某种元素的原子价怎么会有三个数目的?如硫(S)有二价,四价和六价。

当硫与氢结合成硫化氢(H_2S)分子时,二个氢原子各给硫原子一个电子,得到带两个阴电荷的硫离子(S~=)及两个一个阳电荷的氢离子H~+。氢离子被硫离子所吸引,生成硫化氢分子(H_2S): 2H~++S~==H_2S………………(1) 但硫原子不仅能吸入电子,也能放出自己外层的电子,变成阳离子。例如,硫与氧化合时,硫带有阳电荷,而氧带有阴电荷。如: S~(+6)+3O~==SO_3………………(2) 硫原子最外层有6个电子,每个氧原子吸入两个电子,结果硫原子变成+6价,氧变成负2价。但有时硫原子不一定将它全部的价电子放出,却只放出四个电子。例如在SO_2分子组成     

惊人的数字 电视广播的电子总数有多重

你看了兩个鐘头的电視广播。在兩个鐘头里,極细的电子射束时強时弱地奔向电视接收机的發光屏。到底有多少个电子为我們扫描景象呢?讓我們来算算看。我們算出,电視管的陽極电流強度平均等于100微安。我們知道在1安培的电流強度下,每秒鐘通过的电荷是1庫侖。不难算出,每秒通过电視管的电荷就是0.0001庫侖。在兩个鐘头里,总共通过的电荷是0.0001×60×60×2=0.72庫侖。我們也知道每个电子所帶电荷为1.6×10~(-19)庫侖。那么,在兩个鐘头內,就有0.72/1.6×10~(-19)=4.5×10~(18)个电子落在發光屏     

枇杷果肉酶促褐变的研究——I.枇杷果肉中多酚氧化酶的分离、纯化和动力学特征

枇杷果肉制成丙酮粉,经硫酸铵分级沉淀、透析,DEAE-纤维素柱层析、ACA_(34)柱层析和FPLC分离等方法,分离和纯化得到多酚氧化酶的两个同工酶(酶A和酶B).酶B由一个或几个分子量为42×10~3D的亚基组成.酶的动力学研究表明:酶A、酶B的K_m(多巴胺为底物)均为2.40×10~(-3)mol/L,以邻苯二酚为底物时,酶A和酶B的K_m分别为0.163×10~(-3)mol/L和1.54×10~(-3)mol/L.酶底物特异性表明,酶B是邻位二酚酶,不能作用于单酚和间位二酚.     

基于2-(2'-羟基苯)噁唑啉锌的双核及四核配合物的设计合成、晶体结构及荧光性质

利用2-(2'-羟基苯)噁唑啉作为配体,通过与不同的锌盐进行反应,得到结构新颖的双核及四核配合物.对该系列化合物用元素分析,红外光谱进行表征.X-射线衍射单晶结构分析发现在配合物1中2-(2'-羟基苯)噁唑啉配体的羟基氧作为单原子桥连接2个锌离子,配合物2中除配体的羟基氧桥之外还存在甲氧基的氧原子桥连3个锌离子.配合物1属于单斜晶系,空间群为P21,晶胞参数:α=9.384 2 (A)(19),b=13.584 0(A)(30),c=11.138 0(A)(20),β=96.250°(30).配合物2属于三斜晶系,空间群为P-1,晶胞参数为a=9.5517(A)(19),b=11.123 4 (A)(22),c=11.182 6 (A)(22),α=102.820°(30),β=114.988°(30),γ=100.806°(30).对配合物1的甲醇溶液中及固相荧光光谱进行研究,结果显示它有较好的荧光性质.     

极谱法连续测定钼和钨

在硫酸—苯羟乙酸—氯酸钾(钠)—辛可宁或在硫酸—二苯羟乙酸—氯酸钠—二苯胍底液中,钼和钨产生灵敏的催化电流。钼波跨度较大,常规示波极谱波的峰也较圆钝,而钨的示波导数波则较陡。钼和钨的峰电位分别约为-0.26v和-0.76v(对饱和甘汞电极),可以进行连续测定。灵敏度很高,能测定10-7～10-9mol/L的金属离子,在适宜条件下灵敏度甚至可达10-11～10-12mol/L。此法所用仪器比较简单,操作方便,是一种很好的痕量分析手段。     

PM3原子电荷与多氯代二苯并呋喃的 lgK ow的QSPR研究

采用G98W程序包中的PM3方法对135个多氯代二苯并呋喃(PCDFs)分子和二苯并呋喃进行了优化计算，作业命令为#p PM3 opt freq scf(conver=9)，以计算所得的碳、氧原子电荷作为PCDFs分子结构描述符，运用多元线性回归技术建立了对PCDFs的lgKow与原子电荷的七元方程，最优复相关系数为0．9459，相应的标准偏差为0．1897，经检验该模型的稳健性好，并对未有实验数据的85个PCDFs的lgKow进行预测．     

