Britannica seems to be playing innovation with linking.
If you don't have a EB subscription, visiting this URL may only give you a short snipped:
http:// www.britannica. com/eb/article-9433599/ Wikipedia (cut and paste by hand, then remove the blanks)
But there is a new feature that will give you free access to the text. EBI asks you to link to them. If you access a page via that link, the full text is shown.
Of course, if you don't want to play a link farm for britannica, simply open up the page http://en.wikipedia.org/wiki/Free_Access_to_Britannica (which is empty).
Click on "edit this page".
Put in [http://www.britannica.com/eb/article-9433599/Wikipedia Wikipedia] and klick on "Preview"
If you click on that link again, you will see the full text and you don't have to worry about pushing EBI with google juice.
Or you may use that "rel=nofollow"-tag if you really want to link to them...