A collection of 10 chess books on middlegame strategies. All in PDF format with covers:

01. Art of Chess Analysis by Jan Timman
02. Chess Middlegame Planning by Peter Romanovsky
03. Chess Middlegames - Essential Knowledge by Yuri Averbakh
04. Complete Book of Chess Strategy - Grandmaster Techniques from A to Z by Jeremy Silman
05. Complete Chess Strategy - First Principles of the Middlegame by Ludek Pachman
06. From the Middlegame into the Endgame by Edmar Mednis
07. Isolated Pawn - Theory of Chess Middlegame by Adrian Mikhalchishin
08. Soviet Middlegame Technique by Peter Romanovsky
09. Understanding Chess Middlegames by John Nunn
10. Winning Chess Middlegames - An Essential Guide to Pawn Structures by Ivan Sokolov