Perhaps you should try some spelling variations:
"nonlinear change research documents" » "nonlinear change search document", "nonlinear change research arguments", "nonlinear change research comments", "nonlinear changes research documents", "nonlinear exchange research documents", "nonlinear channel research documents"
"online based research contents" » "online based research content", "online based research context", "online based research concept", "online basic research contents", "line based research contents", "spline based research contents", "online band research contents"
"online based research concepts" » "online based research context", "online basic research concepts", "line based research concepts", "spline based research concepts", "online band research concepts"

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: (("nonlinear change research documents") OR ((("online based research contents") OR ("online based research concepts")))).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"nonlinear change research documents\") or (((\"online based research contents\") OR (\"online based research concepts\"))))".
• Removing quotes may allow a broader search: (( nonlinear change research documents ) or ((( online based research contents ) OR ( online based research concepts )))).
• Adding a wildcard symbol may retrieve word variants: (("nonlinear change research documents") or ((("online based research contents") OR ("online based research concepts"))))*.