全文获取类型
收费全文 | 4867篇 |
免费 | 397篇 |
国内免费 | 280篇 |
专业分类
化学 | 856篇 |
晶体学 | 10篇 |
力学 | 745篇 |
综合类 | 27篇 |
数学 | 1893篇 |
物理学 | 2013篇 |
出版年
2024年 | 5篇 |
2023年 | 36篇 |
2022年 | 80篇 |
2021年 | 74篇 |
2020年 | 114篇 |
2019年 | 122篇 |
2018年 | 124篇 |
2017年 | 101篇 |
2016年 | 93篇 |
2015年 | 77篇 |
2014年 | 231篇 |
2013年 | 410篇 |
2012年 | 208篇 |
2011年 | 285篇 |
2010年 | 253篇 |
2009年 | 332篇 |
2008年 | 389篇 |
2007年 | 337篇 |
2006年 | 297篇 |
2005年 | 230篇 |
2004年 | 226篇 |
2003年 | 185篇 |
2002年 | 156篇 |
2001年 | 109篇 |
2000年 | 97篇 |
1999年 | 88篇 |
1998年 | 118篇 |
1997年 | 94篇 |
1996年 | 90篇 |
1995年 | 76篇 |
1994年 | 61篇 |
1993年 | 46篇 |
1992年 | 55篇 |
1991年 | 47篇 |
1990年 | 38篇 |
1989年 | 43篇 |
1988年 | 36篇 |
1987年 | 24篇 |
1986年 | 20篇 |
1985年 | 20篇 |
1984年 | 26篇 |
1983年 | 12篇 |
1982年 | 17篇 |
1981年 | 9篇 |
1980年 | 8篇 |
1979年 | 8篇 |
1978年 | 11篇 |
1977年 | 9篇 |
1976年 | 8篇 |
1973年 | 3篇 |
排序方式: 共有5544条查询结果,搜索用时 22 毫秒
81.
颗粒介质的弹塑性动态本构关系研究 总被引:3,自引:0,他引:3
本文运用多刚体系统动力学和微结构连续力学的理论方法,考虑了颗粒体的拓扑结构及颗粒体之间的局部非线性相互作用,通过引进恢复系数,导出了适合于大变形运动(包括平动与转动)情况下,颗粒体间的滑移和分离的客观弹塑性本构关系。 相似文献
82.
本文用矩量法解薄板塑性动力响应问题,分析阻尼介质对简支方板塑性动力响应的影响,对计算结果进行了讨论. 相似文献
83.
Proper design of operations encountered in preparation, transport and employment of suspensions like coal slurries and coal-oil mixtures require an accurate knowledge of their rheological behaviour.Such concentrated suspensions generally exhibit non-Newtonian behaviour (shearthinning) which is more pronounced at higher coal concentrations. The nature of the dispersing medium influences the aggregation state of the disperse phase and, consequently, affects the stability and the rheology of the systems. In the present paper coal suspensions prepared with different dispersing media and covering a wide range in solid phase concentration are studied, by using a rotational coaxial cylinders viscometer.Different models have been taken into consideration for correlating experimental data. In particular, in order to describe the dependence of viscosity on shear rate and solid phase concentration, the suitability of the model suggested by Smith and Bruce is evaluated. Accordingly, the aggregation state of the disperse phase as well as its dependence on shear rate and dispersing medium can be estimated. 相似文献
84.
85.
V. N. Chekhov 《International Applied Mechanics》2007,43(12):1359-1371
The paper addresses the important issue of allowing for the inelastic properties of rock in stability problems for a stratified
rock mass. A three-dimensional nonlinear problem statement is used. An exact method to study the surface instability of a
regularly layered semi-infinite medium is developed. New numerical results are obtained
__________
Translated from Prikladnaya Mekhanika, Vol. 43, No. 12, pp. 68–81, December 2007. 相似文献
86.
A new mathematical model is proposed for time-independent laminar flow through a rigid isotropic and consolidated porous medium of spatially varying porosity. The model is based upon volumetric averaging concepts. Explicit assumptions regarding the mean geometric properties of the porous microstructure lead to a relationship between tortuosity and porosity. Microscopic inertial effects are introduced through consideration of flow development within the pores. A momentum transport equation is derived in terms of the fluid properties, the porous medium porosity and a characteristic length of the microstructure. In the limiting cases of porosity unity and zero, the model yields the required Navier-Stokes equation for free flow and no flow in a solid, respectively. 相似文献
87.
