unturned

adj.不转动的(未翻转的；没有转向的)

Of course, social science research is almost never conclusive. There are always methodological difficulties and stones left unturned. 当然，社会科学的研究几乎从来没有结论。总是有方法上的困难和人事未能尽到的情形。

The police left no stone unturned in their search for the missing child. 警察为了寻找这个失踪的儿童，使用了一要手段。