全文获取类型
收费全文 | 17899篇 |
免费 | 1977篇 |
国内免费 | 1966篇 |
专业分类
化学 | 5528篇 |
晶体学 | 446篇 |
力学 | 720篇 |
综合类 | 82篇 |
数学 | 9534篇 |
物理学 | 5532篇 |
出版年
2023年 | 63篇 |
2022年 | 209篇 |
2021年 | 234篇 |
2020年 | 243篇 |
2019年 | 469篇 |
2018年 | 488篇 |
2017年 | 468篇 |
2016年 | 497篇 |
2015年 | 431篇 |
2014年 | 647篇 |
2013年 | 1254篇 |
2012年 | 879篇 |
2011年 | 1273篇 |
2010年 | 1086篇 |
2009年 | 1360篇 |
2008年 | 1405篇 |
2007年 | 1461篇 |
2006年 | 1265篇 |
2005年 | 923篇 |
2004年 | 849篇 |
2003年 | 676篇 |
2002年 | 599篇 |
2001年 | 475篇 |
2000年 | 475篇 |
1999年 | 483篇 |
1998年 | 433篇 |
1997年 | 357篇 |
1996年 | 413篇 |
1995年 | 366篇 |
1994年 | 326篇 |
1993年 | 255篇 |
1992年 | 210篇 |
1991年 | 158篇 |
1990年 | 144篇 |
1989年 | 117篇 |
1988年 | 87篇 |
1987年 | 82篇 |
1986年 | 73篇 |
1985年 | 97篇 |
1984年 | 66篇 |
1983年 | 57篇 |
1982年 | 70篇 |
1981年 | 64篇 |
1980年 | 54篇 |
1979年 | 43篇 |
1978年 | 46篇 |
1977年 | 36篇 |
1976年 | 39篇 |
1975年 | 12篇 |
1974年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
12.
This paper deals with the Cauchy–Dirichlet problem for the fractional Cahn–Hilliard equation. The main results consist of global (in time) existence of weak solutions, characterization of parabolic smoothing effects (implying under proper condition eventual boundedness of trajectories), and convergence of each solution to a (single) equilibrium. In particular, to prove the convergence result, a variant of the so-called ?ojasiewicz–Simon inequality is provided for the fractional Dirichlet Laplacian and (possibly) non-analytic (but ) nonlinearities. 相似文献
13.
采用DIS数字信息化系统,对不同浓度的蓝墨水溶液在激光光源照射下的透射平均照度及照度分布图像进行实验研究,得到了平均照度值随溶液浓度变化的规律。对不同颜色塑料膜片对白炽灯光源透过照度值及照度分布图像进行实验研究得到及其相关之规律。 相似文献
14.
Transparent conducting ZnO:AI thin films with good adhesion and Iow resistivity have been prepared on organic substrates and Coming 7059 glass substrates by r.f. magnetron-sputtering technique at Iow substrate temperature (25-210℃). Structural and photoelectric properties of the deposited films are investigated. The deposited films are polycrystalline with hexagonal structure and a preferred orientation with the c-axis perpendicular to the substrate. Only the (002) peak is observed.High quality films with resistivity as Iow as 1.0 x 10- 3Ω@ cm and 8.4 x 10- 4Ω@ cm, the average transmittance over 74% and 85% in the wavelength range of the visible spectrum have been obtained on different substrates. 相似文献
15.
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
16.
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
17.
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
18.
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
19.
20.