Many references to wikipedia

Hello.
I'm thinking about  writing a book and perhaps use wikipedia for that.
And I have some questions about GFDL.
If I make a reference list at the end of the book, should I make references 
to each single URL at wikipedia.org I have visited, or can I make a single 
reference to wikipedia.org ? 

Sometimes perhaps I really should make explicit references when it's 
important that you can find the original text.

If you have any other advices for an author, please tell me.

Gunnar.