全文获取类型
收费全文 | 1281053篇 |
免费 | 29062篇 |
国内免费 | 7664篇 |
专业分类
化学 | 631123篇 |
晶体学 | 20120篇 |
力学 | 73761篇 |
综合类 | 102篇 |
数学 | 238108篇 |
物理学 | 354565篇 |
出版年
2021年 | 13437篇 |
2020年 | 15878篇 |
2019年 | 16004篇 |
2016年 | 27375篇 |
2015年 | 20617篇 |
2014年 | 30286篇 |
2013年 | 74109篇 |
2012年 | 34850篇 |
2011年 | 29512篇 |
2010年 | 35515篇 |
2009年 | 38402篇 |
2008年 | 29751篇 |
2007年 | 24759篇 |
2006年 | 32136篇 |
2005年 | 24230篇 |
2004年 | 26307篇 |
2003年 | 25396篇 |
2002年 | 26804篇 |
2001年 | 24756篇 |
2000年 | 22524篇 |
1999年 | 21435篇 |
1998年 | 20609篇 |
1997年 | 20641篇 |
1996年 | 20896篇 |
1995年 | 19019篇 |
1994年 | 18456篇 |
1993年 | 17968篇 |
1992年 | 17515篇 |
1991年 | 17870篇 |
1990年 | 17107篇 |
1989年 | 17201篇 |
1988年 | 16748篇 |
1987年 | 16788篇 |
1986年 | 15673篇 |
1985年 | 22128篇 |
1984年 | 23514篇 |
1983年 | 19776篇 |
1982年 | 21514篇 |
1981年 | 20757篇 |
1980年 | 20095篇 |
1979年 | 20121篇 |
1978年 | 21535篇 |
1977年 | 21102篇 |
1976年 | 20755篇 |
1975年 | 19438篇 |
1974年 | 19063篇 |
1973年 | 19523篇 |
1972年 | 14057篇 |
1968年 | 11958篇 |
1967年 | 12323篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
The purpose of this paper is to investigate problems of the Navier-Stokes approximation to kinetic equations in terms of the
so-called Chapman-Enskog projection. One considers properties of the Chapman-Enskog projection for the Cauchy problem for
moment approximations of the kinetic equation and primarily the Chapman-Enskog projection for the Boltzmann-Peierls kinetic
equation. The existence of the Chapman-Enskog projection for the Cauchy problem is proved for the phase space of conservative
variables (phenomena of nonlinear diffusion) and for the phase space of physical variables (the second sound projection).
__________
Translated from Trudy Seminara imeni I. G. Petrovskogo, No. 25, pp. 184–225, 2005. 相似文献
942.
I. J. Lozada J. C. Osorio D. V. Griffiths M. Cerrolaza 《Numerical Methods for Partial Differential Equations》2006,22(2):296-316
The semi‐analytical integration of an 8‐node plane strain finite element stiffness matrix is presented in this work. The element is assumed to be super‐parametric, having straight sides. Before carrying out the integration, the integral expressions are classified into several groups, thus avoiding duplication of calculations. Symbolic manipulation and integration is used to obtain the basic formulae to evaluate the stiffness matrix. Then, the resulting expressions are postprocessed, optimized, and simplified in order to reduce the computation time. Maple symbolic‐manipulation software was used to generate the closed expressions and to develop the corresponding Fortran code. Comparisons between semi‐analytical integration and numerical integration were made. It was demonstrated that semi‐analytical integration required less CPU time than conventional numerical integration (using Gaussian‐Legendre quadrature) to obtain the stiffness matrix. © 2005 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2006 相似文献
943.
P. Rudolf R. Raval P. Dumas G.P. Williams 《Applied Physics A: Materials Science & Processing》2002,75(1):147-153
Infrared (IR) spectroscopy of chemisorbed C60 on Ag (111), Au (110) and Cu (100) reveals that a non-IR-active mode becomes active upon adsorption, and that its frequency
shifts proportionally with the charge transferred from the metal to the molecule by about 5 cm-1 per electron. The temperature dependence of the frequency and the width of this IR feature have also been followed for C60/Cu (100) and were found to agree well with a weak anharmonic coupling (dephasing) to a low-frequency mode, which we suggest
to be the frustrated translational mode of the adsorbed molecules.
Additionally, the adsorption is accompanied by a broadband reflectance change, which is interpreted as due to the scattering
of conduction electrons of the metal surface by the adsorbate. The reflectance change allows determination of the friction
coefficient of the C60 molecules, which results in rather small values (∼2×109 s-1 for Ag and Au, and ∼1.6×109 s-1for Cu), consistent with a marked metallic character of the adsorbed molecules.
Pre-dosing of alkali atoms onto the metal substrates drastically changes the IR spectra recorded during subsequent C60 deposition: anti-absorption bands, as well as an increase of the broadband reflectance, occur and are interpreted as due
to strong electron–phonon coupling with induced surface states.
Received: 6 June 2001 / Accepted: 23 October 2001 / Published online: 3 April 2002 相似文献
944.
An experimental method for determining the real-time depth of laser-drilled holes is presented. The proposed method involves
detecting the laser-induced optoacoustic waves generated during the interaction of the laser beam with the material. Our optodynamic
study involved measuring the propagation times of these waves as they traveled through the material and analyzing their temporal
behavior during the drilling process. The experimental observations revealed an exponential relationship between the propagation
time of the longitudinal stress wave and the number of consecutive laser pulses.
Received: 25 October 2001 / Accepted: 27 October 2001 / Published online: 20 December 2001 相似文献
945.
The steady motions of a vertical rotor balanced by two coupled perfectly rigid bodies (PRBs) are analyzed for stability. The rotor executes plane-parallel motions. The PRBs can rotate together about the rotor axis and about its transverse axes through equal angles but in opposite directions. It is established that when the mass of the PRBs is much less than that of the rotor and the rotor spins with a superresonant speed, only the basic steady motions, which are those of the best-balanced rotor, are asymptotically stable. 相似文献
946.
947.
948.
G. S. Asanov 《Foundations of Physics Letters》2002,15(2):199-207
Granted the post-Lorentzian relativistic kinematic transformations are described in the Finslerian framework, the uniformity between the actual light-velocity anisotropy change and the anisotropic deformation of measuring rods can be the reason proper for the null results of the Michelson-Morley-type experiments at the first-order level. 相似文献
949.
We analyze the effect of co-segregation on the mobility of grain boundaries within the framework of the impurity drag theory originally proposed by Cahn and Lücke and Stüwe for an ideal solution. The new derivation extends this model to the case where there are two types of impurities (or three components in the alloy). Since the resultant expression for the boundary mobility is complicated, numerical solutions were obtained for several cases to show how co-segregation affects the boundary mobility. Depending on the relative diffusivities of the two impurities which are both attracted to the boundary, the mobility may either increase or decrease with increasing concentration of one of the impurities. When one of the impurities is attracted to the boundary and the other repelled from the boundary, increasing the concentration of the attractive impurity can lead to a sharp decrease in the boundary mobility. 相似文献
950.
F. Ameli M. Bonori F. Massa 《The European Physical Journal C - Particles and Fields》2002,25(1):67-75
We describe the measurement of the deep sea optical background in some sites south of Capo Passero, Sicily. A continuous
flux of about 440 photons cm
-2
s
-1
in the wavelength interval 440-550 nm is estimated due to the decays of the 40K contained in the sea water. Bioluminescence light bursts are also observed and an example of time evolution is reported.
All the measurements were accomplished using a deep sea module also described in this article.
Received: 20 April 2002 / Published online: 26 July 2002 相似文献