单选题下列物质中能够在底物水平上生成GTP的是

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单选题胺类药物的类似物是（）。

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单选题下列哪种糖代谢途径既不生成ATP或UTP也不消耗ATP或UTP

单选题For years Internet merchants have poured millions of dollars into new technologies to make their sites easier to use. So why aren't online customers happier? Customer satisfaction levels have remained almost fiat through the last several years. The problem, according to Larry Freed, chief executive of a consulting and research firm called ForeSee Results, is not so much that consumers have ignored the many improvements made in recent years. Rather, be said, they still expect more from Internet shopping than it has delivered. "If we walk into a local store, we don't expect that experience to be better than it was a couple years ago," Mr. Freed said. "But we expect sites to be better. The bar goes up every year." In ForeSee's latest survey, released last month, just five e-commerce sites registered scores higher than 80 out of 100, and no site scored higher than 85. It was much the same story a year ago, when just five scored higher than 80, with no site surpassing 85. "Scores have inched up over time for the best e-commerce companies, but the overall numbers haven't moved drastically," Mr. Freed said. "At the same time though, if you don't do anything you see your scores drop steadily." That dynamic has been a challenge for online merchants and investors, who a decade ago envisioned. Internet stores as relatively inexpensive (and therefore extremely profitable) operations. Now some observers predict a future where online retailers will essentially adopt something like the QVC model, with sales staff pitching the site's merchandise with polished video presentations, produced in a high-tech television studio. QVC.com is evolving in that direction. The Web site, which sold more than $1 billion in merchandise in 2006, has for the last five years let visitors watch a live feed of the network's broadcast. But in recent months, QVC.com has also given visitors the chance to watch archives of entire shows, and in the coming months visitors will be able to find more video segments from recent shows, featuring individual products that remain in stock. Bob Myers, senior vice president of QVC.com, said the Web site's video salesmanship is especially effective when combined with detailed product information, customer reviews and multiple photographs. About eight months ago, for instance, a customer said that she could not determine the size of a handbag from the photographs on the site because she could not tell the height of the model who was holding it. Within two weeks the site tested and introduced a new system, showing the bags with women of three different heights. The results were immediate: women who saw the new photographs bought the bags at least 10 percent more frequently than those who had not. Still, Mr. Myers said, video is a critically important element to sales. "E-commerce started with television commerce," he said. "The sites who engage and entertain customers will be winning here in the near future." Such a prospect is not necessarily daunting to other e-commerce executives. Gordon Magee, head of Internet marketing for Drs. Foster & Smith, based in a Rhinelander, Wis., said a transition to video "will be seamless for us." The company, Mr. Magee said, has in recent weeks discussed putting some of its product on video "so customers could see a 360-degree view they don't have to manipulate themselves./

单选题下列哪个反应伴有底物水平磷酸化

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单选题下列哪种碱基不存在于RNA中

单选题孕妇的氮平衡为

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单选题对于关键酶(限速酶)的叙述哪一项是不正确的

单选题A．脱氢、硫解、加水、再脱氢 B．缩合、加氢、脱水、再加氢C．脱氢、加水、再脱氢、硫解 D．加氢、缩合、脱水、再加氢

单选题既能抑制腺苷酸环化酶，又能激活磷酸二酯酶的激素是

单选题NADH氧化呼吸链的排列顺序为