Perhaps you should try some spelling variations:
doc sach » hoc sach, toc sach, nuoc sach
vinh cuu » dinh cuu, sinh cua, tinh cua
hieu van » hieu va, thien van, lieu va
tan hanh » tan thanh, tang hanh, toan hanh
ky dang » ky nang, ky danh
dang xa » dang xay, lang xa, dang ha
bac dac » bac dai, ban dac, cac dac
dinh cu » dinh cuu, dinh chuc, dinh chau
sach ky » sac ky, sach y, sach ty
bac dan » bach dan, cac dan, ban dan

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

• Performing a fuzzy search may retrieve terms with similar spellings: doc sach ky dang xa hoi. hieu van ((bac dac) or (bac dan)) tan hanh ((vinh cuu) OR (dinh cu)) tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: doc sach ky dang xa hoi. hieu van ((bac dac) OR (bac dan)) tan hanh ((vinh cuu) OR (dinh cu)) tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "doc sach ky dang xa hoi. hieu van ((bac dac) or (bac dan)) tan hanh ((vinh cuu) OR (dinh cu)) tre".
• Adding a wildcard symbol may retrieve word variants: doc sach ky dang xa hoi. hieu van ((bac dac) or (bac dan)) tan hanh ((vinh cuu) OR (dinh cu)) tre*.