Perhaps you should try some spelling variations:
"valid analytical measurement" » "valid analysis measurement", "valid optical measurement", "valid clinical measurement", "based analytical measurement", "d analytical measurement", "valued analytic measurement"
valid optical » rapid optical, acid optical, halides optical
solid optical » solids optical, solar optical, speed optical

Try widening your search to All Fields.

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• If you are trying to use Boolean operators, they must be ALL CAPS: (("valid analytical measurement") OR ("((valid optical) OR (solid optical)) measurement")).
• Removing quotes may allow a broader search: (( valid analytical measurement ) or ( ((valid optical) OR (solid optical)) measurement )).
• Adding a wildcard symbol may retrieve word variants: (("valid analytical measurement") or ("((valid optical) OR (solid optical)) measurement"))*.