Perhaps you should try some spelling variations:
dau tren » dau tien, dat tren, dau tieng
mai khoi » mai khoa, tai khoa, cac khoi
hanh vai » hanh vi, hanh tai, hanh van
nam thuc » nam thuoc, am thuc, nam thu
hieu van » hieu va, thien van, lieu va
mai hoi » dai hoi, lai hoi, mai doi
sach ky » sac ky, sach y, sach ty
thuc va » thuc vat, thuc dan, thuc day
ky tang » ky nang, ky dang, kho tang
hanh va » hang va, hanh vi
tu sach » thu sach, su sach, te sach

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 tang ((mai hoi) or (mai khoi)). hieu van nam thuc va ((hanh vai) or (hanh va)) dau tren~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ky tang ((mai hoi) OR (mai khoi)). hieu van nam thuc va ((hanh vai) OR (hanh va)) dau tren.
• Adding a wildcard symbol may retrieve word variants: tu sach ky tang ((mai hoi) or (mai khoi)). hieu van nam thuc va ((hanh vai) or (hanh va)) dau tren*.