全文获取类型
收费全文 | 658360篇 |
免费 | 5290篇 |
国内免费 | 1496篇 |
专业分类
化学 | 320447篇 |
晶体学 | 9250篇 |
力学 | 35788篇 |
综合类 | 24篇 |
数学 | 97157篇 |
物理学 | 202480篇 |
出版年
2021年 | 5640篇 |
2020年 | 6102篇 |
2019年 | 6969篇 |
2018年 | 13428篇 |
2017年 | 13728篇 |
2016年 | 15053篇 |
2015年 | 7276篇 |
2014年 | 11845篇 |
2013年 | 26656篇 |
2012年 | 22872篇 |
2011年 | 31032篇 |
2010年 | 22143篇 |
2009年 | 22320篇 |
2008年 | 28646篇 |
2007年 | 30438篇 |
2006年 | 21163篇 |
2005年 | 21504篇 |
2004年 | 18978篇 |
2003年 | 17767篇 |
2002年 | 16743篇 |
2001年 | 17193篇 |
2000年 | 13373篇 |
1999年 | 10177篇 |
1998年 | 8866篇 |
1997年 | 8676篇 |
1996年 | 8208篇 |
1995年 | 7384篇 |
1994年 | 7328篇 |
1993年 | 7125篇 |
1992年 | 7497篇 |
1991年 | 8093篇 |
1990年 | 7716篇 |
1989年 | 7698篇 |
1988年 | 7475篇 |
1987年 | 7276篇 |
1986年 | 6961篇 |
1985年 | 8883篇 |
1984年 | 9202篇 |
1983年 | 7794篇 |
1982年 | 8083篇 |
1981年 | 7590篇 |
1980年 | 7157篇 |
1979年 | 7832篇 |
1978年 | 8136篇 |
1977年 | 7996篇 |
1976年 | 8012篇 |
1975年 | 7686篇 |
1974年 | 7471篇 |
1973年 | 7866篇 |
1972年 | 5838篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
951.
New heuristics for over-constrained flight to gate assignments 总被引:1,自引:0,他引:1
We consider the over-constrained Airport Gate Assignment Problem where the number of flights exceed the number of gates available, and where the objectives are to minimize the number of ungated flights and the total walking distances. The problem is formulated as a binary quadratic programming problem. We design a greedy algorithm and use a Tabu Search meta-heuristic to solve the problem. The greedy algorithm minimizes ungated flights while we devise a new neighbourhood search technique, the Interval Exchange Move, which allows us flexibility in seeking good solutions, especially when flight schedules are dense in time. Experiments conducted give good results. 相似文献
952.
V E Krivonozhko O B Utkin A V Volodin I A Sablin M Patrin 《The Journal of the Operational Research Society》2004,55(10):1049-1058
The aim of the paper is to present and substantiate a technique to visualize DEA modelling results without any loss of mathematical rigour. The proposed family of parametric optimization methods allows one to construct an intersection of the multidimensional frontier with a two-dimensional plane determined by any pair of given directions. This approach reduces the efficiency analysis of production units to the investigation of well-known functions in economics. We also propose constructive methods to calculate marginal rates of substitution, marginal rates of transformation and so on. 相似文献
953.
954.
955.
Malmquist indexes can be used to estimate technical change over time. The index generally represents the average effect of technical change on all outputs in a multi-output firm. However, changes in technology do not necessarily affect all outputs involved in the analysis equally. In this paper, a method for estimating the effect of technical change on each of the different outputs is proposed. This estimation is done by a modification of quasi-Malmquist indexes. An artificial data set has been used to validate the method proposed in this paper. 相似文献
956.
We construct a universal space for the class of proper metric spaces of bounded geometry and of given asymptotic dimension. As a consequence of this result, we establish coincidence of asymptotic dimension with asymptotic inductive dimension. 相似文献
957.
Tracing is a method of assigning flows in an electricity network to particular generators and loads, assuming perfect mixing at each node. It can be used to assign costs to transmission users. We show that the resulting allocation is equal to the Shapley value of an equivalent co-operative game. 相似文献
958.
Using the result by D. Gessler, we show that any invariant variational bivector (resp., variational 2-form) on an evolution equation with nondegenerate right-hand side is Hamiltonian (resp., symplectic). 相似文献
959.
In 1983, a preconditioner was proposed [J. Comput. Phys. 49 (1983) 443] based on the Laplace operator for solving the discrete Helmholtz equation efficiently with CGNR. The preconditioner is especially effective for low wavenumber cases where the linear system is slightly indefinite. Laird [Preconditioned iterative solution of the 2D Helmholtz equation, First Year's Report, St. Hugh's College, Oxford, 2001] proposed a preconditioner where an extra term is added to the Laplace operator. This term is similar to the zeroth order term in the Helmholtz equation but with reversed sign. In this paper, both approaches are further generalized to a new class of preconditioners, the so-called “shifted Laplace” preconditioners of the form Δφ−k2φ with
. Numerical experiments for various wavenumbers indicate the effectiveness of the preconditioner. The preconditioner is evaluated in combination with GMRES, Bi-CGSTAB, and CGNR. 相似文献
960.
Sergue A. Nazarov Maria Specovius‐Neugebauer 《Mathematical Methods in the Applied Sciences》2004,27(13):1507-1544
The approximation of solutions to boundary value problems on unbounded domains by those on bounded domains is one of the main applications for artificial boundary conditions. Based on asymptotic analysis, here a new method is presented to construct local artificial boundary conditions for a very general class of elliptic problems where the main asymptotic term is not known explicitly. Existence and uniqueness of approximating solutions are proved together with asymptotically precise error estimates. One class of important examples includes boundary value problems for anisotropic elasticity and piezoelectricity. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献