Reminds me of "100 Great Science Fiction Short Short Stories" edited by Asimov. The format works really well for hard sci-fi, gets straight to the point. Some of them have stuck with me for decades.
I've looked up "Microcosmic God" several times because I can't seem to remember the title. But the story was particularly memorable. It wasn't in this Asimov anthology but it was published in the SF Hall of Fame.
A quick search reveals that someone has a copy of the text freely (but perhaps not legitimately) available.