The “Knocking on Wood” Wikipedia page mentions Roud’s conclusion, and this claim of a 19th century origin has circulated online as the final say on the matter. If you go back to the original, though, Roud’s proposal actually ends on an ambivalent note: “Before this theory [of 19th century origins] can be finally accepted, however, an examination of the history of European forms of this custom would be advisable.”
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，这一点在WPS官方版本下载中也有详细论述
The result from Step 2 is a high-level route – a sequence of shortcuts connecting border points.
其中，2703 家企业扩大了研发人员规模，2328 家在收缩，另有278 家因首次披露而未被纳入比较。在研发人员整体增长的背景下，扩张与收缩的比例为1.16:1，低于上年的1.64:1。这表明，本年度扩张研发人员的平均增量，大于收缩企业的平均减量，企业之间研发投入存在分化现象。