全文获取类型
收费全文 | 17045篇 |
免费 | 2058篇 |
国内免费 | 1719篇 |
专业分类
化学 | 3685篇 |
晶体学 | 158篇 |
力学 | 1379篇 |
综合类 | 230篇 |
数学 | 7957篇 |
物理学 | 7413篇 |
出版年
2024年 | 37篇 |
2023年 | 164篇 |
2022年 | 512篇 |
2021年 | 532篇 |
2020年 | 352篇 |
2019年 | 404篇 |
2018年 | 408篇 |
2017年 | 590篇 |
2016年 | 577篇 |
2015年 | 509篇 |
2014年 | 874篇 |
2013年 | 1105篇 |
2012年 | 1072篇 |
2011年 | 900篇 |
2010年 | 867篇 |
2009年 | 1048篇 |
2008年 | 1129篇 |
2007年 | 1177篇 |
2006年 | 1042篇 |
2005年 | 932篇 |
2004年 | 724篇 |
2003年 | 701篇 |
2002年 | 608篇 |
2001年 | 549篇 |
2000年 | 551篇 |
1999年 | 451篇 |
1998年 | 419篇 |
1997年 | 411篇 |
1996年 | 310篇 |
1995年 | 289篇 |
1994年 | 232篇 |
1993年 | 199篇 |
1992年 | 190篇 |
1991年 | 139篇 |
1990年 | 120篇 |
1989年 | 118篇 |
1988年 | 93篇 |
1987年 | 62篇 |
1986年 | 52篇 |
1985年 | 64篇 |
1984年 | 63篇 |
1983年 | 17篇 |
1982年 | 32篇 |
1981年 | 28篇 |
1980年 | 21篇 |
1979年 | 40篇 |
1978年 | 21篇 |
1977年 | 33篇 |
1976年 | 18篇 |
1974年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
本文讨论的是集值优化问题Benson真有效解的高阶Fritz John型最优性条件,利用Aubin和Fraukowska引入的高阶切集和凸集分离定理,在锥-似凸映射的假设条件下,获得了带广义不等式约束的集值优化问题Benson真有效解的高阶Fritz John型必要和充分性条件. 相似文献
972.
In this paper, by using characterization of the point spectrum of the upper triangular infinite dimensional Hamiltonian operator H, a necessary and sufficient condition is obtained on the symmetry of σP(A) and σ1/P(-A^*) with respect to the imaginary axis. Then the symmetry of the point spectrum of H is given, and several examples are presented to illustrate the results. 相似文献
973.
Pablo A. D. Castro Fernando J. Von Zuben 《Journal of Mathematical Modelling and Algorithms》2009,8(2):151-173
Recently, we have proposed a Multi-Objective Bayesian Artificial Immune System (MOBAIS) to deal effectively with building
blocks (high-quality partial solutions coded in the solution vector) in combinatorial multi-objective problems. By replacing
the mutation and cloning operators with a probabilistic model, more specifically a Bayesian network representing the joint
distribution of promising solutions, MOBAIS takes into account the relationships among the variables of the problem, avoiding
the disruption of already obtained high-quality partial solutions. The preliminary results have indicated that our proposal
is able to properly build the Pareto front. Motivated by this scenario, this paper better formalizes the proposal and investigates
its usefulness on more challenging problems. In addition, an important enhancement regarding the Bayesian network learning
was incorporated into the algorithm in order to speed up its execution. To conclude, we compare MOBAIS with state-of-the-art
algorithms taking into account quantitative aspects of the Pareto front found by the algorithms. MOBAIS outperforms the contenders
in terms of the quality of the obtained solutions and requires an amount of computational resource inferior or compatible
with the contenders. 相似文献
974.
本文基于克隆选择学说及基于克隆选择学说及生物免疫响应过程的相关机理,提出用于指数化投资的免疫记忆克隆算法,并将其应用于指数化投资组合优化构建模型的求解,旨在探索指数化投资的优化构建策略。文章首先提出多目标的指数化投资组合构建模型。其次,分别设计了适用于指数化投资组合构建策略的抗原、抗体、亲和度函数、克隆选择算子、免疫记忆算子和相应的进化算法。该算法有效避免了传统遗传算法所存在的计算后期解的多样性差、易早熟以及收敛速度慢等缺点。同时,提出了限制投资组合中股票数量的启发式算法。最后,使用包括上证180指数在内的6组世界主要股票市场指数及其成份股的历史数据对模型及算法进行测算,结果表明算法具有良好的求解能力和收敛速度,所建模型的合理性和有效性亦被论证,模型和算法均具有很强的实践价值; 相似文献
975.
