全文获取类型
收费全文 | 426502篇 |
免费 | 5392篇 |
国内免费 | 1415篇 |
专业分类
化学 | 234272篇 |
晶体学 | 5948篇 |
力学 | 17835篇 |
综合类 | 10篇 |
数学 | 48222篇 |
物理学 | 127022篇 |
出版年
2020年 | 2993篇 |
2019年 | 3039篇 |
2018年 | 3430篇 |
2017年 | 3372篇 |
2016年 | 5997篇 |
2015年 | 4511篇 |
2014年 | 6348篇 |
2013年 | 18783篇 |
2012年 | 14409篇 |
2011年 | 17710篇 |
2010年 | 11506篇 |
2009年 | 11555篇 |
2008年 | 16578篇 |
2007年 | 16626篇 |
2006年 | 16132篇 |
2005年 | 14747篇 |
2004年 | 13276篇 |
2003年 | 11919篇 |
2002年 | 11696篇 |
2001年 | 13987篇 |
2000年 | 10586篇 |
1999年 | 8361篇 |
1998年 | 6422篇 |
1997年 | 6369篇 |
1996年 | 6331篇 |
1995年 | 5795篇 |
1994年 | 5539篇 |
1993年 | 5279篇 |
1992年 | 6141篇 |
1991年 | 6080篇 |
1990年 | 5732篇 |
1989年 | 5511篇 |
1988年 | 5734篇 |
1987年 | 5455篇 |
1986年 | 5162篇 |
1985年 | 7178篇 |
1984年 | 7278篇 |
1983年 | 5925篇 |
1982年 | 6259篇 |
1981年 | 6152篇 |
1980年 | 5902篇 |
1979年 | 6231篇 |
1978年 | 6296篇 |
1977年 | 6257篇 |
1976年 | 6166篇 |
1975年 | 5943篇 |
1974年 | 5807篇 |
1973年 | 5987篇 |
1972年 | 3598篇 |
1971年 | 2694篇 |
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
931.
932.
D.L. Skuratov Yu.L. Ratis I.A. Selezneva J. Pérez P. Fernández de Córdoba J.F. Urchueguía 《Applied Mathematical Modelling》2007
This paper deals with modelling the workpiece temperature field produced during the grinding process. The proposed model is given in terms of a two-dimensional boundary-value problem where the interdependence among the grinding wheel, the workpiece and the coolant is described by two variable functions in the boundary condition. An explicit integral form solution is constructed using the Laplace and Fourier transforms and the Green’s function method. 相似文献
933.
Observation of spontaneous pattern with six-fold symmetry in disk-shaped ZnO complex microstructures
L.W. Yang Y.J. Gao X.L. Wu Y.M. Yang G.S. Huang Z.Y. Zhang P.K. Chu 《Applied Physics A: Materials Science & Processing》2007,89(1):173-176
Using a simple vapor phase transport technique, we have fabricated unique complex disk-shaped ZnO microstructures comprising
a small disk coaxially grown on a large one and observed spatially perfect six-fold symmetric patterns. The observed results
can be explained based on the spontaneous nanoindentation (NI) effect under the geometric constraints and the explanation
can be extended to fathom the growth mechanism of other highly symmetrical ZnO nanostructures. Our results indicate that NI
not only can elucidate the mechanical properties of surfaces and thin films but also is an effective approach to fabricate
ordered nanostructures with high precision on the location of the building blocks.
PACS 81.16.Rf; 81.07.-b; 81.05.Dz 相似文献
934.
J. Xu J. Mei X.H. Huang X. Li Z. Li W. Li K. Chen 《Applied Physics A: Materials Science & Processing》2005,80(1):123-126
The effect of nitrogen surface doping on the electron field emission characteristics of hydrogenated amorphous carbon films was studied. It was found that the emission threshold electric field decreased after nitrogen surface doping which indicated the reduction of the emission barrier at the film surface. It was demonstrated that this improvement arose from the decrease of the effective work function due to the formation of a dipole layer induced by chemical termination and chemical structural change on the film surface. PACS 52.75.Xx; 73.30 +y; 73.61.Jc 相似文献
935.
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
936.
937.
The treatment of tertiary esters with triphenylphosphine and iodine under mild conditions gives the most stable alkene in good yield. Formates, acetates and trifluoroacetates were studied. 相似文献
938.
Theresa J. Hermel-Davidock H. Sean Tang Daniel J. Murray Stephen F. Hahn 《Journal of polymer science. Part A, Polymer chemistry》2007,45(24):3338-3348
It has been found that by the addition of low concentrations of an amphiphilic block copolymer to an epoxy resin, novel disordered morphologies can be formed and preserved through curing. This article will focus on characterizing the influence of the block copolymer and casting solvent on the templated morphology achieved in the thermoset sample. The ultimate goal of this work is to determine the parameters that would control the microphase morphology produced. Epoxy resins blended with a series of amphiphilic block copolymers based on hydrogenated polyisoprene (polyethylene-alt-propylene or PEP) and polyethylene oxide (PEO), specifically, were investigated. In this article, the cure-induced order–order phase transition from the spherical to wormlike micelle morphology will also be discussed. It is proposed that the formation of the wormlike micelle structure from the spherical micelle structure is similar to the phase transition behavior that occurs in dilute block copolymer solutions as a function of the influence of the solvent on micelle morphology. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3338–3348, 2007 相似文献
939.
The hyperfine constants for muonium in elemental and binary inorganic solids suggest formation of three different families
of defect centre, with distinct electronic structures. The overall range of values, spanning nearly five orders of magnitude,
and their correlation with host properties such as band gap and electron affinity, reveal a deep-to-shallow instability which
has profound implications for the electrical properties of hydrogen impurity in electronic materials, both semiconducting
and dielectric. 相似文献
940.
Jae-Yeon Lee Eugene Lubarsky Ben T. Zinn 《Proceedings of the Combustion Institute》2005,30(2):1757-1764
This paper describes an experimental investigation of the feasibility of using “slow” active control approaches, which “instantaneously” change liquid fuel spray properties, to suppress combustion instabilities. The objective of this control approach was to break up the feedback between the combustion process heat release and combustor pressure oscillations that drive the instability by changing the characteristics of the combustion process (e.g., the characteristic combustion time). To demonstrate the feasibility of such control, this study used a proprietary fuel injector (NanomiserTM), which can vary its fuel spray properties, to investigate the dependence of acoustics–combustion process coupling, i.e., the driving of combustion instabilities, upon the fuel spray properties. This study showed that by changing the spray characteristics it is possible to significantly damp combustion instabilities. Furthermore, using combustion zone chemiluminescence distributions, which were obtained by Abel’s deconvolution synchronized with measured acoustic data, it has been shown that the instabilities were mostly driven midway between the combustor centerline and wall, a short distance downstream from the flame holder, where the mean axial flow velocity is approximately zero in the vortex near the flame holder. The results of this study strongly suggest that a “slow” active control system that employs controllable fuel injectors could be effectively used to prevent the onset of detrimental combustion instabilities. 相似文献