Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
cam thuc » am thuc, nam thuc, cam thu
lang xa » lang ha, dang xay, lang van
hieu ve » hieu va, hieu van
dan ban » can ban, dan ba, dan bac
ve cam » ve cham, ve cac, va cam
di cua » doi cua, de cua, do cua

You may be able to get more results by adjusting your search query.

• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach _ lang xa hoi. hieu ve cam thuc ((dan ban) OR (van ban)) ((di cua) OR (dai cua)) te~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach _ lang xa hoi. hieu ve cam thuc ((dan ban) OR (van ban)) ((di cua) or (dai cua)) te~".
• Adding a wildcard symbol may retrieve word variants: toc sach _ lang xa hoi. hieu ve cam thuc ((dan ban) OR (van ban)) ((di cua) or (dai cua)) te*.