Perhaps you should try some spelling variations:
thu sach » tu sach, thuat sach, thuoc sach
hieu van » thien van, lieu va, hieu ve
hieu va » lieu va, hieu qua
cau duc » cao duc, cau luc, chu duc
va doan » va doanh, van doan, va dan
doan vi » doan va, don vi, doan thi
5 tang » 6 tang, 7 tang
v tang » 6 tang, 7 tang, 9 tang
vi cua » vai cua, di cua
cua tu » cua tuc, cua su, cua cu

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 ((v tang) OR (5 tang)) ma hoa. ((hieu van) or (hieu va)) cau duc va doan vi cua tu~.
• If you are trying to use Boolean operators, they must be ALL CAPS: thu sach ((v tang) OR (5 tang)) ma hoa. ((hieu van) OR (hieu va)) cau duc va doan vi cua tu.
• The words AND, OR and NOT may confuse the search; try adding quotes: "thu sach ((v tang) OR (5 tang)) ma hoa. ((hieu van) or (hieu va)) cau duc va doan vi cua tu".
• Adding a wildcard symbol may retrieve word variants: thu sach ((v tang) OR (5 tang)) ma hoa. ((hieu van) or (hieu va)) cau duc va doan vi cua tu*.