Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
thu dong » thuy dong, thu cong, chu dong
hieu va » lieu va, hieu qua
co thuc » do thuc, co thua, mo thuc
thuc va » thuc vat, thuc dan, thuc day
va hanh » van hanh, va thanh, va danh
lai cua » hai cua, lai chau, thai cua
va co » vo co

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 ((thu dong) OR (tu dong)) xa hoi. hieu va co thuc va hanh ((lai cua) or (dai cua)) tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach ((thu dong) OR (tu dong)) xa hoi. hieu va co thuc va hanh ((lai cua) OR (dai cua)) tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach ((thu dong) OR (tu dong)) xa hoi. hieu va co thuc va hanh ((lai cua) or (dai cua)) tre".
• Adding a wildcard symbol may retrieve word variants: toc sach ((thu dong) OR (tu dong)) xa hoi. hieu va co thuc va hanh ((lai cua) or (dai cua)) tre*.