全文获取类型
收费全文 | 8945篇 |
免费 | 360篇 |
国内免费 | 19篇 |
专业分类
化学 | 6108篇 |
晶体学 | 68篇 |
力学 | 340篇 |
数学 | 1366篇 |
物理学 | 1442篇 |
出版年
2023年 | 51篇 |
2022年 | 70篇 |
2021年 | 123篇 |
2020年 | 159篇 |
2019年 | 160篇 |
2018年 | 182篇 |
2017年 | 147篇 |
2016年 | 306篇 |
2015年 | 244篇 |
2014年 | 271篇 |
2013年 | 571篇 |
2012年 | 574篇 |
2011年 | 655篇 |
2010年 | 347篇 |
2009年 | 330篇 |
2008年 | 571篇 |
2007年 | 602篇 |
2006年 | 540篇 |
2005年 | 526篇 |
2004年 | 402篇 |
2003年 | 370篇 |
2002年 | 286篇 |
2001年 | 142篇 |
2000年 | 130篇 |
1999年 | 117篇 |
1998年 | 90篇 |
1997年 | 70篇 |
1996年 | 112篇 |
1995年 | 94篇 |
1994年 | 82篇 |
1993年 | 70篇 |
1992年 | 65篇 |
1991年 | 46篇 |
1990年 | 45篇 |
1989年 | 43篇 |
1988年 | 28篇 |
1987年 | 30篇 |
1985年 | 60篇 |
1984年 | 42篇 |
1983年 | 31篇 |
1982年 | 52篇 |
1981年 | 43篇 |
1980年 | 54篇 |
1979年 | 41篇 |
1978年 | 40篇 |
1977年 | 36篇 |
1976年 | 47篇 |
1975年 | 46篇 |
1974年 | 29篇 |
1973年 | 28篇 |
排序方式: 共有9324条查询结果,搜索用时 15 毫秒
51.
We show in this paper that the average over translations of an operator diagonal in a wavelet packet basis is a convolution. We also show that an operator diagonal in a wavelet packet basis can be decomposed into several operators of the same kind, each of them being better conditioned. We investigate the possibility of using such a convolution to approximate a given convolution (in practice an image blur). Then we use these approximations to deblur images. First, we show that this framework permits us to redefine existing deblurring methods. Then, we show that it permits us to define a new variational method which combines the wavelet packet and the total variation approaches. We argue and show by experiments that this permits us to avoid the drawbacks of both approaches which are, respectively, the ringing and the staircasing. 相似文献
52.
53.
54.
55.
56.
We consider a class of problems originating from a Raman laser amplification model, for which the equations can be written as a Poisson system with boundary conditions. Once reformulated, this system becomes an integro-differential equation that we study here in some detail. In particular, we show the existence of a smooth solution under general assumptions, and prove its uniqueness for boundary values that are not too far apart. Eventually, we completely solve the question of uniqueness for systems of dimensions one and two. To cite this article: F. Castella et al., C. R. Acad. Sci. Paris, Ser. I 336 (2003). 相似文献
57.
Jean-Pierre Françoise 《Journal of Dynamics and Differential Equations》2008,20(4):777-786
This article is devoted to one-dimensional perturbative theory on R × S
1. There is a recursive formula for the successive obstructions to parametric center at any order of the perturbation parameter.
The first obstruction is studied by means of complex analysis techniques. This extends to the trigonometric case what was
done previously for the polynomial case (Israel J. Math. 142, 273–283, 2004).
This article is dedicated to Professor Zhang Zhi-Fen on the occasion of her 80th Birthday 相似文献
58.
Vitali Vogel Jean‐Franois Gohy Bas G. G. Lohmeijer Jacomina A. Van Den Broek Winfried Haase Ulrich S. Schubert Dieter Schubert 《Journal of polymer science. Part A, Polymer chemistry》2003,41(20):3159-3168
In aqueous solutions, amphiphilic block copolymers in which a polystyrene (PS) segment is connected to a poly(ethylene oxide) (PEO) block via a bis(2,2′:6′,2″‐ terpyridine ruthenium) complex can form micelles. Such micelles of the protomer type PS20‐[Ru]‐PEO70, according to the preparation procedure representing frozen micelles, were studied by sedimentation velocity and sedimentation equilibrium analysis in an analytical ultracentrifuge and by transmission electron microscopy, with different techniques applied for the sample preparation. The particles obtained were surprisingly multifarious in size. In ultracentrifugation experiments performed at relatively low salt concentrations, the distributions of the sedimentation coefficient s20,w showed a pronounced peak at 9.6 S and a broad, only partly separated second peak around 14 S. The molar mass of the particles at the peak was around 430,000 g/mol, corresponding to an aggregation number of approximately 85. The average hydrodynamic diameter of the particles in the peak fraction was approximately 13 nm. In electron micrographs of negatively stained samples, spheres of diameters between 10 and 25 nm were the most abundant particles, but larger ones with a wide size range were also visible. The latter particles apparently were composed of smaller ones. The data from both sedimentation analysis and electron microscopy showed that (1) the studied compound formed primary micelles of diameters around 20 nm and (2) the primary micelles had a tendency toward aggregation. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3159–3168, 2003 相似文献
59.
J. Salgado E. Martinho I. F. Gonçalves 《Journal of Radioanalytical and Nuclear Chemistry》2004,260(2):317-320
The resonance neutron self-shielding factor, G
res, is required in neutron metrology and activation data analysis. In a previous paper, the authors have shown that a dimensionless
variable can be introduced which converts the dependence of G
res on the physical and nuclear properties of the material samples into an universal curve, valid for the isolated resonances
of any nuclide. This work presents a methodology based on the universal curve, which enables to calculate G
res for a group of isolated resonances by weighting its individual contributions. A good agreement was reached with results calculated
by the MCNP code and with experimental values for Mo foils and wires.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
60.
Michaël Lejeune Andrea Valsesia Martin Kormunda Pascal Colpo François Rossi 《Surface science》2005,583(1):L142
In this work, chemically and topographically nanopatterned surfaces were produced by a top-down processing approach for biosensing devices. The nanopatterning was the result of the combination of plasma polymerisation (pp) of biofunctional materials and colloidal lithography techniques. The morphological and chemical properties induced by the plasma deposition-etching treatment were characterised by optical method combining ellipsometry and Fourier Transform Infrared spectroscopy studies. This method supported by atomic force microscopy measurements, allowed the full optical characterization of each step of the top-down process. The optical characterization of the end-up nanopatterned samples demonstrated that the chosen process is able to produce well-defined nanostructured surfaces with controlled chemical and morphological properties. 相似文献