Chinese Wikipedia is blocked. I thought parts of English Wikipedia was blocked somehow as well, but seems like that's outdated information (after they started enforcing https in June 2015[0]). You'll find a list of the blocking methods on the Great Firewall wiki article[1].
[0]https://en.wikipedia.org/wiki/Censorship_of_Wikipedia#China [1]https://en.wikipedia.org/wiki/Great_Firewall#Blocking_method...