全文获取类型
收费全文 | 9132篇 |
免费 | 865篇 |
国内免费 | 782篇 |
专业分类
化学 | 3395篇 |
晶体学 | 69篇 |
力学 | 2835篇 |
综合类 | 95篇 |
数学 | 2464篇 |
物理学 | 1921篇 |
出版年
2024年 | 12篇 |
2023年 | 99篇 |
2022年 | 123篇 |
2021年 | 172篇 |
2020年 | 227篇 |
2019年 | 200篇 |
2018年 | 209篇 |
2017年 | 285篇 |
2016年 | 307篇 |
2015年 | 258篇 |
2014年 | 392篇 |
2013年 | 648篇 |
2012年 | 489篇 |
2011年 | 543篇 |
2010年 | 432篇 |
2009年 | 533篇 |
2008年 | 487篇 |
2007年 | 509篇 |
2006年 | 445篇 |
2005年 | 508篇 |
2004年 | 417篇 |
2003年 | 403篇 |
2002年 | 360篇 |
2001年 | 284篇 |
2000年 | 264篇 |
1999年 | 253篇 |
1998年 | 220篇 |
1997年 | 226篇 |
1996年 | 154篇 |
1995年 | 183篇 |
1994年 | 145篇 |
1993年 | 125篇 |
1992年 | 94篇 |
1991年 | 108篇 |
1990年 | 80篇 |
1989年 | 60篇 |
1988年 | 85篇 |
1987年 | 74篇 |
1986年 | 78篇 |
1985年 | 56篇 |
1984年 | 43篇 |
1983年 | 18篇 |
1982年 | 57篇 |
1981年 | 21篇 |
1980年 | 13篇 |
1979年 | 21篇 |
1978年 | 17篇 |
1977年 | 10篇 |
1976年 | 8篇 |
1957年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
951.
Plane surface suddenly set in motion in a viscoelastic fluid with fractional Maxwell model 总被引:6,自引:0,他引:6
The fractional calculus approach in the constitutive relationship model of viscoelastic fluid is introduced. The flow near
a wall suddenly set in motion is studied for a non-Newtonian viscoelastic fluid with the fractional Maxwell model. Exact solutions
of velocity and stress are obtained by using the discrete inverse Laplace transform of the sequential fractional derivatives.
It is found that the effect of the fractional orders in the constitutive relationship on the flow field is significant. The
results show that for small times there are appreciable viscoelastic effects on the shear stress at the plate, for large times
the viscoelastic effects become weak.
The project supported by the National Natural Science Foundation of China (10002003), Foundation for University Key Teacher
by the Ministry of Education, Research Fund for the Doctoral Program of Higher Education 相似文献
952.
In a previous article the authors introduced a Lagrange multiplier based fictitious domain method. Their goal in the present article is to apply a generalization of the above method to: (i) the numerical simulation of the motion of neutrally buoyant particles in a three-dimensional Poiseuille flow; (ii) study – via direct numerical simulations – the migration of neutrally buoyant balls in the tube Poiseuille flow of an incompressible Newtonian viscous fluid. Simulations made with one and several particles show that, as expected, the Segré–Silberberg effect takes place. To cite this article: T.-W. Pan, R. Glowinski, C. R. Mecanique 333 (2005). 相似文献
953.
M. Emin Erdo
an 《International Journal of Non》1999,34(6):660
An exact solution of the Navier–Stokes equations is obtained for the flow between two eccentric disks rotating with the same angular velocity and one of them executing non-torsional oscillations. An analytical solution describing the flow at large and small times after the start is given. The solutions depend on the ratio of the frequency of oscillation to the angular velocity of the disks and the ratio of the amplitude of oscillation to the angular velocity of the disks and to the distance between the axes of rotation, and the Reynolds number based on the distance between the disks and the angular velocity of the disks. The solutions for three cases when the angular velocity is greater than the frequency of oscillation or it is smaller than the frequency or it is equal to the frequency are discussed. 相似文献
954.
