全文获取类型
收费全文 | 10092篇 |
免费 | 737篇 |
国内免费 | 291篇 |
专业分类
化学 | 1318篇 |
晶体学 | 31篇 |
力学 | 1116篇 |
综合类 | 160篇 |
数学 | 6974篇 |
物理学 | 1521篇 |
出版年
2024年 | 22篇 |
2023年 | 103篇 |
2022年 | 335篇 |
2021年 | 335篇 |
2020年 | 209篇 |
2019年 | 224篇 |
2018年 | 245篇 |
2017年 | 335篇 |
2016年 | 321篇 |
2015年 | 231篇 |
2014年 | 464篇 |
2013年 | 558篇 |
2012年 | 634篇 |
2011年 | 480篇 |
2010年 | 458篇 |
2009年 | 569篇 |
2008年 | 561篇 |
2007年 | 634篇 |
2006年 | 512篇 |
2005年 | 441篇 |
2004年 | 344篇 |
2003年 | 323篇 |
2002年 | 303篇 |
2001年 | 270篇 |
2000年 | 271篇 |
1999年 | 199篇 |
1998年 | 220篇 |
1997年 | 203篇 |
1996年 | 138篇 |
1995年 | 161篇 |
1994年 | 134篇 |
1993年 | 117篇 |
1992年 | 101篇 |
1991年 | 86篇 |
1990年 | 78篇 |
1989年 | 63篇 |
1988年 | 50篇 |
1987年 | 41篇 |
1986年 | 39篇 |
1985年 | 57篇 |
1984年 | 50篇 |
1983年 | 15篇 |
1982年 | 23篇 |
1981年 | 21篇 |
1980年 | 19篇 |
1979年 | 31篇 |
1978年 | 22篇 |
1977年 | 30篇 |
1976年 | 19篇 |
1974年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
We consider a multiperiod mean-variance model where the model parameters change according to a stochastic market. The mean
vector and covariance matrix of the random returns of risky assets all depend on the state of the market during any period
where the market process is assumed to follow a Markov chain. Dynamic programming is used to solve an auxiliary problem which,
in turn, gives the efficient frontier of the mean-variance formulation. An explicit expression is obtained for the efficient
frontier and an illustrative example is given to demonstrate the application of the procedure. 相似文献
52.
Supply Chain Management (SCM) is an important activity in all producing facilities and in many organizations to enable vendors,
manufacturers and suppliers to interact gainfully and plan optimally their flow of goods and services. To realize this, a
dynamic modelling approach for characterizing supply chain activities is opportune, so as to plan efficiently the set of activities
over a distributed network in a formal and scientific way. The dynamical system will result so complex that it is not generally
possible to specify the functional forms and the parameters of interest, relating outputs to inputs, states and stochastic
terms by experiential specification methods. Thus the algorithm that will presented is Data Driven, determining simultaneously
the functional forms, the parameters and the optimal control policy from the data available for the supply chain. The aim
of this paper is to present this methodology, by considering dynamical aspects of the system, the presence of nonlinear relationships
and unbiased estimation procedures to quantify these relations, leading to a nonlinear and stochastic dynamical system representation
of the SCM problem. Moreover, the convergence of the algorithm will be proved and the satisfaction of the required statistical
conditions demonstrated. Thus SCM problems may be formulated as formal scientific procedures, with well defined algorithms
and a precise calculation sequence to determine the best alternative to enact. A “Certainty equivalent principle” will be
indicated to ensure that the effects of the inevitable uncertainties will not lead to indeterminate results, allowing the
formulation of demonstrably asymptotically optimal management plans. 相似文献
53.
刘国志 《数学的实践与认识》2006,36(12):1-5
提出一个新的具有积压定单的关于模糊订购量的模糊存储模型.在模糊函数原理下,给出了模糊总存储成本.为了寻找最优解,把最优模糊存储模型转化为双目标最优化模型,利用L ingo8.0求解不等式约束问题,我们发现最优解都是确定的实数.此外,当模糊订购量和模糊总需求都是三角形(或权重均为1/2梯形)模糊数时,我们提出模型的最优解与经典的具有积压定单存储模型具有相同的结果. 相似文献
54.
In single-objective optimization it is possible to find a global optimum, while in the multi-objective case no optimal solution is clearly defined, but several that simultaneously optimize all the objectives. However, the majority of this kind of problems cannot be solved exactly as they have very large and highly complex search spaces. Recently, meta-heuristic approaches have become important tools for solving multi-objective problems encountered in industry as well as in the theoretical field. Most of these meta-heuristics use a population of solutions, and hence the runtime increases when the population size grows. An interesting way to overcome this problem is to apply parallel processing. This paper analyzes the performance of several parallel paradigms in the context of population-based multi-objective meta-heuristics. In particular, we evaluate four alternative parallelizations of the Pareto simulated annealing algorithm, in terms of quality of the solutions, and speedup. 相似文献
55.
Ivan Nunes da Silva Wagner Caradori do AmaralLucia Valeria de Arruda 《Applied Mathematical Modelling》2007
This paper presents an efficient approach based on recurrent neural network for solving nonlinear optimization. More specifically, a modified Hopfield network is developed and its internal parameters are computed using the valid subspace technique. These parameters guarantee the convergence of the network to the equilibrium points that represent an optimal feasible solution. The main advantage of the developed network is that it treats optimization and constraint terms in different stages with no interference with each other. Moreover, the proposed approach does not require specification of penalty and weighting parameters for its initialization. A study of the modified Hopfield model is also developed to analyze its stability and convergence. Simulation results are provided to demonstrate the performance of the proposed neural network. 相似文献
56.
57.
In this paper we characterize the local maxima of a continuous global optimization formulation for finding the independence
number of a graph. Classical Karush-Kuhn-Tucker conditions and simple combinatorial arguments are found sufficient to deduce
several interesting properties of the local and global maxima. These properties can be utilized in developing new approaches
to the maximum independent set problem. 相似文献
58.
Effect of the subdivision strategy on convergence and efficiency of some global optimization algorithms 总被引:2,自引:0,他引:2
Hoang Tuy 《Journal of Global Optimization》1991,1(1):23-36
We investigate subdivision strategies that can improve the convergence and efficiency of some branch and bound algorithms of global optimization. In particular, a general class of so called weakly exhaustive simplicial subdivision processes is introduced that subsumes all previously known radial exhaustive processes. This result provides the basis for constructing flexible subdivision strategies that can be adapted to take advantage of various problem conditions. 相似文献
59.
本主要介绍原木经销商在周期内原木变价销售情况下的最佳期初贮存量的决策方法,在建立期望机会成本的数学模型基础上,探讨原木随机存贮策略的最优化问题。 相似文献
60.
Alexander Ya. Kruger 《Set-Valued Analysis》2006,14(2):187-206
The paper continues investigations of stationarity and regularity properties of collections of sets in normed spaces. It contains
a summary of different characterizations (both primal and dual) of regularity and a list of sufficient conditions for a collection
of sets to be regular. 相似文献