全文获取类型
收费全文 | 4857篇 |
免费 | 131篇 |
国内免费 | 189篇 |
专业分类
化学 | 83篇 |
力学 | 230篇 |
综合类 | 25篇 |
数学 | 4183篇 |
物理学 | 656篇 |
出版年
2024年 | 4篇 |
2023年 | 24篇 |
2022年 | 43篇 |
2021年 | 53篇 |
2020年 | 127篇 |
2019年 | 142篇 |
2018年 | 122篇 |
2017年 | 101篇 |
2016年 | 92篇 |
2015年 | 100篇 |
2014年 | 236篇 |
2013年 | 663篇 |
2012年 | 240篇 |
2011年 | 303篇 |
2010年 | 276篇 |
2009年 | 328篇 |
2008年 | 344篇 |
2007年 | 328篇 |
2006年 | 232篇 |
2005年 | 129篇 |
2004年 | 127篇 |
2003年 | 126篇 |
2002年 | 112篇 |
2001年 | 98篇 |
2000年 | 83篇 |
1999年 | 84篇 |
1998年 | 78篇 |
1997年 | 62篇 |
1996年 | 64篇 |
1995年 | 51篇 |
1994年 | 50篇 |
1993年 | 44篇 |
1992年 | 28篇 |
1991年 | 27篇 |
1990年 | 35篇 |
1989年 | 14篇 |
1988年 | 15篇 |
1987年 | 21篇 |
1986年 | 16篇 |
1985年 | 10篇 |
1984年 | 17篇 |
1983年 | 11篇 |
1982年 | 19篇 |
1981年 | 23篇 |
1980年 | 13篇 |
1979年 | 17篇 |
1978年 | 11篇 |
1977年 | 18篇 |
1976年 | 8篇 |
1975年 | 3篇 |
排序方式: 共有5177条查询结果,搜索用时 15 毫秒
101.
H. J. Plum 《Mathematical Methods of Operations Research》1991,35(5):377-399
In anM/M/1 queueing model, a decision maker can choosem pairs of arrival- and service rates. He can change his action at any time epoch, a switch of action costs an amount depending on the size of the switch. Besides that there are continuously incurring costs. Over a finite time horizon, there exists an optimal monotone hysteretic Markov policy. This is shown essentially by the technique of time discretization.The work producing this article was done during a half year stay at the University of Leiden, The Netherlands, with Prof. Arie Hordijk. A technical report (a more detailled version of this article) was written there [6]. The opportunity for this stay was given by the University of Bonn, Germany, where the author, at that time, worked as scientific assistant of Prof. M. Schäl. 相似文献
102.
K. Marti 《Mathematical Methods of Operations Research》1992,36(3):259-294
In engineering and economics often a certain vectorx of inputs or decisions must be chosen, subject to some constraints, such that the expected costs (or loss) arising from the deviation between the outputA() x of a stochastic linear systemxA()x and a desired stochastic target vectorb() are minimal. Hence, one has the following stochastic linear optimization problem minimizeF(x)=Eu(A()x b()) s.t.xD, (1) whereu is a convex loss function on
m
, (A(), b()) is a random (m,n + 1)-matrix, E denotes the expectation operator andD is a convex subset of
n
. Concrete problems of this type are e.g. stochastic linear programs with recourse, error minimization and optimal design problems, acid rain abatement methods, problems in scenario analysis and non-least square regression analysis.Solving (1), the loss functionu should be exactly known. However, in practice mostly there is some uncertainty in assigning appropriate penalty costs to the deviation between the outputA ()x and the targetb(). For finding in this situation solutions hedging against uncertainty a set of so-called efficient points of (1) is defined and a numerical procedure for determining these compromise solutions is derived. Several applications are discussed. 相似文献
103.
Imaging blur changes the digital output values of imaging systems. It leads to radiometric errors when the system is used for measurement. In this paper, we focus on the radiometric error due to imaging blur in remote sensing imaging systems. First, in accordance with the radiometric response calibration of imaging systems, we provide a theoretical analysis on the evaluation standard of radiometric errors caused by imaging blur. Then, we build a radiometric error model for imaging blur based on the natural stochastic fractal characteristics of remote sensing images. Finally, we verify the model by simulations and physical defocus experiments. The simulation results show that the modeling estimation result approaches to the simulation computation. The maximum difference of relative MSE (Mean Squared Error) between simulation computation and modeling estimation can achieve 1.6%. The physical experimental results show that the maximum difference of relative MSE between experimental results and modeling estimation is only 1.29% under experimental conditions. Simulations and experiments demonstrate that the proposed model is correct, which can be used to estimate the radiometric error caused by imaging blur in remote sensing images. This research is of great importance for radiometric measurement system evaluation and application. 相似文献
104.
Deshabrata Roy Mahapatra Sankar Kumar Roy Mahendra Prasad Biswal 《Applied Mathematical Modelling》2013
In this paper a multi choice stochastic transportation problem is considered where the supply and demand parameters of the constraints follow extreme value distribution. Some of the cost coefficients of the objective function are multi-choice type. At first all the probabilistic constraints are transformed into deterministic constraints. Further using the binary variables, multi-choice type cost coefficients are handled. Then the transformed problem is considered as a deterministic multi-choice transportation problem. Finally, a numerical example is presented to illustrate the solution procedure. 相似文献
105.
Affine semigroups are convex sets on which there exists an associative binary operation which is affine separately in either variable. They were introduced by Cohen and Collins in 1959. We look at examples of affine semigroups which are of interest to matrix and operator theory and we prove some new results on the extreme points and the absorbing elements of certain types of affine semigroups. Most notably we improve a result of Wendel that every invertible element in a compact affine semigroup is extreme by extending this result to linearly bounded affine semigroups. 相似文献
106.
《随机分析与应用》2013,31(2):251-274
Abstract The purpose of this paper is to investigate pathwise stability for certain Hilbert space-valued stochastic evolution equations. We are especially interested in the robustness analysis of perturbed stochastic differential equations in infinite dimensions. Sufficient conditions are established to ensure the almost surely stable decay of the given stochastic systems. Lastly, a corollary and corresponding example are studied to illustrate our theory. 相似文献
107.
Hermann Singer 《The Journal of mathematical sociology》2013,37(1):39-49
In a recent paper it was shown that the aliasing phenomenon, which leads to a severe identification problem in the estimation of stochastic differential equations, can be overcome by using a polygonal (or higher) approximation for the time paths of the exogenous variables. This work attempts to visualize the problem and presents several simulated trajectories of a continuous time AR(2)‐process (Ornstein‐Uhlenbeck‐process) together with the observationally equivalent structures. Furthermore it is shown that aliasing can even change the analytical properties of the time paths of the system: whereas the first component of the Ornstein‐Uhlenbeck‐process is differentiable, the trajectories of the aliasing structures are continuous, but not differentiable any more. 相似文献
108.
Controlled discrete–time stochastic processes axe studied using the convex–analytic approach. Some new properties of strategic measures spaces are established, particular Markov models are considered. The meaningful example is presented. 相似文献
109.
Correlations between single qubit and classical environment are studied by means of the stochastic Liouville equation, where a dephasing coupling between them is assumed. When the dephasing of the qubit is characterized by the two-state-jump Markov process, the properties of the total, classical and quantum correlations are examined. 相似文献
110.