研究煤萃取后的小分子相的赋存方式及其变化规律，用不同溶剂对龙口褐煤进行了分级萃取。
The fractional extraction on Longkou lignite by different solvent was used for the studying of the occurrence modes and the variations of small molecular phases in coal.
通过对黑荆树皮单宁进行醇沉纯化和溶剂萃取分级，可得到分子量分布范围不同的单宁级分。
Tannin fractions with different molecular weight distributions were obtained by purification of alcohol precipitation and fractionation of solvent extractions of black wattle bark tannins.
通过对黑荆树皮单宁进行醇沉纯化和溶剂萃取分级，可得到分子量分布范围不同的单宁级分。
Tannin fractions with different molecular weight distributions were obtained by purification of alcohol precipitation and fractionation of solvent extractions of black wattle bark tannins.
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