Perhaps you should try some spelling variations:
doc sach » hoc sach, toc sach, nuoc sach
hanh di » hanh vi, hanh de, hang di
truc va » thuc va, trung va
hieu ve » hieu va, hieu van
ve cac » va cac, vien cac
va cao » va cac, va co, va dao
va cap » va cac, va dap, va cai
di cua » dai cua, doi cua, de cua

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: doc sach y ((va cap) OR (va cao)) phoi. hieu ve cac ((truc va) OR (thuc vat)) hanh di cua vat~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "doc sach y ((va cap) OR (va cao)) phoi. hieu ve cac ((truc va) or (thuc vat)) hanh di cua vat~".
• Adding a wildcard symbol may retrieve word variants: doc sach y ((va cap) OR (va cao)) phoi. hieu ve cac ((truc va) or (thuc vat)) hanh di cua vat*.