This one of the reasons I hang on to old databooks and app note books. The National Semiconductor, Motorola and Signetics appnote collections in particular are very good for delving into the theory of how the devices work.
I may never need them again for real work, but are they ever fun to read!
Right on! Well since you seem to like that, I've shared a link once here on HN but it went unnoticed. It's about Analog Design and it has a ton of information. Don't get lost:
It give recommendations depending on what you want to do, discusses books and application notes, gives links to treasures, advice, pointers, and insights.
You might know the site; otherwise, I hope you'll enjoy it.
I may never need them again for real work, but are they ever fun to read!