全文获取类型
收费全文 | 14487篇 |
免费 | 1353篇 |
国内免费 | 1847篇 |
专业分类
化学 | 2173篇 |
晶体学 | 27篇 |
力学 | 845篇 |
综合类 | 286篇 |
数学 | 11565篇 |
物理学 | 2791篇 |
出版年
2024年 | 21篇 |
2023年 | 200篇 |
2022年 | 172篇 |
2021年 | 291篇 |
2020年 | 385篇 |
2019年 | 416篇 |
2018年 | 405篇 |
2017年 | 455篇 |
2016年 | 556篇 |
2015年 | 377篇 |
2014年 | 692篇 |
2013年 | 1259篇 |
2012年 | 580篇 |
2011年 | 819篇 |
2010年 | 777篇 |
2009年 | 938篇 |
2008年 | 1001篇 |
2007年 | 1028篇 |
2006年 | 913篇 |
2005年 | 843篇 |
2004年 | 699篇 |
2003年 | 668篇 |
2002年 | 622篇 |
2001年 | 500篇 |
2000年 | 489篇 |
1999年 | 426篇 |
1998年 | 390篇 |
1997年 | 344篇 |
1996年 | 282篇 |
1995年 | 182篇 |
1994年 | 137篇 |
1993年 | 106篇 |
1992年 | 97篇 |
1991年 | 92篇 |
1990年 | 50篇 |
1989年 | 51篇 |
1988年 | 45篇 |
1987年 | 27篇 |
1986年 | 37篇 |
1985年 | 44篇 |
1984年 | 36篇 |
1983年 | 24篇 |
1982年 | 31篇 |
1981年 | 28篇 |
1980年 | 34篇 |
1979年 | 29篇 |
1978年 | 25篇 |
1977年 | 22篇 |
1976年 | 12篇 |
1973年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 609 毫秒
951.
M. Van Barel E. Van Camp N. Mastronardi 《Numerical Linear Algebra with Applications》2005,12(10):981-1000
Very recently, an algorithm, which reduces any symmetric matrix into a semiseparable one of semi‐ separability rank 1 by similar orthogonality transformations, has been proposed by Vandebril, Van Barel and Mastronardi. Partial execution of this algorithm computes a semiseparable matrix whose eigenvalues are the Ritz‐values obtained by the Lanczos' process applied to the original matrix. Also a kind of nested subspace iteration is performed at each step. In this paper, we generalize the above results and propose an algorithm to reduce any symmetric matrix into a similar block‐semiseparable one of semiseparability rank k, with k ∈ ?, by orthogonal similarity transformations. Also in this case partial execution of the algorithm computes a block‐semiseparable matrix whose eigenvalues are the Ritz‐values obtained by the block‐Lanczos' process with k starting vectors, applied to the original matrix. Subspace iteration is performed at each step as well. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
952.
给出了拓扑线性空间中的一个Drop定理.利用此Drop定理,证明了拓扑线性空间中的每个序列紧凸集具有Drop性质;每个可数紧闭凸集具有拟Drop性质.而且结出了拓扑线性空间中Drop性质和拟Drop性质的序列流特征.也讨论了Drop性质和拟Drop性质与泛函取极值之间的联系. 相似文献
953.
In the present paper our aim is to establish convergence and Voronovskaja-type theorems for first derivatives of generalized
Baskakov operators for functions of one and two variables in exponential and polynomial weight spaces.
相似文献
954.
955.
A new matrix additive, poly (N,N-dimethylacrylamide)-functionalized gold nanoparticle (GNP-PDMA), was prepared by “grafting-to” approach, and then incorporated into quasi-interpenetrating network (quasi-IPN) composed of linear polyacrylamide (LPA, 3.3 MDa) and PDMA to form novel polymer/metal composite sieving matrix (quasi-IPN/GNP-PDMA) for DNA sequencing by capillary electrophoresis. Without complete optimization, quasi-IPN/GNP-PDMA yielded a readlength of 801 bases at 98% accuracy in about 64 min by using the ABI 310 Genetic Analyzer at 50 °C and 150 V/cm. Compared with previous quasi-IPN/GNPs, quasi-IPN/GNP-PDMA can further improve DNA sequencing performances. This is because the presence of GNP-PDMA can improve the compatibility of GNPs with the whole sequencing system, enhance the entanglement degree of networks, and increase the GNP concentration in system, which consequently lead to higher restriction and stability, higher apparent molecular weight (MW), and smaller pore size of the total sieving networks. Furthermore, the composite matrix was also compared with quasi-IPN containing higher-MW LPA and commercial POP-6. The results indicate that the composite matrix is a promising one for DNA sequencing to achieve full automation due to the separation provided with high resolution, speediness, excellent reproducibility, and easy loading in the presence of GNP-PDMA. 相似文献
956.
