Not too long ago, when I want to investigate a topic, I tend to make the error of being too broad. Instead of Googling my intended item, I would Google a college course’s lecture notes or similar “all-purpose” resource for a subject. While they can be doubtless rich in information, it will depend on the scope of content that the leader (often, a college professor) wants to contain on his site, both in breadth and depth.
I’m not denying their substantial information is of good quality. I’m just recommending a different means of searching the web.
My solution here is simply to be more specific. For example, say “cephalopods” instead of “invertebrate zoology,” or “sapwood” instead of “plant anatomy,” or “electric potential” instead of “physics.”
And once this rule of thumb is observed, you will probably unleash far more power than by doing a search on a broad topic. You may even cross paths with those “all-purpose” sites mentioned above, such as course notes. But since you are aiming for what you want, when you need it, it doesn’t matter what the identity of the sites are.
I wish you some “bull’s eyes!”