全文获取类型
收费全文 | 42320篇 |
免费 | 1080篇 |
国内免费 | 296篇 |
专业分类
化学 | 27162篇 |
晶体学 | 230篇 |
力学 | 1138篇 |
综合类 | 1篇 |
数学 | 7339篇 |
物理学 | 7826篇 |
出版年
2022年 | 236篇 |
2021年 | 382篇 |
2020年 | 505篇 |
2019年 | 422篇 |
2018年 | 388篇 |
2017年 | 378篇 |
2016年 | 780篇 |
2015年 | 819篇 |
2014年 | 901篇 |
2013年 | 1915篇 |
2012年 | 1950篇 |
2011年 | 2400篇 |
2010年 | 1340篇 |
2009年 | 1162篇 |
2008年 | 2053篇 |
2007年 | 2127篇 |
2006年 | 2207篇 |
2005年 | 2061篇 |
2004年 | 1866篇 |
2003年 | 1532篇 |
2002年 | 1447篇 |
2001年 | 856篇 |
2000年 | 775篇 |
1999年 | 614篇 |
1998年 | 574篇 |
1997年 | 616篇 |
1996年 | 643篇 |
1995年 | 578篇 |
1994年 | 594篇 |
1993年 | 596篇 |
1992年 | 551篇 |
1991年 | 531篇 |
1990年 | 444篇 |
1989年 | 458篇 |
1988年 | 464篇 |
1987年 | 403篇 |
1986年 | 388篇 |
1985年 | 551篇 |
1984年 | 555篇 |
1983年 | 450篇 |
1982年 | 519篇 |
1981年 | 467篇 |
1980年 | 491篇 |
1979年 | 422篇 |
1978年 | 456篇 |
1977年 | 396篇 |
1976年 | 358篇 |
1975年 | 291篇 |
1974年 | 314篇 |
1973年 | 262篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
Periodica Mathematica Hungarica - Let ?= 2ν &;gt; 1. Let M be an orientable manifold of odd dimension m with $\pi _1 (M) = \mathbb{Z}_\ell $ whose universal cover $\tilde M$ is... 相似文献
102.
In the present article, we aim at treating the existence of fundamental solutions of linear partial differential operators with constant coefficients from the viewpoint of setting up explicit formulae yielding fundamental solutions. 相似文献
103.
A new scheme for controlling photodissociation through preparation of a variationally optimized linear superposition of field free vibrational eigenstates is applied for selective control of IBr and HI dissociation. The dependence of photodissociation on various field parameters and initial conditions is examined to investigate the mechanistic basis of selective control. The parametric equations of motion approach for determining vibrational dynamics as a function of field parameters without having to solve the time dependent Schrödinger equation explicitly for each field parameter separately is outlined and its use to identify field characteristics which will provide the requisite population mix represented by the optimal linear superposition of vibrational states is advocated. 相似文献
104.
Th. Gerrits H. A. M. van den Berg J. Hohlfeld O. Gielkens L. Br Th. Rasing 《Journal of magnetism and magnetic materials》2002,240(1-3):283-286
We have measured the response of a 20×10 μm, 8 nm thin NiFe (80:20) permalloy film due to excitation by short in-plane magnetic field pulses. We will show that using a two-pulse-technique a complete control of the precessional motion of the magnetisation can be achieved on picosecond timescales. Furthermore, we will present numerical calculations which show that a complete suppression of magnetisation ringing after switching can only be realised by a cascade of short field pulses. 相似文献
105.
106.
We study the expected delay in cyclic polling models with general ‘branching-type’ service disciplines. For this class of
models, which contains models with exhaustive and gated service as special cases, we obtain closed-form expressions for the
expected delay under standard heavy-traffic scalings. We identify a single parameter associated with the service discipline
at each queue, which we call the ‘exhaustiveness’. We show that the scaled expected delay figures depend on the service policies
at the queues only through the exhaustiveness of each of the service disciplines. This implies that the influence of different
service disciplines, but with the same exhaustiveness, on the expected delays at the queues becomes the same when the system
reaches saturation. This observation leads to a new classification of the service disciplines. In addition, we show monotonicity
of the scaled expected delays with respect to the exhaustiveness of the service disciplines. This induces a complete ordering
in terms of efficiency of the service disciplines. The results also lead to new rules for optimization of the system performance
with respect to the service disciplines at the queues. Further, the exact asymptotic results suggest simple expected waiting-time
approximations for polling models in heavy traffic. Numerical experiments show that the accuracy of the approximations is
excellent for practical heavy-traffic scenarios.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
107.
Properties of nonparametric estimators of autocovariance for stationary random fields 总被引:1,自引:0,他引:1
Summary We introduce nonparametric estimators of the autocovariance of a stationary random field. One of our estimators has the property that it is itself an autocovatiance. This feature enables the estimator to be used as the basis of simulation studies such as those which are necessary when constructing bootstrap confidence intervals for unknown parameters. Unlike estimators proposed recently by other authors, our own do not require assumptions such as isotropy or monotonicity. Indeed, like nonparametric function estimators considered more widely in the context of curve estimation, our approach demands only smoothness and tail conditions on the underlying curve or surface (here, the autocovariance), and moment and mixing conditions on the random field. We show that by imposing the condition that the estimator be a covariance function we actually reduce the numerical value of integrated squared error. 相似文献
108.
Peter Karduck Norbert Ammann Hans Günter Esser Jörg Winter 《Fresenius' Journal of Analytical Chemistry》1991,341(5-6):315-319
Summary The first wall of the fusion device TEXTOR at the Forschungszentrum Jülich has been coated in situ with an amorphous hydrogen rich carbon/boron film (a-C/B:H) which reduces plasma impurities caused by the plasma surface interaction. The results of the coating process of the 35 m2 large inner wall surface have been controlled by a recently developed modification of the quantitative electron probe microanalysis, which has been applied to 12 samples from specified positions inside the tokamak. The quantification itself is based on a Monte Carlo simulation of electron trajectories providing very accurate results for X-ray intensities emitted by elements present in the electron bombarded sample. The Monte Carlo results are used in the present work to calibrate the measured X-ray intensities emitted by boron and carbon from the a-C/B:H layers deposited on pure silicon substrates. As a result the total deposited mass of the layer per area unit as well as the composition of the layers (except hydrogen) could be determined very accurately. The relative errors were less than 7%. The limit of detectability were found to be in the range of one monolayer for boron as well as for carbon. 相似文献
109.
110.
Q. Gong R. N tzel P.J. van Veldhoven T.J. Eijkemans J.H. Wolter 《Journal of Crystal Growth》2005,280(3-4):413-418
We report on the shape transition from InAs quantum dashes to quantum dots (QDs) on lattice-matched GaInAsP on InP(3 1 1)A substrates. InAs quantum dashes develop during chemical-beam epitaxy of 3.2 monolayers InAs, which transform into round InAs QDs by introducing a growth interruption without arsenic flux after InAs deposition. The shape transition is solely attributed to surface properties, i.e., increase of the surface energy and symmetry under arsenic deficient conditions. The round QD shape is maintained during subsequent GaInAsP overgrowth because the reversed shape transition from dot to dash is kinetically hindered by the decreased ad-atom diffusion under arsenic flux. 相似文献