@vicgrinberg

For freely available online textbooks on a variety of courses, LibreTexts is a great resource, especially to begin exploring a subject.

https://libretexts.org/

They're mostly accessible to non-specialists and have many advanced features: https://libretexts.org/advanced.html

Examples:

Astronomy and Cosmology: https://phys.libretexts.org/Bookshelves/Astronomy__Cosmology

Physics: https://phys.libretexts.org/Bookshelves

Math: https://math.libretexts.org/Bookshelves

Biology: https://bio.libretexts.org/Bookshelves

Humanities: https://human.libretexts.org/Bookshelves

#Science #Textbooks