Doubly nonlinear parabolic-type equations as dynamical systems 总被引:1,自引:0,他引:1
In this paper, we study a class of doubly nonlinear parabolic PDEs, where, in addition to some weak nonlinearities, also some mild nonlinearities of porous media type are allowed inside the time derivative. In order to formulate the equations as dynamical systems, some existence and uniqueness results are proved. Then the existence of a compact attractor is shown for a class of nonlinear PDEs that include doubly nonlinear porous medium-type equations. Under stronger smoothness assumptions on the nonlinearities, the finiteness of the fractal dimension of the attractor is also obtained. 相似文献
88.
The numerical path integration method, based on Gauss-Legendre integration scheme, is applied to a Duffing oscillator subject to both sinusoidal and white noise excitations. The response of the system is a Markov process with one of the drift coefficients being periodic. It is a non-homogeneous Markov process that does not have a stationary probability distribution. When applying the numerical procedure, the values of transition probability density at the Gaussian-Legendre quadrature points need only be calculated for time steps of the first period of the sinusoidal excitation, and they can be saved for use in all subsequent periods. The numerical procedure is capable of capturing the evolution of the probability density from an initial distribution to one that is changing and rotating periodically in the phase space. 相似文献
89.
We study the simultaneous one-dimensional flow of water and oil in a heterogeneous medium modelled by the Buckley-Leverett equation. It is shown both by analytical solutions and by numerical experiments that this hyperbolic model is unstable in the following sense: Perturbations in physical parameters in a tiny region of the reservoir may lead to a totally different picture of the flow. This means that simulation results obtained by solving the hyperbolic Buckley-Leverett equation may be unreliable.Symbols and Notation
f
fractional flow function varying withs andx
-
value off outsideI
-
value off insideI
-
local approximation off around¯x
-
f
–,f
+
values of
-
f
j
n
value off atS
j
n
andx
j
-
g
acceleration due to gravity [ms–2]
-
I
interval containing a low permeable rock
-
k
dimensionless absolute permeability
-
k
*
absolute permeability [m2]
-
k
c
*
characteristic absolute permeability [m2]
-
k
ro
relative oil permeability
-
k
rw
relative water permeability
-
L
*
characteristic length [m]
-
L
1
the space of absolutely integrable functions
-
L
the space of bounded functions
-
P
c
dimensionless capillary pressure function
-
P
c
*
capillary pressure function [Pa]
-
P
c
*
characteristic pressure [Pa]
-
S
similarity solution
-
S
j
n
numerical approximation tos(xj, tn)
-
S
1, S2,S
3
constant values ofs
-
s
water saturation
-
value ofs at
-
s
L
left state ofs (wrt.
)
-
s
R
right state ofs (wrt.
)
-
s
s for a fixed value of in Section 3
-
T
value oft
-
t
dimensionless time coordinate
-
t
*
time coordinate [s]
-
t
c
*
characteristic time [s]
-
t
n
temporal grid point,t
n=n t
-
v
*
total filtration (Darcy) velocity [ms–1]
-
W, , v
dimensionless numbers defined by Equations (4), (5) and (6)
-
x
dimensionless spatial coordinate [m]
-
x
*
spatial coordinate [m]
-
x
j
spatial grid piont,x
j=j x
-
discontinuity curve in (x, t) space
-
right limiting value of¯x
-
left limiting value of¯x
-
angle between flow direction and horizontal direction
- t
temporal grid spacing
- x
spatial grid spacing
-
length ofI
-
parameter measuring the capillary effects
-
argument ofS
-
o
dimensionless dynamic oil viscosity
- w
dimensionless dynamic water viscosity
-
c
*
characteristic viscosity [kg m–1s–1]
-
o
*
dynamic oil viscosity [kg m–1s–1]
-
w
*
dynamic water viscosity [k gm–1s–1]
-
o
dimensionless density of oil
-
w
dimensionless density of water
-
c
*
characteristic density [kgm–3]
-
o
*
density of oil [kgm–3]
-
w
*
density of water [kgm–3]
-
porosity
-
dimensionless diffusion function varying withs andx
-
*
dimensionless function varying with s andx
* [kg–1m3s]
-
j
n
value of atS
j
n
andx
j
This research has been supported by VISTA, a research cooperation between the Norwegian Academy of Science and Letters and Den norske stats oljeselskap a.s. (Statoil). 相似文献
90.