In which article did Glashow introduce (1961?) a unified description of the electromagnetic and weak interactions, i.e., the electroweak interaction that earned him the Nobel prize in physics?
Glashow did not introduce it in any article, in 1961 or ever. Glashow's Partial Symmetries of Weak Interactions (Nucl. Phys. 22 (1961) 579-588) did something more modest, it proposed $SU(2)×U(1)$ model that showed the possibility of symmetry between electromagnetic and weak interactions and predicted the $Z$ boson. Since the prediction did not match any experiments it went largely unnoticed.
To get to the electroweak theory, one needed to get a mechanism of spontaneous symmetry breaking, proposed by Higgs in 1964, and to put it together with the $SU(2)×U(1)$ model, which was only done three years later, and not by Glashow. Weinberg published his version in 1967, and Salam gave his, which he called "the electroweak theory", in lectures at the Imperial College later the same year. The lectures were only published in 1968 in the Proceedings of a Nobel symposium. Here is from Kibble's History of electroweak symmetry breaking:
"This led Schwinger  to suggest a gauge theory of weak interactions mediated by $W^+$ and $W^−$ exchange. He even asked: could there be a unified theory of weak and electromagnetic interactions, involving three gauge bosons, $W^+$, $W^−$, and the photon $γ$? But this idea immediately ran into difficulty. If there is in fact a symmetry between these three gauge bosons, it clearly must be severely broken, because there are major differences between them... There was another key difference: it was known that the weak interactions do not conserve parity — they violate mirror symmetry — whereas the electromagnetic interactions are parity-conserving. So how could there be a symmetry between the two?
This latter problem was solved in 1961 by Glashow , who proposed an extended model with a larger symmetry group, $SU(2)×U(1)$, and a fourth gauge boson $Z^0$. He showed that by an intriguing mixing mechanism between the two neutral gauge bosons, one could end up with one boson ($γ$) with parity-conserving interactions and three that violate parity, $W^+$, $W^−$ and $Z^0$. In 1964, Salam and his long-term collaborator John Ward, apparently unaware of Glashow’s work, proposed a very similar model also based on $SU(2)×U(1)$ . But in all these models, the symmetry breaking, giving the $W$ and $Z$ bosons masses, had to be inserted by hand, and theories of spin-1 bosons with explicit masses were well known to be non-renormalizable and thus unphysical."