全文获取类型
收费全文 | 4622篇 |
免费 | 621篇 |
国内免费 | 944篇 |
专业分类
化学 | 3803篇 |
晶体学 | 11篇 |
力学 | 233篇 |
综合类 | 62篇 |
数学 | 1586篇 |
物理学 | 492篇 |
出版年
2024年 | 11篇 |
2023年 | 61篇 |
2022年 | 98篇 |
2021年 | 137篇 |
2020年 | 203篇 |
2019年 | 180篇 |
2018年 | 159篇 |
2017年 | 155篇 |
2016年 | 205篇 |
2015年 | 189篇 |
2014年 | 261篇 |
2013年 | 425篇 |
2012年 | 258篇 |
2011年 | 291篇 |
2010年 | 213篇 |
2009年 | 264篇 |
2008年 | 299篇 |
2007年 | 284篇 |
2006年 | 302篇 |
2005年 | 266篇 |
2004年 | 216篇 |
2003年 | 212篇 |
2002年 | 255篇 |
2001年 | 176篇 |
2000年 | 159篇 |
1999年 | 149篇 |
1998年 | 121篇 |
1997年 | 118篇 |
1996年 | 98篇 |
1995年 | 76篇 |
1994年 | 52篇 |
1993年 | 41篇 |
1992年 | 39篇 |
1991年 | 27篇 |
1990年 | 19篇 |
1989年 | 13篇 |
1988年 | 23篇 |
1987年 | 8篇 |
1986年 | 8篇 |
1985年 | 24篇 |
1984年 | 24篇 |
1983年 | 9篇 |
1982年 | 12篇 |
1981年 | 14篇 |
1980年 | 7篇 |
1979年 | 6篇 |
1978年 | 4篇 |
1977年 | 7篇 |
1976年 | 3篇 |
1957年 | 1篇 |
排序方式: 共有6187条查询结果,搜索用时 15 毫秒
11.
双金属催化剂是一类重要的多相催化剂。其中d电子在催化活性方面起着重要的作用.本文在Co_3[Fe(CN)_6]_2的工作基础上,进一步研究了该配合物在硅胶、氧化铝、以及氧化镁上的热性质,同时考察了CN~-在Co-Fe体系双端基配位的活化加氢,探讨了载体的影响. 相似文献
12.
Aromatic nitro compounds were reduced to the corresponding symmetrically substituted azo compounds using lead as catalyst and triethylammonium formate as hydrogen donor. Various azo compounds containing additional reducible substituents including halogens, nitrile, acid, phenol, ester, methoxy functions, etc, have been synthesized in a single step by the use of this reagent. The conversion is reasonably fast, clean, high yielding and occurs at room temperature in methanol. 相似文献
13.
14.
Continuous dependence on a modelling parameter is established for solutions of a problem for a complex Ginzburg–Landau equation. A homogenizing boundary condition is also used to discuss the continuous dependence results. We derive a priori estimates that indicate that solutions depend continuously on a parameter in the governing differential equation. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
15.
A complete study of the spectrum of a finite-dimensional Bose operator is carried out in the paper. The cases in which the
spectrum is discrete or continuous are studied.
Translated fromMatematicheskie Zametki, Vol. 61, No. 6, pp. 835–854, June, 1997.
Translated by A. M. Chebotarev 相似文献
16.
Daniele Cauzzi Roberto Giordano Enrico Sappa Antonio Tiripicchio Marisa Tiripicchio Camellini 《Journal of Cluster Science》1993,4(3):279-296
The title complex (complex1) was the first alkyne-substituted triruthenium dihydrido cluster to be reported and was characterized by spectroscopy as a triangular cluster with the alkyne parallel to a Ru-Ru edge. Recently, we have found that1 is a key intermediate in the homogeneous hydrogenation of diphenylacetylene catalyzed by tetrahedral Ru4 and FeRu3 clusters. Since the discovery of1, a great number of complexes with alkynes parallel to a cluster edge have been reported; at present this is the more common bonding mode for alkynes on trinuclear clusters. The structural features of1 allow a comparison with those of other ruthenium-containing derivatives and help to draw suggestions of the role of1 in hydrogenation catalysis. 相似文献
18.
L. E. Payne G. A. Philippin V. Proytcheva 《Mathematical Methods in the Applied Sciences》2007,30(15):1885-1898
In this paper, we investigate the continuous dependence on the geometry and the initial time for solutions u( x , t) of a class of nonlinear parabolic initial‐boundary value problems. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
19.
In this paper, we consider questions related to the structure of inverse matrices of linear bounded operators acting in infinite-dimensional complex Banach spaces. We obtain specific estimates of elements of inverse matrices for bounded operators whose matrices have a special structure. Matrices are introduced as special operator-valued functions on an index set. The matrix structure is described by the behavior of the given function on elements of a special partition of the index set. The method used for deriving the estimates is based on an analysis of Fourier series of strongly continuous periodic functions. 相似文献
20.
Many recent algorithmic approaches involve the construction of a differential equation model for computational purposes, typically
by introducing an artificial time variable. The actual computational model involves a discretization of the now time-dependent differential system, usually
employing forward Euler. The resulting dynamics of such an algorithm is then a discrete dynamics, and it is expected to be
“close enough” to the dynamics of the continuous system (which is typically easier to analyze) provided that small – hence
many – time steps, or iterations, are taken. Indeed, recent papers in inverse problems and image processing routinely report
results requiring thousands of iterations to converge. This makes one wonder if and how the computational modeling process
can be improved to better reflect the actual properties sought.
In this article we elaborate on several problem instances that illustrate the above observations. Algorithms may often lend
themselves to a dual interpretation, in terms of a simply discretized differential equation with artificial time and in terms
of a simple optimization algorithm; such a dual interpretation can be advantageous. We show how a broader computational modeling
approach may possibly lead to algorithms with improved efficiency.
AMS subject classification (2000) 65L05, 65M32, 65N21, 65N22, 65D18 相似文献