Perhaps you should try some spelling variations:
hieu van » hieu va, thien van, lieu va
hoa truc » hoc truc, doan truc, hoa trung
dua tren » dung tren
dau tren » dau tien, dat tren, dau tieng
so sach » so sanh, bo sach, co sach
sach ky » sac ky, sach y, sach ty
nang ma » tang ma, sang ma, nang cao
truc va » thuc va, thuc vat, trung va
va doan » va doanh, van doan, va dan
doan vi » doan va, don vi, doan thi
ma hoi » mai hoi, xa hoi, ma hoa

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

• Performing a fuzzy search may retrieve terms with similar spellings: so sach ky nang ma hoi. hieu van hoa truc va doan vi ((dua tren) or (dau tren))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: so sach ky nang ma hoi. hieu van hoa truc va doan vi ((dua tren) OR (dau tren)).
• Adding a wildcard symbol may retrieve word variants: so sach ky nang ma hoi. hieu van hoa truc va doan vi ((dua tren) or (dau tren))*.