How do I get my adept scientist to a master scientist?

unless your maxed out on everything just keep them researching. and than if you are maxed out on everything you have to keep standing over them and making them research anyway.

Also, make sure that they are checked to preferred researching. Even if they are maxed out on another skills, they won't devieate quite as often that way.

But in general it takes longer for the transition from adept to master than previous levels. Just be patient, it'll happen.