全文获取类型
收费全文 | 25816篇 |
免费 | 1060篇 |
国内免费 | 472篇 |
专业分类
化学 | 5869篇 |
晶体学 | 296篇 |
力学 | 635篇 |
综合类 | 51篇 |
数学 | 9514篇 |
物理学 | 8348篇 |
无线电 | 2635篇 |
出版年
2023年 | 134篇 |
2022年 | 182篇 |
2021年 | 136篇 |
2020年 | 182篇 |
2019年 | 514篇 |
2018年 | 329篇 |
2017年 | 368篇 |
2016年 | 248篇 |
2015年 | 249篇 |
2014年 | 316篇 |
2013年 | 1148篇 |
2012年 | 621篇 |
2011年 | 1087篇 |
2010年 | 603篇 |
2009年 | 946篇 |
2008年 | 1095篇 |
2007年 | 1056篇 |
2006年 | 1059篇 |
2005年 | 733篇 |
2004年 | 1124篇 |
2003年 | 1381篇 |
2002年 | 1875篇 |
2001年 | 1886篇 |
2000年 | 1697篇 |
1999年 | 1893篇 |
1998年 | 1609篇 |
1997年 | 1010篇 |
1996年 | 614篇 |
1995年 | 279篇 |
1994年 | 234篇 |
1993年 | 121篇 |
1992年 | 117篇 |
1991年 | 104篇 |
1990年 | 175篇 |
1989年 | 152篇 |
1988年 | 105篇 |
1987年 | 82篇 |
1986年 | 126篇 |
1985年 | 189篇 |
1984年 | 177篇 |
1983年 | 76篇 |
1982年 | 137篇 |
1981年 | 238篇 |
1980年 | 230篇 |
1979年 | 109篇 |
1978年 | 168篇 |
1977年 | 103篇 |
1976年 | 71篇 |
1975年 | 82篇 |
1974年 | 75篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
91.
Fabio A. C. C. Chalub Peter A. Markowich Benoît Perthame Christian Schmeiser 《Monatshefte für Mathematik》2004,142(1-2):123-141
Kinetic models for chemotaxis, nonlinearly coupled to a Poisson equation for the chemo-attractant density, are considered. Under suitable assumptions on the turning kernel (including models introduced by Othmer, Dunbar and Alt), convergence in the macroscopic limit to a drift-diffusion model is proven. The drift-diffusion models derived in this way include the classical Keller-Segel model. Furthermore, sufficient conditions for kinetic models are given such that finite-time-blow-up does not occur. Examples are given satisfying these conditions, whereas the macroscopic limit problem is known to exhibit finite-time-blow-up. The main analytical tools are entropy techniques for the macroscopic limit as well as results from potential theory for the control of the chemo-attractant density.Present address: Centro de Matemática e Aplicações Fundamentais, Universidade de Lisboa, Av. Prof. Gama Pinto 2, 1649-003, Lisboa, Portugal 相似文献
92.
Zhaoyang Yin 《Monatshefte für Mathematik》2004,141(4):337-344
We prove under quite general assumptions the existence of a bounded positive solution to the semilinear Schrödinger equation in a two-dimensional exterior domain. 相似文献
93.
We prove the existence of solutions to nonlinear free boundary problem with singularities at given points. 相似文献
94.
C. Sparber J. A. Carrillo J. Dolbeault P. A. Markowich 《Monatshefte für Mathematik》2004,141(3):237-257
We analyze the long-time behavior of transport equations for a class of dissipative quantum systems with Fokker-planck type diffusion operator, subject to confining potentials of harmonic oscillator type. We establish the existence and uniqueness of a non-equilibrium steady state for the corresponding dynamics. Further, using a (classical) convex Sobolev inequality, we prove an optimal exponential rate of decay towards this state and additionally give precise dispersion estimates in those cases, where no stationary state exists. 相似文献
95.
On a Definitizable Analog of the Trigonometric Moment Problem Generating an Indefinite Toeplitz Form
We prove the existence of an integro-polynomial representation for a sequence of numbers such that there exists a difference operator mapping this sequence to a sequence that generates the solvable trigonometric moment problem. A similar result related to the power moment problem was given in [12]. 相似文献
96.
Walter Benz 《Monatshefte für Mathematik》2004,141(1):1-10
The lines of euclidean and hyperbolic geometries are characterized as metric lines in the sense of Blumenthal–Menger, and the lines of spherical and elliptic geometry as periodic ones. In euclidean geometries there do not exist periodic lines. 相似文献
97.
Phenomena accompanying electrochemical doping of solid fullerene films with potassium were studied by sputter ion depth profiling
(XPS and SIMS). The potassium distribution was determined, and artifacts associated with possible damage of the layer composition
caused by ion impact were investigated and discussed. To compare the charge transfer while reductive doping is taking place
at fullerene/solution interface with doping from gas phase, model layers were prepared and doped by potassium under UHV conditions.
It was found that sputtering by Ar+ primary ions yields both accurate information on the alkaline metal distribution and on its concentration. Sputtering by
O+ ions led to an enrichment of potassium, apparently due to the reactivity of oxygen with the fullerene matrix. It is shown
that the reductive doping starts at the fullerene/solution interface. The concentration of potassium in the doped films was
found to be lower than expected from the charge transferred during the electrochemical reduction. Other phase transformations
such as hydrogenation are discussed.
Received March 4, 2002; accepted July 26, 2002 相似文献
98.
We will prove a result concerning the inclusion of non-trivial invariant ideals inside non-trivial ideals of a twisted crossed
product. We will also give results concerning the primeness and simplicity of crossed products of twisted actions of locally
compact groups on -algebras.
Received: 25 January 2002; in final form: 22 May 2002/Published online: 2 December 2002
This work is partially supported by Hong Kong RGC Direct Grant. 相似文献
99.
The form of the probability density derived from the evolution in time of a previously truncated frequency distribution of animal Liveweights is of interest in animal husbandry. Truncated frequency distributions arise when the heavier animals are sold for slaughter and the lighter animals retained. The demands of modern quality assurance schemes require that, given information on animal growth, the farmer is able to estimate the number of animals that would meet the specifications at some time in the future after truncation. Assuming that animal growth can be described by a linear stochastic differential equation, we derive an explicit expression for the probability density of animal Liveweights at any time after the truncation of an initial Gaussian density. It is shown that this probability density converges rapidly to a Gaussian density, so that after about 20 days of typical growth rates for lambs, the resulting density is practically indistinguishable from Gaussian. 相似文献
100.
报道了一种用国产激光二极管泵浦的1064nm单频NdYVO4红外激光器的设计.利用布氏片和石英晶体组合构成的双折射滤光片技术,在泵浦功率为800mW时,实现了功率为360mW的1064nm红外单频输出.测量结果表明,偏振比超过了10001,功率稳定性优于0.5%,振幅噪声小于0.1%. 相似文献