全文获取类型
收费全文 | 313809篇 |
免费 | 4290篇 |
国内免费 | 1085篇 |
专业分类
化学 | 170607篇 |
晶体学 | 4457篇 |
力学 | 13032篇 |
综合类 | 7篇 |
数学 | 36270篇 |
物理学 | 94811篇 |
出版年
2020年 | 1983篇 |
2019年 | 1954篇 |
2018年 | 1965篇 |
2017年 | 1875篇 |
2016年 | 3858篇 |
2015年 | 3235篇 |
2014年 | 4422篇 |
2013年 | 13978篇 |
2012年 | 10728篇 |
2011年 | 13363篇 |
2010年 | 8270篇 |
2009年 | 8255篇 |
2008年 | 12335篇 |
2007年 | 12571篇 |
2006年 | 12212篇 |
2005年 | 11155篇 |
2004年 | 10034篇 |
2003年 | 8848篇 |
2002年 | 8700篇 |
2001年 | 10109篇 |
2000年 | 7711篇 |
1999年 | 6115篇 |
1998年 | 4894篇 |
1997年 | 4733篇 |
1996年 | 4775篇 |
1995年 | 4363篇 |
1994年 | 4115篇 |
1993年 | 3941篇 |
1992年 | 4431篇 |
1991年 | 4294篇 |
1990年 | 4011篇 |
1989年 | 3830篇 |
1988年 | 4120篇 |
1987年 | 3785篇 |
1986年 | 3677篇 |
1985年 | 5317篇 |
1984年 | 5397篇 |
1983年 | 4378篇 |
1982年 | 4753篇 |
1981年 | 4793篇 |
1980年 | 4545篇 |
1979年 | 4663篇 |
1978年 | 4665篇 |
1977年 | 4644篇 |
1976年 | 4597篇 |
1975年 | 4508篇 |
1974年 | 4356篇 |
1973年 | 4525篇 |
1972年 | 2570篇 |
1971年 | 1881篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
141.
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
142.
143.
144.
We consider the growth of a spherical crystal in a supersaturatedsolution. In the first part, existence and uniqueness resultsfor radially symmetric growth are obtained, provided that thesupersaturation is not too large; conversely, when the far-fieldsupersaturation exceeds a critical value, it is shown that theradially symmetric solution ceases to exist in finite time.In the second part, we examine the linear stability of a radiallysymmetric similarity solution (in which the radius grows ast?) to shape perturbations. The results are compared with previousquasi-static analyses, and, in particular, the critical radiusat which the crystal becomes unstable is found to be largerfor small supersaturations, but smaller for large supersaturations,than those predicted by the quasi-static analysis 相似文献
145.
146.
J. Maul I. Strachnov S. Karpuk P. Bernhard A. Oelsner G. Schönhense G. Huber 《Applied Physics A: Materials Science & Processing》2006,82(1):43-47
We report morphologic changes of metallic surfaces at the onset of ablation, starting from gentle ablation to the emergence of ablation craters. The evolution of both observed melting zones and of ablation craters therein are investigated in dependence of the ablation laser fluence for nanosecond ultraviolet laser pulses. Further, consequences of crater formation for cluster synthesis within the released atomic vapor are pointed out. PACS 52.38.Mf; 79.20.Ds; 65.40.De 相似文献
147.
Marí a J. Martí n Dragan Vukotic 《Proceedings of the American Mathematical Society》2006,134(6):1701-1705
We show that every composition operator which is an isometry of the Dirichlet space is induced by a univalent full map of the disk into itself that fixes the origin. This is an analogue of the Hardy space result for inner functions due to Nordgren. The proof relies on the Stone-Weierstrass theorem and the Riesz representation theorem.
148.
Abstract Under a suitable ellipticity condition, we show that classical SG-pseudodifferential operators of nonnegative order possess
complex powers. We show that the powers are again classical and derive an explicit formula for all homogeneous components.
Keywords: Complex power, Weighted symbols, Noncompact manifolds 相似文献
149.
The interferometric intensity patterns from a 2D shearing interferometer are shown and discussed. The intensity patterns can be obtained in two different approaches incorporating differential and extended wavefront controlled displacements. The reliable directional sensitivity of this interferometer allows the optimization of the measurement parameters to estimate the wavefront of the intensity patterns by regularization techniques. 相似文献
150.
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