Yes, Discover@Bolton can limit your results to online-only.

Run a search on Discover@Bolton using your subject or keywords of interest. 

Then, on the results page click Full Text Online (the top option in the Refine Your Search panel on the left hand side of the screen). 

Now the results are limited to those you can read online. You can further refine your results in lots of different ways. Use the Item Type options to limit your results to Journal Articles, Newspapers etc. 

If you select Book/Ebook after already filtering your results to Full Text Online, this will return just Ebooks.