单选题在我国引起门静脉高压症的最主要原因是

单选题FOR the past two years in Silicon Valley, the centre of America's technology industry, conference-goers have entertained themselves playing a guessing game: how many times will a speaker mention the phrase "long tail"? It is usually a high number, thanks to the influence of the long tail theory, which was first developed by Chris Anderson, the editor of Wired magazine, in an article in 2004. Though technologists and bloggers chuckle at how every business presentation now has to have its long-tail section, most are envious of Mr Anderson, whose brainwave quickly became the most fashionable business idea around. Whether a blockbuster film, a bestselling novel, or a chart-topping rap song, popular culture idolizes the hit. Companies devote themselves to creating them because the cost of distribution and the limits of shelf space in physical shops mean that profitability depends on a high volume of sales. But around the beginning of this century a group of internet companies realized that with endless shelves and a national or even international audience online they could offer a huge range of products—and make money at the same time. The niche, the obscure and the specialist, Mr Anderson argues, will gain ground at the expense of the hit. As evidence, he points to a drop in the number of companies that traditionally calculate their revenue/sales ratio according to the 80/20 rule—where the top fifth of products contribute four-fifths of revenues. Ecast, a San Francisco digital jukebox company, found that 98% of its 10,000 albums sold at least one track every three months. Expressed in the language of statistics, the experiences of Ecast and other companies such as Amazon, an online bookseller, suggest that products down in the long tail of a statistical distribution, added together, can be highly profitable. The internet helps people find their way to relatively obscure material with recommendations and reviews by other people and (for those willing to have their artistic tastes predicted by a piece of software) computer programs which analyze past selections. Long-tail enthusiasts argue that the whole of culture will benefit, not just commercial enterprises. Television, film and music are such bewitching media in their own right that many people are quite happy to watch and listen to what the mainstream provides. But if individuals have the opportunity to pick better, more ideally suited entertainment from a far wider selection, they will take it, according to the theory of the long tail. Some analysts reckon that entire populations might become happier and wiser once they have access to thousands of documentaries, independent films and sub-genres of every kind of music, instead of being subjected to what Mr Anderson calls the tyranny of lowest-common-denominator fare. That might be taking things a bit far. But the long tail is certainly one of the internet's better gifts to humanity.

单选题女，36岁，无明显诱因夜间排黑便3次，伴口渴、一时性眩晕来院，既往无溃疡病、肝炎病史。查体：HR100次/分，BP90/60mmHg，烦躁，皮肤苍白。辅助检查不宜选择

单选题女，45岁，幽门梗阻行持续胃肠减压半个月余，每日补10％葡萄糖2500mL，5％葡萄糖盐水1000mL，10％氯化钾30mL。2天前开始出现全腹膨胀，无压痛及反跳痛，肠鸣音消失，每日尿量1500mL左右，最可能的原因是

单选题健康成人若失血量达多少时应输入浓缩红细胞

单选题下列哪项不是狭颅症的临床表现：

单选题A．吗啡B．度冷丁C．二者均有D．二者均无

单选题关于泌尿系结石排石治疗适应证，错误的是

单选题A．积极寻找易感因素B．用药后症状消失即停药C．用药72小时无效应换药，疗程2周D．用糖皮质激素

单选题创伤性窒息的临床表现最明显的部位是

单选题胫骨中下1/3骨折最常见的并发症是

单选题 妊娠期间不排卵主要是与下列哪种激素的作用有关？ A、雌激素 B、孕激素 C、催乳素 D、催产素 E、雌激素和孕激素

单选题下列关于手部感染的叙述，错误的是

单选题用物理的方法杀灭一切致病微生物称为

单选题A．肥胖B．马尾松毛虫接触史C．硒元素缺乏D．甲型链球菌感染

单选题不符合弥漫性膜性增生性肾小球肾炎的描述是

单选题男，35岁，右腹股沟肿块10年，站立时明显，平卧时消失，有时可降至阴囊。体检：右腹股沟肿块，拳头大小可回纳入腹腔，外环容3指，压迫内环后肿块不突出。

单选题下述应激性溃疡哪个与烧伤有关

单选题关于张力性气胸的叙述，下列哪项正确

单选题有关股骨颈骨折，下列哪项是不恰当的