The Solomon R. Guggenheim Foundation has made a significant collection of art texts/catalogues available online, all free of charge. The catalogues offer an intellectual and visual introduction to the work of Alexander Calder, Edvard Munch, Francis Bacon, Gustav Klimt & Egon Schiele, and Kandinsky. Plus there are other texts (e.g., Masterpieces of Modern Art and Abstract Expressionists Imagists) that tackle meta movements and themes.
LINK: https://archive.org/details/guggenheimmuseum&tab=collection