 |
| |||
| 不稳定顶板强度低的直接顶板，一般为泥岩、泥质页岩、页岩 | |||
| 不稳定顶板 | |||
The server is undergoing maintenance and the site is working in read-only mode. Please check back later.">Add | The server is undergoing maintenance and the site is working in read-only mode. Please check back later.">Report an error
| Get short URL | Language Selection Tips