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排序方式: 共有210条查询结果,搜索用时 31 毫秒
31.
F. Rahaman Peter K. F. Kuhfittig K. Chakraborty A. A. Usmani Saibal Ray 《General Relativity and Gravitation》2012,44(4):905-916
This paper discusses the observed flat rotation curves of galaxies in the context of noncommutative geometry. The energy density
of such a geometry is diffused throughout a region due to the uncertainty encoded in the coordinate commutator. This intrinsic
property appears to be sufficient for producing stable circular orbits, as well as attractive gravity, without the need for
dark matter. 相似文献
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34.
Mubasher Jamil Farook Rahaman 《The European Physical Journal C - Particles and Fields》2009,64(1):97-105
We here investigate a cosmological model in which three fluids interact with each other, involving certain coupling parameters
and energy exchange rates. The motivation of the problem stems from the puzzling ‘triple coincidence problem’ which naively
asks why the cosmic energy densities of matter, radiation and dark energy are almost of the same order of magnitude at the
present time. In our model, we determine the conditions under which triple interacting fluids will cross the phantom divide. 相似文献
35.
F. Rahaman Saibal Ray M. Kalam M. Sarker 《International Journal of Theoretical Physics》2009,48(11):3124-3138
We perform a survey whether higher dimensional Schwarzschild space-time is compatible with some of the solar system phenomena.
As a test we examine four well known solar system effects, viz., (1) Perihelion shift, (2) Bending of light, (3) Gravitational
redshift, and (4) Gravitational time delay. It is shown, under a N-dimensional solutions of Schwarzschild type very narrow class of metrics, that the results related to all these physical
phenomena are mostly incompatible with the higher dimensional version of general relativity. We compare all these restricted
results with the available data in the literature. 相似文献
36.
In this paper we have considered a spherically symmetric domain wall with non vanishing stress component in the direction perpendicular to the plane of the wall. The exact solutions are obtained using functional separability of metric coefficients. Also we have studied the motion of the test particles in different situations. 相似文献
37.
Moumita Majumdar Arup Sinha Tapas Ghatak Sanjib K. Patra Nabanita Sadhukhan S. M. Wahidur Rahaman Jitendra K. Bera Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(8):2574-2585
The complete sequence of reactions in the base‐promoted reduction of [{RuII(CO)3Cl2}2] to [RuI2(CO)4]2+ has been unraveled. Several μ‐OH, μ:κ2‐CO2H‐bridged diruthenium(II) complexes have been synthesized; they are the direct results of the nucleophilic activation of metal‐coordinated carbonyls by hydroxides. The isolated compounds are [Ru2(CO)4(μ:κ2‐C,O‐CO2H)2(μ‐OH)(NPF‐Am)2][PF6] ( 1 ; NPF‐Am=2‐amino‐5,7‐trifluoromethyl‐1,8‐naphthyridine) and [Ru2(CO)4(μ:κ2‐C,O‐CO2H)(μ‐OH)(NP‐Me2)2][BF4]2 ( 2 ), secured by the applications of naphthyridine derivatives. In the absence of any capping ligand, a tetranuclear complex [Ru4(CO)8(H2O)2(μ3‐OH)2(μ:κ2‐C,O‐CO2H)4][CF3SO3]2 ( 3 ) is isolated. The bridging hydroxido ligand in 1 is readily replaced by a π‐donor chlorido ligand, which results in [Ru2(CO)4(μ:κ2‐C,O‐CO2H)2(μ‐Cl)(NP‐PhOMe)2][BF4] ( 4 ). The production of [Ru2(CO)4]2+ has been attributed to the thermally induced decarboxylation of a bis(hydroxycarbonyl)–diruthenium(II) complex to a dihydrido–diruthenium(II) species, followed by dinuclear reductive elimination of molecular hydrogen with the concomitant formation of the RuI? RuI single bond. This work was originally instituted to find a reliable synthetic protocol for the [Ru2(CO)4(CH3CN)6]2+ precursor. It is herein prescribed that at least four equivalents of base, complete removal of chlorido ligands by TlI salts, and heating at reflux in acetonitrile for a period of four hours are the conditions for the optimal conversion. Premature quenching of the reaction resulted in the isolation of a trinuclear RuI2RuII complex [{Ru(NP‐Am)2(CO)}{Ru2(NP‐Am)2(CO)2(μ‐CO)2}(μ3:κ3‐C,O,O′‐CO2)][BF4]2 ( 6 ). These unprecedented diruthenium compounds are the dinuclear congeners of the water–gas shift (WGS) intermediates. The possibility of a dinuclear pathway eliminates the inherent contradiction of pH demands in the WGS catalytic cycle in an alkaline medium. A cooperative binuclear elimination could be a viable route for hydrogen production in WGS chemistry. 相似文献
38.
39.
Rahaman A Collins O Scott C Wang J Hase WL 《The journal of physical chemistry. A》2006,110(27):8418-8422
The effects of temperature on energy transfer during collisions of protonated diglycine ions, Gly(2)-H(+), with a diamond {111} surface were investigated by chemical dynamics simulations. The simulations were performed for a collision energy of 70 eV and angle of 0 degrees with respect to the surface normal. In one set of simulations the initial surface temperature, T(surf), was varied from 300 to 2000 K, while the Gly(2)-H(+) vibrational and rotational temperatures were maintained at 300 K. For the second set of simulations the Gly(2)-H(+) vibrational temperature, T(vib), was varied from 300 to 2000 K, keeping both the Gly(2)-H(+) rotational and surface temperatures at 300 K. Increasing either the surface temperature or Gly(2)-H(+) vibrational temperature to values as high as 2000 K has, at most, only a negligible effect on the partitioning of the incident collision energy to the surface and to the vibrational and rotational modes of Gly(2)-H(+). To a good approximation, the initial surface and peptide ion energies are nearly adiabatic during the collisional energy transfer. This adiabaticity of the initial peptide ion energy agrees with experiments (J. Phys. Chem. A 2004, 108, 1). A more quantitative analysis of the effects of T(vib) and T(surf) shows there are small, but noticeable, effects on the energy transfer efficiencies. Namely, increasing the vibrational or surface temperature results in a near-linear decrease in the energy transfer to the degrees of freedom associated with this temperature. 相似文献
40.
In this study conductive composite of ethylene vinyl acetate (EVA)/polyaniline (Pani) were prepared by in-situ polymerization technique. Dielectric properties (Permittivity) of the composites have been investigated with respect to concentration of Pani and frequency of electric field. For predicting permittivity of the composites, different mixing rules proposed by Lichtenecker, Bruggeman, Jaysundere–Smith, Maxwell–Wagner, and Yamada have been verified at 10, 103, and 106 Hz frequencies. It has been found that the theoretical permittivities predicted by different models differ largely from experimental permittivity when measured at 10 and 103 Hz frequencies. The limitations of the models as well as the cause of deviations between the theoretically predicted and experimentally observed results have been discussed. A new model for permittivity has been proposed by considering the generation of interface polarization between the EVA matrix and Pani particles. This model fits well with the experimentally observed results. 相似文献