White Papers
White papers are informational documents which are provided by organizations of specific chains which were established earlier. They describe the working of the chains and how they were made, following what patterns and based on what technology. In short terms, white papers describe their specific chains.
White papers are amazing sources to learn core blockchain and understand the working of the chains. They provide great material for beginners as well as experts alike.
The three most used chains are - Bitcoin, Ethereum and Polygon.
The white papers for these chains can be found in:
Other than these three, here is a curated list of academic blockchain-related white papers.