1.意思都一样,都是因此；所以
2.so 既能做连词,又能做副词；而therefore 和 as a result 都只能做副词.
So做连词,比如It is raining outside,so I stay at home.做副词 It is raining outside.So I stay at home.
therefore 和 as a result.It is raining outside.Therefore( As a result),I stay at home.