Perhaps you should try some spelling variations:
trinh nhiem » trinh nhiet, trinh nghien, trach nhiem
trinh thiet » trinh thi
hanh trinh » canh tranh, hanh chinh
trinh viet » ninh viet, trinh vat
duoc hoc » quoc hoi
tu hanh » du hanh, lu hanh, thuc hanh
nhiem d » nghiem d, nghiem de, nghiem do
tu sach » thu sach, su sach, te sach
d hoc » du hoc, ad hoc, de hoc

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: (( tu hanh trinh nhiem d hoc ) OR ( tu sach ((trinh thiet) OR (trinh viet)) duoc hoc ))~.
• Adding a wildcard symbol may retrieve word variants: (( tu hanh trinh nhiem d hoc ) or ( tu sach ((trinh thiet) or (trinh viet)) duoc hoc ))*.