Roughly, 1801, 1865, 1900, 1910 are those that are searchable in the whole of Norway. 1891 is in process of being made searchable but s currently browseable for the whole nation.
You can also search the various Norwegian censuses, 1865 and later, at the Norwegian Historical Data Centre website. http://www.rhd.uit.no/indexeng.html
Be sure to read and study the instructions that are included on that website.