全文获取类型
收费全文 | 6140篇 |
免费 | 1358篇 |
国内免费 | 427篇 |
专业分类
化学 | 1087篇 |
晶体学 | 69篇 |
力学 | 1332篇 |
综合类 | 86篇 |
数学 | 1437篇 |
物理学 | 3914篇 |
出版年
2023年 | 39篇 |
2022年 | 81篇 |
2021年 | 125篇 |
2020年 | 166篇 |
2019年 | 133篇 |
2018年 | 163篇 |
2017年 | 147篇 |
2016年 | 216篇 |
2015年 | 151篇 |
2014年 | 338篇 |
2013年 | 402篇 |
2012年 | 340篇 |
2011年 | 426篇 |
2010年 | 357篇 |
2009年 | 407篇 |
2008年 | 497篇 |
2007年 | 481篇 |
2006年 | 447篇 |
2005年 | 391篇 |
2004年 | 306篇 |
2003年 | 311篇 |
2002年 | 259篇 |
2001年 | 215篇 |
2000年 | 206篇 |
1999年 | 165篇 |
1998年 | 157篇 |
1997年 | 128篇 |
1996年 | 136篇 |
1995年 | 86篇 |
1994年 | 96篇 |
1993年 | 72篇 |
1992年 | 58篇 |
1991年 | 51篇 |
1990年 | 64篇 |
1989年 | 34篇 |
1988年 | 38篇 |
1987年 | 39篇 |
1986年 | 26篇 |
1985年 | 27篇 |
1984年 | 28篇 |
1983年 | 7篇 |
1982年 | 21篇 |
1981年 | 24篇 |
1980年 | 6篇 |
1979年 | 8篇 |
1978年 | 6篇 |
1977年 | 11篇 |
1976年 | 7篇 |
1974年 | 4篇 |
1973年 | 7篇 |
排序方式: 共有7925条查询结果,搜索用时 15 毫秒
31.
32.
用波导本征模展开方法对用于高功率微波发射系统的方角锥高斯馈源口面场进行分析,提出结合馈源远场辐射特性和避免高功率击穿折衷选定相应的高斯模注腰半径,进而确定多个波导模幅值,从而为运用模匹配或耦合波理论设计高斯馈源提供依据。 相似文献
33.
A probabilistic teleportation scheme for atomic state via cavity QED [Phys. Rev. A 70 (2004) 054303] is revisited and accordingly some improvements are made. 相似文献
34.
We study the corrections to the Clausius-Mossotti formula for the dielectric constant of a disordered system of polarizable spherical particles. Previously we have derived an exact cluster expansion for the correction terms. Here we study the three-body correction in detail. We derive an explicit expression for the integrand of the three-body cluster integral for a system of polarizable point dipoles. 相似文献
35.
Hans J. Fahr 《Foundations of Physics Letters》2006,19(5):423-440
According to ideas of Mach, Whitrow, Dirac, or Hoyle, inertial masses of particles should not be a genuine, predetermined
quantity; rather they should represent a relational quantity which by its value somehow reflects the deposition and constellation
of all other objects in their cosmic environment. In this paper we want to pick up suggestions given by Thirring and by Hoyle
of how, due to requirements of the equivalence of rotations and of general relativistic conformal scale invariance, the particle
masses of cosmic objects should vary with the cosmic length scale. We study cosmological consequences of comoving cosmic masses
which co-evolve by mass with the expansion of the universe. The vanishing of the covariant divergence of the cosmic energy-momentum
tensor under the new prerequisite that matter density only falls off with the reciproke of the squared cosmic scale S(t) then leads to the astonishing result that cosmic pressuredoes not fall off adiabatically but rather falls off in a quasi-isothermal
behaviour, varying with S(t) as matter density does. Hence, as a new cosmological fact, it arises that, even in the late phases of cosmic expansion,
pressure cannot be neglected what concerns its gravitational action on the cosmic dynamics. We then show that under these
conditions the cosmological equations can, however, only be solved if, in addition to matter, also pressure and energy density
of the cosmic vacuum are included in the calculation. An unaccelerated expansion with a Hubble parameter falling off with
S(t)−1 is obtained for a vacuum energy density decay according to S(t)−2 with a well-tuned proportion of matter and vacuum pressures. As it appears from these results, a universe with particle masses
increasing with the cosmic sale S(t) is in fact physically conceivable in an energetically consistent manner, if vacuum energy at the expansion of the universe
is converted into mass density of real matter with no net energy loss occuring. This universe in addition also happens to
be an economical one which has and keeps a vanishing total energy. 相似文献
36.
W.F. Wang 《Journal of Quantitative Spectroscopy & Radiative Transfer》2004,86(4):437-444
It is shown that by including the second term of Magnus expansion, improved convergence can be achieved for the non-perturbative pressure broadening formalism proposed by Neilson and Gordon (J. Chem. Phys. 58 (1973) 4131). The present method was applied to the line broadening calculations of CO in a bath of Ar. 相似文献
37.
Sally Dixon 《Tetrahedron》2004,60(6):1401-1416
A wide range of carbenoids (1-lithio-1-halo species), including those with α-SiR3, OEt, SPh, SO2Ph, P(O)(OEt)2, and CN substituents, insert into 5-member zirconacycles (saturated and unsaturated, mono- and bi-cyclic) to afford functionalized 6-member zirconacycles. 1-Lithio-1-haloalkenes insert to afford 6-member zirconacycles with an alkylidene substituent next to the metal. Unexpected double insertion of some carbenoids, and evidence for endocylic β-hydride transfer processes provide additional mechanistic interest. 相似文献
38.
介绍F-P干涉滤波器实现中心波长可调的两种机理,给出通过改变腔距来改变中心波工的滤波器的典型结构,并且给出了相应的电压驱动电路,实验表明选择合适的光放大器前置滤波器可以提高系统的灵敏度。 相似文献
39.
A new method for rotation and brightness invariant pattern recognition was proposed by applying multiple circular harmonic expansions to the joint transform correlator. The amplitudes of the multiple orders of circular harmonic expansions made from a detecting image were synthetically modified to respond to the same auto-correlation peaks. These modified circular harmonic expansions were arranged in the input plane as reference patterns together with an arbitrary target pattern, and the correlation signals between them were calculated in the subtracted joint transform correlator. The fraction of the correlation-peak intensities between the target and the references were extracted as a new discrimination parameter. This new parameter performs pattern recognition under rotation and brightness invariance with good discriminability. Its high discriminability has been proved in computer simulations using the face image patterns of many individuals. 相似文献
40.
利用CARS方法研究超短脉冲激光的脉冲宽度 总被引:1,自引:1,他引:0
在理论上提出了利用两光束CARS/CSRS方法测量超短脉冲激光的三阶相关函数。实验上在几种样品中测量了CARS/CSRS的时间特性,得到了泵浦光脉冲,SCDL输出光脉冲以及受激喇曼散射光脉冲的宽度。 相似文献