The problem of the boundedness of the Riesz potential I
α
, 0 < α < n, in local Morrey-type spaces is reduced to the boundedness of the Hardy operator in weighted L
p
-spaces on the cone of non-negative non-increasing functions. This allows obtaining sufficient conditions for the boundedness
in local Morrey-type spaces for all admissible values of the parameters. Moreover, for a certain range of the parameters,
these sufficient conditions coincide with the necessary ones.
V. Guliyev’s research was partially supported by the grant of the Azerbaijan-U. S. Bilateral Grants Program II (project ANSF
Award / AZM1-3110-BA-08) and the Turkish Scientific and Technological Research Council (TUBITAK, programme 2221, no. 220.01-619-4889). 相似文献
957.
Analysis of Ti:LiNbO3 zero-gap directional coupler for wavelength division multiplexer/demultiplexer
Pranabendu Ganguly Juran Chandra Biswas Samir Kumar Lahiri 《Optics Communications》2008,281(12):3269-3274
For the purpose of multichannel integrated-optical wavelength division MUX/DEMUX design, the wavelength tuning method of Ti:LiNbO3 zero-gap directional coupler is analysed by effective-index based matrix method (EIMM). In this method, first, the 2D refractive index profile of the Ti:LiNbO3 zero-gap directional coupler is transformed into lateral 1D effective-index profile by WKB method. Finally, matrix method is applied to this effective-index profile and the propagation constants are computed from the resonance peaks of the excitation efficiency versus propagation constant characteristics. It has been shown that the channel wavelength tuning can be achieved by varying the Y-branching angle at the input and output of the device or by a slight variation of two-mode-section length. The method of electro-optic fine tuning of the channel wavelength and channel separation of the device has also been investigated. A cascaded structure with proper parameters for four-channel application is also simulated and the results are presented. 相似文献
958.
Various authors have studied extensions of Shannon’s entropy but their inferential properties and applications in applied
sciences have not invited proper attention from researchers. In the present paper we explore the motivation and implication
of using various classes of the generalized entropies and conditional entropies. We evaluate β-class and (α, β)-class entropies for multivariate normal density function. We also obtain the measures of dependence in terms of the classes
of generalized entropies.
相似文献
959.
设$M$是右$R$-模, $\aleph$是一个无穷基数. 称右$R$-模$N$是$\aleph$-$M$-凝聚的,如果对任意的$B/A\hookrightarrow mR$,其中设$M$是右$R$-模, $\aleph$是一个无穷基数. 称右$R$-模$N$是$\aleph$-$M$-凝聚的,如果对任意的$B/A\hookrightarrow mR$,其中设$M$是右$R$-模, $\aleph$是一个无穷基数. 称右$R$-模$N$是$\aleph$-$M$-凝聚的,如果对任意的$B/A\hookrightarrow mR$,其中设$M$是右$R$-模, $\aleph$是一个无穷基数. 称右$R$-模$N$是$\aleph$-$M$-凝聚的,如果对任意的$B/A\hookrightarrow mR$,其中$0\leq A相似文献
960.
本文给出了强正则$(\alpha,\beta)-$族的概念,它是[4]和[5]中$SPG-$族概念的推广.进一步,给出了一种用强正则 $(\alpha,\beta)-$族构造强正则$(\alpha,\beta)-$几何的方法.另外,本文还证明了由强正则$(\alpha,\beta)-$线汇构造的强正则$(\alpha,\beta)-$几何是平移强正则$(\alpha,\beta)-$几何;当$t-r>\beta$时,反之亦成立. 相似文献