Perhaps you should try some spelling variations:
tham thuc » nham thuc, pham thuc, tam thuc
hoc viet » hoc hien
hieu van » hieu va, thien van, lieu va
tang van » dang van, hoang van, trong van
va hanh » van hanh, va thanh, va danh
thuc va » thuc vat, thuc dan, thuc day
su sach » so sach
hieu ve » hieu va
van hoc » van hoa
vu sach » vu bach, vu khach
y tang » ky tang, 6 tang, 7 tang
vi hoc » li hoc, va hoc

You may be able to get more results by adjusting your search query.

• If you are trying to use Boolean operators, they must be ALL CAPS: ((su sach) OR (vu sach)) y tang van hoc. ((hieu ve) OR (hieu van)) tham thuc va hanh vi hoc viet~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((su sach) OR (vu sach)) y tang van hoc. ((hieu ve) or (hieu van)) tham thuc va hanh vi hoc viet~".
• Adding a wildcard symbol may retrieve word variants: ((su sach) OR (vu sach)) y tang van hoc. ((hieu ve) or (hieu van)) tham thuc va hanh vi hoc viet*.