全文获取类型
收费全文 | 86635篇 |
免费 | 484篇 |
国内免费 | 420篇 |
专业分类
化学 | 29786篇 |
晶体学 | 870篇 |
力学 | 6990篇 |
数学 | 33521篇 |
物理学 | 16372篇 |
出版年
2021年 | 97篇 |
2020年 | 94篇 |
2019年 | 80篇 |
2018年 | 10475篇 |
2017年 | 10296篇 |
2016年 | 6172篇 |
2015年 | 966篇 |
2014年 | 433篇 |
2013年 | 813篇 |
2012年 | 4108篇 |
2011年 | 10907篇 |
2010年 | 5861篇 |
2009年 | 6249篇 |
2008年 | 7026篇 |
2007年 | 9136篇 |
2006年 | 636篇 |
2005年 | 1713篇 |
2004年 | 1848篇 |
2003年 | 2275篇 |
2002年 | 1351篇 |
2001年 | 386篇 |
2000年 | 420篇 |
1999年 | 251篇 |
1998年 | 283篇 |
1997年 | 260篇 |
1996年 | 340篇 |
1995年 | 200篇 |
1994年 | 180篇 |
1993年 | 200篇 |
1992年 | 162篇 |
1991年 | 167篇 |
1990年 | 149篇 |
1989年 | 141篇 |
1988年 | 151篇 |
1987年 | 152篇 |
1986年 | 128篇 |
1985年 | 199篇 |
1984年 | 189篇 |
1983年 | 157篇 |
1982年 | 177篇 |
1981年 | 190篇 |
1980年 | 194篇 |
1979年 | 169篇 |
1978年 | 166篇 |
1977年 | 145篇 |
1976年 | 133篇 |
1975年 | 120篇 |
1974年 | 117篇 |
1973年 | 130篇 |
1972年 | 82篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
N C Proudlove S Black A Fletcher 《The Journal of the Operational Research Society》2007,58(2):145-158
This paper considers efforts to improve in-patient flows, a particularly urgent issue in the National Health Service (NHS). The context is described and related to reasons why OR has been making relatively little contribution. The paper argues that large complex models may often be unnecessary and even get in the way of providing clear insight and guidance for problem owners. The importance of understanding the generic working of systems to lead to improvement, and the limitations of simply describing them, is stressed. It is demonstrated that some very simple models can be of significant practical value in understanding and managing complex systems, changing mindsets and driving collection and use of operationally valuable data. Recommendations for more effective engagement with the NHS are offered. 相似文献
102.
103.
104.
This note introduces a refinement to a previously proposed tabu search algorithm for vehicle routing problems with time windows. This refinement yields new best known solutions on a set of benchmark instances of the multi-depot, the periodic and the site-dependent vehicle routing problems with time windows. 相似文献
105.
106.
107.
Doan Nguyen 《Ukrainian Mathematical Journal》2004,56(10):1633-1645
We prove a generalization of the Brody reparametrization lemma.__________Published in Ukrains’kyi Matematychnyi Zhurnal, Vol. 56, No. 10, pp. 1369 – 1377, October, 2004. 相似文献
108.
Patrizio Frosini 《Geometriae Dedicata》2004,108(1):105-110
In this paper we prove that for every real-valued Morse function φ on a smooth closed manifold ℳ and every neighborhood U of its critical points a suitable Riemannian metric μ
U
exists such that φ is linear outside
U 相似文献
109.
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
110.
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