全文获取类型
收费全文 | 364390篇 |
免费 | 1541篇 |
国内免费 | 349篇 |
专业分类
化学 | 156623篇 |
晶体学 | 5391篇 |
力学 | 22503篇 |
综合类 | 3篇 |
数学 | 61605篇 |
物理学 | 120155篇 |
出版年
2021年 | 3099篇 |
2020年 | 3415篇 |
2019年 | 4196篇 |
2018年 | 11868篇 |
2017年 | 12350篇 |
2016年 | 10680篇 |
2015年 | 3974篇 |
2014年 | 6937篇 |
2013年 | 12183篇 |
2012年 | 13169篇 |
2011年 | 20449篇 |
2010年 | 14703篇 |
2009年 | 15034篇 |
2008年 | 18750篇 |
2007年 | 21159篇 |
2006年 | 10102篇 |
2005年 | 12395篇 |
2004年 | 10261篇 |
2003年 | 10161篇 |
2002年 | 9160篇 |
2001年 | 7778篇 |
2000年 | 6349篇 |
1999年 | 4531篇 |
1998年 | 4295篇 |
1997年 | 4144篇 |
1996年 | 3909篇 |
1995年 | 3404篇 |
1994年 | 3453篇 |
1993年 | 3460篇 |
1992年 | 3451篇 |
1991年 | 3867篇 |
1990年 | 3867篇 |
1989年 | 3882篇 |
1988年 | 3643篇 |
1987年 | 3732篇 |
1986年 | 3407篇 |
1985年 | 3944篇 |
1984年 | 4202篇 |
1983年 | 3591篇 |
1982年 | 3787篇 |
1981年 | 3471篇 |
1980年 | 3228篇 |
1979年 | 3737篇 |
1978年 | 3819篇 |
1977年 | 3894篇 |
1976年 | 4007篇 |
1975年 | 3731篇 |
1974年 | 3584篇 |
1973年 | 3789篇 |
1972年 | 3221篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
171.
172.
Birational equivalence in the symplectic category 总被引:7,自引:0,他引:7
173.
The diffraction of plane surface gravitational waves by the edge of an ice cover lying on the surface of an incompressible fluid of infinitely great depth is considered. The ice cover is simulated by a thin elastic plate. The wave reflection and transmission coefficients are determined when it interacts with the ice cover. A wave field is constructed in the fluid under the conditions that a periodic lumped force and a lumped moment act on the edge of the ice cover. It is shown that as the incident wavelength increases the reflection coefficient tends to zero and the transmission coefficient tends to unity. 相似文献
174.
Results of an experiment on investigating the fluctuations of a sound signal with a frequency of 295 Hz on a stationary 32-km-long acoustic path in a shallow sea are presented. Hydrological conditions on the path were characterized by the presence of a weak thermocline and a frequent occurrence of intense internal wave trains. The space-time characteristics of these internal waves were measured in detail. Experimental evidence of the repetition of the forms of internal solitons in the variations of the amplitude and phase of an acoustic signal was obtained. 相似文献
175.
Possibilities for the control of the parameters of free-polarization decay (FPD), optical nutation, and photon echo (PE) using the dressing field are studied. Coherent transients are generated with the Stark switching technique and are detected in the radiation of the probe field polarized orthogonally to the dressing field. The evolution-operator technique is employed in the calculations. The experiments are performed at the R(4, 3) transition of the 0 ? 1 v3 13CH3F vibrational band with the radiation of a cw CO2 laser. It is theoretically and experimentally demonstrated that FPD and PE are suppressed upon an increase in the intensity of the dressing field. The observed shapes of the transient FPD and PE signals and their variations with the dressing field intensity are in qualitative agreement with the results of the calculations. 相似文献
176.
177.
E. N. Sobol’ O. I. Baum A. V. Bol’shunov V. I. Sipliviy N. Yu. Ignat’eva O. L. Zakharkina V. V. Lunin A. I. Omel’chenko V. A. Kamenskiy A. V. Myakov 《Laser Physics》2006,16(5):735-740
A new approach to alterations in eye refraction upon nondestructive laser action on the sclera and cornea is studied. It is demonstrated in in vivo experiments on rabbit eyes that sequential laser irradiation of the sclera and cornea yields a significant alteration in the eye refraction. The collagen structure of the sclera and cornea is studied after the nondestructive laser action with noninvasive polarization-sensitive optical coherence tomography. It is demonstrated that collagen fibers that provide for the cornea tension and applanation partially survive in the zone of the local denaturation of sclera. An irradiation mode that corresponds to an increase in the cornea’s plasticity and does not cause visible structural changes is chosen. The simplest theoretical model for alterations in the eye refraction upon the nonablative laser action on sclera is analyzed. The alteration in the cornea curvature upon stretching resulting from the local sclera coagulation and the corresponding decrease in its volume is calculated. The model makes it possible to approximately estimate the laser irradiation modes that provide the desired alterations in eye refraction. 相似文献
178.
N. S. Simonović 《Few-Body Systems》2006,38(2-4):139-145
In agreement with the Kohn theorem the relative motion (rel) of three electrons in a two-dimensional parabolic trap separates
from the centre-of-mass (CM) motion. By introducing new coordinates the Hamiltonian for relative motion in the approximation
of non-interacting electrons can be taken to the normal form. The eigenstates of the normalized Hamiltonian are products of
the Fock-Darwin states for normal modes. The energy levels for relative motion are obtained by diagonalizing the exact Hamiltonian
in the eigenbasis for the non-interacting case. In this basis the interaction matrix elements can be obtained in the analytical
form. Since the rank of the Hamiltonian matrix is significantly reduced, the calculations are faster and more accurate than
those for the full (CM + rel) motion. This advantage is especially important for the calculations of excited states and the
analysis of energy spectra. 相似文献
179.
V. V. Zhikov 《Journal of Mathematical Sciences》2006,132(3):285-294
We study the problem on density of smooth functions in Sobolev spaces of variable orders, also called Sobolev-Orlicz spaces.
In particular, we generalize the earlier obtained logarithmic condition and give a number of examples. Bibliography: 9 titles.
__________
Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 310, 2004, pp. 67–81. 相似文献
180.
A. V. Bobylev 《Journal of statistical physics》2006,124(2-4):371-399
It is well-known that the classical Chapman-Enskog procedure does not work at the level of Burnett equations (the next step after the Navier-Stokes equations). Roughly speaking, the reason is that the solutions of higher equations of hydrodynamics (Burnett's, etc.) become unstable with respect to short-wave perturbations. This problem was recently attacked by several authors who proposed different ways to deal with it. We present in this paper one of possible alternatives. First we deduce a criterion for hyperbolicity of Burnett equations for the general molecular model and show that this criterion is not fulfilled in most typical cases. Then we discuss in more detail the problem of truncation of the Chapman-Enskog expansion and show that the way of truncation is not unique. The general idea of changes of coordinates (based on analogy with the theory of dynamical systems) leads finally to nonlinear Hyperbolic Burnett Equations (HBEs) without using any information beyond the classical Burnett equations. It is proved that HBEs satisfy the linearized H-theorem. The linear version of the problem is studied in more detail, the complete Chapman-Enskog expansion is given for the linear case. A simplified proof of the Slemrod identity for Burnett coefficients is also given. 相似文献