Many answers, including some of my own, provide sources with implicit links, like this. That works fine, but in the long term, links decay: URLs change, sites close down, content moves.
The better way to source material, is to provide both the text and the URL for the link. Like this: Wikipedia contributors, "Diderot," Wikipedia, The Free Encyclopedia.
This way, if the link breaks, it is still possible to find the source from the description. What do you think?
Update: I am now going more radical than originally suggested to prevent link decay. The idea is to use a footnote that points to an explicit link to an archived snapshot of the page (via internet archive).1
I would suggest adopting this as our default style.