Perhaps you should try some spelling variations:
"occupational opportunity" » "occupational opportunities", "exceptional opportunity", "generational opportunity"
"educational opportunity" » "educational opportunities"
"occupational mortality" » "occupational contact", "occupational activity", "occupational toxicity"
"occupational mobility" » "occupational medicine"

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

• If you are trying to use Boolean operators, they must be ALL CAPS: (((("occupational opportunity") OR ((("occupational mortality") OR ("occupational mobility"))))) OR ("educational opportunity")).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((((\"occupational opportunity\") or (((\"occupational mortality\") OR (\"occupational mobility\"))))) or (\"educational opportunity\"))".
• Removing quotes may allow a broader search: (((( occupational opportunity ) or ((( occupational mortality ) OR ( occupational mobility ))))) or ( educational opportunity )).
• Adding a wildcard symbol may retrieve word variants: (((("occupational opportunity") or ((("occupational mortality") OR ("occupational mobility"))))) or ("educational opportunity"))*.