Perhaps you should try some spelling variations:
sach thu » sach thue, sach thieu, sach tham
cac duc » cac du, cao duc, cac dac
sach ty » sach y, sach tu, xach tay
hieu va » hieu qua
nang ma » tang ma, sang ma, nang cao
duc ca » duc cac, duc va, duc ha
ca dan » cac dan, ca dao
dan vi » doan vi, don vi, dan va
vi cua » vai cua, di cua
cua te » cua tu

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

• If you are trying to use Boolean operators, they must be ALL CAPS: thuat ((sach ty) OR (sach thu)) nang ma hoa. ((hieu va) OR (lieu va)) cac duc ca dan vi cua te~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "thuat ((sach ty) or (sach thu)) nang ma hoa. ((hieu va) OR (lieu va)) cac duc ca dan vi cua te~".
• Adding a wildcard symbol may retrieve word variants: thuat ((sach ty) or (sach thu)) nang ma hoa. ((hieu va) OR (lieu va)) cac duc ca dan vi cua te*.