Perhaps you should try some spelling variations:
thu sach » tu sach, thuat sach, thuoc sach
hieu van » hieu va, thien van, lieu va
dua tren » dung tren
van hanh » van thanh, ban hanh, van anh
cham duc » pham duc, pham duy, phan duc
sach ky » sac ky, sach y, sach ty
tang ma » mang may, tang van
ky tang » ky nang, ky dang, kho tang
cua tre » cua te, cuu tre, cua triet
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: thu sach ky tang ma hoi. hieu van ((cham duc) OR (cham soc)) van hanh vi ((dua tren) or (cua tre))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: thu sach ky tang ma hoi. hieu van ((cham duc) OR (cham soc)) van hanh vi ((dua tren) OR (cua tre)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "thu sach ky tang ma hoi. hieu van ((cham duc) OR (cham soc)) van hanh vi ((dua tren) or (cua tre))".
• Adding a wildcard symbol may retrieve word variants: thu sach ky tang ma hoi. hieu van ((cham duc) OR (cham soc)) van hanh vi ((dua tren) or (cua tre))*.