Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
hieu van » hieu va, thien van, lieu va
hang vi » hang va, hanh vi, hang di
dua ban » dia ban, cua ban, qua ban
duc ban » duc tan, duc van, duc man
van hai » van ha, van chat, van hanh
sach ty » sach y, sach tu, sach thu
sang ma » tang ma, nang ma, sang tao
xang ma » tang ma, nang ma, rang ma
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: toc sach ty ((xang ma) or (sang ma)) hoi. hieu van hai ((duc ban) OR (dua ban)) hang vi cua tu~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach ty ((xang ma) OR (sang ma)) hoi. hieu van hai ((duc ban) OR (dua ban)) hang vi cua tu.
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach ty ((xang ma) or (sang ma)) hoi. hieu van hai ((duc ban) OR (dua ban)) hang vi cua tu".
• Adding a wildcard symbol may retrieve word variants: toc sach ty ((xang ma) or (sang ma)) hoi. hieu van hai ((duc ban) OR (dua ban)) hang vi cua tu*.