全文获取类型
收费全文 | 78674篇 |
免费 | 377篇 |
国内免费 | 374篇 |
专业分类
化学 | 24724篇 |
晶体学 | 802篇 |
力学 | 6737篇 |
数学 | 32002篇 |
物理学 | 15160篇 |
出版年
2021年 | 29篇 |
2020年 | 33篇 |
2019年 | 29篇 |
2018年 | 10447篇 |
2017年 | 10281篇 |
2016年 | 6085篇 |
2015年 | 875篇 |
2014年 | 333篇 |
2013年 | 367篇 |
2012年 | 3822篇 |
2011年 | 10524篇 |
2010年 | 5660篇 |
2009年 | 6077篇 |
2008年 | 6625篇 |
2007年 | 8777篇 |
2006年 | 262篇 |
2005年 | 1329篇 |
2004年 | 1550篇 |
2003年 | 1990篇 |
2002年 | 1020篇 |
2001年 | 250篇 |
2000年 | 292篇 |
1999年 | 152篇 |
1998年 | 193篇 |
1997年 | 151篇 |
1996年 | 201篇 |
1995年 | 124篇 |
1994年 | 84篇 |
1993年 | 106篇 |
1992年 | 61篇 |
1991年 | 72篇 |
1990年 | 60篇 |
1989年 | 70篇 |
1988年 | 65篇 |
1987年 | 62篇 |
1986年 | 64篇 |
1985年 | 53篇 |
1984年 | 52篇 |
1983年 | 39篇 |
1982年 | 50篇 |
1981年 | 46篇 |
1980年 | 49篇 |
1979年 | 45篇 |
1978年 | 35篇 |
1914年 | 45篇 |
1913年 | 40篇 |
1912年 | 40篇 |
1909年 | 41篇 |
1908年 | 40篇 |
1907年 | 32篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
141.
Tie-Jun Liu Yue-Sheng Wang Chuanzeng Zhang 《Archive of Applied Mechanics (Ingenieur Archiv)》2008,78(4):267-282
The main interest of this study is a new method to solve the axisymmetric frictionless contact problem of functionally graded
materials (FGMs). Based on the fact that an arbitrary curve can be approached by a series of continuous but piecewise linear
curves, the FGM is divided into a series of sub-layers with shear modulus varying linearly in each sub-layer and continuous
at the sub-interfaces. With this model, the axisymmetric frictionless contact problem of a functionally graded coated half-space
is investigated. By using the transfer matrix method and Hankel integral transform technique, the problem is reduced to a
Cauchy singular integral equation. The contact pressure, contact region and indentation are calculated for various indenters
by solving the equations numerically.
An erratum to this article can be found at 相似文献
142.
Using the multipoles method, we formulate the problems of radiation (both heave and sway) of water waves by a submerged sphere
in deep as well as in uniform finite depth water with an ice-cover, with the ice-cover being modelled as an elastic plate
of very small thickness. In each case this leads to an infinite system of linear equations which are solved numerically by
standard techniques. The added-mass and damping coefficients for a heaving and swaying sphere are obtained and depicted graphically
against the wave number for various values of the radius of the submerged sphere and flexural rigidity of the ice-cover to
show the effect of the presence of ice-cover on these quantities. When the flexural rigidity is taken to be zero, the numerical
results for the added-mass and damping coefficient for water with a free surface are recovered. 相似文献
143.
Alexander Linkov Liliana Rybarska-Rusinek 《Archive of Applied Mechanics (Ingenieur Archiv)》2008,78(10):821-831
The paper presents a general method to find asymptotics for a (multi-)wedge system containing a thin wedge. It employs separation
of the symmetric and anti-symmetric parts of the boundary displacements and tractions of the wedge. The method is applicable
when the angle of the thin wedge turns to zero. A physical interpretation of the derived equations is obtained by using power
expansions of non-polynomial functions, which appear after the Mellin transform. We establish that the first term in the expansion
of the symmetric part corresponds to shear, while the first term of the anti-symmetric part describes deflection of the wedge
axis. Numerical experiments, performed by using a code developed on the basis of the theory, show that using only the first
terms of the expansions insignificantly influence accuracy: the approximate results coincide with the exact values of roots
to the third significant digit even for the wedge angle of 30°. 相似文献
144.
It is wellknown that the technique of character sums together with the tools of algebraic number theory is the adequate method for the study of difference sets in abelian groups, compare for instance Ott [5] or Turyn [6]. In this paper we use this method to prove a new non-existence theorem for certain difference sets in abelian groups of order rpa rp^a , where r 1 2 r \neq 2 and p are distinct primes. 相似文献
145.
Andrei N. Yakunin 《Central European Journal of Physics》2004,2(3):535-555
A cubic structure of polymer colloid complexes is studied. The technique of the research includes i) an analysis of well-known
literature SAXS data; on this basis, ii) constructing a simple model to estimate geometric structure parameters and to obtain
a simulated scattering curve; and iii) comparing the model with the real structure obtained from the SAXS data, using the
reconstruction of electron density distribution. A bicontinuous structure in cubic mesophases is formed.
Dedicated to the memory of Alexander T. Dembo 相似文献
146.
We consider a discretized volume V consisting of finite, congruent and attached copies of a tile t. We find a group L
V
the orbit of which, when applied to t, is just V. We show the connection between the structural matrixQ in the formal solution of a boundary value problem formulated for volume V and the so called auxiliary matrix of the graph Γ
v
associated with V. We show boundary value problems to be isomorphic if the graphs associated with the volumes are isomorphic, or, if the covering
groups are Sunada pairs. 相似文献
147.
148.
Su-Yun Huang Chuhsing Kate Hsiao Ching-Wei Chang 《Annals of the Institute of Statistical Mathematics》2003,55(3):655-670
The article provides a refinement for the volume-corrected Laplace-Metropolis estimator of the marginal likelihood of DiCiccioet al. The correction volume of probability α in DiCiccioet al. is fixed and suggested to take the value α=0.05. In this article α is selected based on an asymptotic analysis to minimize
the mean square relative error (MSRE). This optimal choice of α is shown to be invariant under linear transformations. The
invariance property leads to easy implementation for multivariate problems. An implementation procedure is provided for practical
use. A simulation study and a real data example are presented. 相似文献
149.
Christian Hainzl Vitali Vougalter Semjon A. Vugalter 《Communications in Mathematical Physics》2003,233(1):13-26
We consider a spinless particle coupled to a photon field and prove that even if the Schr?dinger operator p
2
+V does not have eigenvalues the system can have a ground state. We describe the coupling by means of the Pauli-Fierz Hamiltonian
and our result holds in the case where the coupling constant α is small.
Received: 7 January 2002 / Accepted: 8 November 2002 Published online: 13 January 2003 相似文献
150.
We study the focusing problem for the eikonal equation¶¶ ?tu=| ?u| 2, \partial _{t}u=\left| \nabla u\right| ^{2}, ¶¶i.e., the initial value problem in which the support of the initial datum is outside some compact set in Rd \mathbf{R}^{d} . The hole in the support will be filled in finite time and we are interested in the asymptotics of the hole as it closes. We show that in the radially symmetric case there are self-similar asymptotics, while in the absence of radial symmetry essentially any convex final shape is possible. However in R2 \mathbf{R}^2 , for generic initial data the asymptotic shape will be either a vanishing triangle or the region between two parabolas moving in opposite directions (a closing eye). We compare these results with the known results for the porous medium pressure equation which approaches the eikonal equation in the limit as m? 1 m\rightarrow 1 . 相似文献