Perhaps you should try some spelling variations:
"working environments and operational considerations" » "working environments and computational considerations", "working environments and additional considerations", "working environment and operational considerations", "work environments and operational considerations", "learning environments and operational considerations"
"varying environments and operational conditions" » "varying environments and operational definitions", "varying environments and operational control", "varying environment and operational conditions", "learning environments and operational conditions", "changing environments and operational conditions"
"varying environments and operating conditions" » "varying environment and operating conditions", "learning environments and operating conditions", "changing environments and operating conditions", "varying environments and loading conditions"

Try widening your search to All Fields.

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: (((("varying environments and operational conditions") OR ("varying environments and operating conditions"))) OR ("working environments and operational considerations")).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((((\"varying environments and operational conditions\") OR (\"varying environments and operating conditions\"))) or (\"working environments and operational considerations\"))".
• Removing quotes may allow a broader search: (((( varying environments and operational conditions ) OR ( varying environments and operating conditions ))) or ( working environments and operational considerations )).
• Adding a wildcard symbol may retrieve word variants: (((("varying environments and operational conditions") OR ("varying environments and operating conditions"))) or ("working environments and operational considerations"))*.