分级提取 meaning in English

fractional extraction

Commonness analysis of species in different fractionations of phosphorus in sediments
沉积物磷的分级提取方法及提取相的共性分析
In this thesis , we present a scheme of hierarchically characterizing and comparing video streams features from coarse level to fine level - cascading comparison scheme . design and built a video retrieval experiment system
针对分层检索的思想，论文中提出了一种由粗到精分级提取输入视频流特征并进行相似性比较的方法? ?视频特征级联比较法。