Perhaps you should try some spelling variations:
thu sach » tu sach, thuat sach, thuoc sach
nam duoc » nam thuoc, da duoc, dat duoc
hieu van » hieu va, thien van, lieu va
ly vang » ly hang, ly van, ly quang
mai hoi » mai khoi, dai hoi, lai hoi
ly nang » ky nang, ly hang, ly quang
duoc ma » duoc lam
hanh va » hanh vi
cua tre » cua te, cuu tre, cua triet

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