Perhaps you should try some spelling variations:
hieu van » hieu va, thien van, lieu va
van chat » cao chat
thuc day » thuc vat
thuc dan » thuc hanh, hoc dan, thuc vat
tu sach » thu sach, su sach, te sach
sach ky » sac ky, sach y, sach ty
nang xa » nang x, lang xa, nang ma
dau cua » day cua, cau cua, dan cua

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

• Performing a fuzzy search may retrieve terms with similar spellings: tu sach ky nang xa hoi. hieu van chat ((thuc day) OR (thuc dan)) danh ((dau cua) or (dai cua)) tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ky nang xa hoi. hieu van chat ((thuc day) OR (thuc dan)) danh ((dau cua) OR (dai cua)) tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ky nang xa hoi. hieu van chat ((thuc day) OR (thuc dan)) danh ((dau cua) or (dai cua)) tre".
• Adding a wildcard symbol may retrieve word variants: tu sach ky nang xa hoi. hieu van chat ((thuc day) OR (thuc dan)) danh ((dau cua) or (dai cua)) tre*.