Are corrupted data files on a memory stick recoverable?
 

I took some pictures with a Nikon DSLR, battery was sort of running low so I replaced it with another. When I went to upload the photos, they appeared as corrupted data, but the pictures from earlier shots were there.

So I put the card back into the camera, and it doesn't even show up on the display anymore.

Is there any possible way to recover the pictures that have been corrupted?

Try PhotoRec from CGSecurity. It´s a free tool.
PhotoRec - CGSecurity

Here is also an article about data recovery from Flash drives and memory cards.
Beginners Guides: Flash Memory Data Recovery and Protection - PCSTATS.com