全文获取类型
收费全文 | 19926篇 |
免费 | 484篇 |
国内免费 | 437篇 |
专业分类
化学 | 3879篇 |
晶体学 | 933篇 |
力学 | 385篇 |
综合类 | 44篇 |
数学 | 11938篇 |
物理学 | 3668篇 |
出版年
2023年 | 55篇 |
2022年 | 108篇 |
2021年 | 149篇 |
2020年 | 159篇 |
2019年 | 369篇 |
2018年 | 393篇 |
2017年 | 268篇 |
2016年 | 327篇 |
2015年 | 324篇 |
2014年 | 597篇 |
2013年 | 1359篇 |
2012年 | 525篇 |
2011年 | 1578篇 |
2010年 | 1388篇 |
2009年 | 1279篇 |
2008年 | 1376篇 |
2007年 | 1355篇 |
2006年 | 1020篇 |
2005年 | 891篇 |
2004年 | 786篇 |
2003年 | 602篇 |
2002年 | 619篇 |
2001年 | 416篇 |
2000年 | 397篇 |
1999年 | 370篇 |
1998年 | 382篇 |
1997年 | 292篇 |
1996年 | 334篇 |
1995年 | 336篇 |
1994年 | 318篇 |
1993年 | 244篇 |
1992年 | 248篇 |
1991年 | 173篇 |
1990年 | 183篇 |
1989年 | 171篇 |
1988年 | 106篇 |
1987年 | 124篇 |
1986年 | 89篇 |
1985年 | 158篇 |
1984年 | 114篇 |
1983年 | 68篇 |
1982年 | 91篇 |
1981年 | 121篇 |
1980年 | 106篇 |
1979年 | 61篇 |
1978年 | 108篇 |
1977年 | 91篇 |
1976年 | 90篇 |
1975年 | 39篇 |
1974年 | 44篇 |
排序方式: 共有10000条查询结果,搜索用时 125 毫秒
991.
This paper studies the state space and feedback aspects of linear system decoupling. Given a minimal realization for a proper transfer function W (s), a general procedure is given for the parametrization of all the minimal decouplings of W (s) into two proper subsystems. This completes and unifies known results on factorization and cascade decomposition. 相似文献
992.
Raúl?E.?CurtoEmail author Lawrence?A.?Fialkow 《Integral Equations and Operator Theory》2004,50(2):169-196
Given real numbers
with 00 >0 , the truncated parabolic moment problem for entails finding necessary and sufficient conditions for the existence of a positive Borel measure , supported in the parabola p(x, y) = 0, such that
We prove that admits a representing measure (as above) if and only if the associated moment matrix
is positive semidefinite, recursively generated and has a column relation p(X, Y) = 0, and the algebraic variety () associated to satisfies card
In this case, admits a rank
-atomic (minimal) representing measure.Submitted: August 25, 2003 相似文献
993.
We introduce the notion of strong supercommutativity of self-adjoint operators on a
-graded Hilbert space and give some basic properties. We clarify that strong supercommutativity is a unification of strong commutativity and strong anticommutativity. We also establish the theory of super quantization. Applications to supersymmetric quantum field theory and a fermion-boson interaction system are discussed. 相似文献
994.
David?EschwéEmail author Matthias?LangerEmail author 《Integral Equations and Operator Theory》2004,49(3):287-321
Variational principles for eigenvalues of certain functions whose values
are possibly unbounded self-adjoint operators T() are proved. A generalised
Rayleigh functional is used that assigns to a vector x a zero of the
function T()x, x), where it is assumed that there exists at most one zero.
Since there need not exist a zero for all x, an index shift may occur. Using
this variational principle, eigenvalues of linear and quadratic polynomials
and eigenvalues of block operator matrices in a gap of the essential spectrum
are characterised. Moreover, applications are given to an elliptic eigenvalue
problem with degenerate weight, Dirac operators, strings in a medium with a
viscous friction, and a Sturm-Liouville problem that is rational in the eigenvalue
parameter. 相似文献
995.
