全文获取类型
收费全文 | 507篇 |
免费 | 9篇 |
国内免费 | 33篇 |
专业分类
化学 | 193篇 |
晶体学 | 4篇 |
力学 | 11篇 |
数学 | 291篇 |
物理学 | 50篇 |
出版年
2024年 | 3篇 |
2023年 | 25篇 |
2022年 | 14篇 |
2021年 | 17篇 |
2020年 | 32篇 |
2019年 | 12篇 |
2018年 | 23篇 |
2017年 | 17篇 |
2016年 | 12篇 |
2015年 | 7篇 |
2014年 | 17篇 |
2013年 | 58篇 |
2012年 | 10篇 |
2011年 | 27篇 |
2010年 | 30篇 |
2009年 | 31篇 |
2008年 | 28篇 |
2007年 | 25篇 |
2006年 | 17篇 |
2005年 | 22篇 |
2004年 | 22篇 |
2003年 | 18篇 |
2002年 | 13篇 |
2001年 | 7篇 |
2000年 | 3篇 |
1999年 | 12篇 |
1998年 | 2篇 |
1997年 | 6篇 |
1996年 | 2篇 |
1995年 | 9篇 |
1994年 | 4篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1991年 | 3篇 |
1990年 | 1篇 |
1989年 | 3篇 |
1988年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 5篇 |
1972年 | 1篇 |
排序方式: 共有549条查询结果,搜索用时 9 毫秒
81.
Teruo Tanaka 《Journal of Mathematical Analysis and Applications》2011,382(2):549-558
This paper concerns the optimal stopping problem for discrete time multiparameter stochastic processes with the index set Nd. In the classical optimal stopping problems, the comparisons between the expected reward of a player with complete foresight and the expected reward of a player using nonanticipating stop rules, known as prophet inequalities, have been studied by many authors. Ratio comparisons between these values in the case of multiparameter optimal stopping problems are studied by Krengel and Sucheston (1981) [9] and Tanaka (2007, 2006) [14] and [15]. In this paper an additive comparison in the case of finite stage multiparameter optimal stopping problems is given. 相似文献
82.
This work proposes a new copula class that we call the MGB2 copula. The new copula originates from extracting the dependence function of the multivariate GB2 distribution (MGB2) whose marginals follow the univariate generalized beta distribution of the second kind (GB2). The MGB2 copula can capture non-elliptical and asymmetric dependencies among marginal coordinates and provides a simple formulation for multi-dimensional applications. This new class features positive tail dependence in the upper tail and tail independence in the lower tail. Furthermore, it includes some well-known copula classes, such as the Gaussian copula, as special or limiting cases.To illustrate the usefulness of the MGB2 copula, we build a trivariate MGB2 copula model of bodily injury liability closed claims. Extended GB2 distributions are chosen to accommodate the right-skewness and the long-tailedness of the outcome variables. For the regression component, location parameters with continuous predictors are introduced using a nonlinear additive function. For comparison purposes, we also consider the Gumbel and t copulas, alternatives that capture the upper tail dependence. The paper introduces a conditional plot graphical tool for assessing the validation of the MGB2 copula. Quantitative and graphical assessment of the goodness of fit demonstrate the advantages of the MGB2 copula over the other copulas. 相似文献
83.
Manohar Aggrawal Poonam SinghMahesh Kumar Panda 《Statistics & probability letters》2011,81(2):259-266
Chan et al. (1998a) obtained A-optimal designs for an additive quadratic mixture model for q≥3 mixture components. In this paper, we obtain the A-optimal designs for an additive cubic model for q≥3 mixture components using the class of symmetric weighted centroid designs based on barycentres of various depths. We observe that barycentres of depths 0 and 2 are possible support points for an A-optimal design. We have also given the optimal weights of A-optimal designs for 3≤q≤17. 相似文献
84.
Zenkevich IG Eliseenkov EV Kasatochkin AN Zhakovskaya ZA Khoroshko LO 《Journal of chromatography. A》2011,1218(21):3291-3299
Chlorinated derivatives of aliphatic ketones are a class of organic compounds poorly characterized by both mass spectra and chromatographic retention indices up to present. It is caused by objective difficulties of isolation of individual products from reaction mixtures formed in the result of non-selective chlorination of parent carbonyl compounds. Nevertheless the differences of GC retention indices for structurally analogous chlorination products of different ketones and initial substrates indicate the constancy depending on the number and position of chlorine atoms in the molecules. This feature permits us to use the simplest kind of additive schemes in identification of such chlorinated derivatives, including diastereomeric α,α'-dichloro-k-alkanones (k>2). Hence, the identification of chlorination products of aliphatic ketones becomes possible for any compounds of this class without using mass spectrometric data only in the result of accurate measurement of their GC retention indices. 相似文献
85.
Zhou Caijun 《数学学报(英文版)》1996,12(4):413-414
In this short paper, we prove that ifR is a regular local ring of unequal characteristic, then there exists an additive covariant functorG from the category of abelian sheaves on SpecR to the category of abelian groups such that id
R
(G(R))>dimG(R). This result shows that the answer to the question 3.8 (ii) in [3] may be negative. 相似文献
86.
W?odzimierz Fechner 《Journal of Mathematical Analysis and Applications》2006,322(2):774-786
We investigate some inequalities connected with the Hyers-Ulam stability of three functional equations, which have a solution of the form φ=a+q, where a is an additive mapping and q is a quadratic one. 相似文献
87.
88.
从事实逻辑到任务逻辑 总被引:1,自引:1,他引:0
在经典命题逻辑语言中引入附加算子几,较系统地研究近几年刚刚被提出的任务逻辑。这里把公式理解为“任务”,介绍了“任务逻辑”的语义理论,并从语构上定义形式系统L与之对应,证明该系统的可靠性、完备性及可判定性定理.最后建立系统L中的一系列基本定理。 相似文献
89.
90.
A principled framework to generalize variational perturbation approximations (VPAs) formulated within the ambit of the nonadditive statistics of Tsallis statistics, is introduced. This is accomplished by operating on the terms constituting the perturbation expansion of the generalized free energy (GFE) with a variational procedure formulated using q-deformed calculus. A candidate q-deformed generalized VPA (GVPA) is derived with the aid of the Hellmann-Feynman theorem. The generalized Bogoliubov inequality for the approximate GFE are derived for the case of canonical probability densities that maximize the Tsallis entropy. Numerical examples demonstrating the application of the q-deformed GVPA are presented. The qualitative distinctions between the q-deformed GVPA model vis-á-vis prior GVPA models are highlighted. 相似文献