Perhaps you should try some spelling variations:
toc sach » doc sach, thuoc sach, nuoc sach
tay lang » tai lang, tay tang, tay quang
dau tren » dau tien, dat tren, dau tieng
hoc sach » hoc sinh, hoc cac, hoc anh
lang ma » lang mai, lang man, lang ha
hieu va » lieu va, hieu qua
cac tuc » cac toc, cac tu, cac tac
xa hanh » xa thanh, xa khanh, da hanh
va hanh » van hanh, va thanh, va danh
ma hoi » mai hoi, xa hoi, ma hoa
vi dau » vi dai, va dau, bi dau

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) OR (hoc sach)) tay lang ma hoi. hieu va cac tuc ((xa hanh) or (va hanh)) vi dau tren~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((toc sach) OR (hoc sach)) tay lang ma hoi. hieu va cac tuc ((xa hanh) OR (va hanh)) vi dau tren.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((toc sach) OR (hoc sach)) tay lang ma hoi. hieu va cac tuc ((xa hanh) or (va hanh)) vi dau tren".
• Adding a wildcard symbol may retrieve word variants: ((toc sach) OR (hoc sach)) tay lang ma hoi. hieu va cac tuc ((xa hanh) or (va hanh)) vi dau tren*.