Is it necessary to apply spaced repetition when reading research papers? I'm an undergraduate who is going to be a Ph.D candidate this fall. After reading papers extensively for writing the literature review, I realize details in some papers, though I totally understand them at the moment I read them, are almost forgotten when I try to cite these papers.
I wonder what's your habit to keep track of the papers you've read (for long-term retrieval).
If you want to remember something long term, spaced repetition is a good way to remember it.
I interact with hundreds of papers per year.  Trying to remember them all is futile.  You should prioritize.