全文获取类型
收费全文 | 16989篇 |
免费 | 572篇 |
国内免费 | 81篇 |
专业分类
化学 | 11469篇 |
晶体学 | 113篇 |
力学 | 469篇 |
综合类 | 2篇 |
数学 | 2640篇 |
物理学 | 2949篇 |
出版年
2023年 | 121篇 |
2022年 | 348篇 |
2021年 | 442篇 |
2020年 | 380篇 |
2019年 | 350篇 |
2018年 | 379篇 |
2017年 | 315篇 |
2016年 | 672篇 |
2015年 | 541篇 |
2014年 | 630篇 |
2013年 | 1081篇 |
2012年 | 1219篇 |
2011年 | 1270篇 |
2010年 | 855篇 |
2009年 | 797篇 |
2008年 | 1101篇 |
2007年 | 1013篇 |
2006年 | 904篇 |
2005年 | 773篇 |
2004年 | 658篇 |
2003年 | 571篇 |
2002年 | 501篇 |
2001年 | 275篇 |
2000年 | 247篇 |
1999年 | 183篇 |
1998年 | 157篇 |
1997年 | 124篇 |
1996年 | 179篇 |
1995年 | 120篇 |
1994年 | 123篇 |
1993年 | 112篇 |
1992年 | 112篇 |
1991年 | 84篇 |
1990年 | 84篇 |
1989年 | 64篇 |
1988年 | 58篇 |
1987年 | 49篇 |
1986年 | 51篇 |
1985年 | 81篇 |
1984年 | 68篇 |
1983年 | 41篇 |
1982年 | 47篇 |
1981年 | 42篇 |
1980年 | 54篇 |
1979年 | 36篇 |
1978年 | 43篇 |
1976年 | 36篇 |
1975年 | 37篇 |
1974年 | 29篇 |
1973年 | 30篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
131.
Park J Lee G Wolff-Fabris F Koh YY Eom MJ Kim YK Farhan MA Jo YJ Kim C Shim JH Kim JS 《Physical review letters》2011,107(12):126402
We report the observation of highly anisotropic Dirac fermions in a Bi square net of SrMnBi(2), based on a first-principles calculation, angle-resolved photoemission spectroscopy, and quantum oscillations for high-quality single crystals. We found that the Dirac dispersion is generally induced in the (SrBi)(+) layer containing a double-sized Bi square net. In contrast to the commonly observed isotropic Dirac cone, the Dirac cone in SrMnBi(2) is highly anisotropic with a large momentum-dependent disparity of Fermi velocities of ~8. These findings demonstrate that a Bi square net, a common building block of various layered pnictides, provides a new platform that hosts highly anisotropic Dirac fermions. 相似文献
132.
Ansgar Jüngel José Luis López Jesús Montejo–Gámez 《Journal of statistical physics》2011,145(6):1661-1673
A quantum Navier–Stokes system for the particle, momentum, and energy densities is formally derived from the Wigner–Fokker–Planck
equation using a moment method. The viscosity term depends on the particle density with a shear viscosity coefficient which
equals the quantum diffusion coefficient of the Fokker–Planck collision operator. The main idea of the derivation is the use
of a so-called osmotic momentum operator, which is the sum of the phase-space momentum and the gradient operator. In this
way, a Chapman–Enskog expansion of the Wigner function, which typically leads to viscous approximations, is avoided. Moreover,
we show that the osmotic momentum emerges from local gauge theory. 相似文献
133.
134.
An experimental and simulation investigation regarding the effect of various CRAMPS parameters (delays interleaved with the decoupling shape, z-rotation symmetry and offset frequency) on the DUMBO decoupling performance is presented using two model compounds, glycine and tyrosine·HCl. Although the conclusions of this work may be extended to the other homonuclear-decoupling schemes, this work focuses essentially on the effect of adding interleaved delays to DUMBO decoupling during the indirect dimension using different 2D pulse-scheme architectures. While the simulations revealed an increasing loss of the spectral resolution with longer delays (from 0 to 6 μs), the experimental 2D (1)H DUMBO NMR correlation spectra revealed that the inclusion of delays, during the indirect dimension, improves the (1)H resolution whether the z-rotation symmetry was used or not. The best experimental spectra are obtained when z-rotation symmetry and windows are combined. 相似文献
135.
