A textbook on how to construct electronic transistors and amplifiers from 1973. There are a lot of diagram of transistors and CPUs, as well as graphs and equations, presumably related to electrical engineering.
An old operations manual for the Soviet ES EVM, which, according to wikipedia, was a copy of the IBM System/360 mainframes.
This book was found inside the Duga-1 Radar installation, also known as the Russian Woodpecker. Presumably it was located there because the Duga used these ES EVM machines on-site, which means that this very book likely helped the Soviet engineers operate the radar.
Because this book was printed in 1980, it was likely used as part of an upgrade to the system, since Duga had been operating since 1976.