Study of gas drainage for the fully mechanized sub-level caving face with light-duty supports in the coal seam of low air permeability and high risk of gas outb是什么意思_Study of gas drainage for the fully mechanized sub-level caving face with light-duty supports in the coal seam of low air permeability and high risk of gas outb在線(xiàn)翻譯_英語(yǔ)_讀音_用法_例句