全文获取类型
收费全文 | 23054篇 |
免费 | 829篇 |
国内免费 | 564篇 |
专业分类
化学 | 3702篇 |
晶体学 | 133篇 |
力学 | 629篇 |
综合类 | 73篇 |
数学 | 14572篇 |
物理学 | 5338篇 |
出版年
2024年 | 21篇 |
2023年 | 173篇 |
2022年 | 192篇 |
2021年 | 273篇 |
2020年 | 439篇 |
2019年 | 614篇 |
2018年 | 590篇 |
2017年 | 458篇 |
2016年 | 432篇 |
2015年 | 443篇 |
2014年 | 826篇 |
2013年 | 1268篇 |
2012年 | 660篇 |
2011年 | 1752篇 |
2010年 | 1258篇 |
2009年 | 1557篇 |
2008年 | 1763篇 |
2007年 | 1668篇 |
2006年 | 1277篇 |
2005年 | 991篇 |
2004年 | 867篇 |
2003年 | 726篇 |
2002年 | 697篇 |
2001年 | 431篇 |
2000年 | 437篇 |
1999年 | 486篇 |
1998年 | 411篇 |
1997年 | 344篇 |
1996年 | 398篇 |
1995年 | 354篇 |
1994年 | 356篇 |
1993年 | 324篇 |
1992年 | 250篇 |
1991年 | 183篇 |
1990年 | 164篇 |
1989年 | 162篇 |
1988年 | 109篇 |
1987年 | 111篇 |
1986年 | 111篇 |
1985年 | 145篇 |
1984年 | 112篇 |
1983年 | 76篇 |
1982年 | 105篇 |
1981年 | 88篇 |
1980年 | 83篇 |
1979年 | 53篇 |
1978年 | 67篇 |
1977年 | 51篇 |
1976年 | 51篇 |
1974年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 125 毫秒
21.
Masaaki Sugihara 《Numerische Mathematik》1997,75(3):379-395
Summary. In the light of the functional analysis theory we establish the optimality of the double exponential formula. The argument
consists of the following three ingredients: (1) introduction of a number of spaces of functions analytic in a strip region
about the real axis, each space being characterized by the decay rate of their elements (functions) in the neighborhood of
the infinity; (2) proof of the (near-) optimality of the trapezoidal formula in each space introduced in (1) by showing the
(near-) equality between an upper estimate for the error norm of the trapezoidal formula and a lower estimate for the minimum
error norm of quadratures; (3) nonexistence theorem for the spaces, the characterizing decay rate of which is more rapid than
the double exponential.
Received September 15, 1995 / Accepted December 14, 1995 相似文献
22.
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
23.
24.
Summary. We generalise and apply a refinement indicator of the type originally designed by Mackenzie, Süli and Warnecke in [15] and
[16] for linear Friedrichs systems to the Euler equations of inviscid, compressible fluid flow. The Euler equations are symmetrized
by means of entropy variables and locally linearized about a constant state to obtain a symmetric hyperbolic system to which
an a posteriori error analysis of the type introduced in [15] can be applied. We discuss the details of the implementation of the refinement
indicator into the DLR--Code which is based on a finite volume method of box type on an unstructured grid and present numerical results.
Received May 15, 1995 / Revised version received April 17, 1996 相似文献
25.
Summary Consider the solution of one-dimensional linear initial-boundary value problems by a finite element method of lines using a piecewiseP
th
-degree polynomial basis. A posteriori estimates of the discretization error are obtained as the solutions of either local parabolic or local elliptic finite element problems using piecewise polynomial corrections of degreep+1 that vanish at element ends. Error estimates computed in this manner are shown to converge in energy under mesh refinement to the exact finite element discretization error. Computational results indicate that the error estimates are robust over a wide range of mesh spacings and polynomial degrees and are, furthermore, applicable in situations that are not supported by the analysis.This research was partially supported by the U.S. Air Force Office of Scientific Research, Air Force Systems Command, USAF, under Grant Number AFOSR 90-0194; by the U.S. Army Research Office under Contract Number DAAL03-91-G-0215; and by the National Science Foundation under Institutional Infrastructure Grant Number CDA-8805910 相似文献
26.
Summary We present an approximation method of a space-homogeneous transport equation which we prove is convergent. The method is very promising for numerical computation. Comparison of a numerical computation with an exact solution is given for the Master equation. 相似文献
27.
28.
Rajiv Manohar G. Tripathi A.K. Srivastava A.K. Prajapati 《Journal of Physics and Chemistry of Solids》2006,67(11):2300-2304
Dielectric properties of polymer-liquid crystal mixture, having constituent polymer, poly-butyl methacrylate (PBMA) and liquid crystal, cholesteryl nonanoate, are reported as a function of frequency and temperature. The measurement has been done in a temperature range of 300-375 K and frequency range of 100 Hz-10 MHz. The dielectric permittivity and dielectric loss shows significant changes with the addition of polymer molecules in liquid crystal. The significant feature of composite formation is that the pure liquid crystal and polymer do not show dielectric relaxation in the frequency range covered, while the composite shows relaxation peak at a particular frequency. The optical transmittance of pure liquid crystal and composite has also been measured and compared. 相似文献
29.
30.
Let A be a symmetric matrix of size n×n with entries in some (commutative) field K. We study the possibility of decomposing A into two blocks by conjugation by an orthogonal matrix T∈Matn(K). We say that A is absolutely indecomposable if it is indecomposable over every extension of the base field. If K is formally real then every symmetric matrix A diagonalizes orthogonally over the real closure of K. Assume that K is a not formally real and of level s. We prove that in Matn(K) there exist symmetric, absolutely indecomposable matrices iff n is congruent to 0, 1 or −1 modulo 2s. 相似文献