检索结果-南通市图书馆

A Rapid and Convenient Synthesis of Acylals from Aldehydes and Acetic Anhydrides Catalyzed by SnCl_4/SiO_2

在线全文

学校读者我要写书评

暂无评论

Chinese Chemical Letters 2001年第7期12卷 565-568页

作者： Yi Qun li li hui cheng Department of Chemistry Jinan UniversityGuangzhou 510632

A variety of aldehydes were converted into acylals in excellent yields with acetic anhydride in the presence of a catalytic amount of tin (IV) chloride supported on silica gel at room temperature.

关键词： Acylals tin (IV) chloride supported on silica gel

HISTORICAL DESERTIFICATION PROCESS IN HEXI CORRIDOR,CHINA

在线全文

学校读者我要写书评

暂无评论

Chinese Geographical Science 2005年第3期15卷 245-253页

作者： WANG Nai-ang ZHANG Chun-hui li Gang cheng Hong-yi College of Earth and Environment Sciences Lanzhou University Lanzhou 730000P. R. China

Over the last 2000 years, approximately 38 ancient cities were abandoned through desertification in Hexi Corridor, Northwest China. Among them, 21.05% were abandoned during the Northern and Southern Dynasties, 21.05% during the end of the Tang Dynasty and the Five Dynasties, and 57.9% during the Ming and Qing dynasties. At the same time, main lakes were shrinking rapidly from the 5th Century to the 6th Century and the end of the Qing Dynasty. The climate in these periods was relatively arid and cold with frequent dusts. The phase of these changes indicated that there were three periods of desertification enlargement in the northern China. They were Northern and Southern Dynasties, the end of Tang Dynasty and Five Dynasties, the Ming and Qing dynasties. The macro-process of desertification in the study area was controlled mainly by the climatic changes. But from the facts that the population density in the middle of Qing Dynasty had exceeded the critical index of population pressure in arid area and the usage rate of water resources had exceeded 40% in Hexi Corridor, this paper also suggests that human activities have played an important role in desertification processes of the study area mainly during the recent 300 years.

关键词： historical desertification climate change human activities Hexi Corridor

在线全文

学校读者我要写书评

暂无评论

高速道岔心轨扳动力和不足位移控制研究

铁道学报 2008年第2期30卷 48-51页

作者：蔡小培李成辉西南交通大学土木工程学院四川成都610031

为了控制高速道岔心轨扳动力和不足位移,根据双肢弹性可弯心轨的特殊结构外形、受力特性和扳动机理,建立心轨转换仿真模型,以42号道岔为例分析不同牵引点布置方式下心轨扳动力和不足位移的变化规律。计算结果表明:牵引点扳动力随摩擦系... 详细信息

为了控制高速道岔心轨扳动力和不足位移,根据双肢弹性可弯心轨的特殊结构外形、受力特性和扳动机理,建立心轨转换仿真模型,以42号道岔为例分析不同牵引点布置方式下心轨扳动力和不足位移的变化规律。计算结果表明:牵引点扳动力随摩擦系数的增大基本成递增关系,扳动力的很大一部分用于克服滑床板的摩擦力;采用减摩措施、增设牵引点可以减小扳动力和不足位移;在最后一牵引点至跟端间设置反变形,可使不足位移控制在客运专线要求之内。

关键词：高速道岔双肢心轨仿真模型扳动力不足位移

在线全文

学校读者我要写书评

暂无评论

不足位移对高速道岔动力特性的影响

铁道学报 2011年第7期33卷 86-90页

作者：蔡小培李成辉北京交通大学土木建筑工程学院北京100044 西南交通大学土木工程学院四川成都610031

为揭示道岔不足位移对高速行车的影响,根据高速道岔、列车的结构特点、力学特性和相互作用关系,建立车辆-道岔耦合动力学模型,并以高速列车直向350km/h、侧向80km/h通过350km/h客运专线18号无砟道岔为例,分析不同不足位移情形下车辆和... 详细信息

