Perhaps you should try some spelling variations:
hieu van » hieu va, thien van, lieu va
van pham » san pham, van phan, van phat
cua viet » ca viet, hoa viet, cua vat
tan hanh » tan thanh, tang hanh, toan hanh
mai khoi » mai khoa, tai khoa, cac khoi
hanh di » hanh vi, hanh de, hang di
su tien » su kien, su hien, tu tieng
mai hoi » dai hoi, lai hoi, mai doi
sac ky » cac ky, sai ky
tu sac » tu sach, tu cac, tu san

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

• Performing a fuzzy search may retrieve terms with similar spellings: tu sac ky nang ((mai hoi) OR (mai khoi)). hieu van pham duc tan hanh di ((cua viet) or (su tien))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sac ky nang ((mai hoi) OR (mai khoi)). hieu van pham duc tan hanh di ((cua viet) OR (su tien)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sac ky nang ((mai hoi) OR (mai khoi)). hieu van pham duc tan hanh di ((cua viet) or (su tien))".
• Adding a wildcard symbol may retrieve word variants: tu sac ky nang ((mai hoi) OR (mai khoi)). hieu van pham duc tan hanh di ((cua viet) or (su tien))*.