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31.
A convenient method for synthesis of tetragonal FeS using iron powder as iron source, is reported. Nanocrystalline tetragonal FeS samples were successfully synthesized by reacting metallic iron powder with sodium sulfide in acetate buffer solution. The obtained sample is single-phase tetragonal FeS with lattice parameters a = 0.3767 nm and c = 0.5037 nm, as revealed by X-ray diffraction. The sample consists of fiat nanosheets with lateral dimensions from 20 nm up to 200 nm and average thickness of about 20 nm. We found that tetragonal FeS is a fairly good conductor from the electrical resistivity measurement on a pellet of the nanosheets. The temperature dependence of conductivity of the pellet was well fitted using an empirical equation wherein the effect of different grain boundaries was taken into consideration. This study provides a convenient, economic way to synthesize tetragonal FeS in a large scale and reports the first electrical conductivity data for tetragonal FeS down to liquid helium temperature. 相似文献
32.
A gap in the spectrum of spin and ferroelectric waves is investigated versus magnetic and electric fields. It is demonstrated
that the magnetoelectric interaction is amplified with increasing external magnetic field and is weakened with increasing
external electric field. This allows the interaction between the spin and ferroelectric subsystems to be controlled by external
fields.
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 43–47, February, 2009. 相似文献
33.
利用原子级计算机模拟对四方SrTiO3中畴壁能进行了研究.在经典Born模型基础上用来描述离子晶体的原子级模拟,其能量表达式由长程库仑势和短程排斥势构成.后者为一含参数表达式,式中参数可由晶体的晶格常数、晶体结构和弹性常数等实验数据拟合得出.四方SrTiO3由高温立方SrTiO3相变而来,应存在反相畴界、孪晶界和平移孪晶界等3种畴界.本文用原子级模拟的技术对这3种畴界能进行了计算.结果表明畴界能尤其是反相畴界能非常小. 相似文献
34.
运用基于密度泛函理论的投影缀加波方法研究了Heusler合金Mn2NiGa的四方变形,对立方和四方结构的磁矩、电子结构、弹性常数及声子谱进行了计算和分析.Mn原子是Mn2NiGa总磁矩的主要贡献者,但Mn(A)、Mn(B)原子磁矩的值不等且呈反平行耦合,因而Mn2NiGa合金在两种状态下均表现为亚铁磁结构.四方变形中,Mn2NiGa在c/a=0.94和c/a=1.27处出现总能的局域极小值和局域最小值,分别对应一个稳定的马氏体.弹性常数的计算结果显示,Mn2NiGa的立方结构不满足立方相稳定性判据,四方结构(c/a=0.94和c/a=1.27)的弹性常数满足相应的稳定性判据.立方结构声子谱中存在虚频,而四方结构(c/a=0.94和c/a=1.27)则不存在虚频,验证了Mn2NiGa四方结构比立方结构稳定.c/a=1.27的四方结构Mn2NiGa转变为c/a=1.0的立方结构的相变温度在315 K左右. 相似文献
35.
36.
采用基于密度泛函理论框架下的第一性原理超原胞方法和虚晶近似方法, 在局域密度近似和广义梯度近似下, 对四方和正交以及单斜相K0.5Na0.5NbO3的能量和原子结 构以及电子结构进行了系统的研究. 计算结果表明三种K0.5Na0.5NbO3相的能量差别较小, 这与实验上它们之间容易发生相转化是一致的. 进一步发现单斜相的能量比四方相和正交相低, 说明单斜相结构更加稳定, 并且理论计算的结构参数与实验值符合得很好. 电子结构结果也表明单斜相的键合作用比四方相和正交相键合作用更强, 进一步说明单斜相结构更加稳定.
关键词:
铌酸钾钠
四方相
单斜相
密度泛函理论 相似文献
37.
By dynamic calorimetry the temperature dependence of heat capacity for two-dimensional (2D) polymerized tetragonal phase of C60 has been determined over the 300-650 K range at standard pressure mainly with an uncertainty ±1.5%. In the range 490-550 K, an irreversible endothermic transition of the phase, caused by the depolymerization of the polymer, has been found and characterized. Based on the experimental data obtained and literature information, the thermodynamic functions of 2D polymerized tetragonal phase of C60, namely, the heat capacity C°p(T), enthalpy H°(T)−H°(0), entropy S°(T), and Gibbs function G°(T)−H°(0), have been calculated over the range from T→0 to 490 K. From 150 to 330 K in an adiabatic vacuum calorimeter and between 330 and 650 K in a dynamic calorimeter the thermodynamic properties of the depolymerization products have been examined and compared with the corresponding data for the monomeric phase C60. 相似文献
38.
R. Poonguzhali R. Venkatesan T.M. Rajendiran P.S. Rao R.V.S.S.N. Ravikumar Y.P. Reddy 《Crystal Research and Technology》2000,35(10):1203-1207
Magnesium Potassium Phosphate Hexahydrate (MPPH), is analogous to the bio‐mineral struvite. Vanadyl doped MPPH crystals are grown by slow evaporation technique. EPR and optical absorption studies are carried out at room and liquid nitrogen temperatures. Spin‐Hamiltonian, crystal field and bonding parameters are evaluated. 相似文献
39.
A new series of bimetallic Lewis acid, Cu(NCO)2(NCS)2Hg, and its complexes, L2Cu(NCO)2(NCS)2Hg (L =thf,dmso, pyridine, nicotinamide and Ph3P are prepared and studied by physical and spectroscopic methods. 相似文献
40.
The ferroelectric phase of potassium lithium niobate K3Li2–xNb5+xO15+2x (KLN) in the range of 0.15 < x < 0.5 is a very promising material for the second harmonic generation (SHG) in the blue visible region (∼410 nm). The ferroelectric phase transition was shown to occur between 400 and 500°C depending on the composition of the KLN phase. In this study several analysis techniques were used to investigate the phase transition on ferroelectric (x = 0.3) KLN samples. The temperature‐dependent measurements of the relative dielectric constant ε33 provided a phase transition temperature of about 470°C. In our DTA experiments, a small but reproducible thermal effect at the phase transition in KLN was indicated. The temperature‐dependent birefringence measurement technique, applied the first time on KLN, shows a second order behaviour at a temperature of 467 °C. However, this phase transition is accompanied by a small thermal effect. The DSC analysis for the other KLN composition (x = 0.5) provided a phase transition temperature of 514 °C. The appearance of a phase transition in the paraelectric KLN phase (Nb content higher than 55 mol%) was also studied. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献