Perhaps you should try some spelling variations:
tham thuc » nham thuc, pham thuc, tam thuc
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, vu sach
hieu ve » hieu va
van hoc » van hoa
voi hoa » voi hoat, voi khoa, boi hoa
y tang » ky tang, 6 tang, 7 tang
vi hoa » vi hoc, va hoa, bi hoa

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 y tang van hoc. ((hieu ve) OR (hieu van)) tham thuc va hanh ((vi hoa) OR (voi hoa)) viet~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su sach y tang van hoc. ((hieu ve) or (hieu van)) tham thuc va hanh ((vi hoa) OR (voi hoa)) viet~".
• Adding a wildcard symbol may retrieve word variants: su sach y tang van hoc. ((hieu ve) or (hieu van)) tham thuc va hanh ((vi hoa) OR (voi hoa)) viet*.