检索结果-南通市图书馆

Synergistic silver-mediated and palladium-catalyzed nondirected olefination of aryl C–H bond: quick access to multi-substituted aryl olefins

引用

Science China Chemistry 2024年第3期67卷 882-889页

作者： jian Yao Lili Shao xiaohong Huo Xiaoming Wang Shanghai Key Laboratory for Molecular Engineering of Chiral Drugs Frontiers Science Center for Transformative MoleculesSchool of Chemistry and Chemical EngineeringShanghai Jiao Tong UniversityShanghai 200240China State Key Laboratory of Organometallic Chemistry Center for Excellence in Molecular SynthesisShanghai Institute of Organic ChemistryChinese Academy of SciencesShanghai 20032China School of Chemistry and Materials Science Hangzhou Institute for Advanced StudyUniversity of Chinese Academy of SciencesHangzhou 310024China

Transition metal-catalyzed olefination of aryl C-H bond is a powerful tool for the synthesis of alkenes. While the Pd-catalyzed oxidative C-H olefination of arenes, also known as Fujiwara-Moritani reaction, has been established as one of the most efficient methods, the substrates are largely limited to terminal olefins with electron-withdrawing group(s). Herein, we report a synergistic silver-mediated and palladium-catalyzed non-directed C-H olefination of arenes with vinyl(pseudo)halides, which offers a complementary strategy to the typical Fujiwara-Moritani reaction. The reactions proceeded well for a variety of halogenated arenes, heteroarenes, and olefin substrates, providing an efficient access to various multi-substituted aryl olefins, including trisubstituted/tetrasubstituted olefins and several complex olefins derived from medicines or natural products. Mechanistic studies indicated a bimetallic Pd/Ag cooperation is operative in the catalysis, i.e., the reaction is initiated by aryl C-H bond cleavage via ligation with phosphine/Ag species, followed by transferring of the aryl moiety to a vinyl palladium intermediate,which is in turn formed by oxidative addition of vinyl(pseudo)halide to a Pd complex. This method enables the synthesis of a wide range of challenging multi-substituted vinyl products from simple arenes(directing-group free) in a streamlined and controllable fashion.

关键词： direct C–H olefination multi-substituted aryl alkenes bimetallic Pd/Ag cooperation C–H functionalization

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

Spatial-Temporal Analysis of Drinking Water Type of Endemic Fluorosis—China,2009–2022

引用

China CDC weekly 2024年第2期6卷 25-29页

作者： Lijun Zhao Zhe Li Mang Li Hongna Sun Wei Wei Lin Gao Qiaoshi Zhao Yang Liu xiaohong Ji Cheng Li jian Wang Yanhui Gao Junrui Pei Center for Endemic Disease Control Chinese Center for Disease Control and PreventionHarbin Medical UniversityHarbin CityHeilongjiang ProvinceChina Key Lab of Etiology and Epidemiology Education Bureau of Heilongjiang Province(23618504)Ministry of Health of PRHarbin Medical UniversityHarbin CityHeilongjiang ProvinceChina

What is already known about this topic?Endemic fluorosis,caused by high fluoride levels in drinking water,has been a significant health issue in rural areas of China for many decades.What is added by this report?There has been a notable decline in the detection rate of dental fluorosis in children aged 8–12 years in drinking water fluorosis areas across the country from 2009 to 2022.While 14 provincial-level administrative divisions are classified as low-probability clusters,Tianjin remains classified as a high-probability cluster.What are the implications for public health practice?The current policy for preventing and controlling endemic fluorosis in China needs adjustment.Rather than focusing solely on regions with high incidence,there should be a shift towards monitoring and early warning of fluoride exposure.Additionally,local containment measures should be intensified.

