铬渣中铬,镍,锌,锰和铁的X射线荧光法测定

本文首次研究了用X射线荧光光谱法测定铬渣中Cr、Zn、Ni、Mn和Fe元素的模拟标样,样品直接压片不经化学处理。用稀释样品校正试样的基体效应。用人工模拟标样所建立的元素浓度与X射线强度间的线性函数关系令人满意,所试元素的线性相关系数均在0.99以上,测定结果与化学法基本一致。Cr的检测下限为0.036%;Fe为0.039%;Ni为35.33μg/g;Mn为498.18μg/g;Zn为55.61μg/g。各元素的相对标准偏差均低于2.48%。并首次用非线性方法研究了铬渣样品稀释比中Cr、Ni、Zn、Mn、Fe与X射线强度的线性关系。     

Remarkable Stereoelectronic Effect of the Methylenedioxy Phenyl System in the Total Synthesis of Cephalotaxine

Methylenedioxyphenyl unit displays a significant stereoelectronic effect in some key transformations in the total synthesis of cephalotaxine. The ring-strain of methylenedioxy ring may account for some important facile ring-skeleton rearrangements.     

Attempt to Resolute Chiral Clusters by Optically Active Hydrazide

Due to the framework chirality optically active clusters can provide the proof that a cluster as a whole, and not one of its fragments, acts as a catalyst, most of the work have been directed to the synthesis of tetrahedron-type chiral clusters1-3. However, there remains another major problem to obtain the pure enantiomers. Although Vahrenkamp had obtained some pioneering results in this area before 19901, only several racemic chiral clusters have been separated into pure enantiomers until now…     

四阶非线性特征值问题正解的存在性

利用Krasnoselskii不动点定理,证明了边值问题y(4)(x)-λa(x)f(y(x))=0,O相似文献   

关于P_n~3的优美性(英文)

设G(V,E)是一个简单图,对自然数k,当V(G~k)=V(G,E(G~k)=E(G)∪{uv|d(u,v)=k},则称图G~k为k-次方图,本文证明了图P_n~3的优美性。     

辐冷器视场角对其制冷性能的影响

本文对抛物面G型辐冷器,在水平视场角变化的情况下不同工况下的制冷性能进行了计算。通过数值计算发现,视场角的减小导致辐冷器制冷性能的明显下降,虽然视场角影响辐冷器的因素很复杂,但最后的结果是两者呈现出良好的线性关系。其次,通过对辐冷器降温特性的研究,提出了通过改变辐冷器外壳控温方式来减小视场角变化对辐冷器制冷性能的负面影响,计算结果表明这种解决措施是非常有效的。     

Diastereoselective Synthesis of Chiral Pyrrolidine and Piperidine Ring Systems

A diastereoselective method for the synthesis of chiral pyrrolidine and piperidine ring containing compounds was described. The protocol of bromination followed by aminocyclization furnishes an easily handled while highly efficient procedure for the intramolecular amidation of an isolated double bond. High diastereomeric excess was observed in this synthetic procedure.     

A Rapid and Efficient Synthesis of 2, 4, 6-Triarylpyridines under Microwave Irradiation

An rapid and efficient synthesis of 2, 4, 6-triarylpyridines is reported using substituted benzaldehydes, substituted acetophenones and ammonia as starting materials under microwave irradiation in the presence of PEG-400.     

The First Total Synthesis of 3-Oxo-11, 12, 13-trihydroxyeudesm-4-ene

The first total synthesis of 3-oxo-11, 12, 13-trihydroxyeudesm-4-ene, a highly oxygenated natural eudesmane, was described.     

油溶性有机钼添加剂的摩擦学性能及其摩擦化学作用机制

采用四球摩擦磨损试验机考察了2种油溶性有机钼添加剂2-乙基己基-二硫代磷酸氧钼(MoDDP)和硫化-二异丙基-二硫代磷酸钼(MoDTP)的摩擦学性能及其复配体系的抗磨减摩性能,采用扫描电子显微镜和X射线光电子能谱仪分析了磨斑表面形貌和表面膜元素组成,探讨了有机钼添加剂的摩擦化学作用机制.结果表明,有机钼添加剂MoDDP和MoDTP均具有优异的摩擦学性能,其复配体系呈现协同抗磨减摩效应,这是由于有机钼添加剂在摩擦副表面形成由FeS、MoS2及MoO2组成的化学反应膜和由含磷化合物组成的沉积膜所致.