Google will scan the web, and the first instance it sees content, it remembers where it saw it. Duplicate content is penalized.

Don't take my word for it, there is plenty of resources out there that talk about it, like this video from Matt Cutts, former employee of Google:

I really don't want to see authors using steemit just to recycle their material just to earn steem. Either post it here first (best choice), or if you make more money posting it elsewhere, then "reference" it here and make a commentary that talks about the article, and whats in the article, without actually copy/pasting the exact same content from the article.