Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
cam quoc » cac quoc, cao quoc, nam quoc
hieu va » lieu va, hieu qua
y lang » _ lang, tay lang, yen lang
o lang » hoa lang, hoi lang
va cam » va cham, va cac, va cao
te cua » tue cua, le cua, de cua
cua tu » cua tuc, cua su, cua cu

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)) xa hoi. hieu va cam quoc ((buou benh) or (so benh)) te cua tu~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach ((y lang) OR (o lang)) xa hoi. hieu va cam quoc ((buou benh) OR (so benh)) te cua tu.
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach ((y lang) OR (o lang)) xa hoi. hieu va cam quoc ((buou benh) or (so benh)) te cua tu".
• Adding a wildcard symbol may retrieve word variants: toc sach ((y lang) OR (o lang)) xa hoi. hieu va cam quoc ((buou benh) or (so benh)) te cua tu*.