全文获取类型
收费全文 | 940篇 |
免费 | 77篇 |
国内免费 | 21篇 |
专业分类
化学 | 191篇 |
力学 | 321篇 |
综合类 | 15篇 |
数学 | 320篇 |
物理学 | 191篇 |
出版年
2023年 | 6篇 |
2022年 | 28篇 |
2021年 | 28篇 |
2020年 | 22篇 |
2019年 | 23篇 |
2018年 | 18篇 |
2017年 | 40篇 |
2016年 | 35篇 |
2015年 | 28篇 |
2014年 | 55篇 |
2013年 | 92篇 |
2012年 | 39篇 |
2011年 | 48篇 |
2010年 | 33篇 |
2009年 | 43篇 |
2008年 | 47篇 |
2007年 | 51篇 |
2006年 | 48篇 |
2005年 | 58篇 |
2004年 | 37篇 |
2003年 | 46篇 |
2002年 | 32篇 |
2001年 | 23篇 |
2000年 | 13篇 |
1999年 | 28篇 |
1998年 | 21篇 |
1997年 | 14篇 |
1996年 | 6篇 |
1995年 | 9篇 |
1994年 | 8篇 |
1993年 | 6篇 |
1992年 | 5篇 |
1991年 | 8篇 |
1990年 | 6篇 |
1989年 | 7篇 |
1988年 | 3篇 |
1987年 | 4篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1974年 | 2篇 |
1972年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有1038条查询结果,搜索用时 15 毫秒
121.
This paper presents a theoretical formulation in which the stream-tube method (STM) is examined through a variational approach for solving solid strain and fluid flow problems with finite elements. The analysis considers a reference domain, used as computational domain, related to the physical domain by an unknown transformation function to be determined numerically. Mass conservation is automatically verified by STM. The variational approach leads to eliminate the pressure in fluid problems and avoids to set up a mixed displacement–pressure procedure in the case of incompressible solids. Examples are given for fluid flows, applications and comparisons are also provided in the bending problem in elasticity. 相似文献
122.
Hamiltonian restriction of Vlasov equations to rotating isopycnic and isentropic two-layer equations
O. Bokhove 《Applied Mathematics Letters》2005,18(12):1418-1425
A direct link between a Vlasov equation and the equations of motion of a rotating fluid with an effective pressure depending only on a pseudo-density is illustrated. In this direct link, the resulting fluid equations necessarily appear in flux conservative form when there are no topographical and rotational terms. In contrast, multilayer isopycnic and isentropic equations used in atmosphere and ocean dynamics, in the absence of topographical and rotational terms, cannot be brought into a conservative flux form, and, hence, cannot be derived directly from the Vlasov equations. Another route is explored, therefore: deriving the Hamiltonian formulation of the two-layer isopycnic and isentropic equations as a restriction from a Hamiltonian formulation of two decoupled Vlasov equations. The work is motivated by our search for energy-preserving or even Hamiltonian (kinetic) numerical schemes. 相似文献
123.
Several nonlinear Lagrangian formulations have been recently proposed for
bounded integer programming problems. While possessing an asymptotic strong duality
property, these formulations offer a success guarantee for the identification of an optimal
primal solution via a dual search. Investigating common features of nonlinear Lagrangian
formulations in constructing a nonlinear support for nonconvex piecewise constant perturbation function, this paper proposes
a generalized nonlinear Lagrangian formulation of which many existing nonlinear Lagrangian formulations become special cases. 相似文献
124.
T.S. Arthanari 《Discrete Mathematics》2006,306(14):1474-1492
In this paper we define a combinatorial object called a pedigree, and study the corresponding polytope, called the pedigree polytope. Pedigrees are in one-to-one correspondence with the Hamiltonian cycles on Kn. Interestingly, the pedigree polytope seems to differ from the standard tour polytope, Qn with respect to the complexity of testing whether two given vertices of the polytope are nonadjacent. A polynomial time algorithm is given for nonadjacency testing in the pedigree polytope, whereas the corresponding problem is known to be NP-complete for Qn. We also discuss some properties of the pedigree polytope and illustrate with examples. 相似文献
125.
随机微分方程dX_t=(δf~2(t)-h(t)X_t)dt+2f(t) │X_t│~(1/2)dBt,(X_0=x,δ>0)的解X_t是一种推广的δ(δ>0)维Bessel过程.文章对于任意停时τ给出了‖sup0≤t≤τη(t)X_t‖p的L~p估计,其中η:R_+→R_+是一个R+上的可微函数,而且满足微分方程dη/dt-h(t)η=-η~2f~2(t),η(0)=1. 相似文献
126.
Pinyuen Chen 《Annals of the Institute of Statistical Mathematics》1985,37(1):303-314
Summary An inverse sampling procedureR is proposed for selecting a randomsize subset which contains the least probable cell (i.e., the cell with the smallest cell
probabilities) from a multinomial distribution withk cells. Type 2-Dirichlet integrals are used (i) to express the probability of a correct selection in terms of integrals with
parameters only in the limits of integration, (ii) to prove that the least favorable configuration underR is the so-called slippage configuration withk equal cell probabilities, and (iii) to express exactly the expectation of the total number of observations required and the
expectation of the subset size under the procedureR. 相似文献
127.
The complete formulation of B.E.M. applied to the analysis of axisymmetric bodies acting in the plastic range is presented in this paper. The concept of derivative of a singular integral given by Mikhlin has been used in order to calculate the stresses in internal points.Also a semianalytical approach is proposed to compute the matrix coefficients, presenting the way in which it can be done and the results obtained. 相似文献
128.
R. Mélin D. Feinberg 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(1):101-114
We derive a microscopic transport theory of multiterminal hybrid structures in which a superconductor is connected to several
spin-polarized electrodes. We discuss the non-perturbative physics of extended contacts, and show that such contacts can be
well represented by averaging out the phase of the electronic wave function. The intercontact Andreev reflection and elastic
cotunneling conductances are identical if the phase can be averaged out, namely in the presence of at least one extended contact.
The maximal conductance of a two-channel contact is proportional to (e
2/h)(a
0/D)2exp[-D/ξ(ω*)], where D is the distance between the contacts, a0 the lattice spacing, ξ(ω) is the superconducting coherence length, and ω* is the cross-over frequency between a perturbative regime ( ω < ω*) and a non perturbative regime ( ω* < ω < Δ).
Received 18 June 2001 and Received in final form 17 January 2002 相似文献
129.
The mixed form of the areal groundwater flow equations is solved with a least-squares finite element procedure (LESFEM). Hydraulic head and x- and y-directed fluxes are state variables. Physical parameters and state variables are approximated using a bilinear basis. Grid refinements and irregular domain boundaries are implemented on rectangular meshes. Residuals are constructed at collocation points for conservation of mass and Darcy's law. Boundary condition residuals are constructed at discrete points along the boundary. The residuals are weighted, squared and summed. A set of algebraic equations is formed by taking the derivatives of the weighted sum of the squares of the residuals with respect to each unknown parameter in the approximation for the state variable and setting them to zero. Proper choice of a potential scaling parameter and residual weights is essential for the effective application of the algorithm. Test problem results demonstrate that the method is effective for both transient and steady state cases. The LESFEM algorithm generates a C°-continuous velocity field. The continuous velocity field and the rectangular mesh simplify the implementation of algorithms that require tracking. In addition, rectangular meshes simplify mesh and boundary generation. 相似文献
130.