全文获取类型
收费全文 | 15049篇 |
免费 | 1266篇 |
国内免费 | 705篇 |
专业分类
化学 | 3153篇 |
晶体学 | 49篇 |
力学 | 1361篇 |
综合类 | 237篇 |
数学 | 9391篇 |
物理学 | 2829篇 |
出版年
2024年 | 22篇 |
2023年 | 156篇 |
2022年 | 379篇 |
2021年 | 475篇 |
2020年 | 332篇 |
2019年 | 372篇 |
2018年 | 405篇 |
2017年 | 496篇 |
2016年 | 509篇 |
2015年 | 362篇 |
2014年 | 738篇 |
2013年 | 1042篇 |
2012年 | 836篇 |
2011年 | 799篇 |
2010年 | 686篇 |
2009年 | 870篇 |
2008年 | 900篇 |
2007年 | 973篇 |
2006年 | 806篇 |
2005年 | 732篇 |
2004年 | 569篇 |
2003年 | 554篇 |
2002年 | 483篇 |
2001年 | 412篇 |
2000年 | 402篇 |
1999年 | 318篇 |
1998年 | 350篇 |
1997年 | 280篇 |
1996年 | 221篇 |
1995年 | 216篇 |
1994年 | 182篇 |
1993年 | 151篇 |
1992年 | 130篇 |
1991年 | 109篇 |
1990年 | 91篇 |
1989年 | 91篇 |
1988年 | 71篇 |
1987年 | 56篇 |
1986年 | 51篇 |
1985年 | 78篇 |
1984年 | 58篇 |
1983年 | 20篇 |
1982年 | 36篇 |
1981年 | 28篇 |
1980年 | 30篇 |
1979年 | 36篇 |
1978年 | 23篇 |
1977年 | 34篇 |
1976年 | 22篇 |
1957年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
931.
Vincent Kelner Florin Capitanescu Olivier Léonard Louis Wehenkel 《Journal of Computational and Applied Mathematics》2008
Evolutionary algorithms are robust and powerful global optimization techniques for solving large-scale problems that have many local optima. However, they require high CPU times, and they are very poor in terms of convergence performance. On the other hand, local search algorithms can converge in a few iterations but lack a global perspective. The combination of global and local search procedures should offer the advantages of both optimization methods while offsetting their disadvantages. This paper proposes a new hybrid optimization technique that merges a genetic algorithm with a local search strategy based on the interior point method. The efficiency of this hybrid approach is demonstrated by solving a constrained multi-objective mathematical test-case. 相似文献
932.
A stochastic model is developed describing a service system subject to inhomogeneous Poisson interruptions with age dependent interruption periods. By studying the probabilistic flow of the underlying multivariate Markov process, the Laplace transform of the effective service time is explicitly obtained. For general renewal interruptions, only the expected effective service time is derived. As an application, an optimal checkpoint policy is examined for database management. It is shown that an optimal policy maximizing the ergodic availability of the database is to implement a checkpoint as soon as the cumulative uptime of the database reaches a prespecified constantk
*. A computational procedure is then developed for findingk
* and numerical results are exhibited.This work was supported in part by the National Science Foundation under Grant No. ECS-8600992 and by the IBM Program of Support for Education in the Management of Information Systems. 相似文献
933.
The light-oxygen effect consists in a direct excitation of molecular oxygen dissolved in aqueous media of biosystems by the
light; it provides the possibility to use lasers for therapeutic purposes. The wavelength of the used light should strictly
correspond to the oxygen absorption bands. However, laser therapy also makes use of lasers emitting at 0.89 μm (outside the known oxygen bands), which suggests the action of a new photoreceptor. Here we argue that this mechanism of
photoreception is a modification of the light-oxygen effect involving the absorption of photon simultaneously by the oxygen
molecule and O-H stretch of the H20 molecule of liquid water. 相似文献
934.
