CLIMATIC CHANGE SINCE LITTLE ICE AGE RECORDED BY DUNDE ICE CAP

The climatic change since the Little Ice Age recorded in the Dunde Ice Cap is presentedin this paper. There have been three cold periods and three warm periods since 1400AD.Among them, the coldest one was in the 17th century. Many evidences verified the three coldand warm variations recorded in the Dundc Ice Cap. But it was found from the comparison between the Dunde Icc Cap climatic record and thewinter temperature record in Shanghai that there was a temporal dfference in climatic changebetween East China and West China. The general trend is that the cooling and warmingprocesses in West China were earlier than that in East China. In the Dunde Ice Cap, it isnow in an anomalous warm period, while it is not as warm as in Dunde Ice Cap recordaccording to the winter temperature in Shanghai. In addition to the possible cause of temporaldifference in climatic change between West China and East China, another possible cause isthat the greenhouse effect of CO_2 may already be recognizable in the Dunde Ice Cap a     

原子吸收光谱仪器:商品介绍

自从1955年Walsh的首篇论文和Hilger &Watts的专利至今,原子吸收光谱法在仪器方面已经历了持续的发展。本刊最近两期称为原子吸收光谱法的过去、现在和将来的专辑评述了这一发展的主要成果,该专辑是为了纪念Walsh开创性的论文在《Spectrochimica Acta》上发表25周年而出版的。原子吸收     

ASYMMETRIC SYNTHESIS——ENANTIOSELECTIVE SYNTHESIS OF (R)-α-AMINO ACIDS USING L-ISOLEUCINE AS CHIRAL AUXILIARY REAGENT

Enantioselective synthesis of (R)-α-amino acids via heterocyclic intermediate-(3S)-2,5-dimethoxy-3-see-butyl-3, 6-dihydropyrazine (5), using L-isoleucine as chiral auxiliaryreagent and glycine as raw meterial, has been studied. The alkylation of compound 5 withbutyllithium affords its lithium derivative (6) according to the cardanion mechanism. Then 6reacts with alkyl halide RX (7) to give the alkylated products (8) with very high diastereo-selectivity. In this reaction, the group R of 7 enters trans to the see-butyl group at C-3, i. e.the (R)-configuration is induced at C-6 of 8. After hydrolysis the (R)-α-amino acid methylesters (9) are obtained.     

生物硷化学

摆在苏联有关技术发展的化学科学面前的主要问题之一,是进一步加强对天然的生物活性化合物,如生物硷、维生素、激素、配糖体、抗生素等的研究。生物硷是最贵重的药剂,是农业技术上与害虫作斗争的武器,是防止金属腐蚀的物质,近来年已确定生物硷可用于加速生物的生长过程。所有这些用途说明了研究生物硷并在国民经济各部门对之加以利用的意义。俄罗斯学者萨茨基在1889年发表了世界上第一部关于生物硷的详尽的著作,书中提到:“本世纪(19世纪——本文作者)初生物硷的发现,对医学上有甚为重大的意义,可与铁的发现对世界文化的意义相比拟。”     

化学成绩提高的方法

为社会主义建设的成就和伟大的共产主义思想所鼓舞的千千万万的教师大军,坚持不懈地获得巩固的、深刻的和自觉的知识,培养学生们的苏维埃爱国主义和苏维埃民族自豪感,无限忠诚於伟大的苏联共产党。出现了很多没有留级生的教师。作为一个比较年轻的化学教师的我,愿意提供一下我自己如何消灭留级生现象的意见,并且肯定地说,克服留级生现象的任务是完全可以解决的。     

DFT study of the conductance of molecular wire:The effect of coupling geometry and intermolecular interaction on the transport properties

The density functional theory (DFT) combining with the non-equilibrium Green functions (NEGF) method is applied to the study of the electronic transport properties for a Di-thiol-benzene (DTB) molecule coupled to two Au(111) surfaces. The dependence of the transport properties on the bias, the coupling geometry of the molecule-electrode interface, and the intermolecular interaction are examined in detail. The results show that the existence of the hydrogen atom at the end of the DTB molecule would significantly decrease the transmission coefficients, and then the differential conductance (dI/dV). By changing the position of the DTB molecule located between two electrodes a maximum value of calculated current is observed. It is also found that the intermolecular interaction will strongly influence the transport properties of the system studied.     

四川武隆地区二叠—三叠系磁性地层学研究

四川武隆地区的p/T界线为一化石丰富、沉积连续的海相碳酸盐剖面。通过对岩石磁学的研究,鉴别出三叠系灰岩样品以磁铁矿为主,其中约70％为多畴磁铁矿。ChRM由单畴磁铁矿所携带。二叠系灰岩样品主要为单畴与超顺磁颗粒的磁铁矿,样品不同程度地遭受重磁化。然而,根据其退磁中NRM矢量变化的轨迹与极性有关,使确定绝大部分样品的极性成为可能。本文通过与国外剖面的对比,认为Illawarra反转起始于吴家坪阶上部,而Kiaman极性段中则存在着若干正向极性。     

高分子物理学系统讲演

第八講 高聚物的化学特性 1.裂解反应比較小分子与高分子的化学反应,首先应該区別反应平衡与反应动力学,对反应平衡来說,高分子化合物的化学变化与低分子化合物有同样的规律,如聚乙烯醇和乙二醇分子上的OH基团能进行相同的化学反应。而同时高分了化合物的化学变化又有一些显著的特点与小分子化合物不同,例如长链分子出現一种新的反应,就是裂解。裂解反应是高分子化合物的一个特征。它与聚合反应有相似的过程,以两种不同的方式来实现。第一种是无规断链,卽高分子中的任何一个链节都有同样被断裂的可能性。这与縮聚反应很     

Molecular Replacement Studies of Cucurmosin from Cucurbita Moschata:Structure Homology with Trichosanthin

1 INTRODUCTION Many plants contain proteins that are capable of inactivating ribosomes and therefore are called ribosome-inactivating proteins or RIPs[1]. RIPs are RNA N-glycosidases that inactivate ribosomes through a site-specific deadenylation of the large ribosomal RNA[2, 3]. RIPs are also capable of inactivating many nonribosomal nucleic acid substrates and can be considered as polynucleotide: adenosine glycosidases[4～6]. There are two types of RIPs: type I, single chain pr…     

在化学教学中貫徹基本生產技術教育問題

卡尔·馬克思第一次提出了关於基本生產技術教育的問題。他曾寫道:“綜合技術教育使人們熟悉生產全部过程的基本原理,同时使青少年們掌握使用简單生產工具的本领。”弗·依·列寧进一步發展了馬克思对於基本生產技術教育的看法。在1894年他會寫道:“如果沒有对年青一代教学及劳动生產的結合,