Perhaps you should try some spelling variations:
"state vectors" » "state vector", "state detectors"
"state action" » "state reactions"
"state actor" » "state vector", "state sector", "state after"
"state actors" » "state vectors", "state sectors", "state afters", "state factors"

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: (((("state actor") OR ("state action"))) OR ((("state actors") OR ("state vectors")))).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((((\"state actor\") OR (\"state action\"))) or (((\"state actors\") or (\"state vectors\"))))".
• Removing quotes may allow a broader search: (((( state actor ) OR ( state action ))) or ((( state actors ) or ( state vectors )))).
• Adding a wildcard symbol may retrieve word variants: (((("state actor") OR ("state action"))) or ((("state actors") or ("state vectors"))))*.