136.
137.
The cosmological constant problem is examined within the context of the covariant brane-world gravity, based on Nash’s embedding
theorem for Riemannian geometries. We show that the vacuum structure of the brane-world is more complex than General Relativity’s
because it involves extrinsic elements, in specific, the extrinsic curvature. In other words, the shape (or local curvature)
of an object becomes a relative concept, instead of the “absolute shape” of General Relativity. We point out that the immediate
consequence is that the cosmological constant and the energy density of the vacuum quantum fluctuations have different physical
meanings: while the vacuum energy density remains confined to the four-dimensional brane-world, the cosmological constant
is a property of the bulk’s gravitational field that leads to the conclusion that these quantities cannot be compared, as
it is usually done in General Relativity. Instead, the vacuum energy density contributes to the extrinsic curvature, which
in turn generates Nash’s perturbation of the gravitational field. On the other hand, the cosmological constant problem ceases
to be in the brane-world geometry, reappearing only in the limit where the extrinsic curvature vanishes. 相似文献
138.
D. Wardecki R. Przeniosło A. N. Fitch M. Bukowski R. Hempelmann 《Journal of nanoparticle research》2011,13(3):1151-1161
The microstructure of electrodeposited nanocrystalline chromium (n-Cr) was studied by using synchrotron radiation (SR) diffraction,
SEM, TEM, and EDX techniques. The as-prepared n-Cr samples show the standard bcc crystal structure of Cr with volume-averaged
column lengths varying from 25 to 30 nm. The grain growth kinetics and the oxidation kinetics were studied by time resolved
SR diffraction measurements with n-Cr samples annealed at 400, 600, and 800 °C. The grain growth process is relatively fast
and it occurs within the first 10 min of annealing. The final crystallite size depends only on the annealing temperature and
not on the initial grain size or on the oxygen content. The final volume-averaged column lengths observed after 50 min annealing
are 40(4), 80(1), and 120(2) nm for temperatures 400, 600, and 800 °C, respectively. It is shown that annealing ex situ of
n-Cr at 800 °C both under vacuum and in air gives a grain growth process with the same final crystallite sizes. The formation
of the Cr2O3 and CrH phases is observed during annealing. 相似文献
139.
Guadalupe Valverde-Aguilar Jorge A. García-Macedo Víctor M. Rentería-Tapia Raúl W. Gómez Manuel Quintana-García 《Journal of nanoparticle research》2011,13(10):4613-4622
Hexagonal mesostructured films containing silver ions were obtained by sol–gel method. Brij 58 was used to produce channels
into the film, which house these ions. The films were exposure to UV radiation to produced silver metallic nanoparticles.
The presence of the metallic nanoparticles was determined by infrared spectroscopy and optical absorption. Besides, these
nanoparticles and core–shell structures of silver–silver oxide nanoparticles were identified by high-resolution transmission
electronic microscopy. From these measurements, the obtained size range for silver nanoparticles was 6.1 nm. The absorption
spectrum located at 440 nm was modelled and well fitted with the Gans theory considering refractive index higher than the
one coming from host matrix. This index is explained because the silver oxide shell modifies the local surrounding medium
of the metallic nanoparticles. 相似文献
140.
The problem of pattern formation by adsorbates undergoing attractive lateral interactions, is described by a parabolic integrodifferential equation having the scaled inverse temperature ? and the scaled pressure α of the vapor phase as parameters. A coexistence region of high- and low-coverage stable homogeneous states has been reported in the (?, α) plane. In the small interaction-range limit an effective diffusion coefficient can be defined, which becomes however negative for a coverage range in between the stable homogeneous ones. A novel free-energy-like Lyapunov functional is found here for this problem. When evaluated on the homogeneous states, it leads to a Maxwell-like construction which selects essentially the same value α(?) as the originally posited zero front-velocity condition. Moreover, its value on static fronts at this particular α(?) coincides with those of the homogeneous states. This article is dedicated to Prof. Helmut Brand with occasion of his 60th birthday. 相似文献