Perhaps you should try some spelling variations:
sach day » sach dat, sach dau, sach hay
sach dao » lanh dao
hanh va » hanh vi
duc van » duc va, duc tan, duc manh
cac duc » cac du, cao duc, cac dac
cua tre » cua te, cuu tre, cua triet
hieu ve » hieu va, hieu van
va hoi » xa hoi, va hoc, va hoa
ve cac » va cac, vien cac

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

• Performing a fuzzy search may retrieve terms with similar spellings: su ((sach day) or (sach dao)) nano va hoi. hieu ve cac duc van ((hanh va) OR (hang va)) cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su ((sach day) OR (sach dao)) nano va hoi. hieu ve cac duc van ((hanh va) OR (hang va)) cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su ((sach day) or (sach dao)) nano va hoi. hieu ve cac duc van ((hanh va) OR (hang va)) cua tre".
• Adding a wildcard symbol may retrieve word variants: su ((sach day) or (sach dao)) nano va hoi. hieu ve cac duc van ((hanh va) OR (hang va)) cua tre*.