Perhaps you should try some spelling variations:
duoc tren » nuoc tren, thuoc tren, dung tren
tai duoc » tao duoc, tan duoc, mai duoc
hanh tai » thanh tai, hang tai, han tai
hieu van » hieu va, thien van, lieu va
sach ky » sac ky, sach y, sach ty
tu sach » thu sach, su sach, te sach
mai hoi » mai khoi, dai hoi, lai hoi
ky dang » ky nang, ky danh
van cac » van hac, van cau, van bac
xuc va » duc va, luc va, xac va
tuc va » thuc va, truc va, tuc xa
ma hoi » xa hoi, ma hoa, me hoi

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

• Performing a fuzzy search may retrieve terms with similar spellings: tu sach ky dang ((ma hoi) or (mai hoi)). hieu van cac ((xuc va) or (tuc va)) hanh tai duoc tren~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ky dang ((ma hoi) OR (mai hoi)). hieu van cac ((xuc va) OR (tuc va)) hanh tai duoc tren.
• Adding a wildcard symbol may retrieve word variants: tu sach ky dang ((ma hoi) or (mai hoi)). hieu van cac ((xuc va) or (tuc va)) hanh tai duoc tren*.