Perhaps you should try some spelling variations:
"direct selection" » "direct detection", "direct injection", "direct solution"
"direct electron" » "direct electrical"
"effect electron" » "effective electron"

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