Large part of combinatorial optimization research has been devoted to the study of exact methods leading to a number of very
diversified solution approaches. Some of those older frameworks can now be revisited in a metaheuristic perspective, as they
are quite general frameworks for dealing with optimization problems. In this work, we propose to investigate the possibility
of reinterpreting decompositions, with special emphasis on the related Benders and Lagrangean relaxation techniques. We show
how these techniques, whose heuristic effectiveness is already testified by a wide literature, can be framed as a “master
process that guides and modifies the operations of subordinate heuristics”, i.e., as metaheuristics. Obvious advantages arise
from these approaches, first of all the runtime evolution of both upper and lower bounds to the optimal solution cost, thus
yielding both a high-quality heuristic solution and a runtime quality certificate of that same solution. 相似文献
976.
Genetic algorithm based approach for the integrated airline crew-pairing and rostering problem 总被引:1,自引:0,他引:1
Airline crew scheduling problem is a complex and difficult problem faced by all airline companies.To tackle this problem, it was often decomposed into two subproblems solved successively. First, the airline crew-pairing problem, which consists on finding a set of trips – called pairings – i.e. sequences of flights, starting and ending at a crew base, that cover all the flights planned for a given period of time. Secondly, the airline crew rostering problem, which consists on assigning the pairings found by solving the first subproblem, to the named airline crew members. For both problems, several rules and regulations must be respected and costs minimized.It is sure that this decomposition provides a convenient tool to handle the numerous and complex restrictions, but it lacks, however, of a global treatment of the problem. For this purpose, in this study we took the challenge of proposing a new way to solve both subproblems simultaneously. The proposed approach is based on a hybrid genetic algorithm. In fact, three heuristics are developed here to tackle the restriction rules within the GA’s process. 相似文献
977.
We give a bundle method for constrained convex optimization. Instead of using penalty functions, it shifts iterates towards
feasibility, by way of a Slater point, assumed to be known. Besides, the method accepts an oracle delivering function and
subgradient values with unknown accuracy. Our approach is motivated by a number of applications in column generation, in which
constraints are positively homogeneous—so that zero is a natural Slater point—and an exact oracle may be time consuming. Finally,
our convergence analysis employs arguments which have been little used so far in the bundle community. The method is illustrated
on a number of cutting-stock problems.
Research supported by INRIA New Investigation Grant “Convex Optimization and Dantzig–Wolfe Decomposition”. 相似文献
978.
We consider a class of quadratic programs with linear complementarity constraints (QPLCC) which belong to mathematical programs
with equilibrium constraints (MPEC). We investigate various stationary conditions and present new and strong necessary and
sufficient conditions for global and local optimality. Furthermore, we propose a Newton-like method to find an M-stationary
point in finite steps without MEPC linear independence constraint qualification.
The research of this author is partially supported by NSERC, and Research Grand Council of Hong Kong. 相似文献
979.
We propose an algorithm for the global optimization of continuous minimax problems involving polynomials. The method can be
described as a discretization approach to the well known semi-infinite formulation of the problem. We proceed by approximating
the infinite number of constraints using tools and techniques from semidefinite programming. We then show that, under appropriate
conditions, the SDP approximation converges to the globally optimal solution of the problem. We also discuss the numerical
performance of the method on some test problems.
Financial support of EPSRC Grant GR/T02560/01 gratefully acknowledged. 相似文献
980.
For the long-range infrared imaging system, the marine atmospheric turbulence degrades seriously the probability of object recognition and tracking. In this study, the angle of arrival fluctuations of an optical wave, which describes the distortion effects of marine atmospheric turbulence on an infrared optical imaging system, is investigated in detail both analytically and numerically. Analytic expressions of the angle of arrival fluctuations are derived for optical plane and spherical waves propagating through weak marine atmospheric turbulence with horizontal path, and they consider simultaneously finite turbulence inner scale, turbulence outer scale, wavelength, and aperture diameters. Numerical calculations are conducted to analyze the influence of marine weak turbulence on the infrared imaging. The results are useful for understanding the potential impact of deviations from the terrestrial turbulence. 相似文献