Perhaps you should try some spelling variations:
elgar signals » pulsar signals, radar signals, sonar signals
clear signals » clear goals, radar signals, sonar signals
"elgar origin references" » "algal origin references", "solar origin references", "ear origins references"

Try widening your search to All Fields.

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