Perhaps you should try some spelling variations:
toc sach » hoc sach, thuoc sach, nuoc sach
doc sach » hoc sach, nuoc sach, dac sac
hieu van » hieu va, thien van, lieu va
dinh via » dinh gia, dinh vi, dinh va
tang ma » mang may, tang van
ma khoi » mai khoi, ra khoi, xa khoi
van cam » van nam, van lam, van cau
via cua » gia cua, gian cua, giau cua
cua tre » cua te, cuu tre, cua triet
y tang » ky tang, 6 tang, 7 tang
xuc va » tuc va, luc va, xac va

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) or (doc sach)) y tang ma khoi. hieu van cam ((xuc va) or (duc va)) dinh via cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((toc sach) OR (doc sach)) y tang ma khoi. hieu van cam ((xuc va) OR (duc va)) dinh via cua tre.
• Adding a wildcard symbol may retrieve word variants: ((toc sach) or (doc sach)) y tang ma khoi. hieu van cam ((xuc va) or (duc va)) dinh via cua tre*.