本文介绍了世界低煤阶煤炭资源及其分类。

The resources of low rank coal in the world have introduced in this paper.

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内因是煤的渗透性、水分、变质前煤阶、围岩的封闭性。

There are two factors to influence the hydrothermal metamorphism of coal.

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内因是煤的渗透性、水分、变质前煤阶、围岩的封闭性。

There are two factors to influence the hydrothermal metamorphism of coal.

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