Young Min?HanEmail author An-Hyun?KimEmail author 《Integral Equations and Operator Theory》2004,49(4):435-444
In this note we show that if either T or T* is totally *-paranormal
then Weyls theorem holds for f(T) for every f
, and also a-Weyls theorem holds for f(T) if T is totally *-paranormal. We prove that if either
T or T* is *-paranormal then the spectral mapping theorem holds for the
Weyl spectrum and for the essential approximate point spectrum. 相似文献
996.
We establish monotonicity inequalities for the r-area of a complete oriented properly immersed r-minimal hypersurface in Euclidean
space under appropriate quasi-positivity assumptions on certain invariants of the immersion. The proofs are based on the corresponding
first variational formula. As an application, we derive a degeneracy theorem for an entire r-minimal graph whose defining
function ƒ has first and second derivatives decaying fast enough at infinity: Its Hessian operator D2 ƒ has at least n − r null eigenvalues everywhere. 相似文献
997.
Zoltán?M.?BaloghEmail author Kevin?Rogovin Thomas?Zürcher 《Journal of Geometric Analysis》2004,14(3):405-422
We extend Cheeger’s theorem on differentiability of Lipschitz functions in metric measure spaces to the class of functions
satisfying Stepanov’s condition. As a consequence, we obtain the analogue of Calderon’s differentiability theorem of Sobolev
functions in metric measure spaces satisfying a Poincaré inequality.
Communicated by Steven Krantz 相似文献
998.
C. Carstensen. 《Mathematics of Computation》2004,73(247):1153-1165
All first-order averaging or gradient-recovery operators for lowest-order finite element methods are shown to allow for an efficient a posteriori error estimation in an isotropic, elliptic model problem in a bounded Lipschitz domain in . Given a piecewise constant discrete flux (that is the gradient of a discrete displacement) as an approximation to the unknown exact flux (that is the gradient of the exact displacement), recent results verify efficiency and reliability of
in the sense that is a lower and upper bound of the flux error up to multiplicative constants and higher-order terms. The averaging space consists of piecewise polynomial and globally continuous finite element functions in components with carefully designed boundary conditions. The minimal value is frequently replaced by some averaging operator applied within a simple post-processing to . The result provides a reliable error bound with .
in the sense that is a lower and upper bound of the flux error up to multiplicative constants and higher-order terms. The averaging space consists of piecewise polynomial and globally continuous finite element functions in components with carefully designed boundary conditions. The minimal value is frequently replaced by some averaging operator applied within a simple post-processing to . The result provides a reliable error bound with .
This paper establishes and so equivalence of and . This implies efficiency of for a large class of patchwise averaging techniques which includes the ZZ-gradient-recovery technique. The bound established for tetrahedral finite elements appears striking in that the shape of the elements does not enter: The equivalence is robust with respect to anisotropic meshes. The main arguments in the proof are Ascoli's lemma, a strengthened Cauchy inequality, and elementary calculations with mass matrices.
999.
The paper continues the authors work in measure and integration,
which is an attempt at unified systematization. It establishes projective limit
theorems of the Prokhorov and Kolmogorov types in terms of inner premeasures.
Then it specializes to obtain the (one-dimensional) Wiener measure
on the space of real-valued functions on the positive halfline as a probability
measure defined on an immense domain: In particular the subspace of continuous
functions will be measurable of full measure - and not merely of full
outer measure, as the usual projective limit theorems permit to conclude.
Dedicated to Professor Gustave Choquet 相似文献
1000.
The dielectric properties and loss of Bi1.5ZnSb1.5O7 a poor-semiconducting ceramic were investigated by impedance spectroscopy, in the frequency range from 5 Hz to 13 MHz. Electric measurements were performed from 100 to 700 °C. Pyrochlore type phase was synthesized by the polymeric precursor method. Dense ceramic with 97% of the theoretical density was prepared by sintering via constant heating rate. The dielectric permittivity dependence as a function of frequency and temperature showed a strong dispersion at frequency lower than 10 kHz. The losses exhibit slight dependence with the frequency at low temperatures presenting a strong increase at temperatures higher than 400 °C. A decrease of the loss magnitude occurs with increasing frequency. Relaxation times were extracted using the dielectric functions Z″(ω) and M″(ω). The plots of the relaxation times τZ′ and τM″ as a function of temperature follow the Arrhenius law, where a single slope is observed with activation energy values equal to 1.38 and 1.37 eV, respectively. 相似文献