全文获取类型
收费全文 | 332271篇 |
免费 | 2720篇 |
国内免费 | 1099篇 |
专业分类
化学 | 144865篇 |
晶体学 | 4432篇 |
力学 | 19514篇 |
综合类 | 7篇 |
数学 | 68090篇 |
物理学 | 99182篇 |
出版年
2021年 | 1072篇 |
2020年 | 1183篇 |
2019年 | 1186篇 |
2018年 | 18377篇 |
2017年 | 19054篇 |
2016年 | 11205篇 |
2015年 | 3568篇 |
2014年 | 2964篇 |
2013年 | 8229篇 |
2012年 | 13542篇 |
2011年 | 28324篇 |
2010年 | 16565篇 |
2009年 | 17046篇 |
2008年 | 23014篇 |
2007年 | 28101篇 |
2006年 | 7520篇 |
2005年 | 14913篇 |
2004年 | 10810篇 |
2003年 | 10162篇 |
2002年 | 7272篇 |
2001年 | 6409篇 |
2000年 | 5119篇 |
1999年 | 3652篇 |
1998年 | 2855篇 |
1997年 | 2768篇 |
1996年 | 2903篇 |
1995年 | 2481篇 |
1994年 | 2320篇 |
1993年 | 2195篇 |
1992年 | 2464篇 |
1991年 | 2450篇 |
1990年 | 2143篇 |
1989年 | 2132篇 |
1988年 | 2166篇 |
1987年 | 2093篇 |
1986年 | 2001篇 |
1985年 | 2912篇 |
1984年 | 2892篇 |
1983年 | 2337篇 |
1982年 | 2515篇 |
1981年 | 2393篇 |
1980年 | 2358篇 |
1979年 | 2311篇 |
1978年 | 2383篇 |
1977年 | 2256篇 |
1976年 | 2205篇 |
1975年 | 2182篇 |
1974年 | 2075篇 |
1973年 | 2205篇 |
1972年 | 1248篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
141.
142.
J. Berny 《The Journal of the Operational Research Society》1989,40(12):1121-1127
This paper presents an alternative to the beta continuous probability distribution for risk analysis. Particular attention has been given to two major applications of distributions, namely project management risk and critical path analysis (PERT). In conjunction with the beta, the triangular and normal distributions are frequently employed in order to give sufficient robustness to risk analysis. The beta distribution, as used in PERT, has a major theoretical implementation flaw. The new distribution was developed to give a possible alternative method of assessing risk. It is shown that the requirement to estimate the most pessimistic variate may be replaced by the probability to exceed the mode. Proposals for other simplifications in risk analysis are discussed. Practical means to validate the most appropriate distributions for risk analysis are outlined, and a cost-data case study is included. 相似文献
143.
144.
TGA, DTA and DSC analyses indicate that benzotriazole is significantly more stable thermally than 1,2,3-triazole. 相似文献
145.
M I Salema A P B Póvoa A Q Novais 《The Journal of the Operational Research Society》2006,57(6):615-629
In this paper, an MILP formulation is proposed for the design of a reverse logistics network based on a warehouse location–allocation model, which optimizes, simultaneously, the forward and reverse networks. A single product model with unlimited capacity is first defined. Subsequently, the model is extended to a multi-product capacitated recovery network model, where capacity limitations and a multi-product system can be considered. The proposed model is compared to published work in the field, where different model assumptions have been proposed. Two cases are described so as to gain a better insight into the model and allow a comparative analysis. 相似文献
146.
Well-Posedness by Perturbations of Variational Problems 总被引:3,自引:0,他引:3
Lemaire B. Ould Ahmed Salem C. Revalski J. P. 《Journal of Optimization Theory and Applications》2002,115(2):345-368
In this paper, we consider the extension of the notion of well-posedness by perturbations, introduced by Zolezzi for optimization problems, to other related variational problems like inclusion problems and fixed-point problems. Then, we study the conditions under which there is equivalence of the well-posedness in the above sense between different problems. Relations with the so-called diagonal well-posedness are also given. Finally, an application to staircase iteration methods is presented. 相似文献
147.
J. C. Fabris S. V. B. Gonçalves P. E. de Souza 《General Relativity and Gravitation》2002,34(12):2111-2126
The mass power spectrum for a Universe dominated by the Chaplygin gas is evaluated numerically from scales of the order of the Hubble horizon to 100 Mpc. The results are compared with a pure baryonic Universe and a cosmological constant model. In all three cases, the spectrum increases with k, the wavenumber of the perturbations. The slope of the spectrum is higher for the baryonic model and smaller for the cosmological constant model, the Chaplygin gas interpolating these two models. The results are analyzed in terms of the sound velocity of the Chaplygin gas and the moment the Universe begins to accelerate. 相似文献
148.
Allen C. HirshfeldPeter Henselder 《Annals of Physics》2002,302(1):59-77
Deformation quantization, which achieves the passage from classical mechanics to quantum mechanics by the replacement of the pointwise multiplication of functions on phase space by the star product, is a powerful tool for treating systems involving bosonic degrees of freedom, both in quantum mechanics and in quantum field theory. In the present paper we show how these methods may be naturally extended to systems involving fermions. In particular we show how supersymmetric quantum mechanics can be formulated in this approach and consider examples involving both non-relativistic and relativistic systems. 相似文献
149.
Formalization for problems of multicriteria decision making under uncertainty is constructed in terms of guaranteed and weak
estimates. A relevant definition of the vector maximinimax value is given. Parameterization and approximation of maximum,
minimax, and maximinimax values based on the inverse logical convolution are suggested. An application for multicommodity
networks is considered.
Received: December 13, 2000 / Accepted: August 21, 2001?Published online May 8, 2002 相似文献
150.
We show that if A is an abelian compact Lie group, all A-equivariant complex vector bundles are orientable over a complex orientable equivariant cohomology theory. In the process,
we calculate the complex orientable homology and cohomology of all complex Grassmannians.
Received: 14 February 2000; in final form: 4 August 2000 / Published online: 19 October 2001 相似文献