全文获取类型
收费全文 | 188005篇 |
免费 | 14137篇 |
国内免费 | 7158篇 |
专业分类
电工技术 | 9955篇 |
技术理论 | 14篇 |
综合类 | 10444篇 |
化学工业 | 30628篇 |
金属工艺 | 11267篇 |
机械仪表 | 11438篇 |
建筑科学 | 11554篇 |
矿业工程 | 4560篇 |
能源动力 | 4208篇 |
轻工业 | 11551篇 |
水利工程 | 3508篇 |
石油天然气 | 10686篇 |
武器工业 | 1219篇 |
无线电 | 20087篇 |
一般工业技术 | 29141篇 |
冶金工业 | 11847篇 |
原子能技术 | 5033篇 |
自动化技术 | 22160篇 |
出版年
2023年 | 2601篇 |
2022年 | 4795篇 |
2021年 | 7097篇 |
2020年 | 5374篇 |
2019年 | 4625篇 |
2018年 | 5825篇 |
2017年 | 6230篇 |
2016年 | 5747篇 |
2015年 | 6563篇 |
2014年 | 8483篇 |
2013年 | 10261篇 |
2012年 | 11124篇 |
2011年 | 11736篇 |
2010年 | 10082篇 |
2009年 | 9860篇 |
2008年 | 9686篇 |
2007年 | 9073篇 |
2006年 | 8477篇 |
2005年 | 7182篇 |
2004年 | 5482篇 |
2003年 | 5571篇 |
2002年 | 5836篇 |
2001年 | 5215篇 |
2000年 | 4368篇 |
1999年 | 3864篇 |
1998年 | 2932篇 |
1997年 | 2495篇 |
1996年 | 2226篇 |
1995年 | 1934篇 |
1994年 | 1607篇 |
1993年 | 1365篇 |
1992年 | 1294篇 |
1991年 | 1143篇 |
1990年 | 1148篇 |
1989年 | 1038篇 |
1988年 | 922篇 |
1987年 | 846篇 |
1986年 | 772篇 |
1985年 | 718篇 |
1984年 | 702篇 |
1982年 | 670篇 |
1981年 | 671篇 |
1979年 | 736篇 |
1978年 | 777篇 |
1977年 | 739篇 |
1976年 | 755篇 |
1975年 | 713篇 |
1974年 | 719篇 |
1973年 | 723篇 |
1972年 | 705篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
The slight-alkalization of generator internal cooling water (GICW) is widely used to inhibit the corrosion of hollow copper conductor and thereby ensure the safe operation of the generator. CO2 inleakage is increasingly identified as a potential security risk for GICW system. In this paper, the influence of CO2 inleakage on the slight-alkalization of GICW was theoretically discussed. Based on the equilibriums of the CO2-NaOH-H2O system, CO2 inleakage saturation was derived to quantify the amount of the dissolved CO2 in GICW. This parameter can be directly calculated with the measured conductivity and the [Na+] of GICW. The influence of CO2 inleakage on the slight-alkalization conditioning of GICW and the measurement of its water quality parameters were then analyzed. The more severe the inleakage, the narrower the water quality operation ranges of GICW, resulting in the more difficult the slight-alkalization conditioning of GICW. The temperature calibrations of the conductivity and the pH value of GICW show non-linear correlations with the amount of CO2 inleakage and the NaOH dosage. This study provides insights into the influence of CO2 inleakage on the slight-alkalization of GICW, which can serve as the theoretical basis for the actual slight-alkalization when CO2 inleakage occurs. 相似文献
52.
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
53.
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
54.
The Fe/C/SiCN composite ceramics were synthesized by polymer-derived method to obtain the integration of structure and functions. The electromagnetic waves (EMW) absorption properties at X and Ku bands were investigated. The addition of nano-sized Fe particles improved the magnetic loss and impedance matching, and the carbon nanotubes generated by the iron in-situ catalysis increased the internal relaxation polarization and interfacial polarization, which together improved the EMW absorption properties significantly. In particular, the Fe/C/SiCN-9 showed the optimum reflection loss (RL) of ?31.06 dB at 10.03 GHz with an effective absorption bandwidth (EAB, RL < ?10 dB) of 3.03 GHz at 2.51 mm, indicating the excellent EMW absorption properties of Fe/C/SiCN composite ceramics. 相似文献
55.
56.
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
57.
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
58.
59.
尕斯库勒油田E13油藏已经进入高含水时期,储采失衡加剧,综合含水率达到了80%以上,原油产量下降,经济效益变差。为了提高油藏原油采出程度、改善油藏开发效果,调研了国内外减氧空气驱的机理研究以及现场试验的资料,建立了以油藏真实孔渗饱数据为基础的一维条形地层机理模型,并选取该油藏Y12-27井组进行了减氧空气驱可行性验证。研究表明:纵向顶部减氧空气驱驱油效果优于水驱和氮气驱;驱替压力对原油采出程度影响不大;注水转注气可以提高原油采出程度;对于减氧空气驱,由于低温氧化反应的作用,氧气浓度对原油采出程度有一定影响,但比较微弱,其中,氧气浓度为10%时,驱替结束采出程度最高;尕斯库勒油田E13油藏属于注水开发“双高”油藏,适用于减氧空气驱;对于该油藏Y12-27井组,顶部减氧空气驱驱油效果好于水驱和氮气驱,建议氧气浓度超过10%时采取关井等措施。 相似文献
60.