Perhaps you should try some spelling variations:
tham thuc » nham thuc, tam thuc, thai thuc
pham thuc » phap thuc, pham chuc, nham thuc
toc sach » hoc sach, doc sach, thuoc sach
van hanh » van thanh, ban hanh, van anh
hieu vi » hieu voi, hieu va, hieu ve
cua tre » cua te, cuu tre, cua triet
y lang » _ lang, tay lang, yen lang
o lang » hoa lang, hoi lang
vi cua » vai cua, di cua

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 ((y lang) or (o lang)) van hoa. hieu vi ((tham thuc) OR (pham thuc)) van hanh vi cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach ((y lang) OR (o lang)) van hoa. hieu vi ((tham thuc) OR (pham thuc)) van hanh vi cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach ((y lang) or (o lang)) van hoa. hieu vi ((tham thuc) OR (pham thuc)) van hanh vi cua tre".
• Adding a wildcard symbol may retrieve word variants: toc sach ((y lang) or (o lang)) van hoa. hieu vi ((tham thuc) OR (pham thuc)) van hanh vi cua tre*.