at bottom

1. 实际上

He pretends to be very hard, but he's a kind man at bottom.

他假装无情, 实际上却是一个善良的人。

from the bottom of one's heart

1. 衷心地

The mother thanked the man from the bottom of her heart for saving her son's life.

这位母亲衷心感谢那位救了她儿子的性命的人。

get to the bottom of

1. 弄清……的真相

The police are eager to get to the bottom of this mystery.

警方急切地想弄清这一神秘事件的真相。