Haochuan Li Jingyuan Li Yi Zhao Heng Zhang Yukai Yang Zile Hu Chengzhi Zhang Measuring Research Difficulty of Academic Papers: A Case Study in Natural Language Processing. 2026 June abs/2606.25307 CoRR https://doi.org/10.48550/arXiv.2606.25307 db/journals/corr/corr2606.html#abs-2606-25307 streams/journals/corr