全文获取类型
收费全文 | 33881篇 |
免费 | 1280篇 |
国内免费 | 1198篇 |
专业分类
化学 | 9003篇 |
晶体学 | 1055篇 |
力学 | 600篇 |
综合类 | 159篇 |
数学 | 16930篇 |
物理学 | 5476篇 |
无线电 | 3136篇 |
出版年
2023年 | 138篇 |
2022年 | 294篇 |
2021年 | 341篇 |
2020年 | 416篇 |
2019年 | 661篇 |
2018年 | 688篇 |
2017年 | 588篇 |
2016年 | 678篇 |
2015年 | 609篇 |
2014年 | 1130篇 |
2013年 | 2109篇 |
2012年 | 1034篇 |
2011年 | 2348篇 |
2010年 | 2008篇 |
2009年 | 2157篇 |
2008年 | 2157篇 |
2007年 | 2199篇 |
2006年 | 1815篇 |
2005年 | 1624篇 |
2004年 | 1607篇 |
2003年 | 1361篇 |
2002年 | 1230篇 |
2001年 | 873篇 |
2000年 | 826篇 |
1999年 | 714篇 |
1998年 | 662篇 |
1997年 | 545篇 |
1996年 | 622篇 |
1995年 | 553篇 |
1994年 | 560篇 |
1993年 | 428篇 |
1992年 | 408篇 |
1991年 | 267篇 |
1990年 | 253篇 |
1989年 | 251篇 |
1988年 | 170篇 |
1987年 | 205篇 |
1986年 | 150篇 |
1985年 | 225篇 |
1984年 | 165篇 |
1983年 | 83篇 |
1982年 | 132篇 |
1981年 | 166篇 |
1980年 | 159篇 |
1979年 | 130篇 |
1978年 | 161篇 |
1977年 | 144篇 |
1976年 | 128篇 |
1974年 | 57篇 |
1973年 | 50篇 |
排序方式: 共有10000条查询结果,搜索用时 909 毫秒
61.
Kazem Ghanbari 《Positivity》2006,10(4):721-729
We denote the spectrum of an square matrix A by σ(A), and that of the matrix obtained by deleting the first i rows and columns of A by σi(A). It is known that a symmetric pentadiagonal oscillatory (SPO) matrix may be constructed from σ, σ1 and σ2. The pairs σ, σ1 and σ1, σ2 must interlace; the construction is not unique; and the conditions on the data which ensure that A is oscillatory are extremely complicated. Given one SPO matrix A, the paper shows that operations may be applied to A to construct a family of such matrices with σ and σ1 in common. Moreover, given one totally positive (TP) matrix A, we construct a family of TP matrices with σ, σ1 and σ2 in common. 相似文献
62.
一阶形式系统K~*及其完备性 总被引:2,自引:0,他引:2
裴道武 《数学年刊A辑(中文版)》2002,(6)
模糊命题演算的形式系统L*已经在模糊逻辑与模糊推理的结合研究中得到了成功的应用.本文考虑与系统L*相应的一阶逻辑理论,建立了一阶形式系统K*,并证明了这个系统的完备性. 相似文献
63.
非线性编辑系统中常见的外部数字接口 总被引:4,自引:2,他引:2
非线性编辑系统的接口包括计算机内部接口和外部接口。在外部接口中,数字接口由于其自身的特点和优势被用得越来越多。非线性系统的外部数字接口一般包括数字视音频接口和遥控接口,下面对常用的SDI,IEEE1394,SDTI,AES/EBU,RS232C,RS422A等接口进行择要介绍,并对一些接口的特点作了分析和比较。 相似文献
64.
Fillmore在[1]中得到一个定理:设A,T是Banach空间X上的线性变换,A有界,若Lat(A) Lat(T)且AT=TA,则T是A的多项式.在本文里,以此作为引理,讨论了Banach空间上可逆线性变换A在什么情况下,A-1可表示为A的多项式.本文最主要的结论是定理3.4:设X是Banach空间,A是X上的有界线性变换,且可逆,则A-1是A的多项式当且仅当A-1是A的局部多项式. 相似文献
65.
Relying on reliability growth testing to improve system designis neither usually effective nor efficient. Instead it is importantto design in reliability. This requires models to estimate reliabilitygrowth in the design that can be used to assess whether goalreliability will be achieved within the target timescale forthe design process. Many models have been developed for analysisof reliability growth on test, but there has been much lessattention given to reliability growth in design. This paperdescribes and compares two models: one motivated by the practicalengineering process; the other by extending the reasoning ofstatistical reliability growth modelling. Both models are referencedin the recently revised edition of international standard IEC61164. However, there has been no reported evaluation of theirproperties. Therefore, this paper explores the commonalitiesand differences between these models through an assessment oftheir logic and their application to an industrial example.Recommendations are given for the use of reliability growthmodels to aid management of the design process and to informproduct development. 相似文献
66.
Kunyu Guo 《Journal of Functional Analysis》2004,213(2):380-411
This paper mainly concerns defect operators and defect functions of Hardy submodules, Bergman submodules over the unit ball, and Hardy submodules over the polydisk. The defect operator (function) carries key information about operator theory (function theory) and structure of analytic submodules. The problem when a submodule has finite defect is attacked for both Hardy submodules and Bergman submodules. Our interest will be in submodules generated by polynomials. The reason for choosing such submodules is to understand the interaction of operator theory, function theory and algebraic geometry. 相似文献
67.
We show that there are close relations between extremal problems in dual Brunn-Minkowski theory and isotropic-type properties for some Borel measures on the sphere. The methods we use allow us to obtain similar results in the context of Firey-Brunn-Minkowski theory. We also study reverse inequalities for dual mixed volumes which are related with classical positions, such as ?-position or isotropic position. 相似文献
68.
We extend the matrix version of Cochran's statistical theorem to outer inverses of a matrix. As applications, we investigate the Wishartness and independence of matrix quadratic forms for Kronecker product covariance structures. 相似文献
69.
L. Brian Lawrence 《Transactions of the American Mathematical Society》2005,357(7):2535-2556
Working in ZFC, we give an example as indicated in the title.
70.
An attempt is made to present a simple theoretical analysis of the energy-wave vector dispersion relation of the conduction electrons in heavily doped non-parabolic semiconductors forming band tails. We observe that the complex energy spectrum in doped small-gap materials whose unperturbed conduction band is described by the three band model of Kane is due to the interaction of the impurity atoms in the tail with the spin-orbit splitting constant of the valence band (Δ), For band-gap (Eg)<Δ the imaginary part predominates which tails in to the conduction band. For the opposite inequality the real part comes in to play which tails in to the split-off band. In the absence of the band tailing effect, the imaginary part of the complex energy spectrum vanishes and the same is also true for doped two-band Kane-type and parabolic energy bands respectively. The present formulation helps us in investigating the Boltzmann transport equation dependent transport properties of degenerate semiconductors and are expected to agree better with experiments. The well-known results of unperturbed three and two band models of Kane together with wide-gap parabolic energy bands have been obtained as special cases of our generalized analysis under certain limiting conditions. 相似文献