Perhaps you should try some spelling variations:
"online charging research effects" » "online changing research effects", "online sharing research effects", "online caring research effects", "online charging research efforts", "online charging research aspects", "online charging research projects", "online coaching research effects"
"online pain search document" » "online paid search document", "online paging search document", "online paying search document", "online pair search document", "online vain search document"

You may be able to get more results by adjusting your search query.

• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"online pain search document\") OR (\"online charging research effects\"))".
• Removing quotes may allow a broader search: (( online pain search document ) OR ( online charging research effects )).
• Adding a wildcard symbol may retrieve word variants: (("online pain search document") OR ("online charging research effects"))*.