Station supply only from production

Hello, I played the game for a few hours now and I noticed a thing: I can not tell a station that it should only be supplied by the own production not from the import, or I just have not seen it yet?! Can you help me?

In order to change the delivery priority in the station, we must first carry out a study “Import Priorites”.
After that, the “import” tab will be available at the station.