Perhaps you should try some spelling variations:
trinh viet » ninh viet, trinh vat
hieu van » hieu va, thien van, lieu va
dinh vi » dinh ve, dinh viet, dinh tri
cau luc » cau truc, cau phuc
sach ky » sach y, sach ty, sach kem
van cau » van dau, van hau, van chat
cao hoi » cau hoi, co hoi, cao hoc
ca tren » cau tren, cu tren, la tren
luc va » duc va, tuc va, loc va
sac ky » cac ky, sai ky

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

• Performing a fuzzy search may retrieve terms with similar spellings: hoc ((sach ky) OR (sac ky)) nang cao hoi. hieu van cau luc va ((dinh vi) or (trinh viet)) ca tren~.
• If you are trying to use Boolean operators, they must be ALL CAPS: hoc ((sach ky) OR (sac ky)) nang cao hoi. hieu van cau luc va ((dinh vi) OR (trinh viet)) ca tren.
• The words AND, OR and NOT may confuse the search; try adding quotes: "hoc ((sach ky) OR (sac ky)) nang cao hoi. hieu van cau luc va ((dinh vi) or (trinh viet)) ca tren".
• Adding a wildcard symbol may retrieve word variants: hoc ((sach ky) OR (sac ky)) nang cao hoi. hieu van cau luc va ((dinh vi) or (trinh viet)) ca tren*.