Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
hieu van » hieu va, thien van, lieu va
va trien » va truyen, va thiet, va tuyen
xay hoi » xa hoi, cay phoi, gay thoi
tay hoi » tay ho, tao hoi, tay thai
sach ty » sach y, sach tu, sach thu
ty dang » ty xang, ky dang, ty hang
tinh te » kinh te, tinh tu, tinh he
luc va » tuc va, loc va
te va » tu 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 ty dang ((xay hoi) OR (tay hoi)). hieu van nam ((luc va) or (duc va)) tinh te va trien~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach ty dang ((xay hoi) OR (tay hoi)). hieu van nam ((luc va) OR (duc va)) tinh te va trien.
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach ty dang ((xay hoi) OR (tay hoi)). hieu van nam ((luc va) or (duc va)) tinh te va trien".
• Adding a wildcard symbol may retrieve word variants: toc sach ty dang ((xay hoi) OR (tay hoi)). hieu van nam ((luc va) or (duc va)) tinh te va trien*.