Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
dien cua » dieu cua, dien cu, tien cua
dien cuc » dien tu, dieu cua, vien cac
lam duc » lam duoc, pham duc, nam duoc
va danh » va dinh, va dan, va hanh
nang o » nang co, nang ho, nang ro
va lam » van lam, va lap
o hoi » co hoi, o hoc, o hai

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

• Performing a fuzzy search may retrieve terms with similar spellings: ((toc sach) or (thu hoach)) ky nang o hoi. lieu va lam duc va danh ((dien cua) OR (dien cuc)) te~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((toc sach) OR (thu hoach)) ky nang o hoi. lieu va lam duc va danh ((dien cua) OR (dien cuc)) te.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((toc sach) or (thu hoach)) ky nang o hoi. lieu va lam duc va danh ((dien cua) OR (dien cuc)) te".
• Adding a wildcard symbol may retrieve word variants: ((toc sach) or (thu hoach)) ky nang o hoi. lieu va lam duc va danh ((dien cua) OR (dien cuc)) te*.