Perhaps you should try some spelling variations:
"unmanned arterial vehicles" » "unmanned arial vehicles", "damaged arterial vehicles", "unmanned area vehicles", "unmanned aethereal vehicles", "unmanned aerial vehicle"
"skinned arterial vehicles" » "skinned aethereal vehicles", "skinned aerial vehicle", "skinned arial vehicles", "guided arterial vehicles"

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: (((("unmanned arterial vehicles") OR ("skinned arterial vehicles"))) OR ("unmanned aerial vehicles")).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((((\"unmanned arterial vehicles\") OR (\"skinned arterial vehicles\"))) or (\"unmanned aerial vehicles\"))".
• Removing quotes may allow a broader search: (((( unmanned arterial vehicles ) OR ( skinned arterial vehicles ))) or ( unmanned aerial vehicles )).
• Adding a wildcard symbol may retrieve word variants: (((("unmanned arterial vehicles") OR ("skinned arterial vehicles"))) or ("unmanned aerial vehicles"))*.