全文获取类型
收费全文 | 710篇 |
免费 | 25篇 |
国内免费 | 2篇 |
专业分类
化学 | 377篇 |
晶体学 | 7篇 |
力学 | 10篇 |
数学 | 88篇 |
物理学 | 255篇 |
出版年
2023年 | 2篇 |
2022年 | 17篇 |
2021年 | 11篇 |
2020年 | 11篇 |
2019年 | 15篇 |
2018年 | 20篇 |
2017年 | 13篇 |
2016年 | 32篇 |
2015年 | 15篇 |
2014年 | 29篇 |
2013年 | 53篇 |
2012年 | 50篇 |
2011年 | 46篇 |
2010年 | 26篇 |
2009年 | 32篇 |
2008年 | 36篇 |
2007年 | 35篇 |
2006年 | 29篇 |
2005年 | 35篇 |
2004年 | 17篇 |
2003年 | 16篇 |
2002年 | 19篇 |
2001年 | 26篇 |
2000年 | 22篇 |
1999年 | 11篇 |
1998年 | 12篇 |
1997年 | 9篇 |
1996年 | 14篇 |
1995年 | 4篇 |
1994年 | 18篇 |
1993年 | 8篇 |
1992年 | 7篇 |
1991年 | 7篇 |
1990年 | 5篇 |
1989年 | 4篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 4篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 2篇 |
1955年 | 2篇 |
排序方式: 共有737条查询结果,搜索用时 865 毫秒
91.
P.J. Iunes G. Bigazzi J.C. Hadler Neto M.A. Laurenzi M.L. Balestrieri P. Norelli A.M. Osorio Araya S. Guedes C.A. Tello S. S.R. Paulo P.A.F.P. Moreira R. Palissari E.A.C. Curvo 《Radiation measurements》2005,39(6):665-668
Neutron dosimetry based on U and Th thin films was used for fission-track dating of the age standard Moldavite, the central European tektite, from the Middle Miocene deposit of Jankov (southern Bohemia, Czech Republic). Our fission-track age () agrees with a recent 40Ar/39Ar age, , based on several determinations on Moldavites from different sediments, including the Jankov deposit. This result indicates that the U and Th thin film neutron dosimetry represents a reliable alternative for an absolute approach in fission-track dating. 相似文献
92.
93.
94.
95.
A class of Bianchi IX cosmological models is shown to have chaotic gravitational collapse, due to Poincaré's homoclinic phenomena. We can program such models so that for any given positive integer N (N=∞ included) the universe undergoes N non-periodic oscillations (each oscillation requiring a long time) before collapsing. For N=∞ the universe undergoes periodic oscillations. 相似文献
96.
We perform first-principles calculations of the surface and bulk wave functions of the Cu(111) surface and their hybridization energies to a Co adatom, including the potential scattering from the Co. By analyzing the calculated hybridization energies, we find the bulk states dominate the contribution to the Kondo temperature, in agreement with recent experiments. Furthermore, we also calculate the tunneling conductance of a scanning tunneling microscope and compare our results with recent experiments of Co impurities in the Cu(111) surface. Good quantitative agreement is found at short parallel impurity-tip distances (<6 A). Our results indicate the need for a new formulation of the problem at larger distances. 相似文献
97.
E. S. F. Neto N. O. Dantas S. W. da Silva P. C. Morais M. A. Pereira da Silva 《Journal of Raman spectroscopy : JRS》2010,41(10):1302-1305
This work gives the evidence of the lattice contraction in CdSe nanocrystals (NCs) grown in a glass matrix. The CdSe NCs were investigated by atomic force microscopy (AFM), optical absorption (OA), and Raman spectroscopy. The average size of CdSe NCs can be estimated by AFM images. Using the OA spectra and the effective‐mass approximation, it was also possible to estimate the average sizes of CdSe NCs, which agree very well with the AFM data. These results showed that the CdSe NCs grow with increasing time of heat treatment. The blue shift of the longitudinal optical (LO) modes and surface optical (SO) phonon modes with an increase in the average radius of the NCs, shown in the Raman spectra, was explained by the lattice contraction in CdSe NCs caused by thermodynamic interactions at the interface with the host glass matrix. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
98.
E. V. Spinacé Ricardo R. Dias Michele Brandalise Marcelo Linardi Almir Oliveira Neto 《Ionics》2010,16(1):91-95
PtRh/C (90:10), PtRh/C (50:50), PtSn/C (50:50), and PtSnRh/C (50:40:10) electrocatalysts were prepared by an alcohol-reduction
process using ethylene glycol as solvent and reduction agent and Vulcan Carbon XC72 as supports. The electrocatalysts were
characterized by energy-dispersive X-ray analysis, X-ray diffraction, and transmission electron microscopy. The electro-oxidation
of ethanol was studied by cyclic voltammetry chronoamperometry at room temperature and on a single cell of a direct ethanol
fuel cell at 100 °C. Cyclic voltammetry and chronoamperometry experiments showed that PtSnRh/C and PtSn/C electrocatalysts
have similar performance for ethanol oxidation at room temperature, while the activity of PtRh/C electrocatalysts was very
low. At 100 °C on a single cell, PtSnRh/C showed superior performance compared to PtSn/C and PtRh/C electrocatalysts. 相似文献
99.
Douglas G. Macharet Armando Alves Neto Vila F. da Camara Neto Mario F. M. Campos 《Journal of Heuristics》2018,24(1):83-109
In this paper we address the problem of planning optimized routes among dynamically selected target regions for vehicles with a turning radius motion constraint, hereinafter called dynamic Dubins traveling salesman problem with neighborhoods (DDTSPN). Initially, we present a heuristic to solve a simpler version of this problem, called off-line step, where only previously given targets are concerned. We further extend this approach for the more complex case of dynamic scenarios, called on-line step, addressing the inclusion of new targets during the execution of the initial route, whilst minimizing the impact on the total traveled distance. Formal analyzes of our techniques are provided, presenting upper bounds for the total length of the final tour. Results with statistical investigation over a large number of trials in a simulated environment are also provided. Finally, to demonstrate the applicability of our technique in solving the DDTSPN at real-world scenarios, we also report on results of an experiment performed with a real car-like robot. 相似文献
100.
Sissy da S. Souza P.R. Oliveira J.X. da Cruz Neto A. Soubeyran 《European Journal of Operational Research》2010
We present an interior proximal method with Bregman distance, for solving the minimization problem with quasiconvex objective function under nonnegative constraints. The Bregman function is considered separable and zone coercive, and the zone is the interior of the positive orthant. Under the assumption that the solution set is nonempty and the objective function is continuously differentiable, we establish the well definedness of the sequence generated by our algorithm and obtain two important convergence results, and show in the main one that the sequence converges to a solution point of the problem when the regularization parameters go to zero. 相似文献