全文获取类型
收费全文 | 13599篇 |
免费 | 1722篇 |
国内免费 | 842篇 |
专业分类
化学 | 2122篇 |
晶体学 | 27篇 |
力学 | 830篇 |
综合类 | 239篇 |
数学 | 6428篇 |
物理学 | 2754篇 |
无线电 | 3763篇 |
出版年
2024年 | 43篇 |
2023年 | 174篇 |
2022年 | 242篇 |
2021年 | 341篇 |
2020年 | 387篇 |
2019年 | 384篇 |
2018年 | 405篇 |
2017年 | 506篇 |
2016年 | 613篇 |
2015年 | 467篇 |
2014年 | 786篇 |
2013年 | 1137篇 |
2012年 | 748篇 |
2011年 | 856篇 |
2010年 | 755篇 |
2009年 | 798篇 |
2008年 | 825篇 |
2007年 | 871篇 |
2006年 | 735篇 |
2005年 | 663篇 |
2004年 | 565篇 |
2003年 | 551篇 |
2002年 | 499篇 |
2001年 | 407篇 |
2000年 | 380篇 |
1999年 | 316篇 |
1998年 | 275篇 |
1997年 | 220篇 |
1996年 | 205篇 |
1995年 | 173篇 |
1994年 | 123篇 |
1993年 | 117篇 |
1992年 | 103篇 |
1991年 | 93篇 |
1990年 | 52篇 |
1989年 | 54篇 |
1988年 | 40篇 |
1987年 | 25篇 |
1986年 | 32篇 |
1985年 | 31篇 |
1984年 | 28篇 |
1983年 | 15篇 |
1982年 | 17篇 |
1981年 | 20篇 |
1980年 | 15篇 |
1979年 | 19篇 |
1978年 | 12篇 |
1977年 | 14篇 |
1976年 | 7篇 |
1973年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 11 毫秒
111.
Antonio J. Durn 《Journal of Approximation Theory》2009,161(1):88-113
The method developed in [A.J. Durán, F.A. Grünbaum, Orthogonal matrix polynomials satisfying second order differential equations, Int. Math. Res. Not. 10 (2004) 461–484] led us to consider matrix polynomials that are orthogonal with respect to weight matrices W(t) of the form , , and (1−t)α(1+t)βT(t)T*(t), with T satisfying T′=(2Bt+A)T, T(0)=I, T′=(A+B/t)T, T(1)=I, and T′(t)=(−A/(1−t)+B/(1+t))T, T(0)=I, respectively. Here A and B are in general two non-commuting matrices. We are interested in sequences of orthogonal polynomials (Pn)n which also satisfy a second order differential equation with differential coefficients that are matrix polynomials F2, F1 and F0 (independent of n) of degrees not bigger than 2, 1 and 0 respectively. To proceed further and find situations where these second order differential equations hold, we only dealt with the case when one of the matrices A or B vanishes.The purpose of this paper is to show a method which allows us to deal with the case when A, B and F0 are simultaneously triangularizable (but without making any commutativity assumption). 相似文献
112.
David S. Lyubshin 《Discrete Mathematics》2009,309(13):4343-4348
In this paper we give a criterion for the adjacency matrix of a Cayley digraph to be normal in terms of the Cayley subset S. It is shown with the use of this result that the adjacency matrix of every Cayley digraph on a finite group G is normal iff G is either abelian or has the form for some non-negative integer n, where Q8 is the quaternion group and is the abelian group of order 2n and exponent 2. 相似文献
113.
矩阵方程AX=B的双反对称最佳逼近解 总被引:1,自引:0,他引:1
本文主要讨论下而两个问题并得到相关结果:问题Ⅰ:给定A ∈ R~(k×n),B ∈ R~(k×n),求X ∈ BASR~(n×n),使得AX=B.问题Ⅱ:给定X* ∈R~(n×n),求X使得‖X-X~*‖=minX∈S_E‖X-X~*‖,其中S_E是问题Ⅰ的解集合,‖·‖是Frobenius范数.通过对上述问题的讨论给出了问题Ⅰ解存在的充分必要条件和其解的一般表达式同时给出了问题Ⅱ的解,算法,和数值例子. 相似文献
114.