HPLC法同时测定植物油中叔丁基羟基茴香醚(BHA)、2,6-二叔丁基对甲酚(BHT)和特丁基对苯二酚(TBHQ)含量

目的:建立植物油中叔丁基羟基茴香醚(BHA)、2,6-二叔丁基对甲酚(BHT)和特丁基对苯二酚(TBHQ)含量测定方法.方法:采用高效液相色谱法,Nova-pak C18色谱柱4μm (3.9mm×150mm),以甲醇为流动相A、1％乙酸水溶液为流动相B进行二元梯度洗脱,流速为0.8mL/min,检测波长为280nm.结果:叔丁基羟基茴香醚(BHA)的线性范围为0.1040μg～2.6000μg(r=1),平均回收率为86.8％;2,6-二叔丁基对甲酚(BHT)的线性范围为0.1001μg～2.5025μg(r=0.9999),平均回收率为73.5％;特丁基对苯二酚(TBHQ)的线性范围为0.1007μg～2.5175μg(r=0.9997),平均回收率为89.0％.结论:该方法灵敏、准确、重复性好.     

双(2-苯并咪唑基)烷烃的合成及结构表征

优化了双(2-苯并咪唑基)烷烃的合成反应条件,以邻苯二胺和丙二酸,丁二酸及癸二酸为原料,在4mol/L HCI为溶剂,邻苯二胺:脂肪二酸的比例为2.3:1条件下,在油浴中加热回流,反应完全后,经两种后处理方法,合成了三种双(2-苯并咪唑基)烷烃,通过红外,质普,核磁等检测手段对其结构进行了确认.并得到了双(2-苯并咪唑基)癸烷的有机晶体,通过X射线单晶衍射对其结构进行了表征.     

实时BIA技术对蛋白A与免疫球蛋白G相互作用的研究

应用实时BIA技术 ,探讨了蛋白A与小鼠免疫球蛋白G (MIgG)之间的相互作用 ,求出相互作用的动力学速率常数ka=5 0 7× 1 0 4 (mol/L) - 1 s- 1 ,kd=9 65× 1 0 - 5(s- 1 ) ,结合常数KA=5 2 5× 1 0 8(mol/L) - 1 .同时使用蛋白A固定的传感片用于MIgG浓度的检测 ,在 0 64～ 1 2mg/L浓度区间内 ,MIgG的响应值与其浓度有非常好的线性关系 .     

芳基重氮盐—冠醚分子络合物的~(15)N和~(13)C核磁共振研究

本文报道一系列四氟硼酸芳基重氮盐与18-冠醚-6和二苯并24-冠醚-8形成分子络合物的~(15)N和~(13)C NMR,考察它们在络合前后的化学位移变化规律,结合取代基效应,推测这类络合物为重氮盐的π-电子由β-氮通过π-体系向冠醚提供电子而配位。在二苯并-24-冠醚-8络合物中,还可能存在π-π电子转移作用。     

Students' Reactions to the Introduction of Videoconferencing for Classroom Instruction

This study examined how students who had no prior experience with videoconferencing would react to the use of videoconferencing as an instructional medium. Students enrolled in seven different courses completed a questionnaire at the beginning of the semester and again at the end of the semester. Students at the origination and remote sites did not differ in their reactions toward videoconferencing but there was a significant difference for gender. Women reacted less favorably to videoconferencing. Compared to the beginning of the semester, students reported significantly less positive attitudes toward taking a course through videoconferencing at the end of the semester. There were no significant differences in students' attitudes toward videoconferencing across courses at the beginning of the semester but there were significant differences across the courses at the end of the semester. The results suggest the need for better preparation for both students and instructors.     

Cooler temperatures inductive to locust outbreaks

Ajoint study by Prof. ZHANG Zhibin from the CAS Institute of Zoology and his co-workers from Norway, US and Swiss have indicated that historical outbreaks of migratory locusts in China were associated with cold spells, suggesting that China＇s projected climate warming could decrease the pest＇s numbers. The study was published in Proceedings of theNational Academy of Sciences on 17 September, 2007.     

Exploring Multiplexity: Social Network Structures in a Computer-Supported Distance Learning Class

A computer-mediated group is a complex entity whose members exchange many types of information via multiple means of communication in pursuit of goals specific to their environment. Over time, they coordinate technical features of media with locally enacted use to achieve a viable working arrangement. To explore this complex interaction, a case study is presented of the social networks of interactions and media use among members of a class of computer-supported distance learners. Results show how group structures associated with project teams dominated who communicated with whom, about what, and via which media over the term, and how media came to occupy their own communication niches: Webboard for diffuse class-wide communication; Internet Relay Chat more to named others but still for general communication across the class; and e-mail primarily for intrateam communication. Face-to-face interaction, occurring only during a short on-campus session, appears to have had a catalytic effect on social and emotional exchanges. Results suggest the need to structure exchanges to balance class-wide sharing of ideas with subgroup interactions that facilitate project completion, and to provide media that support these two modes of interaction.     

