用法的分別 - partly / partially

partly
1. 部分地;不完全地;在一定程度上
a partly-finished building
部分建成的房屋
We are all partly to blame.
我們都負有一部分責任。

partially
1. 部分地
He is partially responsible for the accident.
他對該事故負有部分責任。
2. 【古】偏袒地;偏愛地

In general, both are the same but only "partially" can be used to imply favourism
e.g. He is 'partial' to pizza.