全文获取类型
收费全文 | 725352篇 |
免费 | 6406篇 |
国内免费 | 2063篇 |
专业分类
化学 | 366487篇 |
晶体学 | 10848篇 |
力学 | 36244篇 |
综合类 | 20篇 |
数学 | 96520篇 |
物理学 | 223702篇 |
出版年
2021年 | 7061篇 |
2020年 | 7505篇 |
2019年 | 7918篇 |
2018年 | 10610篇 |
2017年 | 10877篇 |
2016年 | 15141篇 |
2015年 | 8545篇 |
2014年 | 14184篇 |
2013年 | 33118篇 |
2012年 | 25481篇 |
2011年 | 30462篇 |
2010年 | 22592篇 |
2009年 | 22538篇 |
2008年 | 28417篇 |
2007年 | 28106篇 |
2006年 | 25760篇 |
2005年 | 22946篇 |
2004年 | 21302篇 |
2003年 | 19110篇 |
2002年 | 18979篇 |
2001年 | 20980篇 |
2000年 | 16021篇 |
1999年 | 12482篇 |
1998年 | 10637篇 |
1997年 | 10404篇 |
1996年 | 9744篇 |
1995年 | 8705篇 |
1994年 | 8651篇 |
1993年 | 8345篇 |
1992年 | 8954篇 |
1991年 | 9500篇 |
1990年 | 9065篇 |
1989年 | 8936篇 |
1988年 | 8553篇 |
1987年 | 8509篇 |
1986年 | 8117篇 |
1985年 | 10366篇 |
1984年 | 10785篇 |
1983年 | 9024篇 |
1982年 | 9312篇 |
1981年 | 8734篇 |
1980年 | 8425篇 |
1979年 | 9038篇 |
1978年 | 9276篇 |
1977年 | 9116篇 |
1976年 | 9041篇 |
1975年 | 8676篇 |
1974年 | 8511篇 |
1973年 | 8808篇 |
1972年 | 6321篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
861.
S. Sadiku Ph. D. 《Archive of Applied Mechanics (Ingenieur Archiv)》1990,60(6):351-357
Summary A method of determining the response of a stiffened elastic plate to a dynamic excitation is presented here. Green's function for such a combined system has been systematically derived based on the eigenfunctions of the system obtained through the application of Galerkin's method. With that Green's function a wide range of dynamic forcing functions can be considered.
Zur elastodynamik versteifter platten
Übersicht Vorgestellt wird eine Methode zur Ermittlung der Antwort versteifter Platten auf dynamische Erregungen. Mit Hilfe der Eigenfunktionen des Systems, die durch Anwendung der Galerkin-Methode gewonnen werden, wird die Greensche Funktion solcher kombinierten Tragwerke systematisch hergeleitet. Damit kann ein weiter Bereich dynamischer Anregungsfunktionen behandelt werden.相似文献
862.
For verifying the method of calculating the boundary layer in liquid rocket engine (LRE) nozzles developed by the authors
on the basis of a differential three-parameter turbulence model, the boundary layer on a plate in a zero-gradient flow is
calculated. Over a wide range of variation of the free-stream Mach number, the temperature factor, and the Reynolds number,
based on the momentum thickness of the boundary layer, the calculation agrees satisfactorily with the known experimental data,
with respect to both integral and local flow and heat transfer characteristics.
Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 6, pp. 64–78, November–December,
1998.
The work received financial support from the Russian Foundation for Basic Research (project No.96-012-00260). 相似文献
863.
K. A. Yih 《Heat and Mass Transfer》1998,34(1):55-61
A boundary layer analysis is used to investigate the heat and mass transfer characteristics of mixed convection about a vertical
flat plate embedded in a saturated porous medium under the coupled effects of thermal and mass diffusion. The plate is maintained
at prescribed surface temperature/concentration (PST/PSC) or prescribed heat/mass flux (PHF/PMF). The nonsimilar governing
equations are obtained by using a suitable transformation and solved by Keller box method. Numerical results for the local
heat transfer rate and the local mass transfer rate are presented for various parameters. The local heat and mass transfer
rates increase with increasing n and m and buoyancy parameter ξ. When buoyancy parameter ξ is very small (large) the value of local Nusselt and the local Sherwood
number correspond with the pure forced (free) convection, respectively. Increasing buoyancy ratio N (or N
*) increases the local heat and mass transfer rates. It is apparent that Lewis number has a pronounced effect on the local
mass transfer rate than it does on the local heat transfer rate. Furthermore, increasing Lewis number decreases (increases)
the local heat (mass) transfer rate.
Received on 8 December 1997 相似文献
864.