T.S. Lee 《International Journal of Heat and Fluid Flow》1984,5(1):29-36
Computational and experimental studies of the fluid motion and heat transfer characteristics of an incompressible fluid contained in a non-rectangular inclined enclosure are described in this paper. The enclosure has two 45° inclined side walls one of which was heated and the other cooled. The remaining two sides of the enclosure are parallel and insulated. The enclosure was rotated about the long axis in steps of 30° through 360°. Experiments were performed to study the effects of Rayleigh number, aspect ratios and orientation of the enclosure. The computational method uses a mesh transformation technique coupled with the introduction of ‘false transient’ parameters for the steady state solution of the problem. The experimental method uses smoke for flow visualization studies. With aspect ratios of 3 and 6, the results indicate that the heat transfer and fluid motion within the enclosure is a strong function of both the Rayleigh number and the cavity orientation angle. A minimum and a maximum mean Nusselt number occurred as the angle of inclination was increased from 0 to 360°. A transition in the mode of circulation occurred at the angle corresponding to the minimum or maximum rate of heat transfer. Stream lines and isotherms are presented for the most representative cases 相似文献
955.
M. Zidan 《Rheologica Acta》1981,20(4):324-333
Summary Using elliptic coordinates, the flow pattern of a fluid of grade four between two elliptic tubes is determined. A comparison between the position of the maximum of the axial velocity in the present case and in the case of two concentric circular tubes shows a basic difference. In the elliptic case the maximum is shifted towards the external wall, while in the case of concentric circular tubes the shift is in the direction of the internal wall. The secondary flow shows dissymmetry with reference to the intermediate line
, which itself lies nearer to the external wall.
A planar domain representing the annular region - vector inx 1,x 2-plane - x i rectangular coordinates - rectangular unit vectors - , elliptic coordinates - 1, 2 ellipses representing respectively the internal and external tubes - = 2 – 1 annular widthy = ( – 1)/ - µ 1st grade material constant - i 2nd grade material constants - i 3rd grade material constants - i 4th grade material constants - I unit tensor - T E extra stress (T + pI) - V potential of body forces - material density = (p/) + V = –ax 3 + () - a specific driving force - arbitrary scalar function - A k Rivlin-Eriksen tensors - S stress scalar defined onA - t stress vector defined onA - P stress tensor defined onA - v axial velocity - v i i th term in the approximation ofv - u velocity vector perpendicular to the axis 4( 3 + 4 + 5 + 1/26) –2/µ(2 1 + 2)( 2 + 3) - T stress tensor - p arbitrary hydrostatic pressure - u i i th term in the approximation ofu - stream function definingu - i i th term in the approximation of With 8 figures and 1 table 相似文献
Zusammenfassung Unter Benutzung elliptischer Koordinaten wird die Strömung zwischen zwei elliptischen Rohren bestimmt. Ein Vergleich zwischen der Lage des axialen Geschwindigkeitsmaximums im vorliegenden Fall und im Fall zweier konzentrischer Kreisrohre ergibt einen grundsätzlichen Unterschied: Das Maximum ist im elliptischen Fall zur äußeren Wand hin verschoben, während die Verschiebung im Fall der konzentrischen Kreisrohre zur inneren Wand hin erfolgt. Die Sekundärströmung ist unsymmetrisch relativ zur mittleren Stromlinie , die selbst näher zur äußeren Wand liegt.
A planar domain representing the annular region - vector inx 1,x 2-plane - x i rectangular coordinates - rectangular unit vectors - , elliptic coordinates - 1, 2 ellipses representing respectively the internal and external tubes - = 2 – 1 annular widthy = ( – 1)/ - µ 1st grade material constant - i 2nd grade material constants - i 3rd grade material constants - i 4th grade material constants - I unit tensor - T E extra stress (T + pI) - V potential of body forces - material density = (p/) + V = –ax 3 + () - a specific driving force - arbitrary scalar function - A k Rivlin-Eriksen tensors - S stress scalar defined onA - t stress vector defined onA - P stress tensor defined onA - v axial velocity - v i i th term in the approximation ofv - u velocity vector perpendicular to the axis 4( 3 + 4 + 5 + 1/26) –2/µ(2 1 + 2)( 2 + 3) - T stress tensor - p arbitrary hydrostatic pressure - u i i th term in the approximation ofu - stream function definingu - i i th term in the approximation of With 8 figures and 1 table 相似文献
956.
