全文获取类型
收费全文 | 582篇 |
免费 | 53篇 |
国内免费 | 20篇 |
专业分类
化学 | 101篇 |
晶体学 | 2篇 |
力学 | 96篇 |
综合类 | 7篇 |
数学 | 225篇 |
物理学 | 224篇 |
出版年
2024年 | 1篇 |
2023年 | 5篇 |
2022年 | 2篇 |
2021年 | 6篇 |
2020年 | 15篇 |
2019年 | 15篇 |
2018年 | 10篇 |
2017年 | 13篇 |
2016年 | 10篇 |
2015年 | 20篇 |
2014年 | 36篇 |
2013年 | 42篇 |
2012年 | 22篇 |
2011年 | 34篇 |
2010年 | 27篇 |
2009年 | 31篇 |
2008年 | 31篇 |
2007年 | 45篇 |
2006年 | 37篇 |
2005年 | 25篇 |
2004年 | 28篇 |
2003年 | 29篇 |
2002年 | 26篇 |
2001年 | 18篇 |
2000年 | 17篇 |
1999年 | 15篇 |
1998年 | 11篇 |
1997年 | 15篇 |
1996年 | 19篇 |
1995年 | 6篇 |
1994年 | 5篇 |
1993年 | 2篇 |
1992年 | 5篇 |
1991年 | 5篇 |
1990年 | 5篇 |
1989年 | 1篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1982年 | 1篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有655条查询结果,搜索用时 15 毫秒
1.
In this article, we present a Python‐based library of high quality semi‐global potential energy surfaces for 50 polyatomic molecules with up to six atoms. We anticipate that these surfaces will find widespread application in the testing of new potential energy surface construction algorithms and nuclear ro‐vibrational structure theories. To this end, we provide the ability to generate the energy derivatives required for Taylor series expansions to sixth order about any point on the potential energy surface in a range of common coordinate systems, including curvilinear internal, Cartesian, and normal mode coordinates. The PyPES package, along with FORTRAN, C, MATLAB and Mathematica wrappers, is available at http://sourceforge.net/projects/pypes-lib . © 2015 Wiley Periodicals, Inc. 相似文献
2.
Calin Iulian Martin 《Applicable analysis》2017,96(7):1207-1214
This paper is concerned with the governing equations (together with the free boundary and the bottom boundary conditions) for an inviscid, incompressible fluid, written in spherical coordinates which are fixed at a point on the rotating Earth. For a special type of a steady flow moving only in the azimuthal direction, with no variation in this direction, we provide a functional-analytic study of the link between the pressure at the free surface of the ocean and the distortion of that surface. 相似文献
3.
浅埋的圆柱形孔洞对SH波的散射与地震动 总被引:22,自引:1,他引:22
研究了浅埋的圆柱形孔洞对以任意方向入射的平面SH波的散射与地震动问题。利用复变函数和多极坐标方法构造了问题的位移解。当入射波的波长与圆孔的半径相比较小时,地震动将受到较大的影响。影响地震动有三个主要参数:(1)SH波的入射角0;(2)入射波波数,即圆柱形孔洞的半径与入射波半波长之比;(3)h/R,即圆柱形孔洞至表面的距离与圆孔半径之比。当较大时,地震动幅值变化激烈,位移幅值可出现跳动和放大的现象。当h/R增大至10~12时,位移幅值变化恢复至半空间的情况,表明圆柱形孔洞的影响可被忽略。 相似文献
4.
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
5.
S. Kase 《Rheologica Acta》1982,21(2):210-211
The general integral of the very simple equation
21/n/() was found to describe the cross sectional area of filaments of isothermal power law fluids while in transient stretching where is time and is the initial location of fluid molecules at time = 0 given as the distance from a reference point fixed in space. Any such stretching transient given as a solution of the above equation is physically realizable subject to the restrictions > 0 and/ < 0. 相似文献
6.
Efficient Evaluation of the Elastic Forces and the Jacobian in the Absolute Nodal Coordinate Formulation 总被引:1,自引:0,他引:1
This paper develops a new procedure for evaluating the elastic forces, the elastic energy and the jacobian of the elastic
forces in the absolute nodal coordinate formulation. For this procedure, it is fundamental to use some invariant sparse matrices
that are integrated in advance and have the property of transforming the evaluation of the elastic forces in a matrix multiplication
process. The use of the invariant matrices avoids the integration over the volume of the element for every evaluation of the
elastic forces. Great advantages can be achieved from these invariant matrices when evaluating the elastic energy and calculating
the jacobian of the elastic forces as well. The exact expression of the jacobian of the differential system of equations of
motion is obtained, and some advantages of using the absolute nodal coordinate formulation are pointed out. Numerical results
show that there is important time saving as a result of the use of the invariant matrices. 相似文献
7.
On Solutions of Some Non-Linear Differential Equations Arising in Newtonian and Non-Newtonian Fluids
Mohyuddin M. R. Hayat T. Mahomed F. M. Asghar S. Siddiqui A. M. 《Nonlinear dynamics》2004,35(3):229-248
Some steady as well as unsteady solutions of the equations of motion for an incompressible Newtonian and non-Newtonian (second-grade)
fluids are obtained by applying different methods including the Lie symmetry group method. The flows considered are axially
symmetric with the swirling motion, and the governing equations for second-grade fluid flow have been modeled. Expressions
for streamlines, velocity and vorticity components are constructed explicitly in each case. Exact analytical solutions in
second-grade fluid are obtained and compared with the corresponding viscous solutions. 相似文献
8.
We consider the nonlinear problem of inhomogeneous Allen–Cahn equation where Ω is a bounded domain in with smooth boundary, ? is a small positive parameter, ν denotes the unit outward normal of ?Ω, V is a positive smooth function on . Let Γ be a curve intersecting orthogonally with ?Ω at exactly two points and dividing Ω into two parts. Moreover, Γ satisfies stationary and non-degenerate conditions with respect to the functional . We can prove that there exists a solution such that: as , approaches +1 in one part of Ω, while tends to ?1 in the other part, except a small neighborhood of Γ. 相似文献
9.
10.
Giacomo Luigi Petretto Carlo Ignazio G. Tuberoso Gina Vlahopoulou Alessandro Atzei Alberto Mannu Saadia Zrira 《Natural product research》2016,30(3):286-292
Seven commercial Moroccan honeys were considered for chemical characterisation. Volatile fraction, total polyphenols content, antioxidant and antiradical activities were evaluated by employing different analytical methodologies. Several physical parameters such as refractive index, pH, water content, solids content and colour were measured. Volatile fraction revealed an abundant presence of cis- and trans-linalool oxide in the seven studied samples. The presence of high levels of compounds related to the Maillard reaction, like furfural and hydroxymethylfurfural, could be the result of thermal treatments used to liquefy commercial honeys or of long storage times. The CIE L*a*b*Cab*hab° chromatic coordinates confirmed the advanced stage of the Maillard reaction, showing L* values lower than the common values found for honey of similar typologies. 相似文献