“first day cover”的概念、定义、翻译、参考文献-科学参考

单词	first day cover
释义	first day cover Encyclopedia 工学集邮品释 first day cover首日封在新邮票发行首日，将该套邮票的全套或单枚贴在特制信封、普通信封或纪念信封的右上角，加盖当日邮政日戳或特制的首日纪念邮戳的信封。
随便看	normal base normal basis normal basis theorem normal behavior normal bifurcation normal block bundle normal bundle normal bundle of a submanifold normal bus transit normal calculus normal chain normal channel spillway normal characteristic normal-circulation well clean-up normal class normal closure normal commutation relations normal complement normal complex normal complexion normal complex space normal component normal composition normal concrete normal-conducting maglev train

科学参考收录了854744条科技类词条，基本涵盖了常见科技类参考文献及英语词汇的翻译，是科学学习和研究的有利工具。