全文获取类型
收费全文 | 1749篇 |
免费 | 127篇 |
国内免费 | 15篇 |
专业分类
化学 | 64篇 |
晶体学 | 39篇 |
力学 | 907篇 |
综合类 | 4篇 |
数学 | 331篇 |
物理学 | 546篇 |
出版年
2024年 | 3篇 |
2023年 | 9篇 |
2022年 | 24篇 |
2021年 | 25篇 |
2020年 | 30篇 |
2019年 | 26篇 |
2018年 | 36篇 |
2017年 | 32篇 |
2016年 | 31篇 |
2015年 | 47篇 |
2014年 | 45篇 |
2013年 | 116篇 |
2012年 | 71篇 |
2011年 | 115篇 |
2010年 | 63篇 |
2009年 | 112篇 |
2008年 | 109篇 |
2007年 | 112篇 |
2006年 | 110篇 |
2005年 | 88篇 |
2004年 | 96篇 |
2003年 | 81篇 |
2002年 | 65篇 |
2001年 | 33篇 |
2000年 | 52篇 |
1999年 | 49篇 |
1998年 | 31篇 |
1997年 | 34篇 |
1996年 | 38篇 |
1995年 | 21篇 |
1994年 | 18篇 |
1993年 | 23篇 |
1992年 | 20篇 |
1991年 | 23篇 |
1990年 | 21篇 |
1989年 | 10篇 |
1988年 | 22篇 |
1987年 | 6篇 |
1986年 | 9篇 |
1985年 | 10篇 |
1984年 | 10篇 |
1983年 | 2篇 |
1982年 | 6篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 4篇 |
1978年 | 1篇 |
排序方式: 共有1891条查询结果,搜索用时 0 毫秒
11.
A two-dimensional model for the simulation of a binary dendritic growth with convection has been developed in order to investigate the effects of convection on dendritic morphologies. The model is based on a cellular automaton (CA) technique for the calculation of the evolution of solid/liquid (s/l) interface. The dynamics of the interface controlled by temperature, solute diffusion and Gibbs–Thomson effects, is coupled with the continuum model for energy, solute and momentum transfer with liquid convection. The solid fraction is calculated by a governing equation, instead of some approximate methods such as lever rule method [A. Jacot, M. Rappaz, Acta Mater. 50 (2002) 1909–1926.] or interface velocity method [L. Nastac, Acta Mater. 47 (1999) 4253; L. Beltran-Sanchez, D.M. Stefanescu, Mat. and Mat. Trans. A 26 (2003) 367.]. For the dendritic growth without convection, mesh independency of simulation results is achieved. The simulated steady-state tip velocity are compared with the predicted values of LGK theory [Lipton, M.E. Glicksmanm, W. Kurz, Metall. Trans. 18(A) (1987) 341.] as a function of melt undercooling, which shows good agreement. The growth of dendrite arms in a forced convection has been investigated. It was found that the dendritic growth in the upstream direction was amplified, due to larger solute gradient in the liquid ahead of the s/l interface caused by melt convection. In the isothermal environment, the calculated results under very fine mesh are in good agreement with the Oseen–Ivanstov solution for the concentration-driven growth in a forced flow. 相似文献
12.
Two different problems are proposed as approximations of the usual system modelling natural convection under the Oberbeck-Boussinesq assumptions. The error is evaluated by means of the norm of its gradient in the Hilbert space. The average Nusselt number is also estimated. 相似文献
13.
14.
激光穿透焊的三维数值模拟 总被引:1,自引:0,他引:1
本文对激光穿透焊进行了三维数值模拟,除考虑焊接速度影响外,还研究了Marangoni对流对熔池流动与传热的影响。将三维数值模拟结果与相应的二维模拟结果进行了比较,结果表明,Marangoni对流对熔池的形成有很大的影响,因此不可忽略。本文还给出了估计激光穿透焊中蒸气孔尺寸与焊接热效率的方法。 相似文献
15.
O. E. Aleksandrov 《Fluid Dynamics》2006,41(6):976-983
It is shown that the convective transport in a binary mixture in the presence of vortex convection can be described in terms of Fick’s law with an effective diffusion coefficient independent of the concentration. The form of the effective diffusion coefficient is found for arbitrary convection in the mixture. A generalization of the Stefan-Maxwell diffusion equation is proposed to include an arbitrary rotational mixture velocity field. The characteristics of convective transport are considered with reference to a three-component mixture. A solution of the equation of three-component mixture transport through a long capillary in the presence of convection homogeneous along the capillary axis is presented. It is established that for sharply different component diffusion coefficients a mixture density extremum may appear inside the capillary and then change or disappear depending on the convective flow intensity. 相似文献
16.
A fourth‐order compact finite difference scheme on the nine‐point 2D stencil is formulated for solving the steady‐state Navier–Stokes/Boussinesq equations for two‐dimensional, incompressible fluid flow and heat transfer using the stream function–vorticity formulation. The main feature of the new fourth‐order compact scheme is that it allows point‐successive overrelaxation (SOR) or point‐successive underrelaxation iteration for all Rayleigh numbers Ra of physical interest and all Prandtl numbers Pr attempted. Numerical solutions are obtained for the model problem of natural convection in a square cavity with benchmark solutions and compared with some of the accurate results available in the literature. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
17.
Two-dimensional Marangoni convection in binary mixtures is studied in periodic domains with large spatial period in the horizontal. For negative Soret coefficients convection may set in via growing oscillations which evolve into standing waves. With increasing amplitude these waves undergo a transition to traveling waves, and then to more complex waveforms. Out of this state emerge stable stationary spatially localized structures embedded in a background of small amplitude standing waves. The relation of these states to the time-independent spatially localized states that characterize the so-called pinning region is investigated by exploring the stability properties of the latter, and the associated instabilities are studied using direct numerical simulation in time. 相似文献
18.
X. Y. You 《Heat and Mass Transfer》2003,40(1-2):75-81
Active feedback control for the onset of Rayleigh-Bénard Convection in temperature-dependent-viscosity liquids is investigated.
In this paper, three major problems are addressed: (1) The results of Tang-Bau control are improved by considering the effects
of temperature-dependent viscosity; (2) A more efficient two-plate control strategy is presented. A phenomenon of coalescence
of the unstable modes is observed as the controller gain is large enough; (3) A simple way to estimate the critical Rayleigh
number under the effects of temperature-dependent viscosity is described. Numerical results show that the effects of temperature-dependent
viscosity on the critical Rayleigh number should be taken into account in some cases and the onset of Rayleigh-Bénard convection
can be effectively delayed or advanced by the active feedback control strategies studied here. 相似文献
19.
1引言在微重力下用浮区法生长高质量、大体积单晶体是一种很有应用前景的方法,但热毛细对流所引起的诸如宏观不均匀性、生长条纹等缺陷严重限制了这一方法的应用。目前,人们试着用液封方法抑制热毛细对流。文献[1~3]分别对两层流体系统内的热毛细对流所作的研究表明:通过液封,被封层内的热毛细对流可以得到显著抑制。本文对圆柱三层流体系统内的热毛细对流进行研究,为热毛细对流规律的揭示以及进一步总结出其控制方法提供了理论数值依据。2控制方程和边界条件考虑长为L的互不溶混的三层轴对称同轴液柱,如图1所示,两端壁保持定温T… 相似文献
20.