From the post:
Turns out Google Books does support searching by ISSN, using ordinary fielded search syntax, although I don’t believe it’s documented anywhere.
Mostly what you’ll find is digitized bound journals from libraries (that is, digitization of some volumes of the journal, probably not all of them, which may or may not have full text access). Sometimes things that physically look like monographs but are published serially also get ISSNs, you might get some of those too, not sure. Has to be in GBS, and GBS has to have ISSN metadata for the record, not sure how often that happens.
Of particular interest to library students and librarians.
My only caution is that like many “undocumented” features, this may or may not persist. Still, take advantage of it while it is around.
(And a good excuse for me to add ISSN/ISBN to my category list.)