eg.not so much.as与其说是.不如是.
They weren't so much islands as sandbars.与其说那是些岛屿,还不如说都是些沙
not so much.but
It is not so much the actual population of the world but its rate of increase which is important．重要的与其说是实际的世界人口总数,倒不如说是世界人口增长率.
这两个短语一般翻译成一样的,但有些书中说but不能替换as.