全文获取类型
收费全文 | 381297篇 |
免费 | 4286篇 |
国内免费 | 1327篇 |
专业分类
化学 | 202403篇 |
晶体学 | 6138篇 |
力学 | 16103篇 |
综合类 | 5篇 |
数学 | 44802篇 |
物理学 | 117459篇 |
出版年
2020年 | 2946篇 |
2019年 | 3333篇 |
2018年 | 4123篇 |
2017年 | 4116篇 |
2016年 | 6500篇 |
2015年 | 4159篇 |
2014年 | 6453篇 |
2013年 | 17492篇 |
2012年 | 12719篇 |
2011年 | 15588篇 |
2010年 | 10676篇 |
2009年 | 10648篇 |
2008年 | 14259篇 |
2007年 | 14209篇 |
2006年 | 13320篇 |
2005年 | 12206篇 |
2004年 | 11103篇 |
2003年 | 9899篇 |
2002年 | 9736篇 |
2001年 | 11223篇 |
2000年 | 8427篇 |
1999年 | 6608篇 |
1998年 | 5539篇 |
1997年 | 5460篇 |
1996年 | 5150篇 |
1995年 | 4825篇 |
1994年 | 4634篇 |
1993年 | 4671篇 |
1992年 | 5176篇 |
1991年 | 5129篇 |
1990年 | 4883篇 |
1989年 | 4810篇 |
1988年 | 4864篇 |
1987年 | 4719篇 |
1986年 | 4523篇 |
1985年 | 6112篇 |
1984年 | 6296篇 |
1983年 | 5320篇 |
1982年 | 5732篇 |
1981年 | 5469篇 |
1980年 | 5347篇 |
1979年 | 5508篇 |
1978年 | 5775篇 |
1977年 | 5584篇 |
1976年 | 5790篇 |
1975年 | 5295篇 |
1974年 | 5424篇 |
1973年 | 5863篇 |
1972年 | 3709篇 |
1971年 | 2956篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
R A Forder 《The Journal of the Operational Research Society》2004,55(4):319-332
The paper presents a survey of operational research (OR) as it is currently used in the UK Ministry of Defence (MoD). After a short historical introduction summarising developments since 1945, it identifies the impact which the end of the Cold War has had on defence operational analysis (OA), as the discipline is generally called within MoD, in terms of the problems studied, the technical challenges presented and the techniques employed. The factors, both external and internal, that have led to the MoD maintaining and indeed expanding its OA activity against a background of falling defence budgets are discussed in the context of previously reported research on the survival and success of OR groups. 相似文献
992.
This paper develops a theory for the global solution of nonconvex optimization problems with parameter-embedded linear dynamic systems. A quite general problem formulation is introduced and a solution is shown to exists. A convexity theory for integrals is then developed to construct convex relaxations for utilization in a branch-and-bound framework to calculate a global minimum. Interval analysis is employed to generate bounds on the state variables implied by the bounds on the embedded parameters. These bounds, along with basic integration theory, are used to prove convergence of the branch-and-bound algorithm to the global minimum of the optimization problem. The implementation of the algorithm is then considered and several numerical case studies are examined thoroughly 相似文献
993.
M F Anjos R C H Cheng C S M Currie 《The Journal of the Operational Research Society》2004,55(5):535-541
The paper describes a methodology that has been implemented in a major British airline to find the optimal price to charge for airline tickets under one-way pricing. An analytical model has been developed to describe the buying behaviour of customers for flights over the selling period. Using this model and a standard analytical method for constrained optimization, we can find an expression for the optimal price structure for a flight. The expected number of bookings made on each day of the selling period and in each fare class given these prices can then be easily calculated. A simulation model is used to find the confidence ranges on the numbers of bookings and these ranges can be used to regulate the sale of tickets. A procedure to update the price structure based on the remaining capacity has also been developed. 相似文献
994.
Azuelos G. Benslama K. Costanzo D. Couture G. Garcia J.E. Hinchliffe I. Kanaya N. Lechowski M. Mehdiyev R. Polesello G. Ros E. Rousseau D. 《The European Physical Journal C - Particles and Fields》2004,39(2):13-24
The European Physical Journal C - We discuss possible searches for the new particles predicted by Little Higgs Models at the LHC. By using a simulation of the ATLAS detector, we demonstrate how the... 相似文献
995.
In this paper, three new direct Mutually Orthogonal Latin Squares (MOLS) constructions are presented for 7 MOLS(24), 7 MOLS(75) and 8 MOLS(36); then using recursive methods, several new constructions for 7 and 8 MOLS are obtained. These reduce the largest value for which 7 MOLS are unknown from 780 to 570, and the largest odd value for which 8 MOLS are unknown from 1935 to 419. © 2003 Wiley Periodicals, Inc. 相似文献
996.
R. Hildebrand 《Journal of Mathematical Sciences》2004,121(2):2178-2220
997.
998.
G. S. Osipenko J. V. Romanovsky N. B. Ampilova E. I. Petrenko 《Journal of Mathematical Sciences》2004,120(2):1155-1166
The Morse spectrum is a limit set of Lyapunov exponents of periodic pseudo-trajectories. This notion is especially important in the case where a dynamical system has infinitely many periodic trajectories of large period. A method for estimating the Morse spectrum was suggested by the first author in J. Math. Anal. Appl., 252 (2000). This method is based on ideas of symbolic dynamics which reduces the study of a dynamical system to the study of a certain graph, called a symbolic image. Within the framework of this method, the computation of the Morse spectrum is connected with searching simple closed paths and extracting contours with suitable characteristics. However, under iterations of the symbolic image, the number of such paths sharply increases, which leads to huge expenses of memory and time. We suggest an algorithm for constructing contours with the maximal and minimal mean values. This algorithm is based on a special version of the simplex method. Numerical tests are also described. Bibliography: 13 titles. Illustrations: 3 figures. 相似文献
999.
Monica-Gabriela Cojocaru Leo B. Jonker 《Proceedings of the American Mathematical Society》2004,132(1):183-193
We prove existence and uniqueness of integral curves to the (discontinuous) vector field that results when a Lipschitz continuous vector field on a Hilbert space of any dimension is projected on a non-empty, closed and convex subset.
1000.
R. Milson 《Proceedings of the American Mathematical Society》2004,132(10):2825-2831
Chevalley's theorem and its converse, the Sheppard-Todd theorem, assert that finite reflection groups are distinguished by the fact that the ring of invariant polynomials is freely generated. We show that, in the Euclidean case, a weaker condition suffices to characterize finite reflection groups, namely, that a freely-generated polynomial subring is closed with respect to the gradient product.