Perhaps you should try some spelling variations:
hieu van » hieu va, thien van, lieu va
nam thuc » nam thuoc, am thuc, nam thu
thuc dan » thuc hanh, hoc dan, thuc vat
dan danh » van danh, han danh, ban danh
tu sach » thu sach, su sach, te sach
sach ky » sac ky, sach y, sach ty
ve chu » ve cau, va chu, ve cho
ve che » va che, ke che, de che

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 ((x ho) or (xa hoi)). hieu van nam thuc dan danh ((ve chu) OR (ve che)) tren~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ky nang ((x ho) OR (xa hoi)). hieu van nam thuc dan danh ((ve chu) OR (ve che)) tren.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ky nang ((x ho) or (xa hoi)). hieu van nam thuc dan danh ((ve chu) OR (ve che)) tren".
• Adding a wildcard symbol may retrieve word variants: tu sach ky nang ((x ho) or (xa hoi)). hieu van nam thuc dan danh ((ve chu) OR (ve che)) tren*.