全文获取类型
收费全文 | 27331篇 |
免费 | 3725篇 |
国内免费 | 2110篇 |
专业分类
化学 | 4982篇 |
晶体学 | 267篇 |
力学 | 8935篇 |
综合类 | 322篇 |
数学 | 8030篇 |
物理学 | 10630篇 |
出版年
2024年 | 63篇 |
2023年 | 289篇 |
2022年 | 629篇 |
2021年 | 645篇 |
2020年 | 765篇 |
2019年 | 637篇 |
2018年 | 674篇 |
2017年 | 895篇 |
2016年 | 1057篇 |
2015年 | 889篇 |
2014年 | 1406篇 |
2013年 | 2148篇 |
2012年 | 1412篇 |
2011年 | 1696篇 |
2010年 | 1423篇 |
2009年 | 1622篇 |
2008年 | 1637篇 |
2007年 | 1732篇 |
2006年 | 1581篇 |
2005年 | 1446篇 |
2004年 | 1242篇 |
2003年 | 1227篇 |
2002年 | 1074篇 |
2001年 | 981篇 |
2000年 | 899篇 |
1999年 | 846篇 |
1998年 | 808篇 |
1997年 | 609篇 |
1996年 | 490篇 |
1995年 | 433篇 |
1994年 | 351篇 |
1993年 | 266篇 |
1992年 | 273篇 |
1991年 | 224篇 |
1990年 | 185篇 |
1989年 | 117篇 |
1988年 | 81篇 |
1987年 | 80篇 |
1986年 | 59篇 |
1985年 | 78篇 |
1984年 | 52篇 |
1983年 | 35篇 |
1982年 | 38篇 |
1981年 | 11篇 |
1980年 | 12篇 |
1979年 | 12篇 |
1978年 | 5篇 |
1977年 | 4篇 |
1976年 | 6篇 |
1957年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Zhao Hanzhong 《Acta Mechanica Solida Sinica》2002,15(2):156-162
A finite difference/boundary integral procedure to determine the acoustic reflected pressure from a fluid-loaded bi-laminated
plate is described. The bi-laminate is composed of a piezoelectric layer and an elastic layer in contact with the fluid, and
is held by an acoustically hard baffle. In the numerical model, the fluid pressure at fluid/solid interface is replaced by
a continuum of point sources weighted by the normal acceleration of the elastic plate, and the governing equation system is
solved in the solid domain. With the normal acceleration found, the reflected pressure in the fluid is determined by an integral
expression involving the Green's function. It is demonstrated that an appropriate applied voltage potential across the piezoelectric
layer has the effect of cancelling either the reflected or scattered pressure of the plate at any chosen field points in the
fluid.
Project supported by the National Natural Science Foundation of China (No. 10172039). 相似文献
22.
Mehdi Dehghan 《Numerical Methods for Partial Differential Equations》2002,18(2):193-202
Developement of numerical methods for obtaining approximate solutions to the three dimensional diffusion equation with an integral condition will be carried out. The numerical techniques discussed are based on the fully explicit (1,7) finite difference technique and the fully implicit (7,1) finite difference method and the (7,7) Crank‐Nicolson type finite difference formula. The new developed methods are tested on a problem. Truncation error analysis and numerical examples are used to illustrate the accuracy of the new algorithms. The results of numerical testing show that the numerical methods based on the finite difference techniques discussed in the present article produce good results. © 2002 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 18: 193–202, 2002; DOI 10.1002/num.1040 相似文献
23.
Mingxin Wang 《Journal of Mathematical Analysis and Applications》2002,274(1):424-436
This paper deals with positive solutions of degenerate and quasilinear parabolic systems not in divergence form: ut=up(Δu+av), vt=vq(Δv+bu), with null Dirichlet boundary conditions and positive initial conditions, where p, q, a and b are all positive constants. The local existence and uniqueness of classical solution are proved. Moreover, it will be proved that all solutions exist globally if and only if ab?λ12, where λ1 is the first eigenvalue of −Δ in Ω with homogeneous Dirichlet boundary condition. 相似文献
24.
