Perhaps you should try some spelling variations:
"human causes periodicals." » "human cases periodicals.", "human classes periodicals.", "human courses periodicals.", "human cancers periodicals.", "human viruses periodicals.", "human cancer periodicals."
"human gases periodicals." » "human games periodicals.", "human leases periodicals.", "human gas periodicals.", "human cases periodicals.", "human gamers periodicals.", "human based 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 bees periodicals.") or ((("human gases periodicals.") or ("human causes periodicals."))))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("human bees periodicals.") OR ((("human gases periodicals.") OR ("human causes periodicals."))))*.
• Removing quotes may allow a broader search: (( human bees periodicals. ) or ((( human gases periodicals. ) or ( human causes periodicals. ))))*.