syntax to block complete URL

Hai,

i would like to know what is the correct syntax for allowing few URL like
yahoo.com, cnn.com, google.com.

i tried some syntax but they have some problem actually its allowing but not the full contents of the page.

^https?://[A-Za-z0-9.-]*\.google.com/

^https?://.*wikipedia.org

i tried with ^https?://[A-Za-z0-9.-]*\.yahoo.com/ and ^https?://.*yahoo.com
but the web page is not opening correctly with all its contents of first page.

thanks in advance...