Reaction products of 2,4,6-tris(4-phenyl-phenoxy)-1,3,5-triazine derived from 4-phenylphenol cyanate ester and phenyl glycidyl ether were analyzed. In addition to an isocyanurate compound and an oxazolidone compound w...Reaction products of 2,4,6-tris(4-phenyl-phenoxy)-1,3,5-triazine derived from 4-phenylphenol cyanate ester and phenyl glycidyl ether were analyzed. In addition to an isocyanurate compound and an oxazolidone compound which were well known as reaction products of cyanate esters and epoxy resins, compounds with hybrid ring structure of cyanurate/isocyanurate were determined. Gibbs free energies of the compound having hybrid ring structure of cyanurate/isocyanurate with two isocyanurate moiety were found to be lower than that of the compound with cyanurate ring structure through calculations. Calculation data supported the existence of hybrid ring structure of cy-anurate/isocyanurate. It was revealed that isomerization from cyanurate to isocyanurate occurs via hybrid ring structure of cyanurate/isocyanurate in the reaction of aryl cyanurate and epoxy.展开更多
To enable natural language interfaces to databases more efficient and robust,two kinds of techniques,language paraphrasing and result analyzing,are widely used to help users to understand the system's intermediate...To enable natural language interfaces to databases more efficient and robust,two kinds of techniques,language paraphrasing and result analyzing,are widely used to help users to understand the system's intermediate language,and the query result meaning in some times. For the limitation of intermediate language adopted in some NLIDBs ,they could not give efficient and practical paraphrasing algorithms. Based on semantic dependency tree in NChiql,we present a completed paraphrasing algorithm which is suitable to Chinese languages.展开更多
文章主要介绍了SQL Server 2000的体系结构、安全模式、管理数据库文件的方法、数据的转换、备份、还原和复制以及Transact-SQL语言设计技术。叙述了应用系统存储过程和触发器来保证数据间的完整性和一致性的实现过程。重点对SQL Serve...文章主要介绍了SQL Server 2000的体系结构、安全模式、管理数据库文件的方法、数据的转换、备份、还原和复制以及Transact-SQL语言设计技术。叙述了应用系统存储过程和触发器来保证数据间的完整性和一致性的实现过程。重点对SQL Server数据库底层的配置、管理数据、性能优化和安全性管理进行详细阐述。最后,通过以上学习,将SQL Server 2000和oracle数据库的性能进行了比较,总结出它们各自的特点。目前,在数据库的实际应用领域中,很多数据库管理都还存在一定的问题,导致数据库性能较差。研究此课题对于数据库系统选择和应用有一定意义。展开更多
文摘Reaction products of 2,4,6-tris(4-phenyl-phenoxy)-1,3,5-triazine derived from 4-phenylphenol cyanate ester and phenyl glycidyl ether were analyzed. In addition to an isocyanurate compound and an oxazolidone compound which were well known as reaction products of cyanate esters and epoxy resins, compounds with hybrid ring structure of cyanurate/isocyanurate were determined. Gibbs free energies of the compound having hybrid ring structure of cyanurate/isocyanurate with two isocyanurate moiety were found to be lower than that of the compound with cyanurate ring structure through calculations. Calculation data supported the existence of hybrid ring structure of cy-anurate/isocyanurate. It was revealed that isomerization from cyanurate to isocyanurate occurs via hybrid ring structure of cyanurate/isocyanurate in the reaction of aryl cyanurate and epoxy.
基金Supported by the National Natural Science Foundation of China under Grant Nos.60473071,10476006(国家自然科学基金)the National High-Tech Research and Development Plan of China under Grant No.2006AA01Z414(国家高技术研究发展计划(863))
文摘To enable natural language interfaces to databases more efficient and robust,two kinds of techniques,language paraphrasing and result analyzing,are widely used to help users to understand the system's intermediate language,and the query result meaning in some times. For the limitation of intermediate language adopted in some NLIDBs ,they could not give efficient and practical paraphrasing algorithms. Based on semantic dependency tree in NChiql,we present a completed paraphrasing algorithm which is suitable to Chinese languages.
文摘文章主要介绍了SQL Server 2000的体系结构、安全模式、管理数据库文件的方法、数据的转换、备份、还原和复制以及Transact-SQL语言设计技术。叙述了应用系统存储过程和触发器来保证数据间的完整性和一致性的实现过程。重点对SQL Server数据库底层的配置、管理数据、性能优化和安全性管理进行详细阐述。最后,通过以上学习,将SQL Server 2000和oracle数据库的性能进行了比较,总结出它们各自的特点。目前,在数据库的实际应用领域中,很多数据库管理都还存在一定的问题,导致数据库性能较差。研究此课题对于数据库系统选择和应用有一定意义。
