Perhaps you should try some spelling variations:
"observations theory: advances and applications" » "observations towards: advances and applications"
"operation theory: advances and applications" » "operations theory: advances and applications", "operator theory: advances and applications", "iteration theory: advances and applications"

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