全文获取类型
收费全文 | 233953篇 |
免费 | 2133篇 |
国内免费 | 952篇 |
专业分类
化学 | 117570篇 |
晶体学 | 4008篇 |
力学 | 10802篇 |
综合类 | 6篇 |
数学 | 25599篇 |
物理学 | 79053篇 |
出版年
2020年 | 1836篇 |
2019年 | 2096篇 |
2018年 | 2753篇 |
2017年 | 2699篇 |
2016年 | 3965篇 |
2015年 | 2440篇 |
2014年 | 4019篇 |
2013年 | 10149篇 |
2012年 | 7629篇 |
2011年 | 9459篇 |
2010年 | 6732篇 |
2009年 | 6664篇 |
2008年 | 8758篇 |
2007年 | 8784篇 |
2006年 | 8334篇 |
2005年 | 7517篇 |
2004年 | 6945篇 |
2003年 | 6130篇 |
2002年 | 6079篇 |
2001年 | 7103篇 |
2000年 | 5393篇 |
1999年 | 4255篇 |
1998年 | 3585篇 |
1997年 | 3489篇 |
1996年 | 3307篇 |
1995年 | 3020篇 |
1994年 | 2957篇 |
1993年 | 3052篇 |
1992年 | 3166篇 |
1991年 | 3342篇 |
1990年 | 3092篇 |
1989年 | 3032篇 |
1988年 | 3070篇 |
1987年 | 2958篇 |
1986年 | 2803篇 |
1985年 | 3809篇 |
1984年 | 4011篇 |
1983年 | 3199篇 |
1982年 | 3413篇 |
1981年 | 3336篇 |
1980年 | 3232篇 |
1979年 | 3336篇 |
1978年 | 3423篇 |
1977年 | 3350篇 |
1976年 | 3448篇 |
1975年 | 3141篇 |
1974年 | 3150篇 |
1973年 | 3194篇 |
1972年 | 2235篇 |
1971年 | 1849篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
221.
Modeling and numerical simulations of the convective flows induced by the vibration of the monocrystal during crystal growth have been performed for two configurations simulating the Cz and FZ methods. This permitted to emphasize the role of different vibrational mechanisms in the formation of the average flows. It is shown that an appropriate combination of these mechanisms can be used to counteract the usual convective flows (buoyancy- and/or thermocapillary-driven) inherent to crystal growth processes from the liquid phase. While vibrational convection is rather complex due to these identified mechanisms, the new modeling used in the present paper opens up very promising perspectives to efficiently control heat and mass transfer during real industrial applications of crystal growth from the liquid phase. 相似文献
222.
Ivonin I. V. Krasil'nikova L. M. Lavrent'eva L. G. Porokhovnichenko L. P. 《Russian Physics Journal》2002,45(5):493-497
Experimental proofs of asymmetric trapping of atoms at the growth step in vapor-phase epitaxy of gallium arsenide in the GaAs–AsCl3–H2 system are given. The data obtained confirm the important role of the surface diffusion mass transfer in the growth of epitaxial GaAs layers on vicinals in the neighborhood of (111)A. The effective diffusion length is estimated. 相似文献
223.
S. Moss de Oliveira P. M. C. de Oliveira F. C. de Sá Barreto 《Journal of statistical physics》1995,78(5-6):1619-1627
Using the finite-size scaling renormalization group, we obtain the two-dimensional flow diagram of the Blume-Capel model forS=1 andS=3/2. In the first case our results are similar to those of mean-field theory, which predicts the existence of first- and second-order transitions with a tricritical point. In the second case, however, our results are different. While we obtain in theS=1 case a phase diagram presenting a multicritical point, the mean-field approach predicts only a second-order transition and a critical endpoint. 相似文献
224.
W. A. Rodrigues Jr. Q. A. G. de Souza J. Vaz Jr. P. Lounesto 《International Journal of Theoretical Physics》1996,35(9):1849-1900
In this paper we study Dirac-Hestenes spinor fields (DHSF) on a four-dimensional Riemann-Cartan spacetime (RCST). We prove that these fields must be defined as certain equivalence classes of even sections of the Clifford bundle (over the RCST), thereby being certain particular sections of a new bundle named the spin-Clifford bundle (SCB). The conditions for the existence of the SCB are studied and are shown to be equivalent to Geroch's theorem concerning the existence of spinor structures in a Lorentzian spacetime. We introduce also the covariant and algebraic Dirac spinor fields and compare these with DHSF, showing that all three kinds of spinor fields contain the same mathematical and physical information. We clarify also the notion of (Crumeyrolle's) amorphous spinors (Dirac-Kähler spinor fields are of this type), showing that they cannot be used to describe fermionic fields. We develop a rigorous theory for the covariant derivatives of Clifford fields (sections of the Clifford bundle, CB) and of Dirac-Hestenes spinor fields. We show how to generalize the original Dirac-Hestenes equation in Minkowski spacetime for the case of RCST. Our results are obtained from a variational principle formulated through the multiform derivative approach to Lagrangian field theory in the Clifford bundle. 相似文献
225.
226.
227.
A. P. Krauklis 《Journal of Mathematical Sciences》1997,86(3):2702-2704
This paper justifies the necessity of introducing corrections for the ray curvature into the standard procedure of the tomographic
inversion in the case of using traveltime data for the creeping waves. The results of relevant numerical experiments are presented.
Bibliography: 3 titles.
Translated fromZapiski Nauchnykh Seminarov POMI, Vol. 218, 1994, pp 67–71.
This work was supported by the Russian Foundation of Fundamental Research (Grant 93-05-9961).
Translated by A. P. Krauklis. 相似文献
228.
We construct a correspondence between the set of partitions of a finite set M and the set of pairs of walks to the same vertex on a graph giving the Bratteli diagram of the partition algebra on M. This is the precise analogue of the correspondence between the set of permutations of a finite set and the set of pairs of Young tableaux of the same shape, called the Robinson–Schensted correspondence. 相似文献
229.
P. G. Frayne 《International Journal of Infrared and Millimeter Waves》1992,13(5):713-720
At microwave frequencies, frequent use is made in circuit design of the electrical properties of short lengths of resistively terminated transmission line. It will be shown in the following contribution that circuits based on high frequency distributed lines can usefully be modelled at low audio frequencies using lumped element lines. 相似文献
230.
A radioactive tracer technique is described for the quantitative measurement of the sputtering yield of a target material electroplated on a copper substrate. Sputtering yields of chromium by argon and xenon ions with energies from 50 to 500 eV are reported. The ion beams, having a current density ranging from 0.01 to 0.1 mA/cm2 at an operating pressure of 2×10–5 Torr, were produced by a low-energy ion gun. The sputtered atoms were collected on an aluminum foil surrounding the target. 51Cr was used as the tracer isotope. The results indicate that the radioactive tracer technique is sensitive enough in measuring the extremely small amount of sputtered material at low ion currents and low ion energies. 相似文献