The overall result has been to make entrance to professional geological journals harder for amateurs, a result that has been reinforced by the widespread introduction of refereeing, first by national journals in the 19th century and then by several local geological journals in the 20th century.
想请问一下这一句是干什么成分？如何翻译呢？first by national journals in the 19th century and then by several local geological journals in the 20th century.
The overall result has been to make entrance to professional geological journals harder for amateurs, a result that has been reinforced by the widespread introduction of refereeing, first by national journals in the 19th century and then by several local geological journals in the 20th century.
【翻译】总体结果是，业余喜好者欲在专业地质学期刊上发表论文就比较困难，而被广泛使用的论文评审规范又进一步强化了这一结果，这种规范第一由19世纪的国家级刊物使用，然后又在20世纪被几家地方级地质学刊物使用。
从结构看，first by national journals in the 19th century and then by several local geological journals in the 20th century，是 introduction of refereeing（论文评审规范的使用）的定语。因为定语太长，加之有 fist 和 then 排列，之前加了逗号停顿。
结构为：the introduction of sth. by sb. 某人对某物的引入使用。
