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排序方式: 共有237条查询结果,搜索用时 31 毫秒
191.
A STUDY OF RAMAN SCATTERING AND INFRARED ABSORPTION SPECTRUM IN A NEW SERIES OF MERCURY-BASED HIGH-Tc SUPERCONDUCTOR (Hg,Mo)Sr2(Y1-xCax)Cu2O6+δ
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Lattice vibrations of the (Hg,Mo)Sr2(Y1-xCax)Cu2O6+δ—a new series of mercury-based high-Tc superconductor are analyzed with the aid ofgroup theory. The vibrations of species are given. They are 4A1g+ B1g+ 5Eg+ 7A2u + B2u+ 8Eu. The 4A1g, B1g and 5Eg modes are Ramma active, the 6A2u and 7Eu are infrared active. Phonon vibration characteristics of the samples are studied using Raman scattering and infrared absorption spectra. The experimental results show that the typical phonon vibrational modes appear mainly at 145, 320, 440, 578, 592 and 645cm-1, The intensities of the 145, 320, 440, 578 and 645 peaks decrease with increasing Ca content x and the position of 645 peak moves to higher wavenumber slightly. In this article, the phonan modes are assigned and their variation behavior with increasing Ca content x are discussed. 相似文献
192.
The Na absorption on Si(100) 2×1 surface is studied with quantum chemistry molecular cluster method. The calculated results show that the most favourable absorption site of Na is the cave site and the charge transfer of Na atom to Si is large when the Na coverage is smaller than 0.5 monolayer (ML). A Na chain is formed along the cave sites at the 0.5 ML Na coverage, the charge transfer then becomes small. The calculated density of states show that the Na atoms are metallic along the chain. At 1 ML coverage, the Na atoms occupy both the cave and pedestal sites and form a double-layer. There is a charge transfer of 0.5e from each Na atom to the Si surface. The calculated surface energy shows that the saturation absorption of Na on Si surface is 1 ML. 相似文献
193.
袁松柳 《物理学报(海外版)》1995,4(10):766-773
Based on the scaling rule: R(T, H, θ) = R(T, h), where h = H(sin2θ+cos2θ/γ2)1/2 and θ is field angle with respect to the ab-plane, the scaling approach is performed to examine the c-axis resistances of single crystalline La1.86Sr0.14CuO4 as functions of field and its orientation at different temperatures. The anisotropy parameter γ of the system is extracted from the scaling approach, but shows an unusual temperature-dependent behavior, which is not expected by conventional theory. A phenomenological explanation of this temperature dependence is presented. 相似文献
194.
用溶胶-凝胶法并经过不同温度(TA)处理而制备出La4/3Sr5/3Mn2O7多晶样品.零场下阻温关系测量表明,较低TA处理的样品有较高的绝缘体-金属转变温度Tp,而对较高TA处理的样品,其Tp在表面和体内有较大差别,表面上有较高的Tp值,且电阻率较低,但在体内Tp低且电阻率高.结合结构分析,我们认为,较高温度处理有利于Sr3Ti2O7相的形成,但太高温度(如高于1450℃)处理的样品,虽然以Sr3Ti2O7相为主,但其表面易形成(La,Sr)MnO3相. 相似文献
195.
The nature of spin-state phase transition is investigated with [Fe(C4H4N2)(Pt(CN)4}] that is" a novel 3D Hofmann-like compound. The bistability of this system is obtained by the first-principles calculation. It is demonstrated that thermal expansion is the intrinsic force involved in spin-state transition. Based on these results, we suggest a thermal exciting bistable model of spin-state transition with a temperature dependent crystal-field splitting (CFS). Experimental evidence of spin-state phase transition coincides with our theoretical model. This model approaches something fundamental in the mechanism leading to the transition, and it is important in developing new and practical controllable quantum devices. 相似文献
196.
We investigate the orbital ordering quantitatively for the spinel systems RV 2 O 4(R=Mg,Zn,Cd) in the viewpoint of single-ion physics through the method of diagonalization.Through the quantitative calculation,it is found that the spin-orbit(SO)coupling and the Jahn-Teller(JT) effect enable the orbital ordering under the conditions of negligible electron hopping among different V 3+ sites.For the systems RV 2 O 4,the electron hopping is implied to be observable from the energy gap in conductivity,so the orbital ordering of RV 2 O 4 cannot be induced by the SO coupling and JT effect at definite temperature,which is on contrary to the conclusions in [Phys.Rev.Lett.93(2004) 157206]. 相似文献
197.
Dielectric and ferroelectric properties of Sr_4CaSmTi_3Nb_7O_(30) with tetragonal tungsten bronze structure
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Sr4CaSmTi3Nb7O30ceramics are synthesized and indexed as tetragonal tungsten bronze structure. The dielectric behavior and ferroelectric nature are investigated. Three dielectric anomalies are observed. The phase transition is a displacive phase transition with some diffusive characteristics, which indicates possible compositional variations within the materials on the microscopic scale. The weak distortion disappears in cooling process for differential scanning calorimetry measurement, and the large depression of Curie–Weiss temperature T0 indicates the difficulty in forming macroferroelectric domain. The ferroelectric nature in these filled tungsten bronze niobates originates from the off-center displacement of Bsite cations, but they are primarily dominated by A-site cation occupation. Both the radius and the valence of A1-site cations play an important role on ferroelectric properties of the filled tungsten bronze compounds. Existence of spontaneous polarization with a remanent polarization of 0.16 μC/cm2 a coercive field of Ec = 11.74 kV/cm confirms the room-temperature ferroelectric nature of Sr4CaSmTi3Nb7O30 ceramics. 相似文献
198.
Substantial Enhancements of Low—Field Magnetoresistance at Temperatures near 77K with Doping 4% Cu at Mn Sites of La2.3Ca1/3MnO3 Synthesized at 1000℃
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We report on investigations of magnetoresistance (MR) in polycrystalline La2/3Ca1/3Mn1-xCuxO3(x=0 and 4%)samples prepared by the sol-gel method followed a sintering treatment at 1000℃.For the x=4% sample,the most remarkable MR effect appears at temperatures near 77K and for magnetic fields lower than 1T.For fields-0.3T and at temperatures-77K,the x=4% sample exhibits a giant MR effect with MR0(≡Δρ/ρ(H=0))between-50and-70%,comparable to the so-called colossal MR response observed in the x=0 sample for the 3T field. 相似文献
199.
200.
Correction to the Metal—Insulator Transition Temperature due to Cation Size and Strain Effects for Colossal Magnetoresistance Perovskites
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A phenomenological expression of the metal-insulator transition temperature is proposed for AMnO3 manganese perovskites by taking into account the distortion of the Mn-O-Mn bond due to A-cation size and the strain-dependent effect due to performed Jahn-Teller distortions ,independently.Using reasonable physical parameters ,the calculated results give excellent agreement with experimental data obtained in polycrystalline samples of La2/3(Ca1-xBax)1/3 MnO3,providing a strong support to this approach. 相似文献