全文获取类型
收费全文 | 962篇 |
免费 | 29篇 |
国内免费 | 4篇 |
专业分类
化学 | 641篇 |
力学 | 30篇 |
数学 | 205篇 |
物理学 | 119篇 |
出版年
2023年 | 6篇 |
2022年 | 17篇 |
2021年 | 20篇 |
2020年 | 21篇 |
2019年 | 20篇 |
2018年 | 13篇 |
2017年 | 12篇 |
2016年 | 38篇 |
2015年 | 32篇 |
2014年 | 31篇 |
2013年 | 56篇 |
2012年 | 54篇 |
2011年 | 55篇 |
2010年 | 49篇 |
2009年 | 38篇 |
2008年 | 56篇 |
2007年 | 54篇 |
2006年 | 36篇 |
2005年 | 38篇 |
2004年 | 28篇 |
2003年 | 35篇 |
2002年 | 38篇 |
2001年 | 14篇 |
2000年 | 17篇 |
1999年 | 18篇 |
1998年 | 14篇 |
1997年 | 13篇 |
1996年 | 12篇 |
1995年 | 7篇 |
1994年 | 10篇 |
1993年 | 10篇 |
1992年 | 11篇 |
1991年 | 6篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1988年 | 7篇 |
1987年 | 9篇 |
1986年 | 4篇 |
1985年 | 6篇 |
1984年 | 9篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 4篇 |
1980年 | 7篇 |
1979年 | 4篇 |
1978年 | 5篇 |
1977年 | 9篇 |
1975年 | 5篇 |
1974年 | 4篇 |
1970年 | 3篇 |
排序方式: 共有995条查询结果,搜索用时 31 毫秒
101.
This paper addresses the problem of determining the best scheduling for Bus Drivers, a $\mathcal{NP}$ -hard problem consisting of finding the minimum number of drivers to cover a set of Pieces-Of-Work (POWs) subject to a variety of rules and regulations that must be enforced such as spreadover and working time. This problem is known in literature as Crew Scheduling Problem and, in particular in public transportation, it is designated as Bus Driver Scheduling Problem. We propose a new mathematical formulation of a Bus Driver Scheduling Problem under special constraints imposed by Italian transportation rules. Unfortunately, this model can only be usefully applied to small or medium size problem instances. For large instances, a Greedy Randomized Adaptive Search Procedure (GRASP) is proposed. Results are reported for a set of real-word problems and comparison is made with an exact method. Moreover, we report a comparison of the computational results obtained with our GRASP procedure with the results obtained by Huisman et al. (Transp. Sci. 39(4):491?C502, 2005). 相似文献
102.
103.
This paper describes a methodology which combines finite element analysis and Zoutendijk’s feasible directions method for mufflers shape design. The main goal is to obtain the dimensions of the acoustic muffler with the transmission loss (TL), being maximized in the frequency range of interest. The improved four parameters method is used for TL evaluations and the Helmholtz’s equation is solved numerically with the finite element method (FEM). The quadratic triangular finite element meshes are adequately constructed to control the pollution error and the optimization problem is solved using the Zoutendijk’s feasible directions method due to robustness and efficiency for problems with nonlinear constraints. Numeric experiments performed with circular expansion chambers with extended inlet and outlet show results for constrained and unconstrained shape optimization. 相似文献
104.
105.
Francesco Buccheri Giuseppe Cusmano Renato Noto Rosina Rainieri Giuseppe Werber 《Journal of heterocyclic chemistry》1987,24(2):521-523
The true identity of the 4-methyl-5-phenylimino-δ2-1,3,4-thiadiazoline (A) has been demonstrated. The reactions, previously reported in the literature to give A have been repeated and the structure of the compounds obtained has been established. 相似文献
106.
A nonlinear programming algorithm for solving semidefinite programs via low-rank factorization 总被引:7,自引:0,他引:7
In this paper, we present a nonlinear programming algorithm for solving semidefinite programs (SDPs) in standard form. The
algorithm's distinguishing feature is a change of variables that replaces the symmetric, positive semidefinite variable X of the SDP with a rectangular variable R according to the factorization X=RR
T
. The rank of the factorization, i.e., the number of columns of R, is chosen minimally so as to enhance computational speed while maintaining equivalence with the SDP. Fundamental results
concerning the convergence of the algorithm are derived, and encouraging computational results on some large-scale test problems
are also presented.
Received: March 22, 2001 / Accepted: August 30, 2002 Published online: December 9, 2002
Key Words. semidefinite programming – low-rank factorization – nonlinear programming – augmented Lagrangian – limited memory BFGS
This research was supported in part by the National Science Foundation under grants CCR-9902010, INT-9910084, CCR-0203426
and CCR-0203113 相似文献
107.
108.
We study the algebraizability of the logics constructed using literal‐paraconsistent and literal‐paracomplete matrices described by Lewin and Mikenberg in [11], proving that they are all algebraizable in the sense of Blok and Pigozzi in [3] but not finitely algebraizable. A characterization of the finitely algebraizable logics defined by LPP‐matrices is given. We also make an algebraic study of the equivalent algebraic semantics of the logics associated to the matrices ??32,2, ??32,1, ??31,1, ??31,3, and ??4 appearing in [11] proving that they are not varieties and finding the free algebra over one generator. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
109.
110.