The publicly available medical literature database PubMed can be found here.
I recommend if you are doing a search for a stem cell paper on a disease of you interest that you plug into the search box the following:
stem cells[title] AND XXXX
In this case delete XXXX and put in the name of the disease of interest.
So for example to search for stem cell papers on autism search for:
stem cells[title] AND autism
If you want only recent paper such as this year, you can expand the search terms to:
stem cells[title] AND autism AND 2015.
Hope this helps.