全文获取类型
收费全文 | 271268篇 |
免费 | 22831篇 |
国内免费 | 11899篇 |
专业分类
电工技术 | 16775篇 |
技术理论 | 48篇 |
综合类 | 28328篇 |
化学工业 | 33981篇 |
金属工艺 | 10817篇 |
机械仪表 | 13892篇 |
建筑科学 | 38892篇 |
矿业工程 | 16778篇 |
能源动力 | 10286篇 |
轻工业 | 19853篇 |
水利工程 | 13707篇 |
石油天然气 | 15553篇 |
武器工业 | 3583篇 |
无线电 | 15861篇 |
一般工业技术 | 18546篇 |
冶金工业 | 16077篇 |
原子能技术 | 1829篇 |
自动化技术 | 31192篇 |
出版年
2024年 | 951篇 |
2023年 | 3165篇 |
2022年 | 6311篇 |
2021年 | 8565篇 |
2020年 | 8122篇 |
2019年 | 6061篇 |
2018年 | 5648篇 |
2017年 | 7150篇 |
2016年 | 8888篇 |
2015年 | 9628篇 |
2014年 | 18285篇 |
2013年 | 15832篇 |
2012年 | 19423篇 |
2011年 | 21681篇 |
2010年 | 16350篇 |
2009年 | 16379篇 |
2008年 | 14788篇 |
2007年 | 18302篇 |
2006年 | 16986篇 |
2005年 | 14871篇 |
2004年 | 12414篇 |
2003年 | 10897篇 |
2002年 | 8842篇 |
2001年 | 7355篇 |
2000年 | 6299篇 |
1999年 | 4851篇 |
1998年 | 3471篇 |
1997年 | 2913篇 |
1996年 | 2362篇 |
1995年 | 1917篇 |
1994年 | 1600篇 |
1993年 | 1139篇 |
1992年 | 930篇 |
1991年 | 640篇 |
1990年 | 554篇 |
1989年 | 507篇 |
1988年 | 284篇 |
1987年 | 218篇 |
1986年 | 193篇 |
1985年 | 231篇 |
1984年 | 161篇 |
1983年 | 126篇 |
1982年 | 78篇 |
1981年 | 92篇 |
1980年 | 98篇 |
1979年 | 52篇 |
1978年 | 26篇 |
1977年 | 31篇 |
1959年 | 38篇 |
1955年 | 23篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
51.
《International Journal of Hydrogen Energy》2021,46(69):34449-34462
Three-dimensional Bödewadt flow (fluid rotates at a large enough distance from the stationary plate) of carbon nanomaterial is examined. Single walled and multi walled CNTs are dissolved in water and gasoline oil baseliquids. Darcy-Forchheimer porous medium is considered. Stationary disk is further stretched linearly in radial direction. Heat transfer effect is examined in presence of radiation and convection. Effect of viscous dissipation is accounted. Entropy generation rate is studied. By using adequate transformation (von Kármán relations), the flow field equations (PDEs) are transmitted into ODEs. Solutions to these ODEs are constructed via implementation of shooting method (bvp4c). In addition to Entropy generation rate, Bejan number, heat transfer rate (Nusselt number), skin friction and temperature of fluid are examined through involved physical parameters. Axial component of velocity intensifies with increment in nanoparticles volume fraction and ratio of stretching rate to angular velocity parameter while it decays with higher porosity parameter. Higher nanoparticles volume fraction and porosity parameter lead to decay in radial as well as tangential component of velocity. However it enhances with higher ratio of stretching rate to angular velocity parameter. Temperature of fluid directly varies with higher ratio of stretching rate to angular velocity parameter, radiation parameter, Eckert number, Biot number and nanoparticles volume fraction. Rate of Entropy generation is reduced with higher estimations of porosity parameter, nanoparticles volume fraction and radiation parameter. Skin friction coefficient decays with higher porosity parameter and ratio of stretching rate to angular velocity parameter. Intensification in porosity parameter, nanoparticles volume fraction and Biot number leads to higher Nusselt number. Prominent impact is shown by multiple-walled CNTs with gasoline oil basefluid than single-walled CNTs with water basefluid. 相似文献
52.
