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21.
Effect of defect configuration on the localization of phonons in two-dimensional phononic crystals 总被引:1,自引:0,他引:1
Effects of defect location on the defect frequency and the localization of phonons are investigated in two novel kinds of model, created by moving the location of the native cylinder and inserting an ad-cylinder in the central cellular respectively. The results show that the defect frequency in Model 1 is only related to the distance, while in Model 2, is related not only to the distance, but also to the moving direction. From the pressure distribution, obvious localization phenomenon is found. The position and shape of the localized energy are varied with the position of the defect. 相似文献
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采用第一性原理研究了CdS的六方纤锌矿(WZ), 立方闪锌矿(ZB) 和岩盐矿(RS)相在高压条件下的相稳定性、 相变点、电子结构以及弹性性能.WZ相与RS 相可以在相应的压强范围内稳定存在, 而ZB相不能稳定存在.压强大于2.18 GPa时, WZ相向RS相发生金属化相变.WZ相中S原子电负性大于Cd, 且电负性差值小于1.7, CdS的WZ相为共价晶体.高压作用下, S原子半径被强烈压缩, 有效核电荷增加, 对层外电子吸引能力提高, 电负性急剧增大, 导致S与Cd的电负性差值大于1.7, CdS的RS相以离子晶体存在. WZ相的C44随压强增加呈下降趋势, 导致WZ相力学不稳定, 并向RS相转变.当压强大于2.18 GPa时, RS相C11, C12随压强增加而增大, 并且C44保持稳定, 说明RS相具有良好的高压稳定性与力学性能.
关键词:
第一性原理
相变
电子结构
弹性性质 相似文献
24.
We present two robust three-party quantum secret sharing protocols against two kinds of collective noise. Each logical qubit is made up of two physical qubits and is invariant under a collective noise. The two agents encode their message on each logical qubit with two unitary physical operations on two physical qubits. As each logical qubit received by each agent can carry two bits of information and the classical information exchanged is reduced largely, these protocols have a high intrinsic efficiency. Moreover, the boss Alice can read out her agents' information with two Bell-state measurements on each four-qubit system, not four-photon joint measurements. 相似文献
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28.
Ab initio lattice dynamics and piezoelectric properties of MgS and MgSe alkaline earth chalcogenides
S.?Saib N.?Bouarissa P.?Rodríguez-Hernández A.?Mu?oz 《The European Physical Journal B - Condensed Matter and Complex Systems》2010,73(2):185-193
We have studied structural, elastic, dielectric, vibrational, and piezoelectric properties of rock-salt and zinc-blende Mg
alkaline earth chalcogenides (MgS, and MgSe) by using the plane-wave pseudopotential method within the local density approximation.
The calculated lattice constant, bulk modulus, and elastic constants for these compounds are found to be in good agreement
with experiment. The density functional perturbation theory has been employed to derive the Born effective charge and high-frequency
dielectric constant and to calculate phonon dispersion curves and density of states. The piezoelectric constant has also been
determined. The calculated results are compared with theory and experiment when available and showed reasonable agreement.
In other cases, our results are predictions. The pressure dependence of the studied quantities has been examined and discussed.
The pressure coefficients and mode Grüneisen parameters are determined. 相似文献
29.
The crystal structure of ScB3 is seeked by combining the developed particle swarm optimisation algorithm for crystal structure prediction with first-principles calculations. A new monoclinic phase with the C2/m symmetry is predicted successfully, which is energetically more superior to the early reported R-3m-, P21/m-, P63/mmc-, P-6m2-, Pnma-, and Pm-3m-type structures in the pressure range from 0 to 100?GPa. The obtained elastic constants and phonon dispersion curve reveal that the C2/m-ScB3 is mechanically and dynamically stable. The predicted large bulk module, high shear modulus, small Poisson’s ratio as well as the considerable hardness indicate that the C2/m-ScB3 has outstanding mechanical property. Meanwhile, the dependences of the bulk modulus and Young’s modulus of ScB3 on the crystal orientation are investigated theoretically. Through applying the strain–stress method, the ideal tensile and shear strengths along different crystal directions are also estimated, and the obtained results confirm that the shear mode dominates the failure mode in the C2/m-ScB3 structure and it is intrinsically a hard material. The electronic structure calculation and chemical bonding analysis illustrate that the strong covalent B-B and Sc-B bonds are responsible for its structural stability and high hardness. 相似文献
30.
通过透射光谱、x射线激发发射光谱(XSL)的测试,研究了Bridgman法生长的几种不同+3价离子掺杂钨酸铅晶体的发光性能,并利用正电子湮没寿命谱(PAT)和x光电子能谱(XPS)的实验手段,对不同钨酸铅晶体的微观缺陷进行研究.实验表明,不同的+3价离子掺杂,对钨酸铅晶体发光性能的改善不同,并使得晶体中正电子俘获中心和低价氧的浓度发生不同变化.其中掺镧晶体的正电子俘获中心和低价氧浓度均上升,而掺钇和掺铋晶体的正电子俘获中心和低价氧浓度均下降,掺锑晶体则出现了正电子俘获中心浓度上升、低价氧浓度下降的情况.提
关键词:
钨酸铅晶体
+3价离子掺杂
正电子湮没寿命谱
x光电子能谱 相似文献