Perhaps you should try some spelling variations:
"electrical charging" » "electric charging", "electrical charge", "electrical aging"
"electrical mapping" » "electrical machines", "electrical coupling", "electrical modeling"
"electrical machine" » "electrical machines", "electric machines", "electric machinery"

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: (((("electrical mapping") OR ("electrical machine"))) OR ("electrical charging")).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((((\"electrical mapping\") OR (\"electrical machine\"))) or (\"electrical charging\"))".
• Removing quotes may allow a broader search: (((( electrical mapping ) OR ( electrical machine ))) or ( electrical charging )).
• Adding a wildcard symbol may retrieve word variants: (((("electrical mapping") OR ("electrical machine"))) or ("electrical charging"))*.