Childhood's End by Arthur C. Clarke
Brainwave by Poul Anderson
Downbelow Station by C.J. Cherryh - astrophysics here, but also the sociology of space station life as well as the psychologies of people who have been warped by interstellar warfare their whole lives.
Cyteen by C.J. Cherryh - cloning/gene manipulation sci-fi.
Rainbows End by Vernor Vinge - computers in the latter half of the twentieth century often focused on A.I.s or, later, cyberspace.
The Nanotech Quartet, by Kathleen Goonan - Nanotech malfunction
Matter by Iain M. Banks - huge, artificial "shellworld" built by mysterious, long-dead aliens, pays homage to/updates Niven.
And I don't know it's really hard sci-fi but it sounds like you'd love it - one of my favoriites - Startide Rising by David Brin.
Why do so many books labeled "hard science fiction" actually contain technology that works pretty much like magic in a fantasy novel? Hard science fiction is supposed to be the branch of SF that's rigorously scientific, and doesn't gloss over difficult problems like faster-than-light travel. Larry Niven's Ringworld series, with its long passages on how you'd engineer a giant space structure, is often held up as a prime example of hard SF that works. And yet most lists of hard SF include authors like Frank Herbert, whose Dune series about giant worms who create a substance that allows people to "fold space" with their minds is many wonderful things - but not so much based in science.