关键词： intensified Spatial fluoride

来源：

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

Synergistic asymmetric diarylation of tethered alkenes via C–H functionalization of simple(hetero)arenes

引用

Science China Chemistry 2024年第8期 2710-2718页

作者： jian Yao Can Zhao Lili Shao xiaohong Huo Xiaoming Wang Shanghai Key Laboratory for Molecular Engineering of Chiral Drugs Frontiers Science Center for Transformative Molecules School of Chemistry and Chemical Engineering Shanghai Jiao Tong University State Key Laboratory of Organometallic Chemistry and Shanghai Hongkong Joint Laboratory in Chemical Synthesis Center for Excellence in Molecular Synthesis Shanghai Institute of Organic Chemistry Chinese Academy of Sciences School of Chemistry and Materials Science Hangzhou Institute for Advanced Study University of Chinese Academy of Sciences

By virtue of the atom-and step-economy, utilization of simple arenes as a supplant of pre-prepared aryl metal species or aryl halides for the synthesis of arylated chiral molecules has attracted great attention from the synthetic community. While transition-metal-catalyzed enantioselective diarylation of tethered alkenes has been employed to prepare important chiral cyclic compounds, the direct use of simple arenes as aryl precursors is still underdeveloped, probably due to the difficulties in the effective control of the reactivity, site-selectivity and/or enantioselectivity. Herein we report an asymmetric Pd/Ag dual metal catalytic system for the non-directed, site-and enantioselective domino Heck/intermolecular C–H functionalization of arenes.Mechanistic studies showed that Pd and Ag act in cooperation in the catalysis and the chiral bisphosphine ligand plays a bifunctional role, i.e., assisting the silver species in the cleavage of the aryl C–H bond, while inducing the enantioselectivity on direct complexation with palladium. This method provides an efficient approach to the corresponding chiral oxindoles with good enantiomeric excesses from a broad scope of arenes, including fluoroarenes, heteroarenes and several complex products derived from medicines or natural products.

关键词：

来源：

同方期刊数据库评论

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

Tunnelling of electrons via the neighboring atom

引用

Light(Science & Applications) 2024年第1期13卷 127-134页

作者： Ming Zhu Jihong Tong Xiwang Liu Weifeng Yang Xiaochun Gong Wenyu jiang Peifen Lu Hui Li xiaohong Song jian Wu School of Physics and Optoelectronic Engineering Hainan UniversityHaikou 570288China School of Information and Communication Engineering Hainan UniversityHaikou 570288China State Key Laboratory of Precision Spectroscopy East China Normal UniversityShanghai 200241China Center for Theoretical Physics Hainan UniversityHaikou 570288China

As compared to the intuitive process that the electron emits straight to the continuum from its parent ion,there is an alternative route that the electron may transfer to and be trapped by a neighboring ionic core before the eventual release.Here,we demonstrate that electron tunnelling via the neighboring atomic core is a pronounced process in light-induced tunnelling ionization of molecules by absorbing multiple near-infrared photons.We devised a siteresolved tunnelling experiment using an Ar-Kr+ion as a prototype system to track the electron tunnelling dynamics from the Ar atom towards the neighboring Kr+by monitoring its transverse momentum distribution,which is temporally captured into the resonant excited states of the Ar-Kr+before its eventual releasing.The influence of the Coulomb potential of neighboring ionic cores promises new insights into the understanding and controlling of tunnelling dynamics in complex molecules or environment.

关键词： neighboring straight resonant

来源：

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

Degenerative alterations in noradrenergic neurons of the locus coeruleus in Alzheimer's disease

引用

Neural Regeneration Research 2013年第24期8卷 2249-2255页

作者： Lihua Liu Saiping Luo Leping Zeng Weihong Wang Liming Yuan xiaohong jian Department of Histology & Embryology School of Basic Medical Sciences Central South University Department of Nursing Medical College of Hunan Normal University Third Department of Surgery Agricultural Division Four Hospital Xinjiang Production and Construction Corps Department of Anatomy & Neurobiology School of Basic Medical Sciences Central South University Department of Anatomy Medical College of Hunan Normal University

