全文获取类型
收费全文 | 855篇 |
免费 | 8篇 |
专业分类
化学 | 346篇 |
晶体学 | 3篇 |
力学 | 10篇 |
数学 | 59篇 |
物理学 | 445篇 |
出版年
2018年 | 5篇 |
2016年 | 5篇 |
2015年 | 9篇 |
2014年 | 4篇 |
2013年 | 14篇 |
2012年 | 28篇 |
2011年 | 38篇 |
2010年 | 19篇 |
2009年 | 16篇 |
2008年 | 37篇 |
2007年 | 37篇 |
2006年 | 33篇 |
2005年 | 46篇 |
2004年 | 29篇 |
2003年 | 26篇 |
2002年 | 23篇 |
2001年 | 20篇 |
2000年 | 16篇 |
1999年 | 17篇 |
1998年 | 5篇 |
1997年 | 8篇 |
1996年 | 9篇 |
1995年 | 14篇 |
1994年 | 20篇 |
1993年 | 18篇 |
1992年 | 33篇 |
1991年 | 15篇 |
1990年 | 24篇 |
1989年 | 24篇 |
1988年 | 26篇 |
1987年 | 16篇 |
1986年 | 16篇 |
1985年 | 26篇 |
1984年 | 12篇 |
1983年 | 12篇 |
1982年 | 7篇 |
1981年 | 16篇 |
1980年 | 8篇 |
1979年 | 8篇 |
1977年 | 11篇 |
1976年 | 15篇 |
1975年 | 7篇 |
1974年 | 10篇 |
1973年 | 8篇 |
1968年 | 5篇 |
1967年 | 3篇 |
1966年 | 5篇 |
1937年 | 3篇 |
1934年 | 3篇 |
1931年 | 3篇 |
排序方式: 共有863条查询结果,搜索用时 15 毫秒
141.
Huang GS Miller DH Pavlunin V Sanghi B Shipsey IP Adams GS Cravey M Cummings JP Danko I Napolitano J He Q Muramatsu H Park CS Thorndike EH Coan TE Gao YS Liu F Artuso M Boulahouache C Blusk S Butt J Dorjkhaidav O Li J Menaa N Mountain R Nandakumar R Randrianarivony K Redjimi R Sia R Skwarnicki T Stone S Wang JC Zhang K Csorna SE Bonvicini G Cinabro D Dubrovin M Briere RA Chen GP Chen J Ferguson T Tatishvili G Vogel H Watkins ME Rosner JL Adam NE Alexander JP Berkelman K Cassel DG Crede V 《Physical review letters》2006,96(3):032003
Using data collected at the psi(3770) resonance with the CLEO-c detector at the Cornell e+e- storage ring, we present searches for 25 charmless decay modes of the psi(3770), mostly multibody final states. No evidence for charmless decays is found. 相似文献
142.
Wunderlich J Jungwirth T Kaestner B Irvine AC Shick AB Stone N Wang KY Rana U Giddings AD Foxon CT Campion RP Williams DA Gallagher BL 《Physical review letters》2006,97(7):077201
We observe low-field hysteretic magnetoresistance in a (Ga,Mn)As single-electron transistor which can exceed 3 orders of magnitude. The sign and size of the magnetoresistance signal are controlled by the gate voltage. Experimental data are interpreted in terms of electrochemical shifts associated with magnetization rotations. This Coulomb blockade anisotropic magnetoresistance is distinct from previously observed anisotropic magnetoresistance effects as it occurs when the anisotropy in a band structure derived parameter is comparable to an independent scale, the single-electron charging energy. Effective kinetic-exchange model calculations in (Ga,Mn)As show chemical potential anisotropies consistent with experiment and ab initio calculations in transition metal systems suggest that this generic effect persists to high temperatures in metal ferromagnets with strong spin-orbit coupling. 相似文献
143.
John J. Gibson Mostafa A. Sadek D.J.M. Stone Catherine E. Hughes S. Hankin Dioni I. Cendon 《Isotopes in environmental and health studies》2013,49(1):83-84
Nuclear Chemistry: O. Navratil, J. Hala, R. Kopunec, F. Macasek, V. Mikulaj, L. Leseticky, Translated from Czech to English by J. Hala and P. Huth, Ellis Horwood PTR Prentice Hall, New York (Physical Chemistry Series) and Academia Publishing House, Prague 1992, 389 pp. Limitation of Exposure to Ionizing Radiation: Recommendations of the National Council on Radiation Protection and Measurements. NCRP Report No. 116, Bethesda, Maryland, 1993,88 pp. 相似文献
144.
