全文获取类型
收费全文 | 36906篇 |
免费 | 1315篇 |
国内免费 | 262篇 |
专业分类
化学 | 25449篇 |
晶体学 | 293篇 |
力学 | 752篇 |
综合类 | 1篇 |
数学 | 6210篇 |
物理学 | 5778篇 |
出版年
2023年 | 166篇 |
2022年 | 167篇 |
2021年 | 424篇 |
2020年 | 628篇 |
2019年 | 617篇 |
2018年 | 425篇 |
2017年 | 406篇 |
2016年 | 972篇 |
2015年 | 858篇 |
2014年 | 1052篇 |
2013年 | 1769篇 |
2012年 | 2268篇 |
2011年 | 2573篇 |
2010年 | 1376篇 |
2009年 | 1226篇 |
2008年 | 2393篇 |
2007年 | 2189篇 |
2006年 | 2235篇 |
2005年 | 2087篇 |
2004年 | 1770篇 |
2003年 | 1446篇 |
2002年 | 1396篇 |
2001年 | 549篇 |
2000年 | 514篇 |
1999年 | 411篇 |
1998年 | 262篇 |
1997年 | 397篇 |
1996年 | 444篇 |
1995年 | 347篇 |
1994年 | 411篇 |
1993年 | 388篇 |
1992年 | 329篇 |
1991年 | 290篇 |
1990年 | 266篇 |
1989年 | 239篇 |
1988年 | 237篇 |
1987年 | 248篇 |
1986年 | 208篇 |
1985年 | 395篇 |
1984年 | 358篇 |
1983年 | 300篇 |
1982年 | 364篇 |
1981年 | 299篇 |
1980年 | 315篇 |
1979年 | 259篇 |
1978年 | 251篇 |
1977年 | 233篇 |
1976年 | 226篇 |
1975年 | 216篇 |
1974年 | 180篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
An algorithm is described that determines whether a given polynomial with integer coefficients has a cyclotomic factor. The algorithm is intended to be used for sparse polynomials given as a sequence of coefficient-exponent pairs. A running analysis shows that, for a fixed number of nonzero terms, the algorithm runs in polynomial time.
92.
This paper presents a new generic Evolutionary Algorithm (EA) for retarding the unwanted effects of premature convergence. This is accomplished by a combination of interacting generic methods. These generalizations of a Genetic Algorithm (GA) are inspired by population genetics and take advantage of the interactions between genetic drift and migration. In this regard a new selection scheme is introduced, which is designed to directedly control genetic drift within the population by advantageous self-adaptive selection pressure steering. Additionally this new selection model enables a quite intuitive heuristics to detect premature convergence. Based upon this newly postulated basic principle the new selection mechanism is combined with the already proposed Segregative Genetic Algorithm (SEGA), an advanced Genetic Algorithm (GA) that introduces parallelism mainly to improve global solution quality. As a whole, a new generic evolutionary algorithm (SASEGASA) is introduced. The performance of the algorithm is evaluated on a set of characteristic benchmark problems. Computational results show that the new method is capable of producing highest quality solutions without any problem-specific additions. 相似文献
93.
Adrian Doicu Franz Schreier Michael Hess 《Journal of Quantitative Spectroscopy & Radiative Transfer》2004,83(1):47-61
In this paper we present different inversion algorithms for nonlinear ill-posed problems arising in atmosphere remote sensing. The proposed methods are Landweber's method (LwM), the iteratively regularized Gauss-Newton method, and the conventional and regularizing Levenberg-Marquardt method. In addition, some accelerated LwMs and a technique for smoothing the Levenberg-Marquardt solution are proposed. The numerical performance of the methods is studied by means of simulations. Results are presented for an inverse problem in atmospheric remote sensing, i.e., temperature sounding with an airborne uplooking high-resolution far-infrared spectrometer. 相似文献
94.
We determine the stationary two-point correlation function of the one-dimensional KPZ equation through the scaling limit of a solvable microscopic model, the polynuclear growth model. The equivalence to a directed polymer problem with specific boundary conditions allows one to express the corresponding scaling function in terms of the solution to a Riemann–Hilbert problem related to the Painlevé II equation. We solve these equations numerically with very high precision and compare our, up to numerical rounding exact, result with the prediction of Colaiori and Moore(1) obtained from the mode coupling approximation. 相似文献
95.
We study perturbations of the Erdös–Renyi model for which the statistical weight of a graph depends on the abundance of certain geometrical patterns. Using the formal correspondance with an exactly solvable effective model, we show the existence of a percolation transition in the thermodynamical limit and derive perturbatively the expression of the threshold. The free energy and the moments of the degree distribution are also computed perturbatively in that limit and the percolation criterion is compared with the Molloy–Reed criterion. 相似文献
96.
97.
We consider optimal control problems for systems described by stochastic differential equations with delay. We state conditions
for certain classes of such systems under which the stochastic control problems become finite-dimensional. These conditions
are illustrated with three applications. First, we solve some linear quadratic problems with delay. Then we find the optimal
consumption rate in a financial market with delay. Finally, we solve explicitly a deterministic fluid problem with delay which
arises from admission control in ATM communication networks. 相似文献
98.
A Variable Neighborhood Search for the Multi Depot Vehicle Routing Problem with Time Windows 总被引:6,自引:0,他引:6
Michael Polacek Richard F. Hartl Karl Doerner Marc Reimann 《Journal of Heuristics》2004,10(6):613-627
The aim of this paper is to propose an algorithm based on the philosophy of the Variable Neighborhood Search (VNS) to solve Multi Depot Vehicle Routing Problems with Time Windows. The paper has two main contributions. First, from a technical point of view, it presents the first application of a VNS for this problem and several design issues of VNS algorithms are discussed. Second, from a problem oriented point of view the computational results show that the approach is competitive with an existing Tabu Search algorithm with respect to both solution quality and computation times. 相似文献
99.
Michael T. Battista 《Mathematical Thinking and Learning》2004,6(2):185-204
As part of a discussion of cognition-based assessment (CBA) for elementary school mathematics, I describe assessment tasks for area and volume measurement and a research-based conceptual framework for interpreting students' reasoning on these tasks. At the core of this conceptual framework is the notion of levels of sophistication. I provide details on an integrated set of levels for area and volume measurement that (a) starts with the informal, preinstructional reasoning typically possessed by students, (b) ends with the formal mathematical concepts targeted by instruction, and (c) indicates cognitive plateaus reached by students in moving from (a) to (b). 相似文献
100.
Capacity Constrained Transit Assignment with Common Lines 总被引:1,自引:0,他引:1
Fumitaka Kurauchi Michael G. H. Bell Jan-Dirk Schmöcker 《Journal of Mathematical Modelling and Algorithms》2003,2(4):309-327
This paper proposes the use of absorbing Markov chains to solve the capacity constrained transit network loading problem taking
common lines into account. The approach handles congested transit networks, where some passengers will not be able to board
because of the absence of sufficient space. The model also handles the common lines problem, where choice of route depends
on frequency of arrivals. The mathematical formulation of the problem is presented together with a numerical example.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献