Perhaps you should try some spelling variations:
quoc tuan » quoc quan, quoc toan, quoc quang
thu sach » tu sach, thuat sach, thuoc sach
hieu van » hieu va, thien van, lieu va
nam quoc » nam duoc, nam buoc, nam thuoc
nang xa » nang x, lang xa, mang xa
nang ma » tang ma, sang ma, nang cao
va cua » va chua, via cua, ma cua
ca cua » co cua

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

• Performing a fuzzy search may retrieve terms with similar spellings: thu sach y ((nang xa) or (nang ma)) hoi. hieu van nam quoc tuan anh ((va cua) OR (ca cua)) tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: thu sach y ((nang xa) OR (nang ma)) hoi. hieu van nam quoc tuan anh ((va cua) OR (ca cua)) tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "thu sach y ((nang xa) or (nang ma)) hoi. hieu van nam quoc tuan anh ((va cua) OR (ca cua)) tre".
• Adding a wildcard symbol may retrieve word variants: thu sach y ((nang xa) or (nang ma)) hoi. hieu van nam quoc tuan anh ((va cua) OR (ca cua)) tre*.