I think the current DeviantArt parser follows the link on that download button if the image is sfw. Unfortunately, nsfw image pages don't provide that button for non-logged in users, so I scrape the best I can get from the (I think hidden?) tumblr share link, which may not be full size.
I just tested this on 'nikulina-helena' and I was getting full size images, but if you know a sfw search or a particular file type that doesn't, please let me know. And if you know a way to figure out the full size image url from a logged-out nsfw image page's html, I'd be very interested. I had a long look a while ago but couldn't figure anything better than munging the tumblr link.
A future version of my downloader engine will support login for any site, but I am afraid it doesn't right now.