Perhaps you should try some spelling variations:
quoc lan » quoc ban, nuoc luan, quoc quan
hieu van » hieu va, thien van, lieu va
van tham » van thanh, van tuan, van chat
cuc ban » cua ban, cuu ban, duc ban
cac ban » cac dan, cac van, can ban
cua tre » cua te, cuu tre, cua triet
tang ma » mang may, tang van
ky tang » ky nang, ky dang, kho tang
sac ky » cac ky, sai ky
ma hoi » mai hoi, xa hoi, ma hoa
vi cua » vai cua, di cua
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 tang ma hoi. hieu van tham ((((cuc ban) OR (cac ban))) or (quoc lan)) hanh vi cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sac ky tang ma hoi. hieu van tham ((((cuc ban) OR (cac ban))) OR (quoc lan)) hanh vi cua tre*.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sac ky tang ma hoi. hieu van tham ((((cuc ban) OR (cac ban))) or (quoc lan)) hanh vi cua tre*".