Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
va hanh » van hanh, va thanh, va danh
thuc va » thuc vat, thuc dan, thuc day
co thuc » do thuc, co thua, mo thuc
hieu va » lieu va, hieu qua
tu nang » tru nang, tu nong, tu nano
va cuu » va cau, va chu
va huu » vu huu
x hoi » xa hoi, o hoi, x ho
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: ((te sach) or (toc sach)) tu nang x hoi. hieu va co thuc va hanh ((va cuu) OR (va huu)) tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((te sach) OR (toc sach)) tu nang x hoi. hieu va co thuc va hanh ((va cuu) OR (va huu)) tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((te sach) or (toc sach)) tu nang x hoi. hieu va co thuc va hanh ((va cuu) OR (va huu)) tre".
• Adding a wildcard symbol may retrieve word variants: ((te sach) or (toc sach)) tu nang x hoi. hieu va co thuc va hanh ((va cuu) OR (va huu)) tre*.