A mild and efficient procedure to build up various chromone-2-carboxylates was developed. Condensation of diverse 2-hydroxyacetophones with tetr-butyl oxalate i
中华人民共和国国家标准低温作业分级Classificationofworksincoldenvironment1993-06-10批准(国家技术监督局)GB/T14440-931994-01-01实施1主题内容与适用范围本标准规定了低温作业环境冷强度...
Classification of the People’s Republic of China N