By assuming the weak lens focal length expression to be the first term in a power series, a simple and accurate formula can be derived for the objective focal length of a magnetic electron lens.是什么意思_By assuming the weak lens focal length expression to be the first term in a power series, a simple and accurate formula can be derived for the objective focal length of a magnetic electron lens.在線(xiàn)翻譯_英語(yǔ)_讀音_用法_例句