Perhaps you should try some spelling variations:
"human agents periodicals." » "human aspects periodicals.", "human arts periodicals.", "human plants periodicals.", "human agent periodicals.", "human agency periodicals."
"human genes periodicals." » "human genomes periodicals.", "human games periodicals.", "human gases periodicals.", "human gene periodicals.", "human genetics periodicals.", "human genetic periodicals."
"human bees periodicals." » "human diabetes periodicals.", "human indexes periodicals.", "human devices periodicals.", "human bites periodicals.", "human beast periodicals.", "human bones periodicals."

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: (("human genes periodicals.") or ((("human agents periodicals.") or ("human bees periodicals."))))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("human genes periodicals.") OR ((("human agents periodicals.") OR ("human bees periodicals.")))).
• Removing quotes may allow a broader search: (( human genes periodicals. ) or ((( human agents periodicals. ) or ( human bees periodicals. )))).
• Adding a wildcard symbol may retrieve word variants: (("human genes periodicals.") or ((("human agents periodicals.") or ("human bees periodicals."))))*.