全文获取类型
收费全文 | 7565篇 |
免费 | 477篇 |
国内免费 | 286篇 |
专业分类
化学 | 108篇 |
力学 | 465篇 |
综合类 | 78篇 |
数学 | 7229篇 |
物理学 | 448篇 |
出版年
2023年 | 57篇 |
2022年 | 108篇 |
2021年 | 132篇 |
2020年 | 149篇 |
2019年 | 158篇 |
2018年 | 157篇 |
2017年 | 172篇 |
2016年 | 184篇 |
2015年 | 158篇 |
2014年 | 301篇 |
2013年 | 623篇 |
2012年 | 312篇 |
2011年 | 338篇 |
2010年 | 295篇 |
2009年 | 467篇 |
2008年 | 455篇 |
2007年 | 511篇 |
2006年 | 370篇 |
2005年 | 333篇 |
2004年 | 260篇 |
2003年 | 266篇 |
2002年 | 244篇 |
2001年 | 224篇 |
2000年 | 202篇 |
1999年 | 174篇 |
1998年 | 216篇 |
1997年 | 166篇 |
1996年 | 148篇 |
1995年 | 105篇 |
1994年 | 113篇 |
1993年 | 81篇 |
1992年 | 81篇 |
1991年 | 57篇 |
1990年 | 50篇 |
1989年 | 44篇 |
1988年 | 59篇 |
1987年 | 47篇 |
1986年 | 52篇 |
1985年 | 65篇 |
1984年 | 56篇 |
1983年 | 29篇 |
1982年 | 44篇 |
1981年 | 34篇 |
1980年 | 54篇 |
1979年 | 45篇 |
1978年 | 32篇 |
1977年 | 33篇 |
1976年 | 38篇 |
1975年 | 7篇 |
1974年 | 8篇 |
排序方式: 共有8328条查询结果,搜索用时 15 毫秒
91.
技术的动态发展和企业间的竞争对企业新产品策略有很大影响,直接决定新产品的引进周期。本文在产业技术动态变化的随机环境下构建随机动态规划模型,关注产业技术进步、投资成本和产品市场竞争等影响因素,探讨企业进行新产品引进的周期选择,对新产品引进的周期和质量决策进行方法设计和应用举例。利用随机动态规划模型得出新产品引进的最优时间周期,用算例分析技术进步和产品研发成本对企业引进周期策略的影响,采取策略迭代的方法进行求解,发现技术进步较快时企业的新产品引进步伐也较快,研发成本的提高使企业的新产品引入步伐降低。 相似文献
92.
对于多属性群决策问题的处理,有时需要采用先决策、后综合的处理方法,而含有语言评价信息的多属性群决策问题,定性目标一般用语言评价信息描述,由决策人给出定性目标和权系数的语言变量评价,用梯形模糊数表示,对定量目标进行无量纲化处理;将决策人对于单一目标的评价指标聚合成多个目标的评价模糊数,采用Bass-Kw akernaak模糊数排序方法对方案进行排序;群体的评价通过Borda函数来集结方案集的群体排序. 相似文献
93.
Alexandre N. Carvalho German Lozada-Cruz 《Journal of Mathematical Analysis and Applications》2007,325(2):1216-1239
We obtain existence of asymptotically stable nonconstant equilibrium solutions for semilinear parabolic equations with nonlinear boundary conditions on small domains connected by thin channels. We prove the convergence of eigenvalues and eigenfunctions of the Laplace operator in such domains. This information is used to show that the asymptotic dynamics of the heat equation in this domain is equivalent to the asymptotic dynamics of a system of two ordinary differential equations diffusively (weakly) coupled. The main tools employed are the invariant manifold theory and a uniform trace theorem. 相似文献
94.
A generalized inverse problem for the identification of the absorption coefficient for a hyperbolic system is considered. The well-posedness of the problem is examined. It is proved that the regular part of the solution is an L 2 function, which reduces the inverse problem to minimizing the error functional. The gradient of the functional is determined in explicit form from the adjoint problem, and approximate formulas for its calculation are derived. A regularization algorithm for the solution of the inverse problem is considered. Numerical results obtained for various excitation sources are displayed. 相似文献
95.
In general, we will use the numerical differentiation when dealing with the differential equations. Thus the differential equations can be transformed into algebraic equations and then we can get the numerical solutions. But as we all have known, the numerical differentiation process is very sensitive to even a small level of errors. In contrast it is expected that on average the numerical integration process is much less sensitive to errors. In this paper, based on the Sinc method we provide a new method using Sinc method incorporated with the double exponential transformation based on the interpolation of the highest derivatives (SIHD) for the differential equations. The error in the approximation of the solution is shown to converge at an exponential rate. The numerical results show that compared with the exiting results, our method is of high accuracy, of good convergence with little computational efforts. It is easy to treat nonhomogeneous mixed boundary condition for our method, which is unlike the traditional Sinc method. 相似文献
96.
Chen-liang Li Jin-ping Zeng 《应用数学学报(英文版)》2007,23(1):79-90
We consider several synchronous and asynchronous multisplitting iteration schemes for solving aclass of nonlinear complementarity problems with the system matrix being an H-matrix.We establish theconvergence theorems for the schemes.The numerical experiments show that the schemes are efficient forsolving the class of nonlinear complementarity problems. 相似文献
97.
Optimal production and rationing decisions in supply chains with information sharing 总被引:1,自引:0,他引:1
Boray Huang 《Operations Research Letters》2007,35(5):669-676
This paper considers a two-echelon capacitated supply chain with two non-identical retailers and information sharing. We characterize the optimal inventory policies. We also study the benefits of the optimal stock rationing policy over the first come first served (FCFS) and the modified echelon-stock rationing (MESR) policies. 相似文献
98.
99.
Lina Mallozzi 《Operations Research Letters》2007,35(2):151-154
A noncooperative game theoretical approach is considered for the multifacility location problem. It turns out that the facility location game is a potential game in the sense of Monderer and Shapley and some properties of the game are studied. 相似文献
100.
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