Perhaps you should try some spelling variations:
nam thuc » nam thuoc, am thuc, nam thu
so sach » so sanh, bo sach, co sach
va danh » va dinh, va dan, dia danh
hieu ve » hieu va, hieu van
va hanh » van hanh, va thanh, ban hanh
ve nam » he nam, va nam, le nam
y tang » ky tang, 6 tang, 7 tang
ma hoi » mai hoi, ma hoa, me hoi
vi cua » vai cua, di cua

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

• Performing a fuzzy search may retrieve terms with similar spellings: so sach y tang ((ma hoi) or (xa hoi)). hieu ve nam thuc ((va hanh) OR (va danh)) vi cua vat~.
• If you are trying to use Boolean operators, they must be ALL CAPS: so sach y tang ((ma hoi) OR (xa hoi)). hieu ve nam thuc ((va hanh) OR (va danh)) vi cua vat.
• The words AND, OR and NOT may confuse the search; try adding quotes: "so sach y tang ((ma hoi) or (xa hoi)). hieu ve nam thuc ((va hanh) OR (va danh)) vi cua vat".
• Adding a wildcard symbol may retrieve word variants: so sach y tang ((ma hoi) or (xa hoi)). hieu ve nam thuc ((va hanh) OR (va danh)) vi cua vat*.