/**
 * Unpaywall API client
 *
 * @module research/clients/unpaywall
 */
import { BaseClient } from './base.js';
import { ClientConfig, ResearchPaper } from '../types.js';
/**
 * Unpaywall API client
 */
export declare class UnpaywallClient extends BaseClient {
    private email;
    constructor(config?: Partial<ClientConfig> & {
        email?: string;
    });
    /**
     * Get paper by DOI
     */
    getPaperByDoi(doi: string): Promise<ResearchPaper>;
    /**
     * Check if open access PDF is available for DOI
     */
    checkOpenAccess(doi: string): Promise<string | null>;
    /**
     * Transform Unpaywall response to ResearchPaper
     */
    private transformResponse;
}
//# sourceMappingURL=unpaywall.d.ts.map