Perhaps you should try some spelling variations:
"thu sach va nghien _au hoc" » "thu sach va nghien cuu hoc", "thu sach va nghiep cau hoc", "thu sach va nghiem dau hoc", "tu sach va nghien _au hoc", "thuat sach va nghien _au hoc", "thuoc sach va nghien _au hoc", "thu sach xa nghien _au hoc", "thu sach ha nghien _au hoc", "thu sach dao nghien _au hoc", "thu sach va nghien cau hoc", "thu sach va nghien phau hoc"
"tu lanh van nghe d hoc" » "tu lang van nghe d hoc", "tu anh van nghe d hoc", "tu lanh va nghe d hoc", "tu hanh van nghe d hoc", "tu lenh van nghe d hoc", "tu manh van nghe d hoc", "tu lanh van nghe di hoc", "tu lanh van nghe _ hoc", "tu lanh van nghe 新 hoc", "tu lanh van nghe du hoc", "tu lanh van nghe ad hoc", "tu lanh van nghe de hoc"

Try widening your search to All Fields.

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 va nghien _au hoc") or ("tu lanh van nghe d hoc"))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("thu sach va nghien _au hoc") OR ("tu lanh van nghe d hoc")).
• Removing quotes may allow a broader search: (( thu sach va nghien _au hoc ) or ( tu lanh van nghe d hoc )).
• Adding a wildcard symbol may retrieve word variants: (("thu sach va nghien _au hoc") or ("tu lanh van nghe d hoc"))*.