全文获取类型
收费全文 | 537018篇 |
免费 | 4043篇 |
国内免费 | 1194篇 |
专业分类
化学 | 256534篇 |
晶体学 | 8264篇 |
力学 | 28890篇 |
综合类 | 10篇 |
数学 | 73761篇 |
物理学 | 174796篇 |
出版年
2021年 | 5083篇 |
2020年 | 5407篇 |
2019年 | 6317篇 |
2018年 | 9016篇 |
2017年 | 9304篇 |
2016年 | 12338篇 |
2015年 | 6453篇 |
2014年 | 11454篇 |
2013年 | 24060篇 |
2012年 | 19125篇 |
2011年 | 22631篇 |
2010年 | 17592篇 |
2009年 | 17876篇 |
2008年 | 21030篇 |
2007年 | 20780篇 |
2006年 | 18956篇 |
2005年 | 16493篇 |
2004年 | 15621篇 |
2003年 | 14088篇 |
2002年 | 14208篇 |
2001年 | 15643篇 |
2000年 | 11930篇 |
1999年 | 9148篇 |
1998年 | 8040篇 |
1997年 | 7727篇 |
1996年 | 7164篇 |
1995年 | 6322篇 |
1994年 | 6296篇 |
1993年 | 6177篇 |
1992年 | 6518篇 |
1991年 | 7049篇 |
1990年 | 6761篇 |
1989年 | 6696篇 |
1988年 | 6321篇 |
1987年 | 6501篇 |
1986年 | 6073篇 |
1985年 | 7391篇 |
1984年 | 7672篇 |
1983年 | 6469篇 |
1982年 | 6637篇 |
1981年 | 6213篇 |
1980年 | 6001篇 |
1979年 | 6624篇 |
1978年 | 6662篇 |
1977年 | 6806篇 |
1976年 | 6818篇 |
1975年 | 6383篇 |
1974年 | 6199篇 |
1973年 | 6383篇 |
1972年 | 4988篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
982.
983.
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
984.
The charge distribution of fragments originatingfrom the fission of the 236U compound nucleus is calculated within a stochastic approach based on Langevin equations. The elongation coordinate, the neck-thickness coordinate, and the charge-asymmetry coordinate are chosen as collective variables. The friction parameter of the charge mode is calculated on the basis of two nuclear-viscosity mechanisms, that of one-body and that of two-body dissipation. It is shown that the Langevin approach is applicable to studying isobaric distributions. In addition, the charge distribution in question is studied as a function of the excitation energy of the compound nucleus and as a function of the coefficient of two-body viscosity. 相似文献
985.
Choyal Y. Minami K. Granatstein V.L. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》2004,32(6):2157-2168
The linear dispersion relation of a backward-wave oscillator (BWO), derived earlier by the authors, is modified to include effects of RF surface current at the beam-vacuum interface. This modified dispersion relation results in an unstable interaction between the slow cyclotron mode (SCM) and the structure mode in addition to the conventional Cherenkov instability caused by the slow space charge mode. Numerical analysis is then carried out using parameters of a BWO experiment at University of Maryland. Fine structure of the SCM instability is elucidated. The analysis indicates that BWO radiation would not be suppressed near cyclotron absorption in an infinitely long system. 相似文献
986.
987.
V. V. Klyucharev 《Doklady Chemistry》2003,390(1-3):127-130
988.
989.
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
990.
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