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在线翻译_英语_读音_用法_例句