全文获取类型
收费全文 | 281篇 |
免费 | 84篇 |
国内免费 | 18篇 |
专业分类
化学 | 57篇 |
晶体学 | 2篇 |
力学 | 70篇 |
综合类 | 1篇 |
数学 | 14篇 |
物理学 | 239篇 |
出版年
2023年 | 3篇 |
2022年 | 7篇 |
2021年 | 17篇 |
2020年 | 11篇 |
2019年 | 9篇 |
2018年 | 10篇 |
2017年 | 12篇 |
2016年 | 24篇 |
2015年 | 7篇 |
2014年 | 14篇 |
2013年 | 29篇 |
2012年 | 20篇 |
2011年 | 25篇 |
2010年 | 15篇 |
2009年 | 20篇 |
2008年 | 14篇 |
2007年 | 13篇 |
2006年 | 21篇 |
2005年 | 18篇 |
2004年 | 14篇 |
2003年 | 15篇 |
2002年 | 12篇 |
2001年 | 7篇 |
2000年 | 3篇 |
1999年 | 4篇 |
1998年 | 6篇 |
1997年 | 2篇 |
1996年 | 8篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1993年 | 3篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 5篇 |
1989年 | 2篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1984年 | 1篇 |
排序方式: 共有383条查询结果,搜索用时 31 毫秒
21.
Vladimir P. Zhdanov 《Surface science》2005,575(3):313-320
Heterogeneous catalytic reactions usually contain steps, e.g., adsorption, generating energy-rich (“hot”) precursors for other steps. With increasing the rate of energy relaxation one can observe a transition from the reaction regime dominated by “hot” precursors to conventional thermal activation. To illustrate this transition in detail and to show what may happen in various situations, I present an analytical model based on the Fokker-Planck equation for energy relaxation. 相似文献
22.
Through phase transformation kinetic analysis and experimental observation, the δ/γ transformation occurring in the non-equilibrium peritectic Fe-4.33at.%Ni alloys was systematically investigated. According to JMA solid-state transformation kinetic theory, the Time-Temperature-Transformation (TTT) curves of the δ/γ transformation in peritectic Fe-Ni alloy were calculated. On this basis, the physical correlation between the δ/γ transformation and the initial undercooling of melt (△T) was elucidated. The results indicate that the change of △T can alter not only the overall δ/γ transformation pathways but also the transformation fraction with respect to each transformation mechanism. 相似文献
23.
24.
This paper presents a study to describe the behaviour of a non-equilibrium bubble in a fluid (Fluid 1) that is in contact with another fluid (Fluid 2). Fluid 2 is assumed to incorporate some elastic properties, which are modelled through a pressure term at the fluid–fluid interface. The Laplace equation is assumed to be valid in both fluids and the boundary integral method is employed to simulate the dynamics of the bubble and the fluid–fluid interface. Interesting characteristic phenomena concerning bubble oscillations and the deformation of the fluid–fluid interface are studied for a range of parameters (distance from the fluid–fluid interface, density ratios of the two fluids and elastic properties of Fluid 2). Some of the phenomena observed are jet formation in the bubble, bubble splitting, a ring bubble separating from the main bubble, mushroom-shaped bubbles and the dynamic elevation of the elastic interface. Most of these phenomena are only observed when Fluid 2 possesses some elastic properties (besides the usual formation of a high speed liquid jet). Comparisons with experimental observations confirm the validity of our simulations. 相似文献
25.
《Angewandte Chemie (International ed. in English)》2017,56(20):5475-5479
Gaining external control over self‐organization is of vital importance for future smart materials. Surfactants are extremely valuable for the synthesis of diverse nanomaterials. Their self‐assembly is dictated by microphase separation, the hydrophobic effect, and head‐group repulsion. It is desirable to supplement surfactants with an added mode of long‐range and directional interaction. Magnetic forces are ideal, as they are not shielded in water. We report on surfactants with heads containing tightly bound transition‐metal centers. The magnetic moment of the head was varied systematically while keeping shape and charge constant. Changes in the magnetic moment of the head led to notable differences in surface tension, aggregate size, and contact angle, which could also be altered by an external magnetic field. The most astonishing result was that the use of magnetic surfactants as structure‐directing agents enabled the formation of porous solids with 12‐fold rotational symmetry. 相似文献
26.
本文讨论了高次杂交壳体元在材料非线性分析中的应用,为了更精确估计单元内各部分应力的不同影响,本文应用了分区非线性变分原理推导出杂交壳元在应力增量下应用初始应力法的失衡节点力,这使得高次杂交元在非线性分析中的优点得以充分的发挥,从而大大提高了计算精度。 相似文献
27.
