Claim: The Nebula Awards #18 is a series of English stories of science and astronomy edited by Robert Silverberg that is only available digitally.
Evidence: The Nebula Awards #18 is an anthology of science fiction short works edited by American writer Robert Silverberg. 
It was first published in hardcover by Arbor House in October 1983; a paperback edition with cover art by Gary LoSasso was issued by Bantam Books in September 1984.