Perhaps you should try some spelling variations:
so thiet » soc thiet, hoc thiet, hoa thiet
hanh dai » hanh tai, hanh dao, vanh dai
toc sach » hoc sach, doc sach, thuoc sach
hieu van » hieu va, thien van, lieu va
va hanh » van hanh, va thanh, va danh
thuc va » thuc vat, thuc dan, thuc day
so hoc » co hoc, mo hoc, so hoa
van am » van nam, van lam, van dam
o hoc » co hoc, mo hoc, y hoc

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)) ky nang ((o hoc) or (so hoc)). hieu van am thuc va hanh dai so thiet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((te sach) OR (toc sach)) ky nang ((o hoc) OR (so hoc)). hieu van am thuc va hanh dai so thiet.
• Adding a wildcard symbol may retrieve word variants: ((te sach) or (toc sach)) ky nang ((o hoc) or (so hoc)). hieu van am thuc va hanh dai so thiet*.