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81.
本利用广义梯度近似(GGA)密度泛函和全势能线性缀加平面波(FIAPW)方法,计算给出了LaNi5和LaNisH7的晶体结构、生成焓、价电子轨道分布;晶体结构和焓与试验值作了对比,结果合理、可行;La原子与2c格位Ni原子的成键较强于La原子与3g格位Ni原子的成键,所以LaNi5晶体各向异性特征较为明显;并简单分析了这些性质与LaNi5合金的稳定性、循环寿命的关系。 相似文献
82.
83.
LiTaO3晶体高压结构相变的理论研究 总被引:1,自引:0,他引:1
利用基于密度泛函理论的平面波赝势结合局域密度近似的从头算方法,计算了LiTaO3晶体在0~200 GPa压力范围内的冷压曲线(P-V/V0)和零温焓,以研究它的高压结构相变.参照同构体LiNbO3的高压相结构,对LiTaO3的菱形相(R3c对称群,室温大气压结构)和正交相(Pbnm对称群)进行计算.结果表明,菱形相压缩线与低压冲击实验数据和静压结果符合较好,而正交相压缩线与扣除热压贡献的高压冲击实验数据相符;正交相更难压缩且各轴向的压缩率不同,对应的常态密度比菱形相高约24%.理论预测的相变起始压力约为23 GPa.由此可见LiTaO3的冲击高压相具有正交对称性,与LiNbO3的室温高压相类似. 相似文献
84.
Time-domain analytic solutions of two-wire transmission line excited by a plane-wave field
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This paper reports that an analytic method is used to calculate the load responses of the two-wire transmission line excited by a plane-wave directly in the time domain. By the frequency-domain Baum Liu-Tesehe (BLT) equation, the time-domain analytic solutions are obtained and expressed in an infinite geometric series. Moreover, it is shown that there exist only finite nonzero terms in the infinite geometric series if the time variate is at a finite interval. In other word, the time-domain analytic solutions are expanded in a finite geometric series indeed if the time variate is at a finite interval. The computed results are subsequently compared with transient responses obtained by using the frequency-domain BLT equation via a fast Fourier transform, and the agreement is excellent. 相似文献
85.
First-principles study on the effect of Hf content onmartensitic transformation temperatureof TiNiHf alloy 总被引:1,自引:0,他引:1
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In this paper a first-principles study of the electronic structure and stability of B2
TiDFT TiNiHf 电子结构 马氏体转化温度 平面波 DFT, TiNiHf, electronic structure, martensitic
transformation temperature Project supported by the National Natural Science Foundation of China
(Grant No 50471018). 3/3/2006 12:00:00 AM 6/7/2006 12:00:00 AM In this paper a first-principles study of the electronic structure and stability of B2 Ti1-xNiHfx (x = 0.2, 0.4, 0.6) and B19′ Ti1-xNiHfx(x = 0, 0.5) alloys is presented. The calculations are performed by the plane-wave pseudopotential method in the framework of the density functional theory with the generalized gradient approximation. This paper calculates the lattice parameters, density of states, charge density, and heats of formation. The results show that the electronic structure and stability of B2 Ti1-xNiHfx change gradually with Hf content. However, Hf content has little effect on the electronic structure and stability of B19′ Ti1-xNiHfx. The mechanism of the effect of Hf content on martensitic transformation temperature of TiNiHf alloys is studied from the electronic structure. 相似文献
86.
Ultrasoft pseudopotential was generated for uranium and the plane waves pseudopotential formalism was used to study its crystal structures at zero temperature as a function of pressure. The alpha phases of uranium were fully relaxed. The zero-pressure zero-temperature equilibrium volumes and bulk moduli are consistent with previous calculations, and in excellent agreement with the experiment. This is also the case for cell parameters and pressure-induced phase transitions. In the calculation of NaCl and CaF2 structure type of compound of uranium, the difference of theoretical lattice constant and the experimental value is less than 3%. For UO2+x the trend of the lattice shinking with the x value increase is in accord with the experiment. For large U2C3 and U2N3 complex cells the difference of theoretical lattice constant and the experimental value is less than 3%, and the difference of coordination of atom is less than 5%. 相似文献
87.
Pressure-induced structural transition and thermodynamic properties of RhN2 and the effect of metallic bonding on its hardness
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The elastic constant, structural phase transition, and effect of metallic bonding on the hardness of RhN2 under high pressure are investigated through the first-principles calculation by means of the pseudopotential plane-wave method. Three structures are chosen to investigate for RhN2, namely, simple hexagonal P6/mmm (denoted as SH), orthorhombic Pnnm (marcasite), and simple tetragonal P4/mbm (denoted as ST). Our calculations show that the SH phase is energetically more stable than the other two phases at zero pressure. On the basis of the third-order Birch Murnaghan equation of states, we find that the phase transition pressures from an SH to a marcasite structure and from a marcasite to an ST structure are 1.09 GPa and 354.57 GPa, respectively. Elastic constants, formation enthalpies, shear modulus, Young's modulus, and Debye temperature of RhN2 are derived. The calculated values are, generally speaking, in good agreement with the previous theoretical results. Meanwhile, it is found that the pressure has an important influence on physical properties. Moreover, the effect of metallic bonding on the hardness of RhN2 is investigated. This is a quantitative investigation on the structural properties of RhN2, and it still awaits experimental confirmation. 相似文献
88.
89.
各向异性体内含任意孔洞对反平面波散射的边界元方法 总被引:3,自引:0,他引:3
本文借助于广义格林公式导出了用位移表示的各向异性介质中SH波入射时的边界积分方程.根据本文作者在文献[8]给出的基本解,求解了各向异性介质中孔洞对SH波的散射问题.边界积分方程的离散基于常数元模式.文中给出了一个圆柱、一个椭圆柱和两个椭圆柱形式的孔洞周围的位移场和应力场的数值结果.最后,对入射波频率较高时的情形作了说明. 相似文献
90.
FengYangde WangYuesheng ZhangZimao CuiJunzhi 《Acta Mechanica Solida Sinica》2003,16(3):189-196
A 2D time domain boundary element method (BEM) is developed to solve the transient scattering of plane waves by a unilaterally frictionally constrained inclusion. Coulomb friction is assumed along the contact interface. The incident wave is assumed strong enough so that localized slip and separation take place along the interface. The present problem is in effect a nonlinear boundary value problem since the mixed boundary conditions involve unknown intervals (slip, separation and stick regions). In order to determine the unknown intervals, an iterative technique is developed. As an example, we consider the scattering of a circular cylinder embeddedin an infinite solid. 相似文献