Question

as a matter of fact和in fact意为“实际上，事实上”它们有什么区别吗?

Answer 1

没有什么实质上的区别
as a matter of fact = in fact，“事实上；实际上”，在句中作插入语，
例如： As a matter of fact，I do know her.
事实上，我的确认识她。
He appears to be strong and healthy，but，as a matter of fact，he suffers a very weak heart.
他外表显得健康结实，事实上，他的心脏很衰弱。