Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
nam thuc » nam thuoc, am thuc, nam thu
hieu va » lieu va, hieu qua
lang xa » lang ha, dang xay, lang van
va nam » van nam, ha nam, va nay
y lang » o lang, _ lang, tay lang
va dau » va dao
va cua » va chua, via cua, ma cua
ca cua » co cua
va dan » ca dan, va dao, va dap

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 xa hoi. hieu va nam thuc ((va dan) OR (va dau)) ((va cua) or (ca cua)) tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach y lang xa hoi. hieu va nam thuc ((va dan) OR (va dau)) ((va cua) OR (ca cua)) tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach y lang xa hoi. hieu va nam thuc ((va dan) OR (va dau)) ((va cua) or (ca cua)) tre".
• Adding a wildcard symbol may retrieve word variants: toc sach y lang xa hoi. hieu va nam thuc ((va dan) OR (va dau)) ((va cua) or (ca cua)) tre*.