全文获取类型
收费全文 | 22520篇 |
免费 | 1047篇 |
国内免费 | 1317篇 |
专业分类
化学 | 10608篇 |
晶体学 | 203篇 |
力学 | 147篇 |
综合类 | 65篇 |
数学 | 7969篇 |
物理学 | 2758篇 |
无线电 | 3134篇 |
出版年
2024年 | 20篇 |
2023年 | 142篇 |
2022年 | 258篇 |
2021年 | 311篇 |
2020年 | 329篇 |
2019年 | 748篇 |
2018年 | 466篇 |
2017年 | 659篇 |
2016年 | 475篇 |
2015年 | 582篇 |
2014年 | 800篇 |
2013年 | 1277篇 |
2012年 | 1087篇 |
2011年 | 1413篇 |
2010年 | 1098篇 |
2009年 | 1478篇 |
2008年 | 1515篇 |
2007年 | 1506篇 |
2006年 | 1305篇 |
2005年 | 1015篇 |
2004年 | 956篇 |
2003年 | 858篇 |
2002年 | 787篇 |
2001年 | 581篇 |
2000年 | 498篇 |
1999年 | 486篇 |
1998年 | 465篇 |
1997年 | 416篇 |
1996年 | 390篇 |
1995年 | 426篇 |
1994年 | 355篇 |
1993年 | 327篇 |
1992年 | 299篇 |
1991年 | 176篇 |
1990年 | 165篇 |
1989年 | 168篇 |
1988年 | 118篇 |
1987年 | 98篇 |
1986年 | 81篇 |
1985年 | 105篇 |
1984年 | 105篇 |
1983年 | 63篇 |
1982年 | 85篇 |
1981年 | 70篇 |
1980年 | 68篇 |
1979年 | 65篇 |
1978年 | 67篇 |
1977年 | 35篇 |
1976年 | 38篇 |
1974年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 328 毫秒
11.
12.
We investigate congruence classes and direct congruence classes of m-tuples in the complex projective space ℂP
n
. For direct congruence one allows only isometries which are induced by linear (instead of semilinear) mappings. We establish
a canonical bijection between the set of direct congruence classes of m-tuples of points in ℂP
n
and the set of equivalence classes of positive semidefinite Hermitean m×m-matrices of rank at most n+1 with 1's on the diagonal. As a corollary we get that the direct congruence class of an m-tuple is uniquely determined by the direct congruence classes of all of its triangles, provided that no pair of points of
the m-tuple has distance π/2. Examples show that the situation changes drastically if one replaces direct congruence classes by
congruence classes or if distances π/2 are allowed. Finally we do the same
kind of investigation also for the complex hyperbolic space ℂH
n
. Most of the results are completely analogous, however, there are also some interesting differences.
Received: 15 January 1996 相似文献
13.
Summary. Let be a square matrix dependent on parameters and , of which we choose as the eigenvalue parameter. Many computational problems are equivalent to finding a point such that has a multiple eigenvalue at . An incomplete decomposition of a matrix dependent on several parameters is proposed. Based on the developed theory two new algorithms are
presented for computing multiple eigenvalues of with geometric multiplicity . A third algorithm is designed for the computation of multiple eigenvalues with geometric multiplicity but which also appears to have local quadratic convergence to semi-simple eigenvalues. Convergence analyses of these methods
are given. Several numerical examples are presented which illustrate the behaviour and applications of our methods.
Received December 19, 1994 / Revised version received January 18, 1996 相似文献
14.
15.
Double Michael additions of lithium enolaie of 1,4-dioxaspiro[4.5]dec-6-en-8-one to four acrylates afforded bicyclo[2.2.2]octan-2-ones with high regio- and stereoselectivities in moderate yields. 相似文献
16.
In this paper, the influence functions and limiting distributions of the canonical correlations and coefficients based on affine equivariant scatter matrices are developed for elliptically symmetric distributions. General formulas for limiting variances and covariances of the canonical correlations and canonical vectors based on scatter matrices are obtained. Also the use of the so-called shape matrices in canonical analysis is investigated. The scatter and shape matrices based on the affine equivariant Sign Covariance Matrix as well as the Tyler's shape matrix serve as examples. Their finite sample and limiting efficiencies are compared to those of the Minimum Covariance Determinant estimators and S-estimator through theoretical and simulation studies. The theory is illustrated by an example. 相似文献
17.
18.
Let T and S be invertible measure preserving transformations of a probability measure space (X, ℬ, μ). We prove that if the group generated by T and S is nilpotent, then exists in L
2-norm for any u, v∈L
∞(X, ℬ, μ). We also show that for A∈ℬ with μ(A)>0 one has . By the way of contrast, we bring examples showing that if measure preserving transformations T, S generate a solvable group, then (i) the above limits do not have to exist; (ii) the double recurrence property fails, that
is, for some A∈ℬ, μ(A)>0, one may have μ(A∩T
-n
A∩S
-
n
A)=0 for all n∈ℕ. Finally, we show that when T and S generate a nilpotent group of class ≤c, in L
2(X) for all u, v∈L
∞(X) if and only if T×S is ergodic on X×X and the group generated by T
-1
S, T
-2
S
2,..., T
-c
S
c
acts ergodically on X.
Oblatum 19-V-2000 & 5-VII-2001?Published online: 12 October 2001 相似文献
19.
Balázs Szendröi 《Mathematische Zeitschrift》2002,240(2):233-241
This note shows that a certain toric quotient of the quintic Calabi-Yau threefold in provides a counterexample to a recent conjecture of Cox and Katz concerning nef cones of toric hypersurfaces.
Received: 8 February 2001; in final form: 17 September 2001 / Published online: 1 February 2002 相似文献
20.
Summary In 1980 Dahmen-DeVore-Scherer introduced a modulus of continuity which turns out to reflect invariance properties of compound cubature rules effectively. Accordingly, sharp error bounds are derived, the existence of relevant counterexamples being a consequence of a quantitative resonance principle, established previously. 相似文献