全文获取类型
| 收费全文 | 13559篇 |
| 免费 | 37篇 |
| 国内免费 | 1篇 |
专业分类
| 教育 | 10391篇 |
| 科学研究 | 1331篇 |
| 各国文化 | 20篇 |
| 体育 | 611篇 |
| 文化理论 | 430篇 |
| 信息传播 | 814篇 |
出版年
| 2023年 | 21篇 |
| 2022年 | 42篇 |
| 2021年 | 61篇 |
| 2020年 | 98篇 |
| 2019年 | 186篇 |
| 2018年 | 2339篇 |
| 2017年 | 2234篇 |
| 2016年 | 1697篇 |
| 2015年 | 212篇 |
| 2014年 | 198篇 |
| 2013年 | 563篇 |
| 2012年 | 289篇 |
| 2011年 | 746篇 |
| 2010年 | 877篇 |
| 2009年 | 465篇 |
| 2008年 | 660篇 |
| 2007年 | 1164篇 |
| 2006年 | 97篇 |
| 2005年 | 412篇 |
| 2004年 | 461篇 |
| 2003年 | 376篇 |
| 2002年 | 145篇 |
| 2001年 | 18篇 |
| 2000年 | 32篇 |
| 1999年 | 14篇 |
| 1998年 | 9篇 |
| 1997年 | 23篇 |
| 1996年 | 12篇 |
| 1995年 | 11篇 |
| 1994年 | 8篇 |
| 1993年 | 9篇 |
| 1992年 | 8篇 |
| 1991年 | 15篇 |
| 1990年 | 13篇 |
| 1989年 | 4篇 |
| 1988年 | 3篇 |
| 1987年 | 7篇 |
| 1986年 | 8篇 |
| 1985年 | 6篇 |
| 1984年 | 3篇 |
| 1981年 | 4篇 |
| 1980年 | 3篇 |
| 1979年 | 4篇 |
| 1978年 | 7篇 |
| 1977年 | 5篇 |
| 1976年 | 5篇 |
| 1974年 | 2篇 |
| 1973年 | 3篇 |
| 1970年 | 3篇 |
| 1963年 | 3篇 |
排序方式： 共有10000条查询结果，搜索用时 14 毫秒
81.
82.
83.
84.
85.
86.
The aim of this article was to understand how active power is used in squat and countermovement jumps. A simple empirical model comprising a mass, a spring, an active element and a damper, together with an optimisation principle, was used to identify the mechanical factors that maximise performance of jumps without countermovement (squat jumps, SJ) and with countermovement (CMJ). Twelve amateur volleyball players performed SJ from two initial positions and CMJ with two degrees of counterbalancing, while kinematic data were collected (jump height, push-off duration and position of the centre of mass). The model adjusted well to real data of SJ through all the impulse phase, and slightly less adequately at the end of this phase for CMJ. Nevertheless, it provides a satisfactory explanation for the generation and utilisation of active power for both type of jumps. On average, the estimated power of the active elements, the spring, and the damper were greater in the SJ. Based upon the result obtained with this model, we suggest that active power is best evaluated with SJ. The reason for this is that, during this kind of jump, the elements associated with the damper consume much of the energy produced by the active elements. The participation of the elements that consume the energy generated by the active elements is less in CMJ than in SJ, allowing for a better utilisation of this energy. In this way it is possible to achieve a better performance in CMJ with less active power. 相似文献
87.
88.
John Downer 《Minerva》2017,55(2):229-248
Publics and policymakers increasingly have to contend with the risks of complex, safety-critical technologies, such as airframes and reactors. As such, ‘technological risk’ has become an important object of modern governance, with state regulators as core agents, and ‘reliability assessment’ as the most essential metric. The Science and Technology Studies (STS) literature casts doubt on whether or not we should place our faith in these assessments because predictively calculating the ultra-high reliability required of such systems poses seemingly insurmountable epistemological problems. This paper argues that these misgivings are warranted in the nuclear sphere, despite evidence from the aviation sphere suggesting that such calculations can be accurate. It explains why regulatory calculations that predict the reliability of new airframes cannot work in principle, and then it explains why those calculations work in practice. It then builds on this explanation to argue that the means by which engineers manage reliability in aviation is highly domain-specific, and to suggest how a more nuanced understanding of jetliners could inform debates about nuclear energy. 相似文献
89.
Christopher Hamlin 《Science & Education》2017,26(1-2):191-193
90.