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71.
主要基于细观力学方法揭示了畴极化转动对多晶铁电陶瓷的各向异性断裂特性的平均影响。首先,用Eshelby-Mori-Tanaka理论和统计模型分析了无穷大铁电材料体中一椭球夹杂的内、外电弹性场,得到畴极化转动对电弹性场的平均影响;其次,推导了等效多晶铁电陶瓷中含一钱币状裂纹的裂纹扩展力(能量释放率)Gext,并用它估计了畴极化转动对多晶铁电陶瓷断裂特性的影响。对BaTiO3陶瓷中裂纹扩展力的计算结果表明,对多晶铁电材料断裂特性分析必须考虑畴极化转动的影响。计算结果得出了与实验相一致的结论:在受较小的力时,外加电场对裂纹扩展产生较大的影响,而且在某种程度上能促进了裂纹扩展。 相似文献
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73.
无铅弛豫铁电体具有较好的介电可调性,在顺电相有较大的介电常数和极小的损耗,因较大的优值而被广泛地用于微波器件.根据现有的介电可调性理论,通过参量的适当修正,对介电可调性的表达式做了合理的探讨,结论适用于处理实验结果.比较发现,在电场作用下顺电相保持不变的近似得出的结论与实验结果差距较大,而转化为铁电相与实验结果完全吻合.考虑外加电场和自发极化对弹性吉布斯自由能的修正,导出了高电场对介电常数的修正关系,与实验结果相符.提出了介电可调度的概念与计算公式,能够定量表示掺杂对介电可调性的影响. 相似文献
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75.
Jakob J. Brondijk Kamal Asadi Paul W. M. Blom Dago M. de Leeuw 《Journal of Polymer Science.Polymer Physics》2012,50(1):47-54
Most of the envisaged applications of organic electronics require a nonvolatile memory that can be programmed, erased, and read electrically. Ferroelectric field‐effect transistors (FeFET) are especially suitable due to the nondestructive read‐out and low power consumption. Here, an analytical model is presented that describes the charge transport in organic FeFETs. The model combines an empirical expression for the ferroelectric polarization with a density dependent hopping charge transport in organic semiconductors. Transfer curves can be calculated with parameters that are directly linked to the physical properties of both the comprising ferroelectric and semiconductor materials. A unipolar FeFET switches between a polarized and depolarized state, and an ambipolar FeFET switches between two stable polarized states. A good agreement between experimental and calculated current is obtained. The method is generic; any other analytical model for the polarization and charge transport can be easily implemented and can be used to identify the origin of the different transconductances reported in the literature. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011 相似文献
76.
A SIMPLE CONSTITUTIVE MODEL FOR FERROELECTRIC CERAMICS UNDER ELECTRICAL/MECHANICAL LOADING 总被引:1,自引:0,他引:1
Yu Li Yu Shouwen Feng Xiqiao 《Acta Mechanica Solida Sinica》2007,20(1):1-12
A simple phenomenological model is developed for describing the macroscopic constitutive response of ferroelectric materials based on consideration of the fact that domain switching is a progressive evolution process with loading. The volume fraction of domain switching is taken as an internal variable, which is derived from the domain nucleation theory. The proposed theory can simulate the dielectric hysteresis, reversed butterfly hysteresis, nonlinear strain-stress hysteresis, as well as electric displacement-stress relation of ferroelectric materials. Its comparison with experimental results and two other theoretical models reveals that the model presented can well predict the nonlinear hysteresis of ferroelectrics under electrical or mechanical loading. 相似文献
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78.
Dr. Yi Zhang Dr. Heng‐Yun Ye Dr. Da‐Wei Fu Prof. Ren‐Gen Xiong 《Angewandte Chemie (International ed. in English)》2014,53(8):2114-2118
The host–guest complex [(DIPA)([18]crown‐6)](ClO4) ( 1 ; DIPA=2,6‐diisopropylanilinium) was constructed and found to undergo a sequence of phase transitions (Ibam–Pbcn–Pna21) at T1=278 K and T2=132 K, respectively. Systematic characterizations, such as differential scanning calorimetry, heat capacity, temperature‐dependent dielectric constant, and P–E hysteresis loop, reveal that the centrosymmetric‐to‐polar phase transition at T2 is a paraelectric‐to‐ferroelectric transition. The symmetry breaking was also confirmed by temperature‐dependent second‐harmonic generation effect and X‐ray powder diffraction. The ferroelectric mechanism is attributable to the linear motion of the perchlorate counterions accompanied by the order–disorder transition of the [18]crown‐6 molecules and the anions. 相似文献
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80.
First principles study on the ferroelectricity of the perovskite ABO3 ferroelectrics 总被引:2,自引:0,他引:2 下载免费PDF全文
In order to understand well the different ferroelectric behaviour of quantum paraelectrics and ferroelectrics and the origin of the ferroelectricity of the solid solution KTa0.5Nb0.5O3(KTN),we calculated the electronic structure of CaTiO3,BaTiO3 and KTN by first principles calculation.From total energy analysis,it is shown that,with increasing cell volume,the crystals (CaTiO3,SrTiO3) will have a ferroelectric instability.For BaTiO3,the ferroelectricity will disappear as the cell volume is decreased.From the density of states analysis,it is shown that the hybridization between B d and O p is very important for the ferroelectric stability of ABO3 perovskite ferroelectrics.This is consistent with the analysis of band structure. 相似文献