This peper introduces the concept of direct-projective covers, and prove that a ring R is left perfect if and only if every left R-module(flat left R-module) has a direct-projective cover;
本文引入直投射覆盖的概念，证明了环R为左完全环当且仅当每一个左R-模（平坦左R-模）具有直投射覆盖；
The model was developed to simulate seasonal and annual growth, foliage projective cover (FPC), and evaporative coefficient in the Ordos plateau, where serious desertification happened recently.
该模型用于模拟发生严重荒漠化的鄂尔多斯高原植物群落的季节及年生长、叶片投影盖度、蒸发系数。
The model was developed to simulate seasonal and annual growth, foliage projective cover (FPC), and evaporative coefficient in the Ordos plateau, where serious desertification happened recently.
该模型用于模拟发生严重荒漠化的鄂尔多斯高原植物群落的季节及年生长、叶片投影盖度、蒸发系数。
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