全文获取类型
收费全文 | 424021篇 |
免费 | 14760篇 |
国内免费 | 6741篇 |
专业分类
电工技术 | 14109篇 |
技术理论 | 9篇 |
综合类 | 8917篇 |
化学工业 | 60861篇 |
金属工艺 | 23073篇 |
机械仪表 | 20095篇 |
建筑科学 | 14956篇 |
矿业工程 | 5297篇 |
能源动力 | 8801篇 |
轻工业 | 24765篇 |
水利工程 | 5769篇 |
石油天然气 | 13020篇 |
武器工业 | 1058篇 |
无线电 | 50247篇 |
一般工业技术 | 80191篇 |
冶金工业 | 60730篇 |
原子能技术 | 8987篇 |
自动化技术 | 44637篇 |
出版年
2023年 | 2602篇 |
2022年 | 5281篇 |
2021年 | 7348篇 |
2020年 | 5539篇 |
2019年 | 5227篇 |
2018年 | 14626篇 |
2017年 | 15508篇 |
2016年 | 11463篇 |
2015年 | 7535篇 |
2014年 | 9839篇 |
2013年 | 16656篇 |
2012年 | 16108篇 |
2011年 | 23475篇 |
2010年 | 20601篇 |
2009年 | 20033篇 |
2008年 | 20315篇 |
2007年 | 21602篇 |
2006年 | 12845篇 |
2005年 | 14546篇 |
2004年 | 11711篇 |
2003年 | 11185篇 |
2002年 | 10148篇 |
2001年 | 9572篇 |
2000年 | 8676篇 |
1999年 | 8690篇 |
1998年 | 18143篇 |
1997年 | 12439篇 |
1996年 | 9831篇 |
1995年 | 7456篇 |
1994年 | 6435篇 |
1993年 | 6213篇 |
1992年 | 4554篇 |
1991年 | 4289篇 |
1990年 | 4205篇 |
1989年 | 3947篇 |
1988年 | 3606篇 |
1987年 | 3020篇 |
1986年 | 2991篇 |
1985年 | 3246篇 |
1984年 | 2942篇 |
1983年 | 2643篇 |
1982年 | 2524篇 |
1981年 | 2636篇 |
1980年 | 2376篇 |
1979年 | 2339篇 |
1978年 | 2368篇 |
1977年 | 2691篇 |
1976年 | 3399篇 |
1975年 | 2095篇 |
1974年 | 2034篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Bin Feng Xin Jiang Guisheng Zou Wengan Wang Tianming Sun Heng Yang Guanlei Zhao Mingye Dong Yu Xiao Hongwei Zhu Lei Liu 《Advanced functional materials》2021,31(29):2102359
The realization of liquid metal-based wearable systems will be a milestone toward high-performance, integrated electronic skin. However, despite the revolutionary progress achieved in many other components of electronic skin, liquid metal-based flexible sensors still suffer from poor sensitivity due to the insufficient resistance change of liquid metal to deformation. Herein, a nacre-inspired architecture composed of a biphasic pattern (liquid metal with Cr/Cu underlayer) as “bricks” and strain-sensitive Ag film as “mortar” is developed, which breaks the long-standing sensitivity bottleneck of liquid metal-based electronic skin. With 2 orders of magnitude of sensitivity amplification while maintaining wide (>85%) working range, for the first time, liquid metal-based strain sensors rival the state-of-art counterparts. This liquid metal composite features spatially regulated cracking behavior. On the one hand, hard Cr cells locally modulate the strain distribution, which avoids premature cut-through cracks and prolongs the defect propagation in the adjacent Ag film. On the other hand, the separated liquid metal cells prevent unfavorable continuous liquid-metal paths and create crack-free regions during strain. Demonstrated in diverse scenarios, the proposed design concept may spark more applications of ultrasensitive liquid metal-based electronic skins, and reveals a pathway for sensor development via crack engineering. 相似文献
52.
安全仪表功能(SIF)回路是为了降低特定场景的安全风险而设置的,定级报告中SIF回路的功能描述是工艺设计的完整逻辑要求,包含关键动作及附件动作。安全完整性等级(SIL)验证属于概率学领域研究范畴,影响失效率的因素多且复杂。如果SIL验证无法通过,将造成大量的设计变更,浪费工程投资,影响工期。设计人员应关注SIL定级报告中关键动作的识别、要求平均失效概率以及SIF回路架构的约束。按照文中方法优化测量元件、逻辑控制器、执行元件及辅助元件的设计,可增加通过验证的概率。在没有预验证及安全要求规格书时,可以参考文中典型可通过SIL验证的SIF回路的经验架构进行优化设计,以减少工程变更。 相似文献
53.
54.
Wei Shaowei Yu Guoxian Wang Jun Domeniconi Carlotta Zhang Xiangliang 《Machine Learning》2021,110(6):1505-1526
Machine Learning - Traditional clustering algorithms focus on a single clustering result; as such, they cannot explore potential diverse patterns of complex real world data. To deal with this... 相似文献
55.
World Wide Web - Rule mechanism has been widely used in many areas, such as databases, artificial intelligent and pervasive computing. In a rule mechanism, rule activation decides which rules are... 相似文献
56.
57.
58.
59.
The role of the following factors in the selection of technological bases for manufacturing is considered: the accessibility of the machined surfaces; their parameters and dimensional relationships; their position relative to the forces acting; and the uniformity of the margin distribution. 相似文献
60.
Puneet Parmar Nicolas Lopez-Villalobos John T. Tobin Eoin Murphy Frank Buckley Shane V. Crowley Alan L. Kelly Laurence Shalloo 《International Journal of Food Science & Technology》2021,56(5):2415-2422
The objective of this study was to determine the effect of temperature on whole milk density measured at four different temperatures: 5, 10, 15, and 20 °C. A total of ninety-three individual milk samples were collected from morning milking of thirty-two Holstein Friesian dairy cows, of national average genetic merit, once every two weeks over a period of 4 weeks and were assessed by Fourier transform infrared spectroscopy for milk composition analysis. Density of the milk was evaluated using two different analytical methods: a portable density meter DMA35 and a standard desktop model DMA4500M (Anton Paar GmbH, UK). Milk density was analysed with a linear mixed model with the fixed effects of sampling period, temperature and analysis method; triple interaction of sampling period x analysis method x temperature; and the random effect of cow to account for repeated measures. The effect of temperature on milk density (ρ) was also evaluated including temperature (t) as covariate with linear and quadratic effects within each analytic method. The regression equation describing the curvature and density–temperature relationship for the DMA35 instrument was ρ = 1.0338−0.00017T−0.0000122T2 (R2 = 0.64), while it was ρ = 1.0334 + 0.000057T−0.00001T2 (R2 = 0.61) for DMA4500 instrument. The mean density determined with DMA4500 at 5 °C was 1.0334 g cm−3, with corresponding figures of 1.0330, 1.0320 and 1.0305 g cm−3 at 10, 15 and 20 °C, respectively. The milk density values obtained in this study at specific temperatures will help to address any bias in weight–volume calculations and thus may also improve the financial and operational control for the dairy processors in Ireland and internationally. 相似文献