There are a number of assumptions in your question which make this difficult to answer, as I'm not sure who or when you are talking about.

1. Do you mean 19th century Russia, the Soviet Union, or another era? This would likely significantly change the answer to the question.
2. Do you have any particular engineers or scientists in mind?
3. By thinkers, would this incorporate artists, writers and composers, or are you thinking more in terms of political thinkers?
4. The major problem I have with the question is the phrase "despite being poor", for two reasons. Firstly, why would this preclude the production of "great" figures?
5. Secondly, when exactly was Russia poor? Sure, there are (and have always been) large numbers of poor people in Russia, and the national economy has seen numerous crises (such as hyperinflation in the 1990s, shortages in the late Soviet Union period as just a couple of examples) but Russia / the Soviet Union also has and had a wealth of natural resources, and has also always had an elite.

It would be useful to know your thoughts on these to be able to clarify an answer. However, it is worth highlighting that Russia's particular history has at times produced a political atmosphere highly conducive to artistic expression. Tchaikovsky's 1812 Overture, for example, was produced to commemorate the failed Napoleonic invasion of Russia, whilst the new political values and valorisation of the worker expounded after the 1917 Revolution combined with avant garde artistic trends to produce a wave of revolutionary art, inspiring artists such as Malevich, and later inspiring what was known as Socialist Realism.

https://www.royalacademy.org.uk/exhibition/revolution-russian-art (I'd also recommend David King's book on revolutionary art)

There were also a strong appreciation of French artistic culture among Russian elites in the nineteenth century which has influenced Russian art, music and language, inspiring Russians to take on new avant garden approaches and forms. Stravinsky' 'Rite of Spring' would be a good example.

There are also numerous examples of playwrights, artists and authors taking inspiration from the class-based social and cultural divides, present throughout the country, and by the political events of the nineteenth century as well as by Russian and Eastern European folk culture. This could include Brecht and Chekov, Dostoevsky and Mark Chagall. In these cases, the poverty you refer to is not a limit on artistic expression, but to some extent frames the narratives and contributed to artistic production.