The Role of Intermediating Institutions in the Diffusion of Electronic Data Interchange (EDI): How Industry Associations Intervened in Denmark, Finland, and Hong Kong

Electronic data interchange (EDI) provides means for interorganizational communication, creates network externalities, requires an advanced information technology (IT) infrastructure, and relies on standards. In the diffusion of such innovations, institutional involvement is imperative. Such institutions contain governmental agencies, national and global standardization organizations, local government, and nonprofit private organizations like industry associations. The last type of organizations we call intermediating institutions. They intermediate or coordinate ("inscribe") the activities of a group of would-be adopters. Unfortunately, little is known of how these organizations shape the EDI diffusion trajectory. In this article we examine one specific type of intermediating organizations?industry associations?and how they advanced the EDI diffusion process in the grocery sectors of Hong Kong, Denmark and Finland. We identify six institutional measures, placed into a matrix formed by the mode of involvement (influence vs. regulation) and the type of diffusion force (supply push vs. demand pull), that can be mobilized to further the EDI diffusion. Industry associations were found to be active users of all these measures to varying degrees. Their role was critical especially in knowledge building, knowledge deployment, and standard setting. Furthermore, institutional involvement varied due to policy and cultural contingencies and power dependencies.     

Low doses of a red wine ingredient figh diabetes in mice

Aresearch group led by Prof. ZHAI Qiwei from the Institute for Nutritional Sciences under the CAS Shanghai Institutes for Biological Sciences has discovered that even relatively low doses of resveratrol--a chemical found in the skins of red grapes and in red wine--can improve the sensitivity of mice to the hormone insulin, according to a report in the October,2007 issue of Cell Metabolism. As insulin resistance is often characterized as the most critical factor contributing to the development of Type 2 diabetes, the findings“provide a potential new therapeutic approach for preventing or treating” both conditions, the researchers said.     

How Electronic Publishers are Protecting Against Piracy: Doubts About Technical Systems of Protection

The increasing prospects of digital piracy has prompted the perceived need by electronic publishers to adopt technical systems of protection, and governments to reform their copyright laws. This article is a preliminary study of the management of intellectual property by electronic publishers, defined as those involved in the production of online databases, and CD-ROMs. It focuses on three main issues: (1) how electronic publishers view the increasing threat of piracy; (2) the methods of protection employed to protect intellectual property in digital format; and (3) the importance of technological protection of intellectual property in electronic publications. The analysis is based on a sample of 23 UK electronic publishers. The interviews revealed an interesting assortment of protection methods and did not show that technological protection was a preferred way. Instead, the means of protection, in addition to copyright law, comprised niche markets, pricing, trust, bad publicity, and nontechnical and technical means.     

Rough Justice: A Statistical Assessment of ICANN's Uniform Dispute Resolution Policy

Long-standing conflict between domain name registrants and trademark holders prompted the Internet Corporation for Assigned Names and Numbers (ICANN) to create a global, mandatory arbitration procedure known as the Uniform Dispute Resolution Policy (UDRP). The UDRP has been used in 2166 cases involving 3938 domain names as of 1 November 2000. The policy gives the initiator of a complaint, generally a trademark holder, the right to choose which ICANN-accredited dispute resolution service provider (RSP) will handle the case. During the preparation of the UDRP,some feared that complainant selection would lead to "forum shopping" that might bias the results. This article performs a statistical assessment of the forum-shopping thesis and finds support for it. There are statistically significant differences in the various RSPs' propensity to take away names from defendants; there are also major differences in the number of cases brought to each RSP. RSPs who take away names have the larger share of cases. The study examines other variables that might explain differences in market share, such as price, the plaintiff's nationality, or the time taken to decide a case. It finds that nationality and time also are correlated with market share. The study concludes that shopping for a favorable outcome is an important factor in the UDRP.     

Prevalence of soft neurological signs in Chinese people

Prof. Raymond C.K. Chen, a neuropsychologist with the CAS Institute of Psychology, has made novel progress in his studies of schizophrenia. His work has been reported by a recent issue of Behavioural Neurology.     

Molecular motor assembly of a biomimetic system

Active biological molecules and functional structures can be fabricated into a bio-mimetic system by using molecular assembly method. Such materials can be used for the drug delivery, disease diagnosis and therapy, and new nanodevice construction.     

Monoculture Rubber Plantations Have Negative Ef ects on Controlling Splash Erosion

<正>In Xishuangbanna,one of China’s most biodiverse regions,landscape has changed dramatically during the past three decades due to the conversion of tropical rainforest to rubber plantations.In steep areas,terraces are often constructed before planting rubber trees,which causes two important changes in the soil:the destabilization of soil in the bench terraces and the increased vulnerability of unvegetated riser faces to erosion.Few studies have documented the nature and intensity of erosion on bench terraces.Prof.LIU Wenjie and his colleagues from the Xishuangbanna Tropical Botanical Garden(XTBG)conducted a study in Menglun County(21°5′39″N,101°15′55″E),Xishuangbanna to evaluate the influence