全文获取类型
收费全文 | 17997篇 |
免费 | 279篇 |
国内免费 | 54篇 |
专业分类
教育 | 13423篇 |
科学研究 | 1185篇 |
各国文化 | 201篇 |
体育 | 1255篇 |
综合类 | 45篇 |
文化理论 | 84篇 |
信息传播 | 2137篇 |
出版年
2021年 | 198篇 |
2020年 | 248篇 |
2019年 | 397篇 |
2018年 | 549篇 |
2017年 | 595篇 |
2016年 | 538篇 |
2015年 | 351篇 |
2014年 | 499篇 |
2013年 | 3695篇 |
2012年 | 479篇 |
2011年 | 487篇 |
2010年 | 444篇 |
2009年 | 431篇 |
2008年 | 452篇 |
2007年 | 417篇 |
2006年 | 431篇 |
2005年 | 390篇 |
2004年 | 283篇 |
2003年 | 269篇 |
2002年 | 244篇 |
2001年 | 386篇 |
2000年 | 302篇 |
1999年 | 262篇 |
1998年 | 167篇 |
1997年 | 176篇 |
1996年 | 179篇 |
1995年 | 159篇 |
1994年 | 167篇 |
1993年 | 152篇 |
1992年 | 222篇 |
1991年 | 223篇 |
1990年 | 249篇 |
1989年 | 224篇 |
1988年 | 182篇 |
1987年 | 187篇 |
1986年 | 197篇 |
1985年 | 181篇 |
1984年 | 197篇 |
1983年 | 178篇 |
1982年 | 149篇 |
1981年 | 148篇 |
1980年 | 144篇 |
1979年 | 199篇 |
1978年 | 165篇 |
1977年 | 123篇 |
1976年 | 129篇 |
1975年 | 119篇 |
1974年 | 111篇 |
1973年 | 111篇 |
1971年 | 119篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
This paper quantitatively measures technological change in U.S. jet fighter aircraft from 1944 to the present day using the hedonic pricing approach. The technical and performance characteristics of jet fighters have changed dramatically between the time they were first developed at the beginning of the 1940s and the present. Parallel to this technological change there has been a sharp escalation in costs regarding the new generations of jet fighter aircraft. We estimate a measure of price for the performance and technical characteristics of these aircraft. Embodied technological change in jet fighter airframes is measured using quality-adjusted prices. Although the flyaway cost of jet fighter aircraft has soared, on average, by about 12.63% per year, the quality-adjusted aircraft cost has only risen by about 2.6% per year, a figure lower than the average observed general inflation rate for the period (around 4%). This represents an impressive average technological progress ratio of around 10% per year. A revealed preferences argument shows that the characteristic most valued by the government is stealth capability, followed by advanced avionics. 相似文献
982.
Emergence of new industries from evolving technologies is critical to the global economy, yet has been relatively understudied due to the paucity of available data. This study draws lessons on industry emergence, by analyzing how a solid-state lighting (SSL) industry grew out of light emitting diode (LED) technologies that evolved for half a century, with participation by tens of thousands of researchers in universities, national laboratories, and firms. Using data on publications, patents, and firms combined with business history we trace the evolution of SSL through a succession of market niches. At times a few researchers with unorthodox research approaches made breakthroughs that greatly advanced particular technology trajectories and pushed LED research in unexpected directions. A succession of LED market niches advanced the technology and provided profits to incentivize continuing research while reducing cost and improving efficacy of LEDs. Innovating firms developed a thicket of patents and captured substantial profit, but were embroiled in extensive litigation that was ultimately resolved through cross-licensing. A major new generation of lighting products is now disrupting the traditional lighting industry. Although the leading incumbent lighting firms all invested early and heavily in SSL, the industry's future leadership is uncertain. 相似文献
983.
<正>确分析和评价专业镇竞争力,客观认识和了解专业镇发展现状及竞争优势,对专业镇的政策制定及转型发展具有重要现实意义。从专业镇竞争力的内涵及评价内容入手,从城镇竞争力、产业竞争力、企业竞争力、自主创新能力和环境竞争力五个方面构建出一套相对完整的专业镇竞争力评价指标体系以及与之相应的评价模型,为客观、全面、定量地评价和衡量专业镇竞争力提供理论支撑和实践依据。 相似文献
984.
Gunn B.B. Kristensen Kristin Moberg Aakre Ann Helen Kristoffersen Sverre Sandberg 《Biochemia medica : ?asopis Hrvatskoga dru?tva medicinskih biokemi?ara / HDMB》2014,24(1):114-122
In laboratory medicine, several studies have described the most frequent errors in the different phases of the total testing process, and a large proportion of these errors occur in the pre-analytical phase. Schemes for registration of errors and subsequent feedback to the participants have been conducted for decades concerning the analytical phase by External Quality Assessment (EQA) organizations operating in most countries. The aim of the paper is to present an overview of different types of EQA schemes for the pre-analytical phase, and give examples of some existing schemes. So far, very few EQA organizations have focused on the pre-analytical phase, and most EQA organizations do not offer pre-analytical EQA schemes (EQAS). It is more difficult to perform and standardize pre-analytical EQAS and also, accreditation bodies do not ask the laboratories for results from such schemes. However, some ongoing EQA programs for the pre-analytical phase do exist, and some examples are given in this paper. The methods used can be divided into three different types; collecting information about pre-analytical laboratory procedures, circulating real samples to collect information about interferences that might affect the measurement procedure, or register actual laboratory errors and relate these to quality indicators. These three types have different focus and different challenges regarding implementation, and a combination of the three is probably necessary to be able to detect and monitor the wide range of errors occurring in the pre-analytical phase. 相似文献
985.
[目的/意义]旨在提高我国公共图书馆文化服务效率,为公共图书馆文化服务发展提供参考。[方法/过程]以我国31个省份公共图书馆为数据,运用DEA-BCC模型和K-means聚类分析我国各区域文化服务的效率及差异。[结果/结论]我国公共图书馆文化服务效率整体较低,呈非均衡性,存在不同程度投入冗余和产出不足,最后针对我国公共图书馆文化服务提出相应的改进建议。 相似文献
986.
This discussion focuses on how the rise of America's national sporting pastimes, during the period 1880–1920, was inextricably tied to the ambitions and outpourings of American print capitalism and a concomitant congealing of a sense of modern American nationhood. In examining this thematic, we explicate the manner in which American national sporting audiences during the period 1880–1920 were variously constituted through discourses of national and ethnic sporting difference or Otherness. Hence, we examine the popular representation of turn of the century rodeo practices (as narrated through the spectacle of the western showman William Frederick ‘Buffalo Bill’ Cody's Wild West show productions), the position of early-twentieth-century American baseball in relation to other sporting cultures (graphically depicted by Albert Goodwill, or A.G., Spalding's promotional publications, specifically the 1911 America's National Game) and the national and ethnic differences discerned within the global sporting landscape more generally (explicated within the 1919 National Geographic article ‘The Geography of Games’). These performances and representations of ethnic and national sporting Otherness played an important role in re-inscribing and legitimating the (White European American) normative core of American sport culture (as manifest within and through the dominant practices of playing and/or spectating of football, baseball and basketball). 相似文献
987.
988.
989.
990.