全文获取类型
收费全文 | 546081篇 |
免费 | 8394篇 |
国内免费 | 3809篇 |
专业分类
化学 | 296662篇 |
晶体学 | 8263篇 |
力学 | 23971篇 |
综合类 | 173篇 |
数学 | 62451篇 |
物理学 | 166764篇 |
出版年
2021年 | 5115篇 |
2020年 | 5658篇 |
2019年 | 6029篇 |
2018年 | 7464篇 |
2017年 | 7386篇 |
2016年 | 11199篇 |
2015年 | 7442篇 |
2014年 | 11088篇 |
2013年 | 25646篇 |
2012年 | 20205篇 |
2011年 | 24418篇 |
2010年 | 17196篇 |
2009年 | 17054篇 |
2008年 | 22287篇 |
2007年 | 21827篇 |
2006年 | 20416篇 |
2005年 | 18215篇 |
2004年 | 16751篇 |
2003年 | 14857篇 |
2002年 | 14582篇 |
2001年 | 16893篇 |
2000年 | 12696篇 |
1999年 | 9969篇 |
1998年 | 8052篇 |
1997年 | 7817篇 |
1996年 | 7584篇 |
1995年 | 6826篇 |
1994年 | 6729篇 |
1993年 | 6380篇 |
1992年 | 7298篇 |
1991年 | 7469篇 |
1990年 | 7086篇 |
1989年 | 6892篇 |
1988年 | 6899篇 |
1987年 | 6760篇 |
1986年 | 6314篇 |
1985年 | 8163篇 |
1984年 | 8323篇 |
1983年 | 6594篇 |
1982年 | 6717篇 |
1981年 | 6560篇 |
1980年 | 6159篇 |
1979年 | 6773篇 |
1978年 | 6973篇 |
1977年 | 6849篇 |
1976年 | 6743篇 |
1975年 | 6208篇 |
1974年 | 6211篇 |
1973年 | 6279篇 |
1972年 | 4376篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
A. S. Boreysho S. L. Druzhinin V. M. Malkov I. A. Kiselev A. V. Morozov A. E. Orlov A. V. Savin I. V. Shatalov V. I. Zapryagaev A. V. Sobolev 《Thermophysics and Aeromechanics》2007,14(4):561-576
The matter of development of a high-performance pressure recovery system (PRS) for a high-power HF/DF laser is discussed.
A sequence of design steps is proposed, which involves estimation of basic characteristics of PRS components with the help
of one-dimensional integral and semi-empirical procedures; simulation, to be performed using three-dimensional non-stationary
Navier — Stokes equations; experimental modelling aimed at verification of the calculation procedures and at refinement of
obtained parameters; and a fullscale experiment. An ejector-type system providing for recovery of pressure from 12 Torr to
atmospheric pressure in the gas-dynamic system of an HF/DF laser of several-tens-kilowatt power is developed. Matching conditions
for parameters of individual PRS components as well as joint functioning of the PRS with a continuous chemical laser in an
integral complex are analysed. Conditions for minimization of mass-dimensional characteristics of the laser-PRS complex necessary
for the development of ground-based mobile systems are identified. 相似文献
992.
K.T.A.L. Burm 《等离子体物理论文集》2007,47(6):458-464
The discharge behaviour of an atmospheric dielectric barrier parallel plate discharge, used for surface treatment, is studied. Since an uniform plasma is preferable for surface treatment, filaments must be avoided in the discharge. The occurrence of filaments can be detected by measuring the current flowing through the discharge. Current and voltage measurements give an indication of the power consumption by the plasma. The power consumption of the plasma as function of the applied frequency is examined. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
993.
900 MHz 1H NMR (nuclear magnetic resonance) spectroscopy was used to analyze metabolites in allantoic fluid of the chicken embryo in
the 9th incubation day without any chemical or physical sample separation. The result showed that superhigh spectral dispersion
and sensitivity at 900 MHz are useful in directly analyzing a complex mixture, particularly in resolving the overlapped NMR
resonances. In this study, we had assigned 61 metabolites and 26 chemical fragments in the allantoic fluid. The relative concentrations
of the major metabolites were also measured. Among the assigned metabolites, some were detected by NMR in chicken embryo allantoic
fluids for the first time. The biological functions of these compounds were briefly discussed.
