No, there isn't. Unanswered used to be exactly that, but this way it was found that just one answer, even if not helpful at all, excluded the question from the list. It was much less likely to get answered again.
Maybe a threshhold would be interesting: show me unanswered questions with at most n answers.
Edit This was true at the time of writing.
Now to find zero (0) answers, include the following in the search query:
This will result in all questions with no answer. If you use another number, it shows all questions with a minimum of so many answers. (answers:1 returns all questions with at least one answer.)