Perhaps you should try some spelling variations:
vie » viet, vien, view
viec » vietc, vienc, viewc, viet, vien
vietnam" » viettnam", vientnam", viewtnam"
vientnam" » vietntnam", vienntnam", viewntnam", vienam", vietnams"
viettnams" » vietttnams", vienttnams", viewttnams", vietnams", vietnames"
president » resident, present

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

• Performing a fuzzy search may retrieve terms with similar spellings: "(vie or viec) (president or residents) of (vietnam" or ((vientnam" or viettnams") or vietnam"))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: "(vie OR viec) (president OR residents) of (vietnam" or ((vientnam" OR viettnams") or vietnam")).
• Removing quotes may allow a broader search: (vie or viec) (president or residents) of (vietnam or ((vientnam or viettnams ) or vietnam )).
• Adding a wildcard symbol may retrieve word variants: "(vie or viec) (president or residents) of (vietnam" or ((vientnam" or viettnams") or vietnam"))*.