全文获取类型
收费全文 | 794640篇 |
免费 | 13600篇 |
国内免费 | 2253篇 |
专业分类
电工技术 | 14032篇 |
综合类 | 764篇 |
化学工业 | 124804篇 |
金属工艺 | 30397篇 |
机械仪表 | 24314篇 |
建筑科学 | 19751篇 |
矿业工程 | 4079篇 |
能源动力 | 21727篇 |
轻工业 | 69153篇 |
水利工程 | 7757篇 |
石油天然气 | 14362篇 |
武器工业 | 50篇 |
无线电 | 91024篇 |
一般工业技术 | 153601篇 |
冶金工业 | 149774篇 |
原子能技术 | 16018篇 |
自动化技术 | 68886篇 |
出版年
2021年 | 7914篇 |
2020年 | 5769篇 |
2019年 | 7049篇 |
2018年 | 11719篇 |
2017年 | 11471篇 |
2016年 | 12470篇 |
2015年 | 8796篇 |
2014年 | 14321篇 |
2013年 | 37237篇 |
2012年 | 22615篇 |
2011年 | 30597篇 |
2010年 | 24298篇 |
2009年 | 27025篇 |
2008年 | 27380篇 |
2007年 | 26323篇 |
2006年 | 23312篇 |
2005年 | 21367篇 |
2004年 | 20246篇 |
2003年 | 19694篇 |
2002年 | 19054篇 |
2001年 | 18602篇 |
2000年 | 17281篇 |
1999年 | 18082篇 |
1998年 | 44864篇 |
1997年 | 31975篇 |
1996年 | 24776篇 |
1995年 | 18664篇 |
1994年 | 16349篇 |
1993年 | 15938篇 |
1992年 | 11768篇 |
1991年 | 11157篇 |
1990年 | 10863篇 |
1989年 | 10705篇 |
1988年 | 10070篇 |
1987年 | 8954篇 |
1986年 | 8776篇 |
1985年 | 9917篇 |
1984年 | 9313篇 |
1983年 | 8393篇 |
1982年 | 7849篇 |
1981年 | 8011篇 |
1980年 | 7617篇 |
1979年 | 7449篇 |
1978年 | 7313篇 |
1977年 | 8578篇 |
1976年 | 11223篇 |
1975年 | 6459篇 |
1974年 | 6033篇 |
1973年 | 6101篇 |
1972年 | 5150篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
351.
352.
353.
354.
The design of a microstrip‐fed annular‐ring slot antenna (ARSA) with circular polarization (CP) radiation is initially studied. To obtain CP radiation with broad 3‐dB axial ratio (AR) bandwidth that can cover the WiMAX 2.3 GHz (2305–2320 MHz, 2345–2360 MHz) and WLAN 2.4 GHz (2400–2480 MHz) bands, a novel technique of extending an inverted L‐shaped slot from the bottom section of the annular‐ring is proposed. To suppress the harmonic modes induced by the CP ARSA, the technique of integrating a defected ground structure into the annular‐ring slot is further introduced. From the measured results, 10‐dB impedance bandwidth and 3‐dB AR bandwidth of 44.86 and 9.68% were achieved by the proposed harmonic suppressed CP ARSA. Furthermore, average gain and radiation efficiency of ~4.7 dBic and 71%, respectively, were also exhibited across the bands of interest. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:337–345, 2015. 相似文献
355.
Nassar Sabry S. Faragallah Osama S. El-Bendary Mohsen A. M. 《Wireless Personal Communications》2021,119(1):37-61
Wireless Personal Communications - Due to the widely spreading of fake news utilizing image manipulation and its bad effects, this paper investigates efficient image contents verification and... 相似文献
356.
Nathan M. Wilbur Antin M. O'Sullivan Kerry T. B. MacQuarrie Tommi Linnansaari R. Allen Curry 《河流研究与利用》2020,36(5):769-783
Anthropogenic influences, including climate change, are increasing river temperatures in northern and temperate regions and threatening the thermal habitats of native salmonids. When river temperatures exceed the tolerance levels of brook trout and Atlantic salmon, individuals exhibit behavioural thermoregulation by seeking out cold‐water refugia – often created by tributaries and groundwater discharge. Thermal infrared (TIR) imagery was used to map cold‐water anomalies along a 53 km reach of the Cains River, New Brunswick. Trout and salmon parr did not use all identified thermal anomalies as refugia during higher river temperature periods (>21°C). Most small‐bodied trout (8–30 cm) were observed in 80% of the thermal anomalies sampled. Large‐bodied trout (>35 cm) required a more specific set of physical habitat conditions for suitable refugia, that is, 100% of observed large trout used 30% of the anomalies sampled and required water depths >65 cm within or adjacent to the anomaly. Densities of trout were significantly higher within anomalies compared with areas of ambient river temperature. Salmon parr were less aligned with thermal anomalies at the observed temperatures, that is, 59% were found in 65% of the sampled anomalies; and densities were not significantly different within/ outside anomalies. Salmon parr appeared to aggregate at 27°C, and after several events over 27°C variability in aggregation behaviour was observed – some fish aggregated at 25°C, others did not. We stipulate this is due to variances of thermal fatigue. Habitat suitability curves were developed for velocity, temperature, depth, substrate, and deep water availability to characterize conditions preferred by fish during high‐temperature events. These findings are useful for managers as our climate warms, and can potentially be used as a tool to help conserve and enhance thermal refugia for brook trout and Atlantic salmon in similar systems. 相似文献
357.
High‐intensity sweeteners in espresso coffee: ideal and equivalent sweetness and time–intensity analysis
下载免费PDF全文
![点击此处可从《International Journal of Food Science & Technology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Bruna M. Azevedo Flávio L. Schmidt Helena M. A. Bolini 《International Journal of Food Science & Technology》2015,50(6):1374-1381
The efficient substitution of sucrose by a sweetener in beverages requires the application of some sensory techniques. First, one must determine the concentrations of the sweeteners under study, equivalent in sweetness to the ideal sucrose concentration. In addition, it is fundamental to determine which is most similar to sucrose. The objectives of this study were to determine the ideal sweetness for espresso coffee and the equivalent concentrations in sweetness of different sweeteners, as well as characterise the time–intensity profile of each sweetener in relation to sweetness. The sweeteners evaluated were sucralose, aspartame, neotame, a cyclamate/saccharin mixture (2:1) and stevia. The sucrose concentration considered ideal by consumers was 12.5% (w/v), and the equivalent concentrations of the sweeteners were 0.0159% for sucralose, 0.0549% for aspartame, 0.0016% for neotame, 0.0359% for the cyclamate/saccharin mixture and 0.0998% for stevia. The time–intensity analysis indicated that possibly the sweeteners neotame, aspartame and sucralose would be the best substitutes for sucrose. 相似文献
358.
359.
360.