Roles of electrostatic interaction and dispersion in CH···CH,CH···π, and π···π ethylene dimers

The structural, mechanical, electronic, and optical properties of orthorhombic Bi₂S₃ and Bi₂Se₃ compounds have been investigated by means of first principles calculations. The calculated lattice parameters and internal coordinates are in very good agreement with the experimental findings. The elastic constants are obtained, then the secondary results such as bulk modulus, shear modulus, Young’s modulus, Poisson’s ratio, anisotropy factor, and Debye temperature of polycrystalline aggregates are derived, and the relevant mechanical properties are also discussed. Furthermore, the band structures and optical properties such as real and imaginary parts of dielectric functions, energy-loss function, the effective number of valance electrons, and the effective optical dielectric constant have been computed. We also calculated some nonlinearities for Bi₂S₃ and Bi₂Se₃ (tensors of elasto-optical coefficients) under pressure.

问·题·解·答

问:假根与真根有什么区别?答:假根,一般为低等植物所特有,是具有吸收和固着作用的丝状结构,分枝或不分枝,仅由伸长的单细胞或单列的多细胞所构成,无组织分化。如藻类、真菌就具有这种假根。但是现存的高等植物中,苔藓植物以及蕨类植物的原叶体上也具有假根。真根较之于假根,主要在于有机械、输导等组织的分化。真根植物可以说是由仅有假根的无根类型逐渐进化而来的。一般来说,蕨类的孢子体世代以及种子植物都具有。不过,在某些如水生或腐生的种子植物中,由于其生存环境的特殊性,     

自学·质疑·精讲·练习

自学·质疑·精讲·练习”课堂教学方法,简易可行,便于推广,适宜不同年级、不同教学内容,便于穿插演示实验、讲解法等其他教学方法,使学生的主体作用、教师的主导作用得以充分发挥,有利于增强学生的集体主义精神,有利于培养学生的自学能力,提高分析问题、解决问题...     

·科研快讯·

《科学-转化医学》:按摩或可加速受损肌肉康复按摩疗法近年来被越来越多的人所接受。一项新研究也显示,按摩疗法可通过与大多数镇痛药相同的生物学机制来减轻肌肉疼痛,可能有助于受损肌肉     

Effect of stepwise microhydration on the methylammonium···phenol and ammonium···phenol interaction

A computational study has been performed for studying the characteristics of the interaction of phenol with ammonium and methylammonium cations. The effect of the presence of water molecules has also been considered by microhydrating the clusters with up to three water molecules. Clusters of phenol with ammonium and methylammonium cations present similar characteristics, though ammonium complexes have been found to be more stable than the methylammonium ones. The first water molecule included in the complexes interacts with a N-H group of ammoniun cations and simultaneously with the hydroxyl oxygen atom of phenol (or the aromatic ring). This first water molecule is more tightly bound in the complex, so the stability gain as more water molecules are included drops significantly by 2-3 kcal?mol^?1 with respect to the first one. As more water molecules are included, the differences between favorable coordination sites (the cation, the hydroxyl group or a previous water molecule) decrease. As a consequence, several of the most stable complexes located including three water molecules already exhibit hydrogen bonds between the hydroxyl group and one water molecule. The results indicate that a cyclic pattern formed by a series of hydrogen bonds: π···H-N-H···O-H···O-?, is characteristic of the most stable minima, being kept as more water molecules are included in the system. Therefore, this pattern can be expected to be crucial in ammonium cations···phenol interaction if exposed to the solvent to any degree.     

爱鸟·观鸟·赏鸟·护鸟

<正>"春眠不觉晓,处处闻啼鸟",唐代诗人孟浩然的诗句是我们儿时便能诵读的。春天代表着希望,鸟类寓意着新生。在这样一个春光明媚的时刻,我们怎能忘怀"自在娇莺恰恰啼"的美丽画卷呢?说到鸟类,我们总有无限的美好遐思——它们自由奔放,翱翔长空。它们婀娜多姿,步态轻盈。它们歌喉动听,嘤嘤啼啭……鸟类是自     

读者·作者·审者·编者

《中国生物化学与分子生物学报》自2006年1月起改为月刊为缩短出版周期,提高期刊学术水平和刊印质量,经《中国生物化学与分子生物学报》编委会讨论决定,上报中国生物化学与分子生物学会同意,获得中国科协和北京市新闻出版局批准,本刊自2006年1月起改为月刊,每月20日出版.每期96     

读者·作者·编者

我是一名从教多年的高中生物学教师,也是《生物学通报》的积极读者,我想请教:《生物学通报》2005年第6期第60页刊登2004年第15届国际生物学奥林匹克竞赛理论试题B(2)中的第106题,为什么人的“Y染色体是独特的,在减数分裂中不会发生交叉”。     

读者·作者·编者

编辑同志,上海植物生理学会编写的《植物生理学实验手册,第606页第三行“24.2g三羟甲基氨基甲烷用蒸馏水稀释至200ml”一句中的24.2g应改为4.85g,若是24.2g则应稀释至1000ml。《手册》是基层植物生理学工作者的实验指导,应力求正确,望予以更正     

龙·马·人

<正>几千万年古老的基因风塑成的流线体型优美矫健350度的视角敏锐的嗅觉警惕着临近的危险像离弦的箭逃离步步紧逼的厮杀追风四蹄敲响快速的节拍优胜劣汰的强者遍布全球繁衍生息终未能躲闪抛来的套索生命由此改弦易辙一双手缓缓放在了脊背     

制度·观念·方法

1972年11月16日,联合国教科文组织（UNESCO）于巴黎举行的第十七届会议上通过了《保护世界自然与文化遗产公约》（简称《公约》）,不仅首次将自然遗产与文化遗产同时予以关注,而且以国际法的形式,明确了各缔约国保护本国领土内的文化和自然遗产、     

名药·美食·救命草

亚丁自然保护区地处青藏高原横断山区沙鲁里山脉的南段,区内地势高亢,峡谷深幽,森林茂密,牧草如茵。保护区内小贡嘎雪山主峰仙乃日,海拔高达6032米,是四川省的第五高峰。从保护区东面的雪山到南面的东义河河谷,直线距离仅20公里,海拔相对高差达4000米。特殊的自然条件,为本地区生物的生存和繁衍创造了十分有利的环境,从而也成了四川省的名药主产区。     

读者·作者·编者

本刊三卷五期“遗传学教学”栏刊登了张桂芬同志“怎样解遗传学综合题”一文后,我们陆续收到马伟东、侯利人、薛桂芝、孙义伟等同志的来信,对该文的例题1(5)和3(2)的解答提出了意见。现请张桂芬同志进行答复和说明。我们热诚欢迎广大读者、作者继续关心和支持《遗传》各专栏,以把它们办成活跃的学术交流园地。