研究了具有三个cM公共值的亚纯函数的唯一性,改进了H.Ueda和仪洪勋等人的有关结果. 相似文献
45.
46.
47.
This work is devoted to near-optimal controls of large-scale discrete-time nonlinear dynamic systems driven by Markov chains; the underlying problem is to minimize an expected cost function. Our main goal is to reduce the complexity of the underlying systems. To achieve this goal, discrete-time control models under singularly-perturbed Markov chains are introduced. Using a relaxed control representation, our effort is devoted to finding near-optimal controls. Lumping the states in each irreducible class into a single state gives rise to a limit system. Applying near-optimal controls of the limit system to the original system, near-optimal controls of the original system are derived. 相似文献
48.
In this paper,the concept of the infinitesimal realization factor is extended to the parameter-dependent performance functions in closed queueing networks. Then the concepts of realization matrix (its elements are called realization factors) and performance potential are introduced,and the relations between infinitesimal realization factors and these two quantities are discussed. This provides a united framework for both IPA and non IPA approaches. Finally,another physical meaning of the service rate is given. 相似文献
49.
Traveling wave Ti:LiNbO3 Mach-Zehnder optical modulators with buried electrodes and etched grooves in the SiO2 buffer layer are analyzed by the finite element method. The tradeoff between the bandwidth BW and the half-wave voltage Vπ is discussed. The value of BW/Vπ is used to weight the total performance of the modulator. Taking a thick buffer layer and etching deep grooves in the buffer layer are demonstrated as two effective methods to improve the performance of the modulator. A 3-dB optical bandwidth of 18 GHz with half-wave voltage 5V at a wavelength of 1.55 pm could be obtained even though the electrode is not very thick. When the requirement of half-wave voltage is not very critical, a bandwidth of more than 100 GHz can be obtained. 相似文献
50.
Groove guide is widely recognized as one of the most promising millimeter wave transmission structures. In this paper, the mode-matching method is used to analyse the dispersion characteristics of single and asymmetrical double groove guides, and the unified formulae of Nth-order approximation dispersion equations are presented. Based on this analysis, a general program for calculating the dispersion characteristrics of single and asymmetrical double groove guides has been completed. Some comparisons between the results obtained by present method and published data show that very good agreement has been seen. The effectiveness and the reliability of the given formulae and program are thus verified. 相似文献