Perhaps you should try some spelling variations:
"dung thoi luan van. tac trung hoc mot" » "dung thi luan van. tac trung hoc mot", "dung toi luan van. tac trung hoc mot", "dung thuoc luan van. tac trung hoc mot", "dung hoi luan van. tac trung hoc mot", "dung thai luan van. tac trung hoc mot", "dung thoi luan van. trac trung hoc mot", "dung thoi luan van. tai trung hoc mot", "dung thoi luan van. tac trong hoc mot", "dung thoi luan van. tac trung quoc mot", "dung thoi luan van. tac trung hoc moi"
"dung thoi quen vang. tac dung khoa mon" » "dung thi quen vang. tac dung khoa mon", "dung toi quen vang. tac dung khoa mon", "dung thuoc quen vang. tac dung khoa mon", "dung thoi quan van. tac dung khoa mon", "dung thoi que van. tac dung khoa mon", "dung thoi que lang. tac dung khoa mon", "dung thoi quen vang. tac dung cho mon", "dung thoi quen vang. sach dung khoa mon", "dung thoi quen vang. xay dung khoa mon", "dung thoi quen vang. tin dung khoa mon", "dung thoi quen vang. tac dung khoa mong", "dung thoi quen vang. tac dung khoa cong", "dung thoi quen vang. tac dung khoa minh"

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• Performing a fuzzy search may retrieve terms with similar spellings: (("dung thoi luan van. tac trung hoc mot") or ("dung thoi quen vang. tac dung khoa mon"))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("dung thoi luan van. tac trung hoc mot") OR ("dung thoi quen vang. tac dung khoa mon")).
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• Adding a wildcard symbol may retrieve word variants: (("dung thoi luan van. tac trung hoc mot") or ("dung thoi quen vang. tac dung khoa mon"))*.