全文获取类型
收费全文 | 4453篇 |
免费 | 553篇 |
国内免费 | 488篇 |
专业分类
化学 | 2271篇 |
晶体学 | 30篇 |
力学 | 220篇 |
综合类 | 45篇 |
数学 | 311篇 |
物理学 | 1126篇 |
综合类 | 1491篇 |
出版年
2024年 | 11篇 |
2023年 | 64篇 |
2022年 | 117篇 |
2021年 | 131篇 |
2020年 | 148篇 |
2019年 | 116篇 |
2018年 | 117篇 |
2017年 | 142篇 |
2016年 | 161篇 |
2015年 | 149篇 |
2014年 | 230篇 |
2013年 | 263篇 |
2012年 | 262篇 |
2011年 | 347篇 |
2010年 | 252篇 |
2009年 | 256篇 |
2008年 | 293篇 |
2007年 | 255篇 |
2006年 | 214篇 |
2005年 | 174篇 |
2004年 | 146篇 |
2003年 | 101篇 |
2002年 | 113篇 |
2001年 | 108篇 |
2000年 | 91篇 |
1999年 | 128篇 |
1998年 | 109篇 |
1997年 | 119篇 |
1996年 | 119篇 |
1995年 | 111篇 |
1994年 | 90篇 |
1993年 | 87篇 |
1992年 | 83篇 |
1991年 | 66篇 |
1990年 | 67篇 |
1989年 | 58篇 |
1988年 | 44篇 |
1987年 | 41篇 |
1986年 | 29篇 |
1985年 | 17篇 |
1984年 | 9篇 |
1983年 | 11篇 |
1982年 | 12篇 |
1981年 | 5篇 |
1980年 | 7篇 |
1979年 | 5篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1957年 | 4篇 |
排序方式: 共有5494条查询结果,搜索用时 691 毫秒
991.
提出了一类q变形非简谐振子广义相干态a|β>+beiψ|βeiδ >.研究了这种迭加态的高次方压缩.结果表明:其可能高次方压缩次数可表示为k≠2πn/δ.这里n是整数.当δ=π时,压缩次方数只可能是奇数;当δ取其他值时,压缩次方数可以是偶数.这些结果表明:对于可能的压缩次方数,相位差起着关键性的作用,但是a(b)和β的作用不能忽视. 相似文献
992.
泥石流是一种频繁发生且危害性很大的自然灾害。作为中国泥石流灾害重灾区之一的陇南地区,泥石流不仅严重阻碍G212线的正常运营,也严重影响沿线地区的经济发展和人民生活。通过对G212线陇南段232条泥石流沟的调查资料分不同属性、不同发展阶段和不同危害程度进行统计,结合分形理论,分析了泥石流沟道数与地貌要素的定量关系。结果表明:地貌形态要素对泥石流的属性、发展阶段和危害程度等不同类型泥石流的影响程度不同; 综合分维值、形成区形态参数和地形坡度等参数都在一定程度上定量反映了不同类型泥石流的特征。 相似文献
993.
994.
Extraordinary optical transmission through metal gratings with single and double grooved surfaces
下载免费PDF全文
![点击此处可从《中国物理 B》网站下载免费的PDF全文](/ch/ext_images/free.gif)
We investigate the transmission properties of a normally
incident TM plane wave through metal films with periodic
parabolic-shaped grooves on single and double surfaces using the
finite-difference-time-domain method. Nearly zero transmission
efficiency is found at wavelengths corresponding to surface plasmon
excitation on a flat surface in the case where the single surface is
grooved. Meanwhile, resonant excitation of surface plasmon polariton
(SPP) Bloch modes leads to a strong transmission peak at slightly
larger wavelengths. When the grating is grooved on double surfaces,
the transmission enhancement can be dramatically improved due to the
resonant tunnelling between SPP Bloch modes. 相似文献
995.
