First, the required chiral auxiliary (+)- 23 was available in only moderate yield, requiring an impractically long period to produce (ca. 4 weeks).是什么意思_First, the required chiral auxiliary (+)- 23 was available in only moderate yield, requiring an impractically long period to produce (ca. 4 weeks).在線(xiàn)翻譯_英語(yǔ)_讀音_用法_例句