Perhaps you should try some spelling variations:
toc sach » hoc sach, thuoc sach, nuoc sach
doc sach » hoc sach, nuoc sach, dac sac
thu bang » thu ban, thu hang, chu bang
van hanh » van thanh, ban hanh, van anh
hanh lai » hanh lam, hanh tai, thanh lap
bang va » hang va, ban va, trang va
hieu va » lieu va, hieu qua
cac duc » cac du, cao duc, cac dac
duc van » duc va, duc tan, duc manh
lai cua » dai cua, hai cua, lai chau
cua tre » cua te, cuu tre, cua triet
va hoi » xa hoi, va hoc, va hoa

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

• Performing a fuzzy search may retrieve terms with similar spellings: ((toc sach) or (doc sach)) thu bang va hoi. hieu va cac duc van hanh lai cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((toc sach) OR (doc sach)) thu bang va hoi. hieu va cac duc van hanh lai cua tre.
• Adding a wildcard symbol may retrieve word variants: ((toc sach) or (doc sach)) thu bang va hoi. hieu va cac duc van hanh lai cua tre*.