Perhaps you should try some spelling variations:
hoc ngoc » hoc nuoc, ho ngoc, loc ngoc
dieu tra » kiem tra, dieu cua
tu sach » thu sach, su sach, te sach
sach ky » sac ky, sach y, sach ty
nang xa » nang x, lang xa, nang ma
va hoc » van hoc
va dap » va dao, va dau
ca dan » cac dan, ca dao

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

• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ky nang xa hoi. lieu va hoc ngoc ((va dap) OR (ca dan)) ((dieu tra) OR (dieu tri)) tre~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ky nang xa hoi. lieu va hoc ngoc ((va dap) or (ca dan)) ((dieu tra) OR (dieu tri)) tre~".
• Adding a wildcard symbol may retrieve word variants: tu sach ky nang xa hoi. lieu va hoc ngoc ((va dap) or (ca dan)) ((dieu tra) OR (dieu tri)) tre*.