I do not have much experience with it because I am a writer not a content buyer, so all I can help you with is to Google for "Copyscape" and start from there.
i use advego, copy scape is also good of course no mathes should be found!if you want to have really good article, it must be 100% unique!
There is no parallel to Copyscape. But if you are not willing to purchase Copyscape account, you can try plagium.com. It offers better search next to Copyscape. But try depth search by registering plagium.com. But plagium.com is my personal preferences. Many people don't like it.
You could also try copying and pasting part of your article into the Google search bar. Remember to use open and close inverted commas around the quoted text, so that Google will only return results that match the quoted text exactly. This is a simple way to find out if the exact same article appears anywhere else on the Internet. Of course, Copyscape is a far better plagiarism checker; it doesn't just check for exact word matches but other forms of plagiarism as well. Copyscape can even check whether your article has been copied from offline publications such as books.