全文获取类型
收费全文 | 3936篇 |
免费 | 361篇 |
国内免费 | 68篇 |
专业分类
化学 | 95篇 |
晶体学 | 7篇 |
力学 | 1302篇 |
综合类 | 19篇 |
数学 | 821篇 |
物理学 | 2121篇 |
出版年
2024年 | 15篇 |
2023年 | 40篇 |
2022年 | 38篇 |
2021年 | 59篇 |
2020年 | 145篇 |
2019年 | 130篇 |
2018年 | 89篇 |
2017年 | 106篇 |
2016年 | 86篇 |
2015年 | 119篇 |
2014年 | 196篇 |
2013年 | 228篇 |
2012年 | 146篇 |
2011年 | 236篇 |
2010年 | 178篇 |
2009年 | 222篇 |
2008年 | 271篇 |
2007年 | 224篇 |
2006年 | 219篇 |
2005年 | 171篇 |
2004年 | 166篇 |
2003年 | 172篇 |
2002年 | 150篇 |
2001年 | 109篇 |
2000年 | 107篇 |
1999年 | 78篇 |
1998年 | 89篇 |
1997年 | 71篇 |
1996年 | 64篇 |
1995年 | 52篇 |
1994年 | 42篇 |
1993年 | 45篇 |
1992年 | 39篇 |
1991年 | 48篇 |
1990年 | 23篇 |
1989年 | 27篇 |
1988年 | 22篇 |
1987年 | 20篇 |
1986年 | 18篇 |
1985年 | 26篇 |
1984年 | 18篇 |
1983年 | 6篇 |
1982年 | 17篇 |
1981年 | 7篇 |
1980年 | 7篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1974年 | 2篇 |
1973年 | 6篇 |
1971年 | 2篇 |
排序方式: 共有4365条查询结果,搜索用时 15 毫秒
121.
We study global symmetry breaking in the 2D system of scalar nonconserved order parameter following a quench to zero temperature. We show that the instant of time when the symmetry is broken and the final morphology is chosen corresponds to the saturation of the order parameter inside the domains. There are three possible final morphologies: the positive and negative order parameter final morphology, and the state of the coexisting positive and negative order parameter subsystems with a flat interface between them. We find also that each type of the final morphology constitutes about 1/3 of all cases, what agrees with the results obtained recently by Spirin et al. [Phys. Rev. E 65, 016119 (2001)]. Our results are pertinent for the two dimensional systems, but we suspect that there is also a way to apply similar arguments for the three dimensional ones. 相似文献
122.
Scattering of electromagnetic waves by static and traversable wormholes is discussed. Based on the fact that these spacetimes
have no horizon, and regarding their non-trivial topology, we have developed the perturbation theory of scattering and the
Born approximation for obtaining the differential scattering cross section. Some of the zeros of the scattering pattern at
long wavelengths are determined which can be used for estimating the radius of the throat. The known result that in scattering
by static spacetimes the linear polarization remains unchanged is verified here. 相似文献
123.
Diffuse ultrasonic waves for structural health monitoring offer the advantages of simplicity of signal generation and reception, sensitivity to damage, and large area coverage; however, there are the serious disadvantages of no accepted methodology for analyzing the complex recorded signals and sensitivity to environmental changes such as temperature and surface conditions. Presented here is a methodology for applying diffuse ultrasonic waves to the problem of detecting structural damage in the presence of unmeasured temperature changes. This methodology is based upon the prediction and observation that the first order effect of a temperature change on a diffuse ultrasonic wave is a time dilation or compression. A multi-step procedure is implemented to (1) record a set of baseline waveforms from the undamaged specimen at temperatures spanning the expected operating range, (2) select a waveform from the baseline set whose temperature is the closest to that of a subsequently measured signal, (3) adjust this baseline waveform to best match the signal, and (4) calculate an error parameter between the signal and the adjusted waveform and compare this parameter to a threshold to determine the structural status. This procedure is applied to experimental data from aluminum plate specimens with artificial flaws. Probability of detection and the minimum flaw size detected are presented as a function of the size of the baseline waveform set. It is shown that a probability of detection of over 95% can be achieved with a small number of baseline waveforms. 相似文献
124.
We investigate the effects of a weak gravitational wave, modelled as a gaussian wavepacket, on the polarization state of an
electromagnetic field enclosed in a cavity. Our approach is semiclassical, in that the electromagnetic field is described as a quantum field, while the gravitational perturbation is treated classically,
as a slightly curved background spacetime. Assuming that before the interaction the electromagnetic field has been prepared
in a given polarization state, we show that – due to the gravitational scattering with the wave – some photons having different
polarization states are found in the cavity at late times. Such polarization scattering has some resemblance with Thomson
scattering, well-known in Quantum Electrodynamics: hence the motivation for the title. We give a numerical estimate of the
resulting photon polarization spreading in the case of a typical gravitational burst from a final supernova rebound. We also
briefly comment about the possible influence of such gravitational scattering on the Cosmic Microwave Background (CMB) polarization. 相似文献
125.
