全文获取类型
收费全文 | 6376篇 |
免费 | 380篇 |
国内免费 | 667篇 |
专业分类
化学 | 1213篇 |
晶体学 | 31篇 |
力学 | 121篇 |
综合类 | 96篇 |
数学 | 5061篇 |
物理学 | 901篇 |
出版年
2023年 | 74篇 |
2022年 | 67篇 |
2021年 | 136篇 |
2020年 | 136篇 |
2019年 | 176篇 |
2018年 | 168篇 |
2017年 | 160篇 |
2016年 | 210篇 |
2015年 | 166篇 |
2014年 | 297篇 |
2013年 | 539篇 |
2012年 | 203篇 |
2011年 | 357篇 |
2010年 | 296篇 |
2009年 | 428篇 |
2008年 | 490篇 |
2007年 | 430篇 |
2006年 | 370篇 |
2005年 | 366篇 |
2004年 | 290篇 |
2003年 | 299篇 |
2002年 | 284篇 |
2001年 | 189篇 |
2000年 | 188篇 |
1999年 | 178篇 |
1998年 | 167篇 |
1997年 | 181篇 |
1996年 | 94篇 |
1995年 | 70篇 |
1994年 | 69篇 |
1993年 | 48篇 |
1992年 | 27篇 |
1991年 | 25篇 |
1990年 | 22篇 |
1989年 | 22篇 |
1988年 | 11篇 |
1987年 | 13篇 |
1986年 | 11篇 |
1985年 | 17篇 |
1984年 | 15篇 |
1983年 | 5篇 |
1982年 | 25篇 |
1981年 | 23篇 |
1980年 | 17篇 |
1979年 | 20篇 |
1978年 | 13篇 |
1977年 | 12篇 |
1976年 | 6篇 |
1970年 | 2篇 |
1959年 | 2篇 |
排序方式: 共有7423条查询结果,搜索用时 828 毫秒
71.
In this paper we consider certain matrix equations in the field of Mikusiński operators, and construct a method for obtaining an approximate solution which allows working with numerical constants instead of operators. The theory of diagonally dominant matrices is applied for the analysis, existence and character of the obtained solutions. We introduce a method for determining approximate solutions of a discrete analogue for operational differential equations and give conditions for their existence. The error of the approximation is estimated. 相似文献
72.
Online weighted flow time and deadline scheduling 总被引:1,自引:0,他引:1
Luca Becchetti Stefano Leonardi Alberto Marchetti-Spaccamela Kirk Pruhs 《Journal of Discrete Algorithms》2006,4(3):339
In this paper we study some aspects of weighted flow time. We first show that the online algorithm Highest Density First is an O(1)-speed O(1)-approximation algorithm for P|ri,pmtn|∑wiFi. We then consider a related Deadline Scheduling Problem that involves minimizing the weight of the jobs unfinished by some unknown deadline D on a uniprocessor. We show that any c-competitive online algorithm for weighted flow time must also be c-competitive for deadline scheduling. We then give an O(1)-competitive algorithm for deadline scheduling. 相似文献
73.
《Surface and interface analysis : SIA》2006,38(5):964-974
In this work the maximum entropy method (MEM) is applied, for the first time, to angle‐resolved X‐ray photoelectron spectroscopy (ARXPS) data from oxy‐hydroxide films on iron surfaces. This nondestructively derives information on the in‐depth distribution of the composition and chemical state. An MEM algorithm was created and first tested on the simulated data. The reconstructed composition depth profiles agreed very well with the theoretical ones up to 5% Gaussian noise added to the data. The same algorithm was then applied to ARXPS data from iron samples to investigate the in‐depth variations in the composition and chemical state of the nanosized oxy‐hydroxide film naturally grown on the iron surface. The resulting surface film presents a complex multilayer structure with concentration gradients. The effect of air exposure on the structure was also investigated. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
74.
本文以自然的方式定义了从Z-空间X到Z-空间Y的有界线性算子的和以及它们的数乘.从而得到了与赋范空间的对偶空间理论类似的一系列结论. 相似文献
75.
Carsten Franz 《Proceedings of the American Mathematical Society》2006,134(8):2437-2446
A method to approximate the eigenvalues of linear operators depending on an unknown distribution is introduced and applied to weighted sums of squared normally distributed random variables. This area of application includes the approximation of the asymptotic null distribution of certain degenerated U- and V-statistics.
76.
We report on the lattice-mismatched growth of step-graded InxAl1−xAs buffer layers on GaAs (0 0 1) substrates by molecular beam epitay (MBE). The approach to growing highly lattice-mismatched epilayers is to interpose a buffer layer between the substrate and the active layer. Two samples G30 and G40 with active layer compositions, respectively, x = 0.46 and x = 0.41, are studied by photoluminescence (PL). At low temperature, the PL spectra show a large broadened band whose energy and intensity depend on the active layer composition. The step-graded layer compositions improved the crystalline quality of these structures and increase the active layer PL band intensity. 相似文献
77.
We study the transversal spin–spin correlations in the non-equilibrium steady state of the XY chain constructed by coupling a finite cutout of the chain to the two infinite parts to its left and right acting as thermal reservoirs at different temperatures. We prove that the spatial decay of these correlations is at least exponentially fast. 相似文献
78.
Wei Guoqiang 《数学年刊B辑(英文版)》1998,19(4):465-472
1.IntroductionInwhatfollows,allofHilbertspacesappearedinthispaperareinfinite-dimensionalseparablecomplexHilbertspace.IfHisaHilbertspace,thenC(n)denotestheC*--algebraofallboundedlinearoperatorsonHandK(H)denotesthesetofcompactoperatorsonn.TwooperatorsSandTarecalledapproximatelyequivalentifthereisasequenc{Un}ofunitaryoperatorssuchthatlIU:SUn--Tll-0(n-- co).SimilarlytwooperatosSandTareapproximatelysimilarifthereisasequence{Vn}ofinvertibleoperatorswithsup(llVn11,11VJ'11)相似文献
79.
We consider the semilinear Cauchy problem for a class of pseudo-differential operators generating sub-Markovian semigroups.
Solutions of such problems with negative definite nonlinearity play an important role in constructing branching measure-valued
processes. We establish local existence and uniqueness of solutions in the context of the Dirichlet space associated to the
problem. Comparison and global properties of solutions are also studied.
Accepted 29 August 2001. Online publication 17 December 2001. 相似文献
80.
Mircea Martin 《Proceedings of the American Mathematical Society》2002,130(10):2971-2983
Three natural multi-dimensional substitutes for the self-commutator of a Hilbert space operator are introduced and generalizations of Putnam's inequality to tuples of operators with semidefinite self-commutators are indicated. In addition, a Riesz transform model is developed and investigated.