Comparative study of different properties of GaN films grown on(0001) sapphire using high and low temperature AlN interlayers
下载免费PDF全文
![点击此处可从《中国物理 B》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Comparative study of high and low temperature AlN
interlayers and their roles in the properties of GaN epilayers
prepared by means of metal organic chemical vapour deposition on
(0001) plane sapphire substrates is carried out by high resolution
x-ray diffraction, photoluminescence and Raman spectroscopy. It is
found that the crystalline quality of GaN epilayers is improved
significantly by using the high temperature AlN interlayers, which
prevent the threading dislocations from extending, especially for
the edge type dislocation. The analysis results based on
photoluminescence and Raman measurements demonstrate that there
exist more compressive stress in GaN epilayers with high temperature
AlN interlayers. The band edge emission energy increases from
3.423~eV to 3.438~eV and the frequency of Raman shift of $E_{2
}$(TO) moves from 571.3~cm$^{ - 1}$ to 572.9~cm$^{ - 1}$ when the
temperature of AlN interlayers increases from 700~$^{\circ}$C to
1050~$^{\circ}$C. It is believed that the temperature of AlN
interlayers effectively determines the size, the density and the
coalescence rate of the islands, and the high temperature AlN
interlayers provide large size and low density islands for GaN
epilayer growth and the threading dislocations are bent and
interactive easily. Due to the threading dislocation reduction in
GaN epilayers with high temperature AlN interlayers, the approaches
of strain relaxation reduce drastically, and thus the compressive
stress in GaN epilayers with high temperature AlN interlayers is
high compared with that in GaN epilayers with low temperature AlN
interlayers. 相似文献
996.
The first order differential matrix equations of the host shell and constrained layer for a sandwich rotational shell are derived based on the thin shell theory.Employing the layer wise principle and first order shear deformation theory, only considering the shearing deformation of the viscoelastic layer, the integrated first order differential matrix equation of a passive constrained layer damping rotational shell is established by combining with the normal equilibrium equation of the viscoelastic layer.A highly precise transfer matrix method is developed by extended homogeneous capacity precision integration technology.The numerical results show that present method is accurate and effective. 相似文献
997.
In this paper, we prove the existence of Hermitian-Einstein metrics for holomorphic vector bundles on a class of complete Kähler manifolds which include Hermitian symmetric spaces of noncompact type without Euclidean factor, strictly pseudoconvex domains with Bergman metrics and the universal cover of Gromov hyperbolic manifolds etc. We also solve the Dirichlet problem at infinity for the Hermitian-Einstein equations on holomorphic vector bundles over strictly pseudoconvex domains.
998.
Zhi’an Ren Guangcan Che Shunlian Jia Hong Chen Yongming Ni Zhongxian Zhao 《中国科学 数学(英文版)》2001,44(9):1205-1208
The effect of Mg and C contents on TC in MgCN3, and structure and superconductivity of MgCNi3-x Co x were studied. It is found that the excess of Mg and C in initial material mixture is favorable to improvement inT c and helps to obtain single-phase samples. For preparing MgCNi3 superconductor, the optimum composition of starting materials is MgC1.45Ni3 with excess of Mg (20 wt.%) of the stoichiometric composition. In gCNi3-x Co x system, a continuous solid solution is formed, lattice parameter decreases slightly andT c decreases obviously with increasingx. A suppression of superconductivity is observed due to the substitution of Co (Mn) for Ni. The suppression effect is smaller for the substitution of Co than that of Mn 相似文献
999.
A simple long-range-order parameterPis defined for describing the process of formation of chains in the electric field direction. The free energy of the system is taken to be the sum of the internal energy, the electrostatic interaction and configuration entropy as a function o P. Calculated results indicate that the critical parameter is a function of electric field, temperature, misfit dielectric coefficients and concentration of particles. 相似文献
1000.
The complex separated flows induced by shock wave/boundary layer interaction were studied at hypersonic speed of Mach number 5. The experimental results on hypersonic flow over a set of rectangular cylinders are presented in this paper. The rectangular cylinder mounted on a flat plate worked as a typical model to simulate the obstacle on the vehicle surface. The effects of flow interaction on the aerodynamic characteristics have to be predicted for various geometrical parameters. So the static pressure distributions on the model surface were measured, the complex shock wave system was shown by schlieren photos, and the separated flow patterns around the obstacle were visualized by oil flow technique. All of the results describe the interactive flowfield features including peak pressure levels and their locations as well as separated boundaries associated with influence regions. 相似文献