Several situations, in which an empty wave causes an observable effect, are reviewed. They include an experiment showing surrealistic trajectories proposed by Englert et al. and protective measurement of the density of the quantum state. Conditions for observable effects due to empty waves are derived. The possibility (in spite of the existence of these examples) of minimalistic interpretation of Bohmian quantum mechanics in which only Bohmian positions supervene on our experience is discussed. 相似文献
126.
Tetsu Mizumachi 《Journal of Differential Equations》2004,200(2):312-341
We study the asymptotic stability of solitary wave solutions to the regularized long-wave equation (RLW) in . RLW is an equation which describes the long waves in water. To prove the result, we make use of the monotonicity of the local H1-norm and apply the Liouville property of (RLW) as in Merle and Martel (J. Math. Pures Appl. 79 (2000) 339; Arch. Rational Mech. Anal. 157 (2001) 219). 相似文献
127.
I discuss the experiments of Joseph Weber (1919-2000) of the University of Maryland between
1960 and 1973 that were aimed at the detection of gravity waves. He used throughout a quadratic
detector to demodulate his antenna signal, which I analyze and compare to a linear detector.The
latter was used by all of the other groups that entered the field. Of these, Richard Garwin and I at
IBM were one of the first groups to publish, and I discuss in detail our experiments between 1973
and 1975. I then discuss the experiments that were carried out at Bell Labs-Rochester, Glasgow,
Munich-Frascati,Moscow, and Tokyo. I compare the results, all of which were negative, with Webers
claimed detection of large numbers of gravity-wave events, as many as seven per day. I conclude
that these were not in fact gravity waves, but artifacts of his extremely hands-on data-analysis procedures,
which I discuss in detail. Finally, I speculate on how this came about. 相似文献
128.
A pair of kinematical conservation laws (KCL) in a ray coordinatesystem (,t) are the basic equations governing the evolutionof a moving curve in two space dimensions. We first study elementarywave solutions and then the Riemann problem for KCL when themetric g, associated with the coordinate designating differentrays, is an arbitrary function of the velocity of propagationm of the moving curve. We assume that m>1 (m is appropriatelynormalized), for which the system of KCL becomes hyperbolic.We interpret the images of the elementary wave solutions inthe (,t)-plane to the (x,y)-plane as elementary shapes of themoving curve (or a nonlinear wavefront when interpreted in aphysical system) and then describe their geometrical properties.Solutions of the Riemann problem with different initial datagive the shapes of the nonlinear wavefront with different combinationsof elementary shapes. Finally, we study all possible interactionsof elementary shapes. 相似文献
129.
Acceleration waves propagating in isotropic solids at finite temperatures are studied by applying the method of singular surfaces to a new continuum model derived statistical-mechanically from a three-dimensional lattice model. The continuum model explicitly takes into account the microscopic thermal vibrations of the constituent atoms as one of the field variables. The propagation speeds and the ratios of mechanical and thermal amplitudes for both longitudinal and transverse waves are consistently determined. The differential equations that govern the time variation of the amplitudes of the waves are also derived. The analytical results, which are valid over a wide temperature range that includes the melting point, are evaluated numerically for several materials, and their physical implications are discussed. One of the findings to be emphasized is that of the singularities of the characteristic quantities at the melting point.Received: 13 March 2003, Accepted: 20 June 2003PACS:
62.30. + d, 65.40.-bM. Sugiyama: Correspondence to
Dedicated to Prof. Ingo Müller on the occasion of his 65th birthday. 相似文献
130.
Wave cycles, i.e. pairs of local maxima and minima, play an important role in many engineering fields. Many cycle definitions are used for specific purposes, such as crest–trough cycles in wave studies in ocean engineering and rainflow cycles for fatigue life predicition in mechanical engineering. The simplest cycle, that of a pair of local maximum and the following local minimum is also of interest as a basis for the study of more complicated cycles. This paper presents and illustrates modern computational tools for the analysis of different cycle distributions for stationary Gaussian processes with general spectrum. It is shown that numerically exact but slow methods will produce distributions in almost complete agreement with simulated data, but also that approximate and quick methods work well in most cases. Of special interest is the dependence relation between the cycle average and the cycle range for the simple maximum–minimum cycle and its implication for the range distribution. It is observed that for a Gaussian process with rectangular box spectrum, these quantities are almost independent and that the range is not far from a Rayleigh distribution. It will also be shown that had there been a Gaussian process where exact independence hold then the range would have had an exact Rayleigh distribution. Unfortunately no such Gaussian process exists.This revised version was published online in March 2005 with corrections to the cover date. 相似文献