为揭示道岔不足位移对高速行车的影响,根据高速道岔、列车的结构特点、力学特性和相互作用关系,建立车辆-道岔耦合动力学模型,并以高速列车直向350km/h、侧向80km/h通过350km/h客运专线18号无砟道岔为例,分析不同不足位移情形下车辆和道岔的动力学特性。结果表明:尖轨、心轨不足位移对列车动轮载、钢轨动应力影响较小,对轮缘力、车体横向加速度、轮重减载率、脱轨系数影响较大;不足位移会严重影响高速列车直、侧向过岔的舒适性及安全性,影响高速道岔正常工作状态;牵引转换设计时,应严格控制道岔尖轨、心轨不足位移。

关键词：高速道岔不足位移动力特性动轮载脱轨系数

一个基于多钒酸盐与柔性吡啶基配体的三维非中心对称杂化物(英文)

在线全文

学校读者我要写书评

暂无评论

无机化学学报 2010年第9期26卷 1549-1555页

作者：杜晓迪李承辉南京大学化学化工学院配位化学国家重点实验室南京微结构国家实验室南京210093

基于柔性吡啶基配体和钒酸盐,合成得到了一个非中心对称的杂化化合物[CuⅠ4(bpp)4(VⅤ6O17)](1)(bpp=1,3-二(4-吡啶基)丙烷),并通过元素分析、红外光谱、X-射线单晶衍射、热重分析等测试对其进行了表征。晶体数据表明该化合物属于正交晶... 详细信息

基于柔性吡啶基配体和钒酸盐,合成得到了一个非中心对称的杂化化合物[CuⅠ4(bpp)4(VⅤ6O17)](1)(bpp=1,3-二(4-吡啶基)丙烷),并通过元素分析、红外光谱、X-射线单晶衍射、热重分析等测试对其进行了表征。晶体数据表明该化合物属于正交晶系,Pca21空间群。在化合物1中,一维链状的多钒酸根与[CuⅠ(bpp)]单元通过Cu-O键连接形成沿ab平面的层,这些层进一步通过Cu髣…Cu髣弱相互作用(Cu髣…Cu髣距离为0.281nm)连接成一个三维的框架结构。

关键词：有机-无机杂化物多钒酸盐柔性吡啶基配体晶体结构

Comparison of endotracheal intubation with the Shikani Optical Stylet using the left molar approach and direct laryngoscopy

在线全文

学校读者我要写书评

暂无评论

Chinese Medical Journal 2008年第14期121卷 1324-1327页

作者： YAO Yun-tai JIA Nai-guang li cheng-hui ZHANG Ya-jun YIN Yi-qing Department of Anesthesiology China-Japan Friendship Hospital Beijing 100029 China

The Shikani Optical StyletTM or SOS （Clarus Medical, USA） was developed as an aid to intubation for difficult airways.^1 The-SOS is composed of a J-shaped malleable body and a lens and light source at the tip and an eyepiece at the proximal end. It combines the features of a fiberoptic bronchoscope and a lightwand. It can be used alone or combined with a camera or monitor and both adult and pediatric versions are available.^2.3

关键词： Shikani Optical Stylet left molar approach endotracheal intubation

在线全文

学校读者我要写书评

暂无评论

无取代酞荭的高效制备及其新衍生物的研究

化学学报 2021年第1期79卷 81-86页

作者：李凌燕郑玮李承辉南京大学化学化工学院配位化学国家重点实验室南京210093

酞荭具有独特的稠环结构、光谱性质及多样的配位方式,是一类颇具潜力的新兴材料.在酞荭研究起步阶段,无取代酞荭Pr-2是研究反应与探索应用最重要的化合物.然而目前制备Pr-2的方法仅能基于Pr-1的脱氰基反应.该方法成本高昂并难以放大,限... 详细信息

酞荭具有独特的稠环结构、光谱性质及多样的配位方式,是一类颇具潜力的新兴材料.在酞荭研究起步阶段,无取代酞荭Pr-2是研究反应与探索应用最重要的化合物.然而目前制备Pr-2的方法仅能基于Pr-1的脱氰基反应.该方法成本高昂并难以放大,限制了酞荭类材料的后续研究与发展.本工作利用Ni(Ⅱ)催化剂替代昂贵的Rh(Ⅰ),高效制备Pr-2,且该方法可放大至十克级别,产率超过50%.同时,在调整反应条件的过程中,新生成氰基(Pr-1.5)与甲基(Pr-1.6)取代的酞荭化合物,都展现出良好的平面性与π-π相互作用,而不同取代基对酞荭的荧光性质有着重要的影响.本论文所报道的工作,尤其是便捷的合成方法对于酞荭的推广和应用具有极为重要而深远的意义.

