Are Classic Thor and Modern Thor the exact same beings?

I do not know Thor's classic history that well. But it seems current Modern Thor (Worthy) is extremely different from his classic counterpart. Especially in abilities! I mean classic Thor could shrink people and steal people's abilities! Modern Thor has not shown to be able to replicate this! So please answer me these questions!

1. Are they the same?

2. Was there a retcon for Thor that made classic Thor so different from Modern Thor? If so where can I find information and read about it.

Please share any information you can. This has bugged me forever!