全文获取类型
收费全文 | 428805篇 |
免费 | 3544篇 |
国内免费 | 1060篇 |
专业分类
化学 | 204125篇 |
晶体学 | 6967篇 |
力学 | 21491篇 |
综合类 | 7篇 |
数学 | 62078篇 |
物理学 | 138741篇 |
出版年
2021年 | 2634篇 |
2020年 | 2940篇 |
2019年 | 3289篇 |
2018年 | 11682篇 |
2017年 | 12397篇 |
2016年 | 9835篇 |
2015年 | 4612篇 |
2014年 | 6346篇 |
2013年 | 15721篇 |
2012年 | 15583篇 |
2011年 | 24811篇 |
2010年 | 16301篇 |
2009年 | 16245篇 |
2008年 | 22255篇 |
2007年 | 25230篇 |
2006年 | 12836篇 |
2005年 | 17041篇 |
2004年 | 13407篇 |
2003年 | 12296篇 |
2002年 | 10353篇 |
2001年 | 10621篇 |
2000年 | 8255篇 |
1999年 | 6229篇 |
1998年 | 5134篇 |
1997年 | 5042篇 |
1996年 | 4811篇 |
1995年 | 4482篇 |
1994年 | 4309篇 |
1993年 | 4096篇 |
1992年 | 4658篇 |
1991年 | 4593篇 |
1990年 | 4475篇 |
1989年 | 4232篇 |
1988年 | 4299篇 |
1987年 | 4328篇 |
1986年 | 4032篇 |
1985年 | 5283篇 |
1984年 | 5563篇 |
1983年 | 4732篇 |
1982年 | 4968篇 |
1981年 | 4781篇 |
1980年 | 4652篇 |
1979年 | 4856篇 |
1978年 | 4991篇 |
1977年 | 4858篇 |
1976年 | 5000篇 |
1975年 | 4729篇 |
1974年 | 4670篇 |
1973年 | 4963篇 |
1972年 | 3203篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
181.
G. Panina 《Central European Journal of Mathematics》2003,1(2):157-168
All 3-dimensional convex polytopes are known to be rigid. Still their Minkowski differences (virtual polytopes) can be flexible
with any finite freedom degree. We derive some sufficient rigidity conditions for virtual polytopes and present some examples
of flexible ones. For example, Bricard's first and second flexible octahedra can be supplied by the structure of a virtual
polytope. 相似文献
182.
183.
184.
W. L. Liang B. K. A. Ngoi L. E. N. Lim K. Venkatakrishnan C. W. Hee 《Optics & Laser Technology》2003,35(4):285-290
In this paper, integration of interference phenomenon into femtosecond laser micromachining was reported as the femtosecond laser pulses were reshaped spatially to perform ablation. The generation of circular interference pattern was demonstrated by overlapping infrared femtosecond laser pulses. The interference pattern was subsequently focused on a copper substrate to ablate microstructures of concentric circular rings. The present technique is expected to open up new applications in the areas of rapid fabrication of micro-Fresnel lenses, hybrid microlenses and lens arrays. 相似文献
185.
G. Montero L. Gonzlez E. Flrez M. D. García A. Surez 《Numerical Linear Algebra with Applications》2002,9(3):239-247
Parallel preconditioners are presented for the solution of general linear systems of equations. The computation of these preconditioners is achieved by orthogonal projections related to the Frobenius inner product. So, minM∈??∥AM?I∥ F and matrix M0∈?? corresponding to this minimum (?? being any vectorial subspace of ??n(?)) are explicitly computed using accumulative formulae in order to reduce computational cost when subspace ?? is extended to another one containing it. Every step, the computation is carried out taking advantage of the previous one, what considerably reduces the amount of work. These general results are illustrated with the subspace of matrices M such that AM is symmetric. The main application is developed for the subspace of matrices with a given sparsity pattern which may be constructed iteratively by augmenting the set of non‐zero entries in each column. Finally, the effectiveness of the sparse preconditioners is illustrated with some numerical experiments. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
186.
Demixing during film casting of blends of polystyrene, polymethylmethacrylate, and a symmetric diblock copolymer of styrene and methylmethacrylate is discussed. The concentration fluctuations in the homogeneous solutions were calculated in mean field approximation. The structures in the homogeneous and demixed solutions and in the dry films were measured by small-angle x-ray scattering, and the morphologies of the dry films were characterized by transmission electron microscopy. The structure of the dry blends is evidently already pre-formed in solution. 相似文献
187.
188.
D. J. Plazek C. A. Bero S. Neumeister G. Floudas G. Fytas K. L. Ngai 《Colloid and polymer science》1994,272(11):1430-1438
By making creep and recoverable creep measurements of a nearly monodisperse low molecular weight poly(methyl phenyl siloxane) sample, we have found on decreasing temperature towardsT
g that there is continuously a change in the viscoelastic spectrum concomitant with a decrease of the steadystate recoverable compliance. This behavior is exactly the same as previously observed in low molecular weight poly(styrene), proving that this spectacular anomaly in the viscoelasticity of low molecular weight polymers is general and deserves an explanation. Photon correlation spectroscopic measurements performed on the same sample have extended the observation of the viscoelastic response to shorter times and the result corroborates the trend of variation established by the creep data.Dedicated to Prof.Dr. E. W. Fischer on his 65th Birthday. Prof.Dr. Fischer is known for his valuable contribution to fosterine, international collaboration of research in polymer science. This work is an example of his contribution because it would not be possible without him bringing us together. One of us (KLN) would like to take this opportunity to thank Prof. Dr. Fischer for his unwaiving support of the 1st (Crete) and the 2nd (Alicante) International Discussion Meeting on Relaxations in Complex Systems 相似文献
189.
ON A PAIR OF NON-ISOMETRIC ISOSPECTRAL DOMAINS WITH FRACTAL BOUNDARIES AND THE WEYL-BERRY CONJECTURE
ONAPAIROFNONISOMETRICISOSPECTRALDOMAINSWITHFRACTALBOUNDARIESANDTHEWEYLBERRYCONJECTURESLEEMAN,B.D.CHENHUAManuscriptrec... 相似文献
190.