Authors' address: Maili Liu, State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute
of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071, People's Republic of China 相似文献
994.
L. Bernal-Gonzalez A. Bonilla M.C. Calderon-Moreno J.A. Prado-Bassas 《Constructive Approximation》2007,25(2):211-219
Let Ώ be a domain in the N-dimensional real space, let L be an elliptic differential operator, and let (Tn) be a sequence whose members belong to a certain class of operators defined on the space of L-analytic functions on Ώ. This
paper establishes the existence of a dense linear manifold of L-analytic functions all of whose nonzero members have maximal
cluster sets under the action of every Tn along any curve ending at the boundary of Ώ such that its closure does not contain any component of the boundary. The above
class contains all partial differentiation operators ∂α, hence the statement extends earlier results due to Boivin, Gauthier, and Paramonov, and due to the first, third, and fourth
authors. 相似文献
995.
H.D. Fonseca Filho R. Prioli M.P. Pires A.S. Lopes P.L. Souza F.A. Ponce 《Applied Physics A: Materials Science & Processing》2007,89(4):945-949
Atomic-force nanolithography was used to control the nucleation sites of InAs nanostructures on InP substrates. Indentations
with a wide range of dimensions were produced on InP. InAs nanostructures were selectively grown by metal organic vapor phase
epitaxy. It is shown that the number of active nucleation sites depends on the normal force applied during nanoindentation.
Crystalline defects introduced by nanoindentation are shown to be nucleation sites for these nanostructures. The presence
of screw dislocations within the grown nanostructures further supports this observation.
PACS 81.07.-b; 68.37.Ps; 81.16.Nd 相似文献
996.
Nanometer scale Al/AlN multilayers have been prepared by dc magnetron sputtering technique with a columnar target. A set of Al/AlN multilayers with the Al layer thickness of 2.9 nm and the AlN layer thickness variation from 1.13 to 6.81 nm were determined. Low angle X-ray diffraction (LAXRD) was used to analyze the layered structure of multilayers. The phase structure of the coatings was investigated with grazing angle XRD (GAXRD). Mechanical properties of these multilayers were thoroughly studied using a nanoindentation and ball-on-disk micro-tribometer. It was found that the multilayer hardness and reduced modulus showed no strong dependence on the AlN layer thickness. Al2.9 nm/AlN1.13 nm multilayer had more excellent tribological properties than single layers and other proportion multilayers with a lowest friction coefficient of 0.15. And the tribological properties of all the multilayers are superior to the AlN single layer. 相似文献
997.
O. Životský K. Postava L. Kraus M. Foldyna J. Pištora 《Journal of magnetism and magnetic materials》2006
In this paper we investigate the surface magnetic properties of as-quenched (AQ) CoFeCrBSi ribbons prepared by planar flow casting method with using magneto-optic Kerr effect (MOKE). Measured hysteresis loops in longitudinal and transversal configurations enable us to obtain the information of ribbons surface magnetic properties. Moreover, we suggest new magneto-optic method, which is based on measurements of magneto-optical effects depending on DC current flowing through the ribbon. Experimental data of AQ ribbons are then compared with the model, which describes the influence of incidence angle on magneto-optical angles. 相似文献
998.
999.
H. D. Dahmen P. Manakos T. Mannel T. Ohl 《Zeitschrift fur Physik C Particles and Fields》1989,44(1):139-147
The photon two-point function is calculated using the exponential representation for the time-evolution operator taking into account terms up to second order ine in the exponent. The limiting case of vanishing electron mass is examined and it is shown that mass singularities cancel by means of unitarity. Near mass shell the causal Green function exhibits in the limit of vanishing electron mass the expected cut behaviour, off mass shell we recover the result of the usual perturbation theory. 相似文献
1000.
We construct estimators of the expectation of a nonstationary stochastic process with time-dependent variance. Limit relations are obtained for particular correlation dependences.Translated from Statisticheskie Metody, pp. 98–103, 1982. 相似文献