Al.Th. Kermanidis D.G. Stamatelos G.N. Labeas Sp.G. Pantelakis 《Theoretical and Applied Fracture Mechanics》2006,45(2):148-158
The synergetic effect of corrosion and corrosion induced hydrogen embrittlement damage processes which occur at local scale has been found to result in a dramatic macroscopic tensile ductility loss of the 2024 aluminum alloy. In the present work, the tensile behaviour of corroded 2024 T351 specimens has been estimated on the basis of FE analysis by taking into account the local material properties in the damaged areas. A parametric study is involved to account for the effect of thickness in the results. Calculated tensile properties obtained with the analysis agree well with experimental data. 相似文献
25.
The finite-difference method is a numerical technique for obtaining approximate solutions to differential equations. The main
objective of the present study is to give a new aspect to the finite-difference method by using a variational derivative.
By applying this formulation, accurate values of the buckling loads of beams and frames with various end supports are obtained.
The performance of this formulation is verified by comparison with numerical examples in the literature
__________
Published in Prikladnaya Mekhanika, Vol. 41, No. 7, pp. 139–144, July 2005. 相似文献
26.
We consider the plane-strain buckling of a cylindrical shellof arbitrary thickness which is made of a Varga material andis subjected to an external hydrostatic pressure on its outersurface. The WKB method is used to solve the eigenvalue problemthat results from the linear bifurcation analysis. We show thatthe circular cross-section buckles into a non-circular shapeat a value of µ1 which depends on A1/A2 and a mode number,where A1 and A2 are the undeformed inner and outer radii, andµ1 is the ratio of the deformed inner radius to A1. Inthe large mode number limit, we find that the dependence ofµ1 on A1/A2 has a boundary layer structure: it is constantover almost the entire region of 0 < A1/A2 < 1 and decreasessharply from this constant value to unity as A1/A2 tends tounity. Our asymptotic results for A1 1 = O(1) and A1 1 = O(1/n) are shown to agree with the numerical resultsobtained by using the compound matrix method. 相似文献
27.
We present all-atom molecular dynamics simulations ofn-hexane on the basal plane of graphite at monolayer and multilayer coverages. In keeping with experimental data, we find the
presence of ordered adsorbed layers both at single monolayer coverage and when the adsorbed layer coexists with excess liquid
adsorbate. Using a simulation method that does not impose any particular periodicity on the adsorbed layer, we quantitatively
compare our results to the results of neutron diffraction experiments and find a structural transition from a uniaxially incommensurate
lattice to a fully commensurate structure on increasing the coverage from a monolayer to a multilayer. The zig-zag backbone
planes of all the alkane molecules lie parallel to the graphite surface at the multilayer coverage, while a few molecules
are observed to attain the perpendicular orientation at monolayer coverage.
Dedicated to Professor C N R Rao on his 70th birthday 相似文献
28.
We treat here of the question of absorbing boundary conditionsfor nonlinear diffusion equations. We use the conditions designedfor the linear equation, we prove them to be well posed forthe nonlinear problem, and through numerical experiments thatthey are well suited for reactiondiffusion equations. 相似文献
29.
何先应 《南昌大学学报(理科版)》2004,28(4):338-340
设G是有限群。H是G的一个正规子群。P是|H|的一个素因子。P是H的一个Sylow p-子群。若下列条件之一满足。则H是p-幂零:1)P的极大子群都是G的CAP-子群且(|H|,P-1)=1;2)P的二次极大子群都是G的CAP-子群且(|H|,P^2-1)=1。特别地,若进一步假设G/H为P-幂零且(|G|,P-1)=1或(|G|,P^2-1)=1。则G自身亦为P-幂零。 相似文献
30.