O. Briant C. Lemaréchal Ph. Meurdesoif S. Michel N. Perrot F. Vanderbeck 《Mathematical Programming》2008,113(2):299-344
When a column generation approach is applied to decomposable mixed integer programming problems, it is standard to formulate
and solve the master problem as a linear program. Seen in the dual space, this results in the algorithm known in the nonlinear
programming community as the cutting-plane algorithm of Kelley and Cheney-Goldstein. However, more stable methods with better
theoretical convergence rates are known and have been used as alternatives to this standard. One of them is the bundle method;
our aim is to illustrate its differences with Kelley’s method. In the process we review alternative stabilization techniques
used in column generation, comparing them from both primal and dual points of view. Numerical comparisons are presented for
five applications: cutting stock (which includes bin packing), vertex coloring, capacitated vehicle routing, multi-item lot
sizing, and traveling salesman. We also give a sketchy comparison with the volume algorithm.
This research has been supported by Inria New Investigation Grant “Convex Optimization and Dantzig-Wolfe Decomposition”. 相似文献
935.
We present a geometrical interpretation of the weighting method for constrained (finite dimensional) vector optimization.
This approach is based on rigid movements which separate the image set from the negative of the ordering cone. We study conditions
on the existence of such translations in terms of the boundedness of the scalar problems produced by the weighting method.
Finally, using recession cones, we obtain the main result of our work: a sufficient condition under which weighting vectors
yield solvable scalar problems.
An erratum to this article can be found at 相似文献
936.
In this paper a control strategy is formulated that minimizes the costs for a single chemical cleaning of a dead-end ultra filtration membrane. From the process model, the performance index and the constraints it can be derived that dynamic optimization will lead to a ‘maximum effort control problem’, in which the controls (cleaning flow and cleaning agent concentration) are either zero or maximum. The change from maximum to zero is called the switching point. This switching point depends on the overall cleaning time and the requested cleaning effectiveness. From the calculated optimal control strategy it follows that cleaning time can be significantly reduced, compared to conventional cleaning. 相似文献
937.
Let A be a finitely generated abelian group. We describe the automorphism group Aut(A) using the rank of A and its torsion part p-part A
p
.
For a finite abelian p-group A of type (k
1, ..., k
n
), simple necessary and sufficient conditions for an n × n-matrix over integers to be associated with an automorphism of A are presented. Then, the automorphism group Aut(A) for a finite p-group A of type (k
1, k
2) is analyzed.
This work has begin during the visit of the second author to the Faculty of Mathematics and Computer Science, Nicolaus Copernicus
University during the period July 31–August 13, 2005. This visit was supported by the Nicolaus Copernicus University and a
grant from Cnpq. 相似文献
938.
S. Nobakhtian 《Journal of Optimization Theory and Applications》2008,136(1):61-68
A mixed-type dual for a nonsmooth multiobjective optimization problem with inequality and equality constraints is formulated.
We obtain weak and strong duality theorems for a mixed-type dual without requiring the regularity assumptions and the nonnegativeness
of the Lagrange multipliers associated to the equality constraints. We apply also a nonsmooth constraint qualification for
multiobjective programming to establish strong duality results. In this case, our constraint qualification assures the existence
of positive Lagrange multipliers associated with the vector-valued objective function.
This work was supported by Center of Excellence for Mathematics, University of Isfahan, Isfahan, Iran. 相似文献
939.
This paper is concerned with a shape sensitivity analysis of a viscous incompressible fluid driven by Stokes equations. The structures of continuous shape gradients with respect to the shape of the variable domain for some given cost functionals are established by introducing the Piola transformation and then deriving the state derivative and its associated adjoint state. Finally we give the finite element approximation of the problem and a gradient type algorithm is effectively used for our problem. 相似文献
940.
This paper presents new bounds, heuristics, and an exact algorithm for the Pallet Loading Problem (PLP). PLP maximizes the number of boxes placed on a rectangular pallet. All boxes have identical rectangular dimensions and, when placed, must be located completely within the pallet. Boxes may be rotated 90° so long as they are placed with edges parallel to the pallet’s edges. The set of all PLP instances with an area ratio (pallet area divided by box area) less than 101 boxes can be represented by 3,080,730 equivalent classes. Our G5-heuristic finds optimal solutions to 3,073,724 of these 3,080,730 classes and in the remaining 7006 classes only differs from the best known bound by one box. We develop three other heuristics that solve another 54 instances. Finally, we solve the 6952 remaining classes with our exact HVZ algorithm. Only a subset of these classes has been solved previously. 相似文献