全文获取类型
收费全文 | 6600篇 |
免费 | 195篇 |
国内免费 | 4篇 |
专业分类
化学 | 4140篇 |
晶体学 | 38篇 |
力学 | 258篇 |
数学 | 822篇 |
物理学 | 1541篇 |
出版年
2023年 | 30篇 |
2022年 | 34篇 |
2021年 | 54篇 |
2020年 | 77篇 |
2019年 | 78篇 |
2018年 | 105篇 |
2017年 | 72篇 |
2016年 | 150篇 |
2015年 | 181篇 |
2014年 | 161篇 |
2013年 | 351篇 |
2012年 | 410篇 |
2011年 | 415篇 |
2010年 | 266篇 |
2009年 | 175篇 |
2008年 | 418篇 |
2007年 | 365篇 |
2006年 | 337篇 |
2005年 | 339篇 |
2004年 | 280篇 |
2003年 | 272篇 |
2002年 | 222篇 |
2001年 | 133篇 |
2000年 | 154篇 |
1999年 | 79篇 |
1998年 | 95篇 |
1997年 | 69篇 |
1996年 | 91篇 |
1995年 | 55篇 |
1994年 | 60篇 |
1993年 | 67篇 |
1992年 | 60篇 |
1991年 | 44篇 |
1990年 | 44篇 |
1989年 | 41篇 |
1988年 | 54篇 |
1986年 | 37篇 |
1985年 | 53篇 |
1984年 | 68篇 |
1983年 | 35篇 |
1982年 | 49篇 |
1981年 | 60篇 |
1980年 | 51篇 |
1979年 | 38篇 |
1978年 | 53篇 |
1977年 | 47篇 |
1976年 | 58篇 |
1975年 | 38篇 |
1974年 | 34篇 |
1973年 | 35篇 |
排序方式: 共有6799条查询结果,搜索用时 31 毫秒
31.
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
32.
In this paper, we study the central limit theorem and its weak invariance principle for sums of a stationary sequence of random
variables, via a martingale decomposition. Our conditions involve the conditional expectation of sums of random variables
with respect to the distant past. The results contribute to the clarification of the central limit question for stationary
sequences.
Magda Peligrad is supported in part by a Charles Phelps Taft research support grant at the Univeristy of Cincinnati and the
NSA grant H98230-05-1-0066. 相似文献
33.
Marc Chaperon Mathilde Kammerer-Colin De Verdière Santiago López De Medrano 《Comptes Rendus Mathematique》2006,342(5):301-305
Near partially elliptic rest points of generic families of vector fields or transformations, many types of normally hyperbolic invariant compact manifolds can appear, diffeomorphic to intersections of quadrics. To cite this article: M. Chaperon et al., C. R. Acad. Sci. Paris, Ser. I 342 (2006). 相似文献
34.
Summary. In this paper we are interested in two phase flow problems in porous media. We use a Dual Mesh Method to discretize this
problem with finite volume schemes. In a simplified case (elliptic - hyperbolic system) we prove the convergence of approximate
solutions to the exact solutions. We use the Dual Mesh Method in physically complex problems (heterogeneous cases with non
constant total mobility). We validate numerically the Dual Mesh Method on practical examples by computing error estimates
for different test-cases.
Received March 21, 1997 / Revised version received October 13, 1997 相似文献
35.
Agnès Tourin 《Numerische Mathematik》1992,62(1):75-85
Summary The reconstruction from a shaded image of a Lambertian and not self-shadowing surface illuminated by a single distant pointwise light source may be written as a first-order Hamilton-Jacobi equation.In this paper, we continue the investigation begun in E. Rouy and A. Tourin into the uniqueness of the solution of this equation; the approach is based on the viscosity solutions theory and the dynamic programming principle.More precisely, we concentrate here on the uniqueness of the viscosity solution of this equation in case the measured luminous intensity reflected by the surface is discontinuous along a smooth curve. We prove a general comparison result for a piecewise Lipschitz continuous Hamiltonian and illustrate it by numerical experiments. 相似文献
36.
Hermann Grabert Gert-Ludwig Ingold Michel H. Devoret Daniel Estève Hugues Pothier Cristian Urbina 《Zeitschrift für Physik B Condensed Matter》1991,84(1):143-155
The rate of electron tunneling through normal metal tunnel junctions is calculated for the case of ultrasmall junction capacitances. The so-called Coulomb blockade of electron tunneling at low temperatures is shown to be strongly affected by the external electrical circuit. Under the common experimental condition of a low impedance environment the Coulomb blockade is suppressed for single tunnel junctions. However, a Coulomb gap structure emerges for junctions embedded in a high impedance environment. For a double junction setup a Coulomb blockade of tunneling arises even for low impedance environments due to the charge quantization on the metallic island between the junctions. An approach using circuit analysis is presented which allows to reduce the calculation of tunneling rates in multijunction circuits to those of a single junction in series with an effective capacitance. The range of validity of the socalled local rule and global rule rates is clarified. It is found that the tunneling rate tends towards the global rule rate as the number of junctions is increased. Some specific results are given for a one-dimensional array of tunnel junctions. 相似文献
37.
G. Meillère 《Analytical and bioanalytical chemistry》1899,38(9-10):674-675
38.
39.
Quantization consists in studying the L
r
-error induced by the approximation of a random vector X by a vector (quantized version) taking a finite number n of values. We investigate this problem for Gaussian random vectors in an infinite dimensional Banach space and in particular, for Gaussian processes. A precise link proved by Fehringer(4) and Dereich et al.
(3) relates lower and upper bounds for small ball probabilities with upper and lower bounds for the quantization error, respectively. We establish a complete relationship by showing that the same holds for the direction from the quantization error to small ball probabilities. This allows us to compute the exact rate of convergence to zero of the minimal L
r
-quantization error from logarithmic small ball asymptotics and vice versa. 相似文献
40.