全文获取类型
收费全文 | 20516篇 |
免费 | 1376篇 |
国内免费 | 960篇 |
专业分类
化学 | 1478篇 |
晶体学 | 31篇 |
力学 | 1409篇 |
综合类 | 148篇 |
数学 | 6958篇 |
物理学 | 1669篇 |
综合类 | 11159篇 |
出版年
2024年 | 113篇 |
2023年 | 308篇 |
2022年 | 583篇 |
2021年 | 644篇 |
2020年 | 509篇 |
2019年 | 489篇 |
2018年 | 493篇 |
2017年 | 643篇 |
2016年 | 620篇 |
2015年 | 610篇 |
2014年 | 1081篇 |
2013年 | 1143篇 |
2012年 | 1306篇 |
2011年 | 1221篇 |
2010年 | 982篇 |
2009年 | 1115篇 |
2008年 | 1094篇 |
2007年 | 1308篇 |
2006年 | 1106篇 |
2005年 | 916篇 |
2004年 | 764篇 |
2003年 | 668篇 |
2002年 | 604篇 |
2001年 | 553篇 |
2000年 | 498篇 |
1999年 | 428篇 |
1998年 | 419篇 |
1997年 | 362篇 |
1996年 | 283篇 |
1995年 | 283篇 |
1994年 | 232篇 |
1993年 | 227篇 |
1992年 | 198篇 |
1991年 | 180篇 |
1990年 | 149篇 |
1989年 | 144篇 |
1988年 | 112篇 |
1987年 | 83篇 |
1986年 | 55篇 |
1985年 | 61篇 |
1984年 | 54篇 |
1983年 | 14篇 |
1982年 | 25篇 |
1981年 | 22篇 |
1980年 | 17篇 |
1979年 | 32篇 |
1978年 | 21篇 |
1977年 | 30篇 |
1976年 | 18篇 |
1955年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Arno Jüschke Johannes Jahn Andreas Kirsch 《Computational Optimization and Applications》1997,7(3):261-276
In this paper we consider a special optimization problem withtwo objectives which arises in antenna theory. It is shown that thisabstract bicriterial optimization problem has at least one solution.Discretized versions of this problem are also discussed, and therelationships between these finite dimensional problems and the infinitedimensional problem are investigated. Moreover, we presentnumerical results for special parameters using a multiobjectiveoptimization method. 相似文献
62.
多级制造系统是现代制造业的主要加工方式,系统的每一级的加工速度和加工周期是系统设计的主要决策变量,正确确定这两个变量是系统得到优化的主要目标。本文导出了系统优化的基本模型,它包括系统各级的生产时间、等待时间、生产速度、生产成本以及系统的循环时间、总成本、产品利润和利润率等,并给出了一个应用实例。 相似文献
63.
We present a numerical implementation of the parallel gradient distribution (PGD) method for the solution of large-scale unconstrained optimization problems. The proposed parallel algorithm is characterized by a parallel phase which exploits the portions of the gradient of the objective function assigned to each processor; then, a coordination phase follows which, by a synchronous interaction scheme, optimizes over the partial results obtained by the parallel phase. The parallel and coordination phases are implemented using a quasi-Newton limited-memory BFGS approach. The computational experiments, carried out on a network of UNIX workstations by using the parallel software tool PVM, show that parallelization efficiency was problem dependent and ranged between 0.15 and 8.75. For the 150 problems solved by PGD on more than one processor, 85 cases had parallelization efficiency below 1, while 65 cases had a parallelization efficiency above 1. 相似文献
64.
ELSO is an environment for the solution oflarge-scale optimization problems. With ELSO the user is required to provide only code for the evaluation of a partially separable function. ELSO exploits the partialseparability structure of the function to computethe gradient efficiently using automatic differentiation.We demonstrate ELSO's efficiency by comparing thevarious options available in ELSO.Our conclusion is that the hybrid option in ELSOprovides performance comparable to the hand-coded option, while having the significantadvantage of not requiring a hand-coded gradient orthe sparsity pattern of the partially separable function.In our test problems, which have carefully coded gradients,the computing time for the hybrid AD option is within a factor of two of thehand-coded option. 相似文献
65.
In this paper, we investigate a constrained optimization problem with a quadratic cost functional and two quadratic equality constraints. It is assumed that the cost functional is positive definite and that the constraints are both feasible and regular (but otherwise they are unrestricted quadratic functions). Thus, the existence of a global constrained minimum is assured. We develop a necessary and sufficient condition that completely characterizes the global minimum cost. Such a condition is of essential importance in iterative numerical methods for solving the constrained minimization problem, because it readily distinguishes between local minima and global minima and thus provides a stopping criterion for the computation. The result is similar to one obtained previously by the authors. In the previous result, we gave a characterization of the global minimum of a constrained quadratic minimization problem in which the cost functional was an arbitrary quadratic functional (as opposed to positive-definite here) and the constraints were at least positive-semidefinite quadratic functions (as opposed to essentially unrestricted here). 相似文献
66.
IGCC空气侧整体综合优化的研究 总被引:4,自引:1,他引:3
主要符号表X。。氮气回注系数如空分整体化系数E。;c燃气轮机压气机效率G。l回注氮气流量万燃气轮机透平前温尼。”系统相对效率G。。煤气氮气掺混流量Ea;,c空气专用压缩机效率N。”系统相对功率1前言整体煤气化联合循环(IGCC)系统模拟与优化逐步受到重视,开展了许多相关研究[‘-‘]。但是,现有的方法[‘,‘]一个突出的问题,它是在设定的具体流程方案下的数值分析,这常常导致落入“局部优化掩盖了整体最优”的误区。本文是研究以空分系统为中心的空气侧子系统的整体优化,阐述基本概念,尝试新方法,并结合大型商业化装… 相似文献
67.
研究了电子线路的数值化设计方法.它是一种自动化程度高、通用性强、精度高的电路设计方法。介绍了电子线路数值优化设计软件系统YJX—1.它具有广泛的通用性和快速收敛的特点。 相似文献
68.
N. H. Al-Assady 《Journal of Optimization Theory and Applications》1997,94(3):747-755
We present a method which generates conjugate search directions and maintains the quadratic convergence property, when applied to a quadratic function, even when the line searches are not exact. The method is similar to that given by Dixon, but needs one less vector store. When the method is applied to a number of general functions of different dimensionality, results show the efficiency of the method. 相似文献
69.
发电厂相变干冷排热系统优化与不确定性分析初探 总被引:3,自引:0,他引:3
通过火力发电厂相变空气干式冷却排热系统的热经济学分析,提出了相变干式冷却系统优化的目标函数和优化参数,利用数值计算的可变容差法进行优化计算,取得了满意的结果,为了保证优化在可变经济环境的可靠性动力稳定性, 对优化结果进行了不确定性分析。 相似文献
70.
Wei Wang Li-Ping Pang Zun-Quan Xia 《应用数学学报(英文版)》2007,23(1):29-38
In this paper,the UV-theory and P-differential calculus are employed to study second-order ex-pansion of a class of D.C.functions and minimization problems.Under certain conditions,some properties ofthe U-Lagrangian,the second-order expansion of this class of functions along some trajectories are formulated.Some first and second order optimality conditions for the class of D.C.optimization problems are given. 相似文献