Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
vat hanh » vat thanh, van hanh, va hanh
nam thuc » nam thuoc, am thuc, nam tu
lang hoa » hang hoa, lang ha, nang hoa
hoa hoi » khoa hoi, hoa hoc, hoa doi
hieu ve » hieu va, hieu van
sach ky » sac ky, sach y, sach ty
ky lang » ky nang, ky dang, ky tang

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 ky lang hoa hoi. hieu ve ((nam thuc) or (nam thu)) vat hanh ((ve su) OR (va su)) triet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach ky lang hoa hoi. hieu ve ((nam thuc) OR (nam thu)) vat hanh ((ve su) OR (va su)) triet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach ky lang hoa hoi. hieu ve ((nam thuc) or (nam thu)) vat hanh ((ve su) OR (va su)) triet".
• Adding a wildcard symbol may retrieve word variants: toc sach ky lang hoa hoi. hieu ve ((nam thuc) or (nam thu)) vat hanh ((ve su) OR (va su)) triet*.