句子分析：
第一、句子可以拆分为三段：This trend began during the Second World War,when several governments came to the conclusion / that the specific demands that a government wants to make of its scientific establishment / cannot generally be foreseen in detail.]
我的理解是This trend began during the Second World War,/（定语从句WHEN=DURING WHICH .） when several governments came to the conclusion / that the specific demands /定语从句 that a government wants to make of its scientific establishment cannot generally be foreseen in detail.
第二、句子的结构：
1)主干结构是主句+ when引导的定语从句,when = DURING that time当时,那时.
2)第一个that从句是主句宾语the conclusion的同位语.对
3)that a government wants to make of its scientific establishment是定语从句修饰demands
4)cannot generally be foreseen in detail是同位语从句的谓语.
完整的译文：
这种趋势始于第二次世界大战期间,当时一些国家的政府得出结论：政府向科研机构提出的具体要求通常是无法详尽预见的.好!
【that a government wants to make of its scientific establishment是定语从句中的（主语从句）是什么意思呢,定语从句补全是不是a government wants to make of the specific demands its scientific establishment?】
同位语从句含有定语从句.分开来就是
the specific demands cannot generally be foreseen in detail.
a government wants to make specific demands of its scientific establishment
make specific demands of SB/STH对.提出要求