全文获取类型
收费全文 | 24637篇 |
免费 | 1516篇 |
国内免费 | 854篇 |
专业分类
化学 | 18233篇 |
晶体学 | 202篇 |
力学 | 547篇 |
综合类 | 66篇 |
数学 | 3725篇 |
物理学 | 4234篇 |
出版年
2023年 | 227篇 |
2022年 | 326篇 |
2021年 | 439篇 |
2020年 | 540篇 |
2019年 | 531篇 |
2018年 | 479篇 |
2017年 | 471篇 |
2016年 | 958篇 |
2015年 | 884篇 |
2014年 | 985篇 |
2013年 | 1647篇 |
2012年 | 1995篇 |
2011年 | 2162篇 |
2010年 | 1334篇 |
2009年 | 1090篇 |
2008年 | 1801篇 |
2007年 | 1756篇 |
2006年 | 1568篇 |
2005年 | 1428篇 |
2004年 | 1201篇 |
2003年 | 888篇 |
2002年 | 781篇 |
2001年 | 332篇 |
2000年 | 314篇 |
1999年 | 239篇 |
1998年 | 158篇 |
1997年 | 170篇 |
1996年 | 198篇 |
1995年 | 144篇 |
1994年 | 112篇 |
1993年 | 133篇 |
1992年 | 117篇 |
1991年 | 89篇 |
1990年 | 91篇 |
1989年 | 70篇 |
1988年 | 69篇 |
1987年 | 68篇 |
1986年 | 83篇 |
1985年 | 118篇 |
1984年 | 97篇 |
1983年 | 57篇 |
1982年 | 81篇 |
1981年 | 75篇 |
1980年 | 87篇 |
1979年 | 65篇 |
1978年 | 64篇 |
1977年 | 47篇 |
1976年 | 53篇 |
1975年 | 37篇 |
1974年 | 39篇 |
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
51.
We present a general risk model where the aggregate claims, as well as the premium function, evolve by jumps. This is achieved by incorporating a Lévy process into the model. This seeks to account for the discrete nature of claims and asset prices. We give several explicit examples of Lévy processes that can be used to drive a risk model. This allows us to incorporate aggregate claims and premium fluctuations in the same process. We discuss important features of such processes and their relevance to risk modeling. We also extend classical results on ruin probabilities to this model. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
52.
Juan A. Barceló Jonathan Bennett Alberto Ruiz 《Journal of Fourier Analysis and Applications》2003,9(6):541-562
We study the continuity properties of a projection derived from a recent characterization of Herglotz Wave Functions in the plane. Herglotz Wave Functions are the entire solutions of the Helmholtz equation which have L2-Far-Field-Pattern. The behavior of this projection is reminiscent of the Disc Multiplier Operator on both Lp and mixed Lp-normed spaces. In particular a Kakeya type set plays a central role in our analysis. As a consequence we answer a question posed by Alvarez, Folch-Gabayet and Pérez-Esteva. 相似文献
53.
Toluene adsorption reactions on the (1 1 0) surface of VSbO4 have been analyzed following the changes in the electronic structure of the hydrocarbon molecule and metal cation sites of the oxide using the Just Another Extended Hückel Molecular Orbital Program (JAEHMOP) code. The bonding character of these interactions has also been studied in the same theoretical framework. The calculations indicate that the exothermic hydrocarbon parallel interaction on Sb-V sites results in the weakening of one of the C-H bonds of the methyl fragment. This leads to a H-abstraction that involves the participation of a Sb-cation. Both methyl and phenyl fragments decrease their electronic population and so does the V-cation site. Most of these electrons are transferred to other V atoms in the bulk solid. As a result the LUMO of the toluene-oxide system fully populates. The analysis reveals that methyl-Sb bonding interactions mainly involve C2px and H1s orbitals with Sb5s orbital, while non-bonding phenyl-V interactions involve C2px orbitals with V3dx2−y2 orbital. This last interaction facilitates the desorption of the benzyl species after H-abstraction. 相似文献
54.
José A. Anquela Teresa Cortés Miguel Gómez-Lozano Mercedes Siles-Molina 《Acta Mathematica Hungarica》2004,103(3):177-196
We investigate the basic properties of the different socles that can be considered in not necessarily semiprime associative
systems. Among other things, we show that the socle defined as the sum of minimal (or minimal and trivial) inner ideals is
always an ideal. When trivial inner ideals are included, this inner socle contains the socles defined in terms of minimal
left or right ideals.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
55.
The determination of the enantiomeric purity of 2 or 3-substituted cyclanones, particularly cyclohexanones, is conveniently achieved by derivatisation into cyclic aminals with commercially available (R, R)-1,2-diphenylethylenediamine. The derivatisation procedure is directly done into the NMR tube, instantaneously, and 13C NMR allows an accurate measure of the ee. 相似文献
56.
Hyperfine Interactions - A “coherent-path” model for nuclear-resonant scattering of gamma radiation from resonant matter has been developed and is summarized here. The solution provides... 相似文献
57.
Simple expressions are given for the mean delay, mean waiting time, and mean busy period length in a multiplexer. Data streams with active periods having a general distribution are permitted, and the data rate during the active periods can be random. Data can also arrive in batches. The key restrictions of the model are that the sources are independent, idle periods are exponentially distributed, and a source generates at least enough data during an active period to keep the server busy throughout the period. The exact formulas allow evaluation of the error in approximations such as a heavy traffic diffusion approximation.Both continuous and discrete time models are considered. The discrete-time model includes that studied by Viterbi and subsequently generalized by Neuts. The Pollaczek-Khinchine formula for the mean amount of work in anM/GI/1 queue is retrieved as a limiting case.Preliminary version presented at IEEE INFOCOM, San Francisco, April 1993. 相似文献
58.
Summary We consider a one-dimensional linear wave equation with a small mean zero dissipative field and with the boundary condition imposed by the so-called Goursat problem. In order to observe the effect of the randomness on the solution we perform a space-time rescaling and we rewrite the problem in a diffusion approximation form for two parameter processes. We prove that the solution converges in distribution toward the solution of a two-parameter stochastic differential equation which we identify. The diffusion approximation results for oneparameter processes are well known and well understood. In fact, the solution of the one-parameter analog of the problem we consider here is immediate. Unfortunately, the situation is much more complicated for two-parameter processes and we believe that our result is the first one of its kind.Partially supported by ONR N00014-91-J-1010 相似文献
59.
60.
We give several equivalent characterisations of left (and hence, by duality, also of right) supported algebras. These characterisations are in terms of properties of the left and the right parts of the module category, or in terms of the classes L0 and R0 which consist respectively of the predecessors of the projective modules, and of the successors of the injective modules. 相似文献