本文将汽车绕流模块化为各典型局部流动,通过常用湍流模型对各典型局部流动进行数值模拟,结果验证了湍流模型对转捩的捕捉能力是准确模拟汽车绕流的关键. 在分析汽车绕流分离及转捩机理的基础上,优化了稳态和瞬态求解方法,改进了湍流模型对转捩的预测能力,进而提高了湍流模型在汽车流场模拟上的精度. 针对汽车绕流的稳态问题,将流线曲率因子及 响应阈值引入 LRN $k$-$\varepsilon $ (low Reynolds number $k$-$\varepsilon $) 模型,获得了一种能够更准确预 测转捩的改进低雷诺数湍流模型 (modified LRN $k$-$\varepsilon $),改善了原模型对湍流耗散率的过强依赖性及全应力发展预测不足等问题;针对汽车绕流瞬态求解,通过分析 RANS/LES 混合湍流模型的构造思想及特点,引入约束大涡模拟方法,结合本文提出的改进的 LRN $k$-$\varepsilon $ 湍流模型,提出了一种能准确捕捉转捩现象 的转捩 LRN CLES 模型. 分别将改进的模型用于某实车外流场和风振噪声仿真中,通过 Ansys Fluent 求解器计算,并将计算结果与常用湍流模型的仿真结果、HD-2 风洞试验结果和实车道路实验结果进行对比,表明改进后的湍流模型能够更准确模拟复杂实车的稳态和瞬态特性,为汽车气动特性的研究提供了可靠理论依据及有效数值解决方法. 相似文献
957.
Understanding the role of shuttle vibrations in pore fluid distribution is an essential task in the exploration of plant growth
in root modules aboard space flights. Results from experimental investigations are reported in this paper on the distribution
of immiscible fluid phases in glass beads under vibrations. Hexadecane, a petroleum compound immiscible with and lighter than
water, was used in the experiments. The higher freezing point of Hexadecane (18 °C) allowed the solidification of the entrapped
blobs in the presence of water in porous media, so that their size distribution can be obtained. van Genuchten function, commonly
used to express moisture retention curves, is found to be an adequate fit for blob size distribution at residual saturation.
The effect of vibrations on the fate (mobilization, stranding, or breakup) of a solitary ganglion in porous media was studied
using a network model. A mobility criterion considering viscous, gravity, and capillary forces was developed to determine
the fate of a solitary ganglion in a porous medium. It is concluded that the effect of vibrations is to increase the likelihood
of breakup and mobilization of blobs entrapped in porous media at residual saturation. The pore fluid distributions after
vibrations are less uniform than those before vibrations. 相似文献
958.
This paper develops a theoretical analysis of a Bingham fluid in slipping squeeze flow. The flow field decomposition consists
in combining a central extensional flow zone in the plane of symmetry and shear flow zones near the plates. It is also considered
that the slipping zone is located around a central sticking zone as previously shown from experiments. It is assumed that
the shear stress at the plates is constant in the slipping zone and equals a fixed friction yield value. The squeeze force
required to compress a Bingham fluid under the slipping behaviour as well as the radial evolution of the transition point
between both sticking and slipping zones are finally determined. 相似文献
959.
The main features of the unsteady outflow of a fluid from a cylindrical vessel rotating together with it at a constant angular velocity through a central drain hole in the bottom are studied. The software package STAR-CD tested on the results of experiments with water in the absence of rotation is used. Certain important features of the phenomenon under consideration related with the formation of vortex funnels in the fluid are established. The effect of the main control parameters of the problem, namely, angular velocity, viscosity, initial depth, etc., is analyzed. 相似文献
960.
We propose a boundary integral method to study the shape of a bubble rising under gravity in a dilute polymer solution. Constitutive properties are modelled using a FENE model [M.D. Chilcott, J.M. Rallison, J. Non-Newtonian Fluid Mech. 29 (1988) 381] with a pure surface tension interface. We employ a birefringent strand representation [O.G. Harlen, J.M. Rallison, M.D. Chilcott, High-Deborah-number flows of dilute polymer, J. Non-Newtonian Fluid Mech.34 (1990) 319–349] of the wake to simulate the shape and the time-dependent motion of the bubble. Steady and non-steady solutions reproduce qualitatively the bubble deformation seen in experiment with a small region of very high curvature near the rear stagnation point of the bubble. We find a limit point for steady axisymmetric solutions if the polymer concentration is increased or the surface tension is decreased. Rise speed jump discontinuities were not found. 相似文献