全文获取类型
收费全文 | 462013篇 |
免费 | 4668篇 |
国内免费 | 1557篇 |
专业分类
化学 | 237748篇 |
晶体学 | 7167篇 |
力学 | 21633篇 |
综合类 | 13篇 |
数学 | 54219篇 |
物理学 | 147458篇 |
出版年
2021年 | 3890篇 |
2020年 | 4192篇 |
2019年 | 4659篇 |
2018年 | 6064篇 |
2017年 | 6303篇 |
2016年 | 9148篇 |
2015年 | 5585篇 |
2014年 | 8904篇 |
2013年 | 21864篇 |
2012年 | 16959篇 |
2011年 | 20719篇 |
2010年 | 14644篇 |
2009年 | 14565篇 |
2008年 | 18673篇 |
2007年 | 18697篇 |
2006年 | 17323篇 |
2005年 | 15417篇 |
2004年 | 14229篇 |
2003年 | 12466篇 |
2002年 | 12417篇 |
2001年 | 14537篇 |
2000年 | 10981篇 |
1999年 | 8533篇 |
1998年 | 6899篇 |
1997年 | 6837篇 |
1996年 | 6488篇 |
1995年 | 5671篇 |
1994年 | 5496篇 |
1993年 | 5312篇 |
1992年 | 5944篇 |
1991年 | 6112篇 |
1990年 | 5692篇 |
1989年 | 5592篇 |
1988年 | 5411篇 |
1987年 | 5442篇 |
1986年 | 5145篇 |
1985年 | 6906篇 |
1984年 | 6913篇 |
1983年 | 5696篇 |
1982年 | 5975篇 |
1981年 | 5627篇 |
1980年 | 5504篇 |
1979年 | 5714篇 |
1978年 | 5785篇 |
1977年 | 5782篇 |
1976年 | 5669篇 |
1975年 | 5451篇 |
1974年 | 5313篇 |
1973年 | 5403篇 |
1972年 | 3642篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
A model of a helical nanotube permitting analytical calculation of the spectrum and wave functions is proposed and studied. It is shown that the specific character of the symmetry of the Hamiltonian results in an electronic spectrum having no band structure despite the periodicity of the potential along the system axis. A two-dimensional ribbon rolled into a helix and a quasi-one-dimensional helix in a magnetic field are considered as limiting cases of the model. It is shown that the presence of additional local minima in the subbands of the electronic spectrum leads to a nonmonotonic dependence of the ballistic conductance of the system on the chemical potential. 相似文献
982.
Darshan C. Kundaliya 《Solid State Communications》2004,131(8):489-491
The intermetallic compound, YRhAl, has been prepared and is found to be isomorphic with RRhAl (R=Pr, Nd, Gd, Ho and Tm) compounds crystallizing in the orthorhombic TiNiSi-type structure (space group Pnma). Heat capacity and electrical resistivity measurements in the He-3 temperature range reveal that this compound is superconducting with a transition temperature, Tc, of 0.9 K. The electronic specific heat coefficient, γ, and the Debye temperature are found to be 6.1 mJ/mol K and 197 K, respectively. The specific heat jump at the superconducting transition is found to be consistent with the BCS weak-coupling limit. This combined with the earlier observation of superconductivity in LaRhAl (Tc=2.4 K) having a different structure than that of YRhAl, suggests that the underlying structure is not very crucial for the occurrence of superconductivity in RRhAl series of compounds. 相似文献
983.
984.
985.
986.
Audrey A S G Lonni Ieda S Scarminio Lucas M C Silva Dalva T Ferreira 《Analytical sciences》2003,19(7):1013-1017
Phytochemical investigation of the aerial parts of three Baccharis species (Asteraceae family) was performed using HPLC and chemometric methods, with the objective of distinguishing between three morphologically very similar species: Baccharis genistelloides Persoon var. trimera (Less.) DC, B. milleflora (Less.) DC and B. articulata (Lam.) Persoon. With the help of Principal Component Analysis (PCA) and variance weights, it was possible to characterize the chromatographic profiles of the alcoholic extracts of the three species. Application of Soft Independent Modeling of Class Analogy (SIMCA) and K-Nearest Neighbor (KNN) methods on a training set of 74 extracts resulted in models that correctly classified all eight samples in an independent test set. 相似文献
987.
C. Bréchignac Ph. Cahuzac F. Carlier C. Colliex M. de Frutos N. Kébaïli J. Le Roux A. Masson B. Yoon 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):265-268
We studied shape relaxation of nano-fractal islands,
during annealing, after their growth from antimony cluster
deposition on graphite surface. Annealing at
180°C shows evidence of an increase
of the fractal branch width with time followed by branch
fragmentation, without changing the fractal dimension. The time
evolution of the width of the arm suggests the surface
self-diffusion mechanism as the main relaxation process. With
Monte Carlo simulations, we confirmed the observed behavior.
Comparison is done with our previous results on fragmentation of
nano-fractal silver islands when impurity added to the incident
cluster promotes rapid fragmentation by surface self-diffusion
enhancement [1]. 相似文献
988.
E. Casarejos P. Armbruster L. Audouin J. Benlliure M. Bernas A. Boudard R. Legrain S. Leray B. Mustapha S. Czajkowski T. Enqvist B. Fernandez J. Pereira M. Pravikoff F. Rejmund K. -H. Schmidt C. Stephan J. Taieb L. Tassan-Got C. Villagrasa C. Volant W. Wlazlo 《Physics of Atomic Nuclei》2003,66(8):1413-1420
The isotopic production cross sections of heavy residues in relativistic heavy-ion collisions have been investigated in inverse kinematics. The primary reaction products were fully identified in mass and atomic number prior to beta decay using the fragment separator FRS. The huge collection of data obtained helps in the understanding of the two main reaction mechanisms involved: fragmentation and fission. These data provide basic information for future radioactive ion beam facilities and for technical applications like intense neutron sources by means of spallation targets. 相似文献
989.
V. T. Bublik S. Yu. Matsnev K. D. Shcherbachev M. V. Mezhennyi M. G. Mil’vidskii V. Ya. Reznik 《Physics of the Solid State》2003,45(10):1918-1925
Diffuse x-ray scattering (DXS) is used to study the formation of microdefects (MDs) in heat-treated dislocation-free large-diameter silicon wafers with vacancies. The DXS method is shown to be efficient for investigating MDs in silicon single crystals. Specific defects, such as impurity clouds, are found to form in the silicon wafers during low-temperature annealing at 450°C. These defects are oxygen-rich regions in the solid solution with diffuse coherent interfaces. In the following stages of decomposition of the supersaturated solid solution, oxide precipitates form inside these regions and the impurity clouds disappear. As a result of the decomposition of the supersaturated solid solution of oxygen, interstitial MDs form in the silicon wafers during multistep heat treatment. These MDs lie in the {110} planes and have nonspherical displacement fields. The volume density and size of MDs forming in the silicon wafers at various stages of the decomposition are determined. 相似文献
990.
M. Dubé C. Daneault V. Vuorinen M. Alava M. Rost 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,56(1):15-26
We investigate the structure and dynamics of the interface between
two immiscible liquids in a three-dimensional disordered porous
medium. We apply a phase-field model that includes explicitly
disorder and discuss both spontaneous and forced imbibition.
The structure of the interface is dominated by a length scale
ξ× which arises from liquid conservation. We further show
that disorder in the capillary and permeability act on different
length scales and give rise to different scalings and
structures of the interface properties. We conclude with a
range of applications. 相似文献