Perhaps you should try some spelling variations:
thu sach » tu sach, thuat sach, thuoc sach
hieu van » hieu va, thien van, lieu va
ky tang » ky nang, ky dang, kho tang
tang ma » mang may, tang van
su sach » so sach, vu sach
duc ban » duc tan, dua ban, duc man
duc van » duc va, duc tan, duc manh
cua tre » cua te, cuu tre, cua triet
ma hoi » mai hoi, xa hoi, ma hoa
vi cua » vai cua, di cua

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) or (su sach)) ky tang ma hoi. hieu van nam ((duc ban) OR (duc van)) hanh vi cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((thu sach) OR (su sach)) ky tang ma hoi. hieu van nam ((duc ban) OR (duc van)) hanh vi cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((thu sach) or (su sach)) ky tang ma hoi. hieu van nam ((duc ban) OR (duc van)) hanh vi cua tre".
• Adding a wildcard symbol may retrieve word variants: ((thu sach) or (su sach)) ky tang ma hoi. hieu van nam ((duc ban) OR (duc van)) hanh vi cua tre*.