A. Ya. Kuzin 《Journal of Applied Mechanics and Technical Physics》1995,36(1):98-104
Tomsk. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, No. 1, pp. 106–112, January–February, 1995. 相似文献
865.
The finite amplitude, free vibrational characteristics of a simple mechanical system consisting of an axisymmetric rigid body supported by a highly elastic tubular shear spring subjected to axial, rotational, and coupled shearing motions are studied. Two classes of elastic tube materials are considered: a compressible material whose shear response is constant, and an incompressible material whose shear response is a quadratic function of the total amount of shear. The class of materials with constant shear response includes the incompressible Mooney-Rivlin material and certain compressible Blatz-Ko, Hadamard, and other general kinds of models. For each material class, the quasi-static elasticity problem is solved to determine the telescopic and gyratory shearing deformation functions needed to evaluate the elastic tube restoring force and torque exerted on the body. For all materials with constant shear response, the differential equations of motion are uncoupled equations typical of simple harmonic oscillators. Hence, exact solutions for the forced vibration of the system can be readily obtained; and for this class, engineering design formulae for the load-deflection relations are discussed and compared with experimental results of others'. For the quadratic material, however, the general motion of the body is characterized by a formidable, coupled system of nonlinear equations. The free, coupled shearing motion for which either the axial or the azimuthal shear deformation may be small is governed by a pair of equations of the Duffing and Hill types. On the other hand, the finite amplitude, pure axial and pure rotational motions of the load are described by the classical, nonlinear Duffing equation alone. A variety of problems are solved exactly for these separate free vibrational modes, and a number of physical results are presented throughout. 相似文献
866.
An equation describing the kinetics of the mass transfer accompanying the process of gas bubble growth in an incompressible liquid is proposed. The equation of state of the two-phase system, whose derivation is based on the mechanism of interphase mass transfer due to the solubility of the gas atoms in the liquid, is obtained. An evolution equation generalizing the usual Burgers-Korteweg-de Vries (BKdV) equation is derived for describing the nonlinear waves in a gas-containing liquid. The solution of this equation is obtained in the form of a solitary wave.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 3, pp. 114–119, May–June, 1989. 相似文献
867.
The shadowgraph method is applied to thermal convection experiments and electro-hydrodynamic convection (EHC) in nematic liquid crystals. In both cases convection leads to a spatially periodic field of the refractive index causing a spatially periodic intensity modulation of parallel light passing the cell. Close to the onset of convection the temperature or director field is given by linear stability analysis. Knowing these functions the determination of their amplitudes becomes possible by means of the shadowgraph method. The method is demostrated using various examples of thermal and EHC convection experiments. 相似文献
868.
Ahmed A. Afify 《Heat and Mass Transfer》2004,40(6-7):495-500
The effect of chemical reaction on free convective flow and mass transfer of a viscous, incompressible and electrically conducting fluid over a stretching surface is investigated in the presence of a constant transverse magnetic field. The non-linear boundary layer equations with the boundary conditions are transferred by a similarity transformation into a system of non-linear ordinary differential equations with the appropriate boundary conditions. Furthermore, the similarity equations are solved numerically by using a fourth order Runge-Kutta scheme with the shooting method. Numerical results of the skin friction coefficient, the local Nusselt number Nu, the local Sherwood number Sh, as will as the velocity, temperature and concentration profiles are presented for gases with a Prandtl number of 0.71 for various values of chemical reaction parameter, order of reaction, magnetic parameter and Schmidt number. 相似文献
869.
S.?N.?AntontsevEmail author J.?I.?Díaz H.?B.?de?Oliveira 《Journal of Mathematical Fluid Mechanics》2004,6(4):439-461
We consider a planar stationary flow of an incompressible viscous fluid in a semiinfinite strip governed by the Stokes system
with a body forces field. We show how this fluid can be stopped at a finite distance of the entrance of the semi-infinite
strip by means of a feedback field depending in a sub-linear way on the velocity field. This localization effect is proved
reducing the problem to a non-linear bi-harmonic type one for which the localization of solutions is obtained by means of
the application of a suitable energy method. Since the presence of the non-linear terms defined through the body forces field
is not standard in the fluid mechanics literature, we establish also some results about the existence and uniqueness of weak
solutions for this problem. 相似文献
870.
The natural oscillations of a submerged elastic jet membrane modeling an axisymmetric hydrodynamic direct-flow radiator are analyzed. The fundamental frequency is calculated as a function of the geometric and hydrodynamic characteristics of the jet. The principle possibility of adjusting the frequency by changing the elasticity of the fluid, which is a function of hydrostatic pressure, is demonstrated. Numerical and experimental data are compared.__________Translated from Prikladnaya Mekhanika, Vol. 40, No. 12, pp. 92–98, December 2004. 相似文献