单选题A.花生四烯酸B.乙酰CoAC.草酰乙酸D.甘油二酯

单选题下列关于呼吸链的叙述，正确的是

单选题有关变构酶的叙述哪项是不正确的( )(1988年)

单选题类固醇激素受体复合物发挥作用需要通过

单选题有关RNA聚合酶的叙述，不恰当的是

单选题下述哪种酶与切除修复无关

单选题下列氨基酸中属于碱性氨基酸的是

单选题糖酵解途径中，催化第二次底物水平磷酸化反应的酶是

单选题原核生物乳糖操纵子受CAP调节，结合并活化CAP的分子是

单选题胞液内进行的代谢途径有( )(1993年)

单选题In 1998 consumers could purchase virtually anything over the Internet. Books, compact discs, and even stocks were available from World Wide Web Sites that seemed to spring up almost daily. A few years earlier, some people had predicted that consumers accustomed to shopping in stores would be reluctant to buy things that they could not see or touch in person. For a growing number of time-starved consumers, however, shopping from their home computer was proving to be a convenient alternative to driving to the store. A research estimated that in 1998 US consumers would purchase $ 7.3 billion of goods over the Internet, double the 1997 total. Finding a bargain was getting easier, owing to the rise of online auctions and Web sites that did comparison shopping on the Internet for the best deal. For all the consumer interest, retailing in cyberspace was still a largely unprofitable business, however. Internet pioneer Amazon. com, which began selling books in 1995 and later branched into recorded music and videos, posted revenue of $153.7 million in the third quarter, up from $37.9 minion in the same period of 1997. Overall, however, the company's loss widened to $45.2 million from $9.6 million, and analysts did not expect the company to turn a profit until 2001. Despite the great loss, Amazon. com had a stock market value of many billions, reflecting investors' optimism about the future of the industry. Internet retailing appealed to investors because it provided an efficient means for reaching millions of consumers without having the cost of operating conventional stores with their armies of salespeople. Selling online carried its own risks, however. With so many companies competing for consumers' attention, price competition was intense and profit margins thin or nonexistent. One video retailer sold the hit movie Titanic for $9.99, undercutting the $19.99 suggested retail price and losing about $6 on each copy sold. With Internet retailing still in its initial stage; companies seemed willing to absorb such losses in an attempt to establish a dominant market position.

单选题下列选项中，符合tRNA结构特点的是( )(2010年)

单选题生长因子的作用模式不正确的是

单选题脂肪酸氧化过程中不需要的化合物是

单选题A.双链DNA解链成单链DNAB.单链DNA恢复成双链DNAC.50%DNA变性时的温度D.OD280增高

单选题经脱羧基后可作为多胺生成原料的氨基酸是

单选题能直接识别、结合TATA盒的基本转录因子是

单选题不能进入三羧酸循环被氧化的物质是

单选题下述哪种化合物中不含高能磷酸键

单选题维系蛋白质三级结构稳定的最重要的键或作用力是