关键词：酞荭稠环脱氰基染料杂环

Real-world evidence on the efficacy and safety of vonoprazanamoxicillin dual therapy for Helicobacter pylori treatment in elderly patients

在线全文

学校读者我要写书评

暂无评论

World Journal of Gastroenterology 2025年第1期31卷 68-78页

作者： Wen Gao Jing-Wen li hui Ye Xue-Zhi Zhang Jian-Xiang liu Hong cheng Department of Gastroenterology Peking University First HospitalBeijing 100034China School of Medicine Tsinghua MedicineTsinghua UniversityBeijing 100034China Department of Traditional Chinese Medicine and Integrative Medicine Peking University First HospitalBeijing 100034China

BACKGROUND A dual therapy regimen containing amoxicillin is a common treatment option for the eradication of Helicobacter pylori(***).While substantial research supports the efficacy and safety of vonoprazan and amoxicillin(VA)dual therapy in the general population,there is still a lack of studies specifically focusing on its safety in elderly *** To evaluate efficacy and safety of VA dual therapy as first-line or rescue treatment for *** in elderly *** As a real-world retrospective study,data were collected from elderly patients aged 60 years and above who accepted VA dual therapy(vonoprazan 20 mg twice daily+amoxicillin 1000 mg thrice daily for 14 days)for *** eradication in the Department of Gastroenterology at Peking University First Hospital between June 2020 and January *** status was evaluated by^(13)C-urease breath test 6 weeks after *** adverse events(AEs)during treatment were *** In total,401 cases were ***-one cases were excluded due to loss to follow-up,lack of re-examination,or unwillingness to take *** total of 380 included cases comprised 250 who received VA dual therapy as first-line treatment and 130 who received VA dual therapy as rescue *** was successfully eradicated in 239 cases(95.6%)in the first-line treatment group and 116 cases(89.2%)in the rescue treatment *** overall incidence of AEs was 9.5%for both ***,9.2%of patients experienced an AE in the first-line treatment group and 10.0%in the rescue treatment *** patients discontinued treatment due to AE,with a discontinuation rate of 1.3%.No serious AE *** The VA dual therapy regimen as a first-line treatment and a rescue therapy was effective and safe for elderly patients aged 60 and older.

关键词： Helicobacter pylori Vonoprazan Amoxicillin Dual therapy Elderly

简支梁桥上CRTSⅡ型板式无砟轨道制动力影响因素分析

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

铁道学报 2012年第1期34卷 72-76页

作者：方利王志强李成辉中铁二院重庆勘察设计研究院有限责任公司线路处重庆400023 中冶赛迪建筑设计研究院轨道交通所重庆400013 西南交通大学土木工程学院四川成都610031

运用ANSYS分析软件建立轨道-桥梁系统模型。分析列车在桥上CRTSⅡ型板式无砟轨道施加制动力情况下,底座与桥面间设置的滑动层和底座与桥梁间设置的固结机构共同作用,以及滑动层单独作用时,不同滑动层摩擦系数对轨道各结构部件受力影响... 详细信息

运用ANSYS分析软件建立轨道-桥梁系统模型。分析列车在桥上CRTSⅡ型板式无砟轨道施加制动力情况下,底座与桥面间设置的滑动层和底座与桥梁间设置的固结机构共同作用,以及滑动层单独作用时,不同滑动层摩擦系数对轨道各结构部件受力影响。计算分析结果表明:固结机构是传递制动力的主要结构;当采用合理滑动层摩擦系数时,依靠滑动层和固结机构相互作用,可削弱梁-轨相互作用,使桥梁墩台受力合理。

关键词：固结机构滑动层 CRTSⅡ