全文获取类型
收费全文 | 26405篇 |
免费 | 571篇 |
国内免费 | 104篇 |
专业分类
化学 | 15032篇 |
晶体学 | 155篇 |
力学 | 788篇 |
综合类 | 9篇 |
数学 | 3688篇 |
物理学 | 7408篇 |
出版年
2022年 | 244篇 |
2021年 | 414篇 |
2020年 | 390篇 |
2019年 | 340篇 |
2018年 | 416篇 |
2017年 | 373篇 |
2016年 | 646篇 |
2015年 | 553篇 |
2014年 | 639篇 |
2013年 | 1033篇 |
2012年 | 1319篇 |
2011年 | 1514篇 |
2010年 | 845篇 |
2009年 | 810篇 |
2008年 | 1268篇 |
2007年 | 1238篇 |
2006年 | 1120篇 |
2005年 | 1544篇 |
2004年 | 1586篇 |
2003年 | 1115篇 |
2002年 | 769篇 |
2001年 | 628篇 |
2000年 | 573篇 |
1999年 | 369篇 |
1998年 | 305篇 |
1997年 | 325篇 |
1996年 | 382篇 |
1995年 | 325篇 |
1994年 | 315篇 |
1993年 | 345篇 |
1992年 | 338篇 |
1991年 | 277篇 |
1990年 | 233篇 |
1989年 | 230篇 |
1988年 | 198篇 |
1987年 | 201篇 |
1986年 | 197篇 |
1985年 | 256篇 |
1984年 | 233篇 |
1983年 | 203篇 |
1982年 | 210篇 |
1981年 | 201篇 |
1980年 | 180篇 |
1979年 | 176篇 |
1978年 | 203篇 |
1977年 | 166篇 |
1976年 | 169篇 |
1975年 | 129篇 |
1974年 | 149篇 |
1973年 | 146篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
Ilda Abe Rafael E. de Ges Jos L. Fabris Hypolito J. Kalinowski Mrcia Müller Meire C. Fugihara Rosane Falate Barbara W. Diesel Ricardo C. Kamikawachi Carmen L. Barbosa 《Optics and Lasers in Engineering》2003,39(5-6):537-548
In this work, we report production and modelling of both Bragg gratings and rocking filters in high birefringence fibre optics. Bragg gratings are produced by UV (257.0 nm) external interferometric exposition of a frequency-doubled Ar+ ion laser, whereas for rocking filters formation the visible Ar+ ion laser lines in 488.0 and 514.5 nm are used in an internal method. The spectral characteristics due to the birefringence properties are studied through numerical methods and experimental techniques. The spectral responsivity of the structures under temperature changes and stress application is presented. 相似文献
102.
103.
104.
Background
Repeated execution of a tactile task enhances task performance. In the present study we sought to improve tactile performance with unattended activation-based learning processes (i.e., focused stimulation of dermal receptors evoking neural coactivation (CA)). Previous studies show that the application of CA to a single finger reduced the stationary two-point discrimination threshold and significantly increased tactile acuity. These changes were accompanied by an expansion of the cortical finger representation in primary somatosensory cortex (SI). Here we investigated the effect of different types of multifinger CA on the tactile performance of each finger of the right hand. 相似文献105.
Boris Andreianov Franck Boyer Florence Hubert 《Numerical Methods for Partial Differential Equations》2007,23(1):145-195
Discrete duality finite volume schemes on general meshes, introduced by Hermeline and Domelevo and Omnès for the Laplace equation, are proposed for nonlinear diffusion problems in 2D with nonhomogeneous Dirichlet boundary condition. This approach allows the discretization of non linear fluxes in such a way that the discrete operator inherits the key properties of the continuous one. Furthermore, it is well adapted to very general meshes including the case of nonconformal locally refined meshes. We show that the approximate solution exists and is unique, which is not obvious since the scheme is nonlinear. We prove that, for general W?1,p′(Ω) source term and W1‐(1/p),p(?Ω) boundary data, the approximate solution and its discrete gradient converge strongly towards the exact solution and its gradient, respectively, in appropriate Lebesgue spaces. Finally, error estimates are given in the case where the solution is assumed to be in W2,p(Ω). Numerical examples are given, including those on locally refined meshes. © 2006 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2007 相似文献
106.
Márcio D. Lima Mônica J. de Andrade Viera Skákalová Felipe Nobre Carlos P. Bergmann Siegmar Roth 《固体物理学:研究快报》2007,1(4):165-167
A method for the production of transparent carbon nanotube networks (CNTNs) over transparent substrates was developed. In this method, CNTNs were grown directly in the target surface by applying the catalyst in specific zones of the substrate through lithographic techniques. The networks can be also transferred from the original substrate to other surfaces. The newly grown carbon nanotubes have a very high aspect ratio (>50000). Thus far, networks with an optical transmittance of 94% at 550 nm and a surface resistivity of 3.6 kΩ/sq have been produced. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
107.
C. Bréchignac Ph. Cahuzac F. Carlier C. Colliex M. de Frutos N. Kébaïli J. Le Roux A. Masson B. Yoon 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):265-268
We studied shape relaxation of nano-fractal islands,
during annealing, after their growth from antimony cluster
deposition on graphite surface. Annealing at
180°C shows evidence of an increase
of the fractal branch width with time followed by branch
fragmentation, without changing the fractal dimension. The time
evolution of the width of the arm suggests the surface
self-diffusion mechanism as the main relaxation process. With
Monte Carlo simulations, we confirmed the observed behavior.
Comparison is done with our previous results on fragmentation of
nano-fractal silver islands when impurity added to the incident
cluster promotes rapid fragmentation by surface self-diffusion
enhancement [1]. 相似文献
108.
In recent publications, it has been shown that high-order harmonic generation can be manipulated by employing a time delayed attosecond-pulse train superposed to a strong, near-infrared laser field. It is an open question, however, which is the most adequate way to approximate the attosecond-pulse train in a semianalytic framework. Employing the strong-field approximation and saddle-point methods, we make a detailed assessment of the spectra obtained by modeling the attosecond-pulse train by either a monochromatic wave or a Dirac-Delta comb. These are the two extreme limits of a real train, which is composed by a finite set of harmonics. Specifically, in the monochromatic limit, we find the downhill and uphill sets of orbits reported in the literature, and analyze their influence on the high-harmonic spectra. We show that, in principle, the downhill trajectories lead to stronger harmonics, and pronounced enhancements in the low plateau region. These features are analyzed in terms of quantum interference effects between pairs of quantum orbits, and compared to those obtained in the Dirac-Delta limit. 相似文献
109.
110.
Jesús de la Cal Javier Cárcamo 《Journal of Mathematical Analysis and Applications》2007,334(2):1106-1115
As a consequence of Jensen's inequality, centered operators of probabilistic type (also called Bernstein-type operators) approximate convex functions from above. Starting from this fact, we consider several pairs of classical operators and determine, in each case, which one is better to approximate convex functions. In almost all the discussed examples, the conclusion follows from a simple argument concerning composition of operators. However, when comparing Szász-Mirakyan operators with Bernstein operators over the positive semi-axis, the result is derived from the convex ordering of the involved probability distributions. Analogous results for non-centered operators are also considered. 相似文献