Perhaps you should try some spelling variations:
doc sach » hoc sach, toc sach, nuoc sach
nay thuc » nam thuc, cay thuc, day thuc
ky dang » ky nang, ky danh
dang xa » dang xay, lang xa, dang ha
hieu va » lieu va, hieu qua
thuc va » thuc vat, thuc dan, thuc day
hai cuu » hai cua, hai cuc, thai cua
hai chu » hai chau, hoi chu, hai chi
va nay » va ngay, va cay
va dau » va dao

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

• Performing a fuzzy search may retrieve terms with similar spellings: ((doc sach) or (hoc sinh)) ky dang xa hoi. hieu va nay thuc va dau ((hai cuu) OR (hai chu)) tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((doc sach) OR (hoc sinh)) ky dang xa hoi. hieu va nay thuc va dau ((hai cuu) OR (hai chu)) tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((doc sach) or (hoc sinh)) ky dang xa hoi. hieu va nay thuc va dau ((hai cuu) OR (hai chu)) tre".
• Adding a wildcard symbol may retrieve word variants: ((doc sach) or (hoc sinh)) ky dang xa hoi. hieu va nay thuc va dau ((hai cuu) OR (hai chu)) tre*.