全文获取类型
收费全文 | 22632篇 |
免费 | 1800篇 |
国内免费 | 627篇 |
学科分类
工业技术 | 25059篇 |
出版年
2024年 | 39篇 |
2023年 | 216篇 |
2022年 | 481篇 |
2021年 | 627篇 |
2020年 | 625篇 |
2019年 | 456篇 |
2018年 | 470篇 |
2017年 | 567篇 |
2016年 | 649篇 |
2015年 | 732篇 |
2014年 | 1541篇 |
2013年 | 1119篇 |
2012年 | 1712篇 |
2011年 | 1935篇 |
2010年 | 1514篇 |
2009年 | 1467篇 |
2008年 | 1287篇 |
2007年 | 1681篇 |
2006年 | 1469篇 |
2005年 | 1287篇 |
2004年 | 872篇 |
2003年 | 809篇 |
2002年 | 690篇 |
2001年 | 553篇 |
2000年 | 505篇 |
1999年 | 400篇 |
1998年 | 277篇 |
1997年 | 229篇 |
1996年 | 158篇 |
1995年 | 128篇 |
1994年 | 122篇 |
1993年 | 87篇 |
1992年 | 64篇 |
1991年 | 53篇 |
1990年 | 32篇 |
1989年 | 36篇 |
1988年 | 29篇 |
1987年 | 25篇 |
1986年 | 15篇 |
1985年 | 16篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1981年 | 6篇 |
1980年 | 23篇 |
1979年 | 6篇 |
1975年 | 5篇 |
1965年 | 3篇 |
1964年 | 5篇 |
1959年 | 6篇 |
1951年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 660 毫秒
1.
Qiqi Peng Xu Jiang Yifan Chen Wei Zhang Jun Jiang Anquan Jiang 《Ceramics International》2021,47(16):22753-22759
Large domain wall (DW) conductivity in an insulating ferroelectric plays an important role in the future nanosensors and nonvolatile memories. However, the wall current was usually too small to drive high-speed memory circuits and other agile nanodevices requiring high output-powers. Here, a large domain-wall current of 67.8 μA in a high on/off ratio of ~4460 was observed in an epitaxial Au/BiFeO3/SrRuO3 thin-film capacitor with the minimized oxygen vacancy concentration. The studies from read current-write voltage hysteresis loops and piezo-response force microscope images consistently showed remaining of partially unswitched domains after application of an opposite poling voltage that increased domain wall density and wall current greatly. A theoretical model was proposed to explain the large wall current. According to this model, the domain reversal occurs with the appearance of head-to-head and tail-to-tail 180° domain walls (DWs), resulting in the formation of highly conductive wall paths. As the applied voltage increased, the domain-wall number increased to enhance the on-state current, in agreement with the measurements of current-voltage curves. This work paves a way to modulate DW currents within epitaxial Au/BiFeO3/SrRuO3 thin-film capacitors through the optimization of both oxygen vacancy and domain wall densities to achieve large output powers of modern domain-wall nanodevices. 相似文献
2.
凌庄子水厂蓄水池进水口处有一保水堰,为非标准薄壁堰,不能使用已有堰流公式对其过流量进行准确计算。为了得出较为精确的过流流量,按照重力相似准则制作几何比尺为1∶5的模型进行试验研究。在已有自由出流公式的基础上,对自由出流流量系数进行修正并对淹没情况下流量变化过程进行研究。对该非标准堰自由出流流量系数的实测值与经验值进行分析比较,发现堰板槽降低了实际自由出流过流能力。淹没出流的流量系数主要与下游尾水位有关,试验中形成的淹没式堰流受实际堰型尺寸影响,下游尾水位和堰上水位近似相等,不完全适用已有淹没出流流量公式,通过试验给出了修正淹没系数随h/p的变化关系。结果表明利用堰前、堰后水位初步计算过流流量是可行的,可为该工程提供参考,也可为实际工程中非标准矩形堰的流量计算提供思路。 相似文献
3.
4.
5.
6.
7.
8.
Fault detection and isolation in water distribution networks is an active topic due to the nonlinearities of flow propagation and recent increases in data availability due to sensor deployment. Here, we propose an efficient two-step data driven alternative: first, we perform sensor placement taking the network topology into account; second, we use incoming sensor data to build a network model through online dictionary learning. Online learning is fast and allows tackling large networks as it processes small batches of signals at a time. This brings the benefit of continuous integration of new data into the existing network model, either in the beginning for training or in production when new data samples are gathered. The proposed algorithms show good performance in our simulations on both small and large-scale networks. 相似文献
9.
10.
Joon‐Young Jun Sosuke Nakajima Koji Yamazaki Yuji Kawai Hajime Yasui Yasuyuki Konishi 《International Journal of Food Science & Technology》2015,50(4):871-877
Cystoseira hakodatensis is an unutilised brown algae belonging to family Sargassaceae. A crude methanol extract from the algae showed inhibitory effects on the growths of Bacillus cereus and Bacillus licheniformis. To isolate the major antimicrobial agent, a sequential active‐guided isolation procedure was applied: liquid–liquid extraction, column chromatography and bio‐autography. A marked antimicrobial agent (active α) was isolated in hydrophobic fraction and was determined to phenolics without carbohydrates and proteins by phytochemical test. Regarding the antimicrobial potential, the isolated active α showed better inhibitory effects against B. cereus and B. licheniformis at 2 and 4 times of lower concentrations (62.5 and 31.3 μg mL?1) in comparison with epigallocatechin gallate. These results showed that C. hakodatensis is a potential source of antimicrobial agent capable of preventing the growth of the two bacteria. 相似文献