According to book The Unknown Stalin by Roy Medvedev and Zhores Medvedev, 2003, it was especially just after WW2. Few paragraphs:

[In 1946 Stalin announced much higher material support for science and less of ideological interference] Yet despite the rejection of the class basis of science, including the natural sciences, there was still no recognition of a 'world scientific community'. Scientific theories or trends were still divided into 'ma-tcrialistic' and 'idealistic' categories. 'Soviet science' came to mean 'science of the motherland' in order to stress a continuity between the Soviet period and pre-revolutionary Russia. 'Anti-patriotic' now became, along with 'anti-Soviet', a term of abuse; anyone accused of 'anti-patriotic' behaviour would be subject to severe criticism or punishment. Soviet scientists were strictly forbidden to publish the results of their work abroad. (pg 186-187)

and

Arriving in Moscow in 1946 Zhdanov energetically set about taking charge of the ideological sphere. He was responsible for a number of extremely conservative initiatives which later came to be known as the zhdanovshchina. Censorship was reinforced and a campaign set in motion to eliminate 'toadying before the West'; scientists were deprived of access to most foreign publications and the practice of translating certain Soviet academic journals into English was stopped. (pg 188)