Mice carrying mutant amyloid precursor protein and presenilin-1 genes （APP/PS1 double trans- genic mice） have frequently been used in studies of Alzheimer＇s disease; however, such studies have focused mainly on hippocampal and cortical changes. The severity of Alzheimer＇s disease is known to correlate with the amount of amyloid-13 protein deposition and the number of dead neurons in the locus coeruleus. In the present study, we assigned APP/PS1 double transgenic mice to two groups according to age： young mice （5-6 months old） and aged mice （16-17 months old）. Age-matched wild-type mice were used as controls. Immunohistochemistry for tyrosine hydroxylase （a marker of catecholaminergic neurons in the locus coeruleus） revealed that APP/PS1 mice had 23% fewer cells in the locus coeruleus compared with aged wild-type mice. APP/PS1 mice also had increased numbers of cell bodies of neurons positive for tyrosine hydroxylase, but fewer tyrosine hydroxylase-positive fibers, which were also short, thick and broken. Quantitative analysis using unbiased stereology showed a significant age-related increase in the mean volume of tyrosine hy- droxylase-positive neurons in aged APP/PS1 mice compared with young APP/PS1 mice. Moreover, the mean volume of tyrosine hydroxylase-positive neurons was positively correlated with the total volume of the locus coeruleus. These findings indicate that noradrenergic neurons and fibers in the locus coeruleus are predisposed to degenerative alterations in APP/PS1 double transgenic mice.

关键词： neural regeneration presenilin-1 Alzheimer＇s disease tyrosine hydroxylase locus coeruleus noradrenergic neuron ^-amyloid senile plaques grants-supported paper neuroregeneration

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

基于流固耦合的屏蔽电机多物理场仿真分析

引用

机床与液压 2024年第2期52卷 155-160页

作者：王康刘晓红柯坚西南交通大学机械工程学院四川成都610030

针对内置螺旋管换热的屏蔽电机内部发热和冷却的复杂性及其工况的特殊性,借助有限元分析软件建立屏蔽电机三维温度场整机物理模型,通过仿真计算揭示电机内部温度场的分布规律和冷却介质的流动状态,并分析原因。结果表明:电机的峰值温度... 详细信息

针对内置螺旋管换热的屏蔽电机内部发热和冷却的复杂性及其工况的特殊性,借助有限元分析软件建立屏蔽电机三维温度场整机物理模型,通过仿真计算揭示电机内部温度场的分布规律和冷却介质的流动状态,并分析原因。结果表明:电机的峰值温度出现在定子绕组上端部,值为98.3℃,绝缘按180℃考核,各部件的温升均没有超过其材料的温升限值;热态额定工况下,电机处于安全状态。计算结果可为同类型屏蔽电机的冷却系统设计及温度场计算提供参考。

关键词：屏蔽电机流固耦合温度场流体场

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

祁连山国家公园生态系统服务供需匹配

引用

生态学杂志 2024年第6期43卷 1901-1909页

作者：陈红邓晓红李宗省薛健兰州大学经济学院兰州730000 祁连山同位素生态水文与国家公园观测研究站兰州730000 干旱区生态安全与可持续发展全国重点实验室兰州730000 中国科学院西北生态环境资源研究院兰州730000

生态系统服务的供需分析是生态系统综合管理和实现区域可持续发展的重要内容。本文以祁连山国家公园为例,运用InVEST模型测算食物供给、水源涵养、土壤保持、固碳、气候调节、生境质量和休闲游憩7项生态系统服务的供需量,结合供需比和... 详细信息

生态系统服务的供需分析是生态系统综合管理和实现区域可持续发展的重要内容。本文以祁连山国家公园为例,运用InVEST模型测算食物供给、水源涵养、土壤保持、固碳、气候调节、生境质量和休闲游憩7项生态系统服务的供需量,结合供需比和局部莫兰指数分析其供需特征和空间匹配状况。结果表明:祁连山国家公园综合供需比为0.0608,除固碳和休闲游憩服务外,食物供给、水源涵养、土壤保持、气候调节和生境质量生态系统服务供给均大于需求,但不同区域和生态系统服务间存在差异;祁连山国家公园生态系统服务供需空间匹配类型有高高空间匹配、低低空间匹配、低高空间错位和高低空间错位4种,天祝县和肃南县为低供给-高需求区域,山丹县、民乐县和凉州区为高供给-低需求区域。建议祁连山国家公园高低空间错位区域以保护为主,提高管理水平;低高空间错位区域以综合改良为主,提高土地效益。

关键词：祁连山国家公园生态系统服务供需关系空间匹配

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

Influence of environmental enrichment on hippocampal synapses in adolescent offspring of mothers exposed to prenatal stress

