a milestone
(epoch-making)

Я хотела было проголосовать за "key issue", но речь идет о _научной_ проблеме, а научная проблема — это, скорее, scientific problem, а не scientific issue, то решила дать свой вариант ответа.


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Note added at 4 hrs (2023-01-26 11:45:11 GMT)
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*поэтому* решила

as an option

https://en.wiktionary.org/wiki/знаковый

Terra do Meio, a region in the state of Pará, the most conflict-ridden in the Brazilian Amazon, presents an emblematic challenge for integrated public administration in the country, since it typifies characteristic frontier geopolitics: illegal occupation of public lands, irrational resource usage, absence of government, and inconsistent public policies for the region.
https://minashill.com.au/cocoa/

It could be viewed as an emblematic problem consisting of two central tensions: the classic tension between economic growth and environmental protection as well as the escalating tension between the urgency of post-carbon transition and the pertinacity of fossil fuel consumption (Dodge & Metze, 2017).
https://summit.sfu.ca/_flysystem/fedora/sfu_migrate/20295/et...

At first glance, these questions seem to draw scholarly attention in multiple directions. Yet in the case of energy-society relationship, these directions eventually converge into an emblematic challenge concerning the future of humanity: the escalating tension between a ‘business-as-usual’ model, characterised by continuing fossil fuel dependency, and a radical transition towards a carbon-free, sustainable energy system.
https://summit.sfu.ca/_flysystem/fedora/sfu_migrate/20295/et...

In his first parliamentary speech after the election, he promised to make equality between the sexes an “emblematic task".
https://www.theguardian.com/world/2004/apr/16/gayrights.gend...

A second issue affecting all major U.S. relationships is humanitarian intervention, in some ways the emblematic problem of the first post-Cold War decade.
https://monthlyreview.org/wp-content/uploads/2003/05/Imperia...

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Note added at 3 hrs (2023-01-26 11:29:24 GMT)
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The predominant slogan seems to be “Black Lives Matter” – underscoring the long standing emblematic issue of racism and police brutality mainly impacting...
https://newsroom.iium.edu.my/index.php/2021/03/10/time-to-co...

...this long-standing emblematic problem opens new avenues in autonomous dissipative dynamics, whose considerations, in turn, impact the study of...
https://digital.csic.es/bitstream/10261/272042/1/bouncing_ob...





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Note added at 12 hrs (2023-01-26 19:42:19 GMT)
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Если какие-либо события, явления и т. д. вы называете знаковыми, вы имеете в виду, что они отражают нечто типичное, характерное для определённого периода времени.
https://dic.academic.ru/dic.nsf/dmitriev/1548/знаковый

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Note added at 10 days (2023-02-06 06:28:00 GMT)
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An iconic problem in quantum mechanics is the particle in a box. In this problem, an electron is put into an electric potential box of unit width...
https://www.chegg.com/homework-help/questions-and-answers/pr...

Knowing when a wound can safely be closed is an iconic problem for
surgery.
https://www.thelancet.com/article/S2352-3964(15)30099-2/pdf

he satisfiability problem is another iconic problem that frequently arises in the study of computational complexity theory.
https://books.google.by/books?id=4lryDwAAQBAJ&pg=PA201&lpg=P...