<span style="font-size: 11pt; font-family: "微软雅黑","sans-serif"; mso-ascii-font-family: Tahoma; mso-hansi-font-family: Tahoma; mso-bidi-font-family: "Times New Roman"; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA">平朔东露天矿采空区上覆岩层安全厚度研究</span>