The formulism of a two-equation model for heat conduction in porous media, developed in a previous paper, is applied to the case of steady state one-dimensional heat transfer in a porous medium that is made up of geometrically similar units of similar size and of ordered spatial distribution. For this case study, the model-predicted locally volume-averaged temperature distributions for the solid and the fluid phase are compared to a numerical solution at a microscopic level, showing excellent agreement. 相似文献
28.
Towards a new partially integrated transport model for coarse grid and unsteady turbulent flow simulations 总被引:1,自引:0,他引:1
A new two-equation model is proposed for large eddy simulations (LESs) using coarse grids. The modeled transport equations are obtained from a direct transposition of well-known statistical models by using multiscale spectrum splitting given by the filtering operation applied to the Navier–Stokes equations. The model formulation is compatible with the two extreme limits that are on one hand a direct numerical simulation and on the other hand a full statistical modeling. The characteristic length scale of subgrid turbulence is no longer given by the spatial discretization step size, but by the use of a dissipation equation. The proposed method is applied to a transposition of the well-known k- statistical model, but the same method can be developed for more advanced closures. This approach is intended to contribute to non-zonal hybrid models that bridge Reynolds-averaged Navier–Stokes (RANS) and LES, by using a continuous change rather than matching zones. The main novelty in the model is the derivation of a new equation for LES that is formally consistent with RANS when the filter width is very large. This approach is dedicated to applications to non-equilibrium turbulence and coarse grid simulations. An illustration is made of large eddy simulations of turbulence submitted to periodic forcing. The model is also an alternative approach to hybrid models. PACS 47.27.Eq 相似文献
29.
30.
We report non-equilibrium molecular dynamics simulations of rigid and non-rigid dumbbell fluids to determine the contribution of internal degrees of freedom to strain-rate-dependent shear viscosity. The model adopted for non-rigid molecules is a modification of the finitely extensible nonlinear elastic (FENE) dumbbell commonly used in kinetic theories of polymer solutions. We consider model polymer melts — that is, fluids composed of rigid dumbbells and of FENE dumbbells. We report the steady-state stress tensor and the transient stress response to an applied Couerte strain field for several strain rates. We find that the rheological properties of the rigid and FENE dumbbells are qualitatively and quantitatively similar. (The only exception to this is the zero strain rate shear viscosity.) Except at high strain rates, the average conformation of the FENE dumbbells in a Couette strain field is found to be very similar to that of FENE dumbbells in the absence of strain. The theological properties of the two dumbbell fluids are compared to those of a corresponding fluid of spheres which is shown to be the most non-Newtonian of the three fluids considered.Symbol Definition
b
dimensionless time constant relating vibration to other forms of motion
-
F
force on center of mass of dumbbell
-
F
i
force on bead i of dumbbell
-
F
force between center of masses of dumbbells and
-
F
ij
force between beads i and j
-
h
vector connecting bead to center of mass of dumbbell
-
H
dimensionless spring constant for dumbbells, in units of /
2
-
I
moment of inertia of dumbbell
-
J
general current induced by applied field
-
k
B
Boltzmann's constant
-
L
angular momentum
-
m
mass of bead, (= m/2)
-
M
mass of dumbbell, g
-
N
number of dumbbells in simulation cell
-
P
translational momentum of center of mass of dumbbell
-
P
pressure tensor
-
P
xy
xy component of pressure tensor
-
Q
separation of beads in dumbbell
-
Q
eq
equilibrium extension of FENE dumbbell and fixed extension of rigid dumbbell
-
Q
0
maximum extension of dumbbell
-
r
ij
vector connecting beads i and j
-
r
position vector of center of mass dumbbell
-
R
vector connecting centers of mass of two dumbbells
-
t
time
-
t
*
dimensionless time, in units of m/
-
T
*
dimensionless temperature, in units of /k
-
u
potential energy
-
u
velocity vector of flow field
-
u
x
x component of velocity vector
-
V
volume of simulation cell
-
X
general applied field
-
strain rate, s–1
-
*
dimensionless shear rate, in units of /m 2
-
general transport property
-
Lennard-Jones potential well depth
-
friction factor for Gaussian thermostat
-
shear viscosity, g/cms
-
*
dimensionless shear viscosity, in units of m/
2
-
*
dimensionless number density, in units of
–3
-
Lennard-Jones separation of minimum energy
-
relaxation time of a fluid
-
angular velocity of dumbbell
-
orientation angle of dumbbell 相似文献