引用

Neural Regeneration Research 2011年第5期6卷 378-382页

作者： Yaojin Peng xiaohong jian Lihua Liu jianbin Tong Deliang Lei Department of Human Anatomy Medical College of Hunan Normal University Changsha 410006 Hunan Province China Department of Basic Nursing Medical College of Hunan Normal University Changsha 410006 Hunan Province China Department of Human Anatomy and Neurobiology Xiangya School of Medicine Central South University Changsha 410013 Hunan Province China

Environmental enrichment attenuates hippocampal synaptic injury induced by prenatal stress in offspring. However, the influence of hippocampal synaptic changes and regional differences in prenatal stress remains poorly understood. The present study induced stress in Sprague Dawley rats, which were at gestational age 13-19 days. Following weaning, the offspring were raised in an enriched environment to establish models of stress ＋ enriched environment. Dendritic spine density and synaptophysin expression were detected in hippocampal neurons using Golgi staining and western blot analysis, respectively. Results showed that enriched environment increased dendritic spine density of apical dendrites in CA1 pyramidal cells and basal dendrites of granular cells in the outer layer of the dentate gyrus. In addition, hippocampal synaptophysin expression increased and the effects of prenatal stress on neuronal dendritic spines were reversed in adolescence.

关键词： dendritic spine enriched environment hippocampus offspring prenatal stress synaptophysin neural regeneration

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

MR型船舶骨材选型优化研究

引用

广船科技 2024年第1期44卷 28-31页

作者：柳小红付志明范剑广船国际技术中心

为减少MR船型船体骨材现场施工工作量,对其骨材选型进行优化研究,经过优化选型,减少零件数量,减少型材规格,提高钢材利用率,降低采购成本。

关键词： MR船型骨材外板纵骨选型

来源：

维普期刊数据库博看期刊

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

考虑台风事件影响的日降水预报检验与订正

引用

水利水电技术（中英文） 2024年第3期55卷 40-50页

作者：简志健赵铜铁钢田雨吴永研李波陈晓宏水利部水网工程与调度重点实验室广东广州510275 中山大学广东广州510275 中国水利水电科学研究院水资源研究所北京海淀100036 长江勘测规划设计研究有限责任公司湖北武汉430019

【目的】台风带来的强降水常给当地带来洪涝等灾害,在台风事件下提供准确可靠的降水预报是科学研究和业务预报的重要工作。【方法】通过台风路径缓冲区筛选台风场次,检验台风事件和非台风事件分布情况;对美国国家环境预报中心提供的GEFS... 详细信息

【目的】台风带来的强降水常给当地带来洪涝等灾害,在台风事件下提供准确可靠的降水预报是科学研究和业务预报的重要工作。【方法】通过台风路径缓冲区筛选台风场次,检验台风事件和非台风事件分布情况;对美国国家环境预报中心提供的GEFSv12逐日原始降水预报检验数据精度情况,评价原始预报技巧;应用伯努利-伽马-高斯模型对GEFSv12降水预报,在我国粤港澳大湾区格点,设计不同订正方案,在不同降水场景下,评估不同情况下模型订正前后预报性能。【结果】影响我国东南沿海台风登陆时间主要集中于7—9月,台风等级集中在14级以前;台风事件下,利用台风事件样本训练模型订正后预报BIAS接近0,排序概率技巧得分CRPSS平均提高了近15%,α-index相对原始预报提升了约0.16。【结论】伯努利-伽马-高斯模型能有效订正原始预报存在的系统偏差,提高预报的准确性;不同降水场景订正效果有所区别,对出现极值降水较少的非台风事件,订正后效果有更好的表现;台风事件下,利用台风样本训练模型订正效果相对较好,提高了原始预报精度技巧、可靠性,减少预报偏差;订正的效果和相关系数大小有关,相关系数表现好的区域有更好的预报精度技巧得分,经订正后有利于后续水文集合预报应用、模型发展和备灾应灾工作。

关键词：逐日降水台风降水预报订正预报检验预报精度

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

欢迎您,

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

请选择保存的检索档案：

请选择收藏分类：

通借通还

欢迎您,

建议与咨询 留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

请选择保存的检索档案： 新增检索档案 确定 取消

请选择收藏分类： 新增自定义分类 确定 取消

通借通还

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

请选择保存的检索档案：

请选择收藏分类：