So 的后面直接接句子.
He is not good at physics,so he must work hard.
as a result 单独使用,后面一般用逗号隔开,并且不能连结2个句子.
He worked hard at his study.As a result,he passed the exam easily.
as a result of + 名词或者代词.
As a result of his hard work,he passed the exam easily.