Khademloo, Somayeh, and Shapur Heidarkhani. “Existence of Non-Negative Solutions for Semilinear Elliptic Systems via Variational Methods”. Nonlinear Analysis: Modelling and Control 17, no. 2 (April 25, 2012): 194–209. Accessed October 28, 2025. https://test.zurnalai.vu.lt/nonlinear-analysis/article/view/14068.