Perhaps you should try some spelling variations:
doc sach » hoc sach, toc sach, nuoc sach
hieu van » hieu va, thien van, lieu va
nang cho » nang chon, ngang cho, nang cao
nuoc van » nuoc va, nuoc san, luoc van
cac nuoc » cap nuoc, hoc nuoc, dat nuoc
hang di » hang doi, hang vi, hang dien
hanh di » hanh vi, hanh de, danh di
sach ty » sach y, sach tu, sach thu
hieu ve » hieu va
cho hoc » co hoc, khoa hoc
ty nang » ky nang, ty xang, ty hang
cua chu » sua chua

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 ty nang cho hoc. ((hieu ve) or (hieu van)) cac nuoc van ((hanh di) OR (hang di)) cua chu~.
• If you are trying to use Boolean operators, they must be ALL CAPS: doc sach ty nang cho hoc. ((hieu ve) OR (hieu van)) cac nuoc van ((hanh di) OR (hang di)) cua chu*.
• The words AND, OR and NOT may confuse the search; try adding quotes: "doc sach ty nang cho hoc. ((hieu ve) or (hieu van)) cac nuoc van ((hanh di) OR (hang di)) cua chu*".