There is no way to show only some of the expansions your are subscribed to. You can show them by expansion, though, by clicking on the expansion name on the left (here: base set).
If you want to make sure that the kingdom will only consist of cards from given expansions, you can click on the checkboxes beside them:
That method can be used to learn new cards a few at a time. Say you want to test how Sea Hag and Lookout from Seaside play, but otherwise only use cards you know from Base/Intrigue. You mark the checkboxes as above, but select Sea Hag and Lookout from Seaside:
This will create a Kingdom with Sea Hag, Lookout and 8 random cards from Base/Intrigue.
I hope this helped, feel free to ask if something is unclear.