全文获取类型
收费全文 | 803篇 |
免费 | 22篇 |
专业分类
教育 | 620篇 |
科学研究 | 38篇 |
各国文化 | 13篇 |
体育 | 43篇 |
文化理论 | 6篇 |
信息传播 | 105篇 |
出版年
2023年 | 10篇 |
2022年 | 7篇 |
2021年 | 15篇 |
2020年 | 23篇 |
2019年 | 47篇 |
2018年 | 41篇 |
2017年 | 43篇 |
2016年 | 40篇 |
2015年 | 23篇 |
2014年 | 27篇 |
2013年 | 177篇 |
2012年 | 28篇 |
2011年 | 23篇 |
2010年 | 21篇 |
2009年 | 14篇 |
2008年 | 18篇 |
2007年 | 16篇 |
2006年 | 15篇 |
2005年 | 13篇 |
2004年 | 9篇 |
2003年 | 12篇 |
2002年 | 11篇 |
2001年 | 10篇 |
2000年 | 11篇 |
1999年 | 14篇 |
1998年 | 7篇 |
1996年 | 5篇 |
1995年 | 8篇 |
1994年 | 6篇 |
1993年 | 9篇 |
1992年 | 10篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1987年 | 5篇 |
1985年 | 5篇 |
1983年 | 5篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1980年 | 4篇 |
1979年 | 7篇 |
1978年 | 5篇 |
1977年 | 7篇 |
1976年 | 4篇 |
1974年 | 4篇 |
1971年 | 7篇 |
1969年 | 3篇 |
1868年 | 3篇 |
1865年 | 3篇 |
排序方式: 共有825条查询结果,搜索用时 15 毫秒
51.
Many scientists and coaches are interested in mechanical power produced during cycling, and use Schoberer Rad Me\technik (SRM)
bicycle power cranks to obtain this data. However, it has been expensive and difficult to calibrate SRM cranks, causing much
of the collected data to be unreliable. We present a static method, derived from first principles, for obtaining a calibration
factor for SRM cranks.
A known mass and lever arm (chainring of a known diameter) are used to apply a known torque load to the instrument in four
positions, and the output frequencies are used to calculate the calibration factor in Hz/Nm. The reproducibility of this method
is ±0.01 Hz/Nm, which is acceptable for the application of the instrument, which is measurement of mechanical power application
by cyclists at the crank.
The method is reliable, inexpensive, and easy to set up, and will allow higher confidence in data collected using SRM power
cranks. We recommend calibration of the power meter once every six months because of the measured drift of the calibration
factor over time. 相似文献
52.
53.
The authors report on the discovery of a 19th century document that illustrates an early example of educational measurement. The text, copied from the original in the British Museum, is presented in its entirety in the article. 相似文献
54.
55.
56.
Stefanie Demming Gena Peterat Andreu Llobera Hannah Schmolke Alexander Bruns Michael Kohlstedt Ala‘aldeen Al-Halhouli Claus-Peter Klages Rainer Krull Stephanus Büttgenbach 《Biomicrofluidics》2012,6(3)
This paper presents a vertically positioned microfluidic system made of poly(dimethylsiloxane) (PDMS) and glass, which can be applied as a microbubble column (μBC) for biotechnological screening in suspension. In this μBC, microbubbles are produced in a cultivation chamber through an integrated nozzle structure. Thus, homogeneous suspension of biomass is achieved in the cultivation chamber without requiring additional mixing elements. Moreover, blockage due to produced carbon dioxide by the microorganisms—a problem predominant in common, horizontally positioned microbioreactors (MBRs)—is avoided, as the gas bubbles are released by buoyancy at the upper part of the microsystem. The patterned PDMS layer is based on an optimized two-lithographic process. Since the naturally hydrophobic PDMS causes problems for the sufficient production of microbubbles, a method based on polyelectrolyte multilayers is applied in order to allow continuous hydrophilization of the already bonded PDMS-glass-system. The μBC comprises various microelements, including stabilization of temperature, control of continuous bubble formation, and two optical configurations for measurement of optical density with two different sensitivities. In addition, the simple and robust application and handling of the μBC is achieved via a custom-made modular plug-in adapter. To validate the scalability from laboratory scale to microscale, and thus to demonstrate the successful application of the μBC as a screening instrument, a batch cultivation of Saccharomyces cerevisiae is performed in the μBC and compared to shake flask cultivation. Monitoring of the biomass growth in the μBC with the integrated online analytics resulted in a specific growth rate of 0.32 h−1, which is almost identical to the one achieved in the shake flask cultivation (0.31 h−1). Therefore, the validity of the μBC as an alternative screening tool compared to other conventional laboratory scale systems in bioprocess development is proven. In addition, vertically positioned microbioreactors show high potential in comparison to conventional screening tools, since they allow for high density of integrated online analytics and therefore minimize time and cost for screening and guarantee improved control and analysis of cultivation parameters. 相似文献
57.
58.
59.
60.