Let e and n be positive integers and S={x1,…,xn} a set of n distinct positive integers. For x∈S, define . The n×n matrix whose (i,j)-entry is the eth power (xi,xj)e of the greatest common divisor of xi and xj is called the eth power GCD matrix on S, denoted by (Se). Similarly we can define the eth power LCM matrix [Se]. Bourque and Ligh showed that (S)∣[S] holds in the ring of n×n matrices over the integers if S is factor closed. Hong showed that for any gcd-closed set S with |S|≤3, (S)∣[S]. Meanwhile Hong proved that there is a gcd-closed set S with maxx∈S{|GS(x)|}=2 such that (S)?[S]. In this paper, we introduce a new method to study systematically the divisibility for the case maxx∈S{|GS(x)|}≤2. We give a new proof of Hong’s conjecture and obtain necessary and sufficient conditions on the gcd-closed set S with maxx∈S{|GS(x)|}=2 such that (Se)|[Se]. This partially solves an open question raised by Hong. Furthermore, we show that such factorization holds if S is a gcd-closed set such that each element is a prime power or the product of two distinct primes, and in particular if S is a gcd-closed set with every element less than 12. 相似文献
115.
116.
Rasmus Havelund Martin P. Seah Ian S. Gilmore 《Surface and interface analysis : SIA》2019,51(13):1332-1341
Four simple methods are evaluated to determine their accuracies for establishing the interface location in secondary ion mass spectrometry intensity depth profiles of organic layers where matrix effects have not been measured. Accurate location requires the separate measurement of each ion's matrix factor. This is often not possible, and so estimates using matrix-less methods are required. Six pure organic material interfaces are measured using many secondary ions to compare their locations from the four methods with those from full evaluation with matrix terms. For different secondary ions, matrix effects cause the apparent interface positions to vary over 20 nm. The shifts in the intensity profiles on going from a layer of P into a layer of Q are in the opposite direction to that for going from Q into P, so doubling layer thickness errors. The four methods are as follows: M1, use of the median interface position in the intensity profiles for the five lightest ions for 15 ≤ m/z ≤ 150; M2, extrapolation of the position for each ion to m/z = 0 for ions with m/z ≤ 150; M3, as M2 but for m/z ≤ 300; and M4, the extreme positions for all m/z ≤ 100. Comparison with the location using matrix terms shows their ranking, from best to worst, to be M4, M3, M1, and M2 with average errors of 10%, 12%, 14%, and 17%, respectively, of the profile interface full widths at half maximum. Use of pseudo-molecular ions is very much poorer, exceeding 50%, and should be avoided. 相似文献
117.
本文用矩阵光学的方法研究了内含柱面透镜的象散腔,给出了其稳定图,此图清楚地显示出由于象散作而使用腔稳定工作区域大大缩小,本文还给了显示象散特征的稳定脸膜参数计算公式,并作了数值计算。 相似文献
118.
周后卿 《浙江大学学报(理学版)》2018,45(1):10
对近年来图的Laplacian谱半径上界的研究成果进行了简单梳理.利用2个图的卡氏积图的特征值,讨论了2个循环图的卡氏积图的Laplacian谱半径的上界问题,得到了几个上界,推广了已有文献的结论. 相似文献
119.
通信数据包含人类活动的时空以及社会关系等信息,对人类行为分析有重要的价值.为了帮助分析者对用户的行为进行分析和理解,构建了从通信数据中探索用户的时空、社交等信息以分析用户行为的可视化流程,旨在理解用户的行为模式并通过行为的对比发现用户的社会角色以及用户之间的真实社交关系,通过迭代式交互过程,对用户不同时段的行为进行有效的理解和分析.在此基础上,构建了用户行为可视分析系统,采用半年的通信数据对该方法以及系统进行评估,结果显示,本方法能够有效理解个人行为、识别用户之间的关系. 相似文献
120.
常莉红 《浙江大学学报(理学版)》2018,45(4):416
一幅图像可以分解成几何特征不同的纹理部分和卡通部分,基于这两大特征提出了一种图像融合方法.利用卡通和纹理特征的差异,通过学习分别得到卡通字典和纹理字典.在融合过程中,分别利用特定的卡通和纹理字典对源图像的卡通和纹理部分进行融合,融合后的卡通和纹理部分经简单相加得到融合图像.实验结果表明,所提方法是有效的. 相似文献