Katherine A. Koenig Ken E. Sakaie Mark J. Lowe Jian Lin Lael Stone Robert A. Bermel Erik B. Beall Stephen M. Rao Bruce D. Trapp Micheal D. Phillips 《Magnetic resonance imaging》2013
Introduction
Diffusion tensor imaging (DTI) measures in patients with multiple sclerosis (MS), particularly those measures associated with a specific white matter pathway, have consistently shown correlations with function. This study sought to investigate correlations between DTI measures in the fornix and common cognitive deficits in MS patients, including episodic memory, working memory and attention.Materials and Methods
Patients with MS and group age- and sex-matched controls underwent high-resolution diffusion scanning (1-mm isotropic voxels) and cognitive testing. Manually drawn forniceal regions of interest were applied to individual maps of tensor-derived measures, and mean values of transverse diffusivity (TD), mean diffusivity (MD), longitudinal diffusivity (LD) and fractional anisotropy (FA) were calculated.Results
In 40 patients with MS [mean age±S.D.= 42.55±9.1 years; Expanded Disability Status Scale (EDSS)=2.0±1.2; Multiple Sclerosis Functional Composite (MSFC) score=0.38±0.46] and 20 healthy controls (mean age±S.D.= 41.35±9.7 years; EDSS=0.0±0; MSFC score=0.74±0.24), we found that FA, MD and TD values in the fornix were significantly different between groups (P< .03), and patient performance on the Brief Visuospatial Memory Test-Revised (BVMT-R) was correlated with DTI measures (P< .03).Discussion
These results are consistent with findings of axonal degeneration in MS and support the use of DTI as an indicator of disease progression. 相似文献145.
Internal friction and dynamic shear modulus in an indium–21?at.% thallium alloy were measured as functions of frequency and cooling rate using broadband viscoelastic spectroscopy during the martensitic transformation which occurs in this material occurs around 50°C. Microstructural evolution of martensitic bands was captured using time-lapse optical microscopy. The amplitude of damping peaks due to the temperature-induced transformation in the polycrystalline alloy was found to exceed those reported by others for single crystals of similar alloy compositions, in contrast to the usual reduction in damping in polycrystals. The high temperature portion of the damping peak occurs before martensitic bands are observed; therefore this portion cannot be due to interfacial motion. Constrained negative stiffness of the grains can account for this damping, as well as for amplification of internal friction peaks in these polycrystals and for sigmoid-shaped anomalies in the shear modulus at high cooling rates. Surface features associated with a previously unreported pre-martensitic phenomenon are seen at temperatures above martensite-start. 相似文献
146.
147.
Johan Sundberg Thomas F. Cleveland R.E. Stone Jr. Jenny Iwarsson 《Journal of voice》1999,13(2):168-183
Voice source characteristics as derived from inverse filtering were analyzed in 6 country singers' speech and singing. Results showed that the closed quotient varied systematically with vocal loudness, and that glottal compliance (the ratio between transglottal AC volume displacement and subglottal pressure) decreased with increases in fundamental frequency but remained unaffected by vocal loudness. No striking differences were found in source characteristics between speech and singing within subjects. The degree of phonatory press, as judged by a panel of 19 expert listeners, appeared related to the range in which the singer was singing and to the sound pressure level gain from a doubling of subglottal pressure. 相似文献
148.
Costantino DJ Scheidemantel TJ Stone MB Conger C Klein K Lohr M Modig Z Schiffer P 《Physical review letters》2008,101(10):108001
We explore the process of initiating motion through a granular medium by measuring the force required to push a flat circular plate upward from underneath the medium. In contrast with previous measurements of the drag and penetration forces, which were conducted during steady state motion, the initiation force has a robust dependence on the diameter of the grains in the medium. We attribute this dependence to the requirement for local dilation of the grains around the circumference of the plate, as evidenced by an observed linear dependence of the initiation force on the plate diameter. 相似文献
149.
When a liquid drop contacts a wettable surface, the liquid spreads over the solid to minimize the total surface energy. The first moments of spreading tend to be rapid. For example, a millimeter-sized water droplet will wet an area having the same diameter as the drop within a millisecond. For perfectly wetting systems, this spreading is inertially dominated. Here we identify that even in the presence of a contact line, the initial wetting is dominated by inertia rather than viscosity. We find that the spreading radius follows a power-law scaling in time where the exponent depends on the equilibrium contact angle. We propose a model, consistent with the experimental results, in which the surface spreading is regulated by the generation of capillary waves. 相似文献
150.
At half filling, the electronic structure of graphene can be modeled by a pair of free two-dimensional Dirac fermions. We explicitly demonstrate that in the presence of a geometrically induced gauge field an everywhere-real Kekulé modulation of the hopping matrix elements can correspond to a nonreal Higgs field with nontrivial vorticity. This provides a natural setting for fractionally charged vortices with localized zero modes. For fullerenelike molecules we employ the index theorem to demonstrate the existence of six low-lying states that do not depend strongly on the Kekulé-induced mass gap. 相似文献