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A thermionic valve or tube with a hard vacuum, or evacuated sufficiently for any remaining gas not to affect its performance.
Early 20th century; earliest use found in Wireless World.
雅致网英汉双解词典包含236457条英汉翻译词条，涵盖了常用英语单词及词组短语的翻译及用法，是英语学习的必备工具。