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51.
A pair of novel molecular indices has been proved to contain important information on the coupling between atomic displacement and electronic properties based on the electron density function within the Density Functional Theory: the nuclear reactivity (Φ) and nuclear stiffness (G). Appropriate calculation procedure has been developed and their role in describing anharmonicity of diatomic molecules has been demonstrated. This present work provides analysis of this effect for small molecules, unveiling the role of symmetry of molecular vibrational modes in modifying the affinity of a molecule to intermolecular electron transfer. The indices have been found to be a crucial factor determining thermal fluctuations in the molecular energy derivatives: electronegativity (χ) and hardness (η). The fluctuations of hardness play a specific role, as they bring a molecule uniquely to a critical region (η0), when molecule becomes unstable to an electron exchange process, due to its excitation in a selected destructive vibrational mode. 相似文献
52.
本文研究了五种有机锡化合物的光电子能谱图,讨论了影响锡原子内层d轨道电子结合能化学位移的几种因素,比如,取代基的影响,基团电负性的影响。 相似文献
53.
Slater's transition state concept and the relativistic numerical Hartree-Fock-Slater theory has been used to calculate the electronegativity and first ionization potential for the rare earth atoms. Based on these results the electron affinity has also been estimated. The theory predicts almost constant values of the electronegativity as 2 eV, first ionization potential as 8 eV and the electron affinity of -(4–5) eV respectively.This work is dedicated to the memory of Prof. J. C. Slater.Alexander von Humboldt fellow, on leave from school of chemistry, University of Hyderabad, India. 相似文献
54.
55.
Boris ?emva 《Journal of fluorine chemistry》2006,127(11):1463-1466
The low electronegativity of an oxidation state in an anion enables high oxidation states, e.g. NiIV, and AgIII, to be easily attained in liquid anhydrous HF (aHF), made basic with fluoride-ion donors. The oxidation state can be enhanced if elemental fluorine is photo-dissociated. Teflon® valves and lines, especially transparent and kinetically stable fluorocarbon containers for the aHF solutions, provide for this. Binary fluorides that are of low solubility in aHF, can be displaced by stronger F− acceptors from their high oxidation-state anions. NiF4, NiF3, and AgF3, which can be made in this manner, are thermodynamically unstable with respect to loss of fluorine. The electronegativity of the oxidation state in the binary fluoride is higher than in the anion (hence the metastability) and when a strong F− acceptor converts the binary fluoride into a cationic species, the electronegativity is further enhanced. Thus cationic AgIII and NiIV are superior to KrF+, as one-electron oxidizers and are the most potent oxidizers known thus far. They are able to remove the electron from all platinum-metal hexafluoro-anions, MF6−, to liberate the hexafluorides. All of this chemistry can be achieved at or below room temperature. 相似文献
56.
Site‐Specific Substitution Preferences in the Solid Solutions Li12Si7–xGex,Li12–yNaySi7, Na7LiSi8–zGez,and Li3NaSi6–vGev
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The mixed silicide‐germanides Li12Si7–xGex, Na7LiSi8–zGez, and Li3NaSi6–vGev which could serve as potential precursors for Si1–xGex materials were synthesized and characterized by X‐ray diffraction methods. The full solid solution series Li12Si7–xGex (0 ≤ x ≤ 7) is easily accessible from the elements and features preferential occupation of the more negatively charged crystallographic tetrel positions by Ge, which is the more electronegative element. In case of Na7LiSi8–zGez a broad solid solution range of 1.3 ≤ x ≤ 8 is available but the ternary silicide Na7LiSi8 could not be obtained by the tested methods of synthesis. The solubility of Ge in Li3NaSi6–vGev is highly limited to a maximum of v ≈ 0.5, and again the formally more negatively charged tetrel positions are preferred by Ge. Additionally, the two crystallographic Li positions in Li12Si7 with unusually large displacement parameters can be partially substituted by Na in Li12–yNaySi7 with 0 ≤ y ≤ 0.6. The statistical mixing of Li and Na in this solid solution contrasts the typical ordering of Li and Na in most ternary tetrelides. 相似文献
57.
18世纪末,拉瓦锡在氧化学说范式下,建立了“得失氧”角度上的氧化还原反应的概念。19世纪,约翰逊在化合价学说的基础上,发现氧化还原反应的共同特征是“化合价升降”,其概念扩大至反应前后化合价发生升降的一类反应。20世纪初,弗莱从“电子转移”的角度解释了化合价升降的原因,揭示了氧化还原反应的微观本质。1948年,格拉斯顿在价键理论和电负性基础上,从“氧化数变化”的角度提出了氧化还原反应的人为表征概念。20世纪末,古德斯坦和李良助分别从“电负性顺序”和“极性翻转”角度提出了氧化还原反应的现代理解。氧化还原反应概念的发展史,反映了化学思想的发展和科学认识的变化,对化学研究有重要的启示。 相似文献
58.
原子-键电负性均衡方法中的σπ模型及应用 总被引:8,自引:1,他引:7
带有双键或共轭双键的化合物可进行加成、氧化和聚合等反应,在有机、生物和制药等领域用途广泛.密度泛函理论下的电负性均衡方法在研讨分子电荷分布和反应性等方面有独特优势[1~4].在电负性均衡方法中,Mortier[1]的电负性均衡方法引人注目,但其未考虑分子中化学键的存在.Ghosh[2]的半经验电负性均衡方法考虑了化学键电荷,但键电荷取值假定太简单,只能处理双原子分子.Yang[3,4]等的原子-键电负性均衡方法同时考虑了分子中原子和化学键的存在,取得令人满意的结果.至今尚无人明确地考虑双键的结构… 相似文献
59.
电负性拓扑指数mF及其对无机物理化性质的预测 总被引:2,自引:0,他引:2
受Randic分子连接性拓扑指数 mX的启发 ,构建了电负性拓扑指数 mF .用 mF的 0、1阶指数分别与 2 0种碱金属卤化物的晶格能U、生成焓ΔrHm、离子水化能ΔrGθm、5 1种金属离子水合热ΔrHθh 和 80种离子标准生成热ΔfHθm 进行关联 ,拟合的回归方程的相关系 (指 )数分别为 0 .995 4( 0 .995 4)、0 .983 5 ( 0 .9840 )、0 .9794( 0 .9795 )、0 .9948和 0 .9865 ,满足优级或良级标准 .结构选择性达到唯一性表征 ,预测取得满意的结果 相似文献
60.
原子电荷计算方法的对比 总被引:2,自引:0,他引:2
原子电荷是对化学体系中电荷分布最简单、最直观的描述形式之一,在理论和实际应用中都有重要意义.本文介绍了12种重要的原子电荷计算方法的原理和特点,通过大量实例从不同角度比较了它们的优缺点.这些方法包括Mulliken、分子环境中的原子轨道(AOIM)、Hirshfeld、原子偶极矩校正的Hirshfeld布居(ADCH)、自然布居分析(NPA)、Merz-Kollmann(MK)、分子中的原子(AIM)、Merck分子力场94(MMFF94)、AM1-BCC、Gasteiger、电荷模型2(CM2)以及电荷均衡(QEq)方法.最后本文对如何在实际应用中选择合适的计算方法给出了建议. 相似文献