Perhaps you should try some spelling variations:
"do sanh nha nghien du hoc" » "do sanh phap nghien du hoc", "do sanh phan nghien du hoc", "do sanh cham nghien du hoc", "do sanh nha nghiep du hoc", "do sanh nha nghien cuu hoc", "do sanh nha nghiem dau hoc", "do sach nha nghien du hoc", "do hanh nha nghien du hoc", "do danh nhan nghien du hoc", "do sanh nha nghien tu hoc", "do sanh nha nghien duoc hoc"
"tu sach bai nghe de hoc" » "tu sach dao nghe de hoc", "tu cac bai nghe de hoc", "tu sach xa nghe de hoc", "tu sach thai nghe de hoc", "tu sach van nghe de hoc", "tu sach nam nghe de hoc", "thu sach bai nghe de hoc", "su sach bai nghe de hoc", "te sach bai nghe de hoc", "tu sach bai nghe det hoc", "tu sach bai nghe di hoc", "tu sach bai nghe te hoc", "tu sach bai nghe dien 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: (("do sanh nha nghien du hoc") or ("tu sach bai nghe de hoc"))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("do sanh nha nghien du hoc") OR ("tu sach bai nghe de hoc")).
• Removing quotes may allow a broader search: (( do sanh nha nghien du hoc ) or ( tu sach bai nghe de hoc )).
• Adding a wildcard symbol may retrieve word variants: (("do sanh nha nghien du hoc") or ("tu sach bai nghe de hoc"))*.