first roof caving 中文意思是什麼
first roof caving
解釋
直接頂初次垮落-
First roof caving
直接頂初次垮落 -
Practice of first roof caving technology at comprehensive mechanical mining face in steep thick coal seam
急傾斜特厚煤層綜放工作面超段高初次放頂的實踐
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