Perhaps you should try some spelling variations:
hieu van » hieu va, thien van, hieu ve
dau thai » dau thau, da thai, dau hai
dao thai » dao thi, do thai, da thai
cau tren » cu tren, dau tren, ca tren
tu sach » thu sach, su sach, te sach
sach ky » sac ky, sach y, sach ty
nang xa » nang x, lang xa, nang ma
dat doc » dat duoc, day doc, dat nuoc
doc va » duoc va, hoc va, duc va

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) or (lieu va)) dat doc va ((dau thai) OR (dao thai)) cau tren~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ky nang xa hoi. ((hieu van) OR (lieu va)) dat doc va ((dau thai) OR (dao thai)) cau tren.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ky nang xa hoi. ((hieu van) or (lieu va)) dat doc va ((dau thai) OR (dao thai)) cau tren".
• Adding a wildcard symbol may retrieve word variants: tu sach ky nang xa hoi. ((hieu van) or (lieu va)) dat doc va ((dau thai) OR (dao thai)) cau tren*.