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51.
52.
使用均苯三甲酸与碳酸镍在水热条件下反应得到了一例新的二维双层Ni(II)配位聚合物Ni3(BTC)2(μ-H2O)26H2O。二维层包含syn-syn羧酸桥和水桥连接的三核Ni3单元,进一步用均苯三甲酸上的苯环连接成二维层状结构。磁性研究表明,相邻Ni2+离子间存在弱的铁磁耦合作用。水桥连镍离子的桥联键角为122.8(3)deg,所以通过该水桥镍离子间应该呈现反铁磁耦合。因此,实验结果证明了syn-syn羧酸桥传递铁磁耦合,而且铁磁耦合大于反铁磁作用,最终配合物呈弱的铁磁耦合。基于本工作和文献报道的含syn-syn 羧酸混合桥联镍配合物的磁性,我们总结出下面结论:Ni–O–C–O–Ni的共面性与否决定了配合物的磁性。共面性好的Ni–O–C–O–Ni导致中等强度的反铁磁耦合,而共面性差会消弱反铁磁作用,甚至出现由反铁磁变为铁磁耦合。标题配合物中羧酸桥所传递的铁磁性可能就归因于Ni–O–C–O–Ni的不共平面性。因此,与含羧酸桥的混合桥联双核铜(II)配合物类似,轨道补偿效应(the orbital complementary effect (OCE))对于解释水/羧酸混合桥联镍(II)配合物的磁性也同样适用。 相似文献
53.
Coherent Dynamics of Direct-Current-Driven Quantum-Dot-Array with Two Time-Dependent Embedded Impurities
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The coherent dynamics of dc-driven quantum-dot array with two embedded time-dependent impurities is investigated, the exact crossings and avoided crossings in the quasienergies are associated with the evolution dynamics of the electron by the introduction of the envelope lines of the site's maximum returning probability. Through a perturbative scheme, the time-dependent Hamiltonian is replaced by an equivalent static one, whose structure reveals the new quantum tunnelling mechanism in the time-periodic driving system and sheds light on the alternative interpretation of dynamic localization and delocalization. 相似文献
54.
L. A. Falkovsky 《Journal of Experimental and Theoretical Physics》2001,92(5):840-843
The zone-center phonon frequencies of polar lattices are calculated for uniaxial crystals proceeding from the symmetry considerations. The long-range Coulomb forces and crystal anisotropy are explicitly taken into account. The free-carrier contributions to the dielectric constant are included. The angular dispersion of the optical-phonon modes is compared to data for a hexagonal 6H-SiC polytype. 相似文献
55.
Ceren ATLA DNER Ceren G
KALP Bengü GETREN Atila YILDIZ Nuray YILDIZ 《Turkish Journal of Chemistry》2021,45(4):1248
Usnic acid (UA) was extracted from Usnea longissima (L.) Ach. in supercritical carbon dioxide (SC-CO2) medium. The selected process parameters were extraction temperature (35–45 °C), amount of co-solvent (0%–5%) and extraction time (5–9 h). These parameters were applied to Box-Behnken design (BBD) belonging to response surface methodology (RSM) to determine optimum process parameters for the highest amount of UA in the extract. g UA/100g lichen, extraction yield % and UA content values were calculated in the range of 0.045–0.317, 2.77–5.4 and 71%–82% in different experimental conditions, respectively. The optimum conditions were predicted as 42 °C, 4.3% (ethanol) and 7.48 h. It was determined that the predicted and experimental values of g UA/100g lichen were compatible, and the suggested model was valid. 相似文献
56.
We propose a kinetic model of transient nonequilibrium phenomena in metals exposed to ultrashort laser pulses when heated
electrons affect the lattice through direct electron-phonon interaction. This model describes the destruction of a metal under
intense laser pumping. We derive the system of equations for the metal, which consists of hot electrons and a cold lattice.
Hot electrons are described with the help of the Boltzmann equation and equation of thermoconductivity. We use the equations
of motion for lattice displacements with the electron force included. The lattice deformation is estimated immediately after
the laser pulse up to the time of electron temperature relaxation. An estimate shows that the ablation regime can be achieved.
Zh. éksp. Teor. Fiz. 115, 149–157 (January 1999)
Published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor. 相似文献
57.
L. A. Falkovsky 《JETP Letters》2016,103(2):106-111
A small difference between the rhombohedral phosphorus lattice (A-7 phase) and the simple cubic phase, as well as between phosphorene and the cubic structure, is used in order to construct their quasiparticle band dispersion. We exploit the Peierls idea of the Brillouin zone doubling/folding, which has been previously employed in consideration of semimetals of the V period and IV–VI semiconductors. In a common framework, individual properties of phosphorus allotropes are revealed. 相似文献
58.
L. A. Falkovsky 《JETP Letters》2013,97(7):429-438
The optical conductivity of graphene and bilayer graphene in quantizing magnetic fields is studied. Both dynamical conductivities, longitudinal and Hall’s, are analytically evaluated. The conductivity peaks are explained in terms of electron transitions. Correspondences between the transition frequencies and the magneto-optical features are established using the theoretical results. The main optical transitions obey the selection rule Δn = 1 with the Landau number n. The Faraday rotation and light transmission in the quantizing magnetic fields are calculated. The effects of temperatures and magnetic fields on the chemical potential are considered. 相似文献
59.
J. MEDINA YU. G. GUREVICH G. N. LOGVINOV P. RODRÍGUEZ G. GONZÁLEZ DE LA CRUZ 《Molecular physics》2013,111(19):3133-3138
The problem of the effective thermal diffusivity of two-layer systems is investigated using the photoacoustic spectroscopy. The experimental results are examined in terms of the effective thermal parameters of the composite system determined from a homogeneous material that produces the same physical response under an external perturbation in the detector device. It is shown that the effective thermal conductivity is not symmetric under exchange of the two layers of the composite, i.e. the effective thermal parameters depend upon which layer is illuminated in the photoacoustic experiments. Particular emphasis is given to the characterization of the interface thermal conductivity between the layer system. 相似文献
60.