Perhaps you should try some spelling variations:
doc sach » hoc sach, toc sach, nuoc sach
hieu van » hieu va, thien van, lieu va
hanh doi » thanh doi, hanh noi, hang doi
ban hanh » ban hang
chat duc » chat xuc, chat doc, chet duoc
doi cua » dai cua, hoi cua
duc ban » duc tan, duc van, dua ban
cua tre » cua te, cuu tre, cua triet
hieu ve » hieu va
tu tong » tu tuong, tu trong, tu dong
tu lang » cu lang, tu lanh, xu lang

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: doc sach ((tu lang) or (tu tong)) xa hoi. ((hieu ve) OR (hieu van)) chat duc ban hanh doi cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: doc sach ((tu lang) OR (tu tong)) xa hoi. ((hieu ve) OR (hieu van)) chat duc ban hanh doi cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "doc sach ((tu lang) or (tu tong)) xa hoi. ((hieu ve) OR (hieu van)) chat duc ban hanh doi cua tre".
• Adding a wildcard symbol may retrieve word variants: doc sach ((tu lang) or (tu tong)) xa hoi. ((hieu ve) OR (hieu van)) chat duc ban hanh doi cua tre*.