全文获取类型
收费全文 | 13747篇 |
免费 | 1771篇 |
国内免费 | 762篇 |
专业分类
化学 | 815篇 |
晶体学 | 14篇 |
力学 | 759篇 |
综合类 | 107篇 |
数学 | 3876篇 |
物理学 | 2882篇 |
无线电 | 7827篇 |
出版年
2024年 | 27篇 |
2023年 | 183篇 |
2022年 | 250篇 |
2021年 | 280篇 |
2020年 | 349篇 |
2019年 | 278篇 |
2018年 | 320篇 |
2017年 | 457篇 |
2016年 | 557篇 |
2015年 | 547篇 |
2014年 | 921篇 |
2013年 | 910篇 |
2012年 | 947篇 |
2011年 | 925篇 |
2010年 | 729篇 |
2009年 | 790篇 |
2008年 | 955篇 |
2007年 | 946篇 |
2006年 | 868篇 |
2005年 | 737篇 |
2004年 | 595篇 |
2003年 | 621篇 |
2002年 | 494篇 |
2001年 | 458篇 |
2000年 | 393篇 |
1999年 | 353篇 |
1998年 | 270篇 |
1997年 | 214篇 |
1996年 | 200篇 |
1995年 | 141篇 |
1994年 | 95篇 |
1993年 | 81篇 |
1992年 | 74篇 |
1991年 | 52篇 |
1990年 | 39篇 |
1989年 | 41篇 |
1988年 | 31篇 |
1987年 | 22篇 |
1986年 | 17篇 |
1985年 | 33篇 |
1984年 | 17篇 |
1983年 | 6篇 |
1982年 | 9篇 |
1981年 | 3篇 |
1980年 | 10篇 |
1979年 | 13篇 |
1978年 | 3篇 |
1977年 | 4篇 |
1976年 | 4篇 |
1971年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 453 毫秒
121.
Boris Andreianov Franck Boyer Florence Hubert 《Numerical Methods for Partial Differential Equations》2007,23(1):145-195
Discrete duality finite volume schemes on general meshes, introduced by Hermeline and Domelevo and Omnès for the Laplace equation, are proposed for nonlinear diffusion problems in 2D with nonhomogeneous Dirichlet boundary condition. This approach allows the discretization of non linear fluxes in such a way that the discrete operator inherits the key properties of the continuous one. Furthermore, it is well adapted to very general meshes including the case of nonconformal locally refined meshes. We show that the approximate solution exists and is unique, which is not obvious since the scheme is nonlinear. We prove that, for general W?1,p′(Ω) source term and W1‐(1/p),p(?Ω) boundary data, the approximate solution and its discrete gradient converge strongly towards the exact solution and its gradient, respectively, in appropriate Lebesgue spaces. Finally, error estimates are given in the case where the solution is assumed to be in W2,p(Ω). Numerical examples are given, including those on locally refined meshes. © 2006 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2007 相似文献
122.
Anuradha Sharma Gurmeet K. Bakshi Madhu Raka 《Finite Fields and Their Applications》2007,13(4):1071-1085
Polyadic codes constitute a special class of cyclic codes and are generalizations of quadratic residue codes, duadic codes, triadic codes, m-adic residue codes and split group codes, which have good error-correcting properties. In this paper, we give necessary and sufficient conditions for the existence of polyadic codes of prime power length. Examples of some good codes arising from the family of polyadic codes of prime power length are also given. 相似文献
123.
We study algebraic geometric codes obtained from rational normal scrolls. We determine the complete weight hierarchy and spectrum
of these codes.
相似文献
124.
We introduce new classes of 2-weight cyclic codes which are direct sums of 1-weight irreducible cyclic codes
相似文献
125.
We consider the problem of solving the integral form of the radiative transfer equation in an atmosphere with optical thickness τ0?1. We propose two methods transforming this problem to a finite set of the independent problems of the same type set in an atmosphere with optical thickness much less then τ0. The error estimates are derived. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
126.
Vince Grolmusz 《Designs, Codes and Cryptography》2006,38(3):363-372
We define, construct and sketch possible applications of a new class of non-linear codes: co-orthogonal codes, with possible
applications in cryptography and parallel processing. We also describe a fast and general method for generating (non-linear)
codes with prescribed dot-products with the help of multi-linear polynomials. 相似文献
127.
S. Juneja 《Queueing Systems》2007,57(2-3):115-127
Efficient estimation of tail probabilities involving heavy tailed random variables is amongst the most challenging problems
in Monte-Carlo simulation. In the last few years, applied probabilists have achieved considerable success in developing efficient
algorithms for some such simple but fundamental tail probabilities. Usually, unbiased importance sampling estimators of such
tail probabilities are developed and it is proved that these estimators are asymptotically efficient or even possess the desirable
bounded relative error property. In this paper, as an illustration, we consider a simple tail probability involving geometric
sums of heavy tailed random variables. This is useful in estimating the probability of large delays in M/G/1 queues. In this setting we develop an unbiased estimator whose relative error decreases to zero asymptotically. The key
idea is to decompose the probability of interest into a known dominant component and an unknown small component. Simulation
then focuses on estimating the latter ‘residual’ probability. Here we show that the existing conditioning methods or importance
sampling methods are not effective in estimating the residual probability while an appropriate combination of the two estimates
it with bounded relative error. As a further illustration of the proposed ideas, we apply them to develop an estimator for
the probability of large delays in stochastic activity networks that has an asymptotically zero relative error.
相似文献
128.
双对数模型对模型模拟误差的放缩问题探讨 总被引:1,自引:0,他引:1
对双对数模型lg Y=a0+a1lg X1+a2lg X2+…+anlg Xn与其对应的指数模型y=c0xa11xa22…xann的模拟相对误差的关系进行了探讨,指出双对数模型具有放大和缩小指数模型相对误差的特性.对二者的关系进行了理论推导和实例验证,并给出了二者的定量关系式. 相似文献
129.
In this paper we derive a priori and a posteriori error estimates for cell centered finite volume approximations of nonlinear conservation laws on polygonal bounded domains. Numerical experiments show the applicability of the a posteriori result for the derivation of local adaptive solution strategies.
130.
Wei Gang SU Huai Jie ZHONG 《数学学报(英文版)》2006,22(2):515-522
This paper introduces the concept of the generalized Riesz operators and the concept of the generalized West decomposition of a general operator which generalizes the definition of the West decomposition of Riesz operators, and proves that the following three statements are equivalent on a general Banach space:
(a) Every generalized Riesz operator has the generalized West decomposition;
(b) Every operator makes strong Stampfli theorem true; Every operator has Apostol's compact correction. 相似文献