Perhaps you should try some spelling variations:
thu sach » thuat sach, thuoc sach, thu hoach
hieu van » hieu va, thien van, lieu va
doan thi » dan thi, doanh tai, hoang thi
doan vi » doan va, don vi, doan van
cau duc » cao duc, cau luc, chu duc
van cau » van dau, van hau, van chat
tu sach » su sach, te sach, tu cach
tang ma » mang may, tang van
5 tang » 6 tang, 7 tang
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) or (tu sach)) 5 tang ma hoa. hieu van cau duc va ((doan vi) OR (doan thi)) cua tu~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((thu sach) OR (tu sach)) 5 tang ma hoa. hieu van cau duc va ((doan vi) OR (doan thi)) cua tu.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((thu sach) or (tu sach)) 5 tang ma hoa. hieu van cau duc va ((doan vi) OR (doan thi)) cua tu".
• Adding a wildcard symbol may retrieve word variants: ((thu sach) or (tu sach)) 5 tang ma hoa. hieu van cau duc va ((doan vi) OR (doan thi)) cua tu*.