While previous and recent etiological analyses remain non-conclusive, environmental factors were shown to be associated with BN.

虽然前期和最近的病原分析不具决定性，但是环境因素却显示出同树皮坏死有联系。

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D. C. and A. C. characteristics of non-ideal operational amplifiers are examined from a general viewpoint, and a set of useful expressions and conclusive results are obtained.

本文从普遍性的意义上讨论了非理想运算放大器的交、直流性能，给出了一系列有用的公式和结论。

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