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 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 causes periodicals."))) or ("human bees periodicals."))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (((("human genes periodicals.") OR ("human causes periodicals."))) OR ("human bees periodicals."))*.
• Removing quotes may allow a broader search: (((( human genes periodicals. ) or ( human causes periodicals. ))) or ( human bees periodicals. ))*.