This calibration device of radio comprehensive tester is studied and established in this paper. It solves the verification and
calibration of a large number of general-purpose radio comprehensive testers. The calibration device consists of four calibration sub-
systems and calibration software system, including RF generator, audio generator, audio analyzer and RF analyzer. It also researches
on the configuration of standard equipment and analyzes the uncertainty of the calibration devices, ensuring accurate and reliable val-
ue transfer. 相似文献
53.
Wenshu Chen Jiajun Gu Yongping Du Fang Song Fanxing Bu Jinghan Li Yang Yuan Ruichun Luo Qinglei Liu Di Zhang 《Advanced functional materials》2020,30(25)
Large‐scale production of hydrogen from water‐alkali electrolyzers is impeded by the sluggish kinetics of hydrogen evolution reaction (HER) electrocatalysts. The hybridization of an acid‐active HER catalyst with a cocatalyst at the nanoscale helps boost HER kinetics in alkaline media. Here, it is demonstrated that 1T–MoS2 nanosheet edges (instead of basal planes) decorated by metal hydroxides form highly active / heterostructures, which significantly enhance HER performance in alkaline media. Featured with rich / sites, the fabricated 1T–MoS2 QS/Ni(OH)2 hybrid (quantum sized 1T–MoS2 sheets decorated with Ni(OH)2 via interface engineering) only requires overpotentials of 57 and 112 mV to drive HER current densities of 10 and 100 mA cm?2, respectively, and has a low Tafel slope of 30 mV dec?1 in 1 m KOH. So far, this is the best performance for MoS2‐based electrocatalysts and the 1T–MoS2 QS/Ni(OH)2 hybrid is among the best‐performing non‐Pt alkaline HER electrocatalysts known. The HER process is durable for 100 h at current densities up to 500 mA cm?2. This work not only provides an active, cost‐effective, and robust alkaline HER electrocatalyst, but also demonstrates a design strategy for preparing high‐performance catalysts based on edge‐rich 2D quantum sheets for other catalytic reactions. 相似文献
54.
As a solid state joining process, ultrasonic spot welding has been proven to be a promising technique for joining copper alloys. However, challenges still remain in employing ultrasonic spot welding to join copper alloys. This article comprehensively reviews the current state of ultrasonic spot welding of copper alloys with a number of critical issues including materials flow, plastic deformation, temperature distribution, vibration, relative motion, vertical displacement, interface friction coefficient, online monitoring technique, coupled with the macrostructure and microstructure, the mechanical properties and electrical conductivity. In addition, the future trends in this field are provided. 相似文献
55.
伏彩萍 《有色金属(冶炼部分)》2020,(6):66-69
针对现有柠檬酸铋制备工艺合成时间长、能耗高、产品纯度不高等不足,介绍了一种常温下制备柠檬酸铋的新工艺。新工艺制备时间短,制备的柠檬酸铋产品质量好,合成过程产生的废水可循环利用,废气经碱液循环吸收可生产硝酸钠副产品。 相似文献
56.
57.
This study proposes that a novel integrated circuit (IC) and system design for renewable energy inverters can harvest renewable energy to power direct current (DC) and alternating current (AC) loads. In addition, an intelligent synthesis and management tool is developed to design the proposed system and to judge the system’s operational maintenance decisions. Finally, a renewable energy inverter’s information is posted to an online system. Users can obtain the proposed system’s information at any time and place. The accurate and superior performance of the proposed IC and system is confirmed by computer simulations and experimental results. 相似文献
58.
Lissy Z. F. Gross Mariana Sacerdoti Prof. Albrecht Piiper Prof. Stefan Zeuzem Dr. Alejandro E. Leroux Dr. Ricardo M. Biondi 《ChemMedChem》2020,15(18):1682-1690
Angiotensin converting enzyme 2 (ACE2) is the human receptor that interacts with the spike protein of coronaviruses, including the one that produced the 2020 coronavirus pandemic (COVID-19). Thus, ACE2 is a potential target for drugs that disrupt the interaction of human cells with SARS-CoV-2 to abolish infection. There is also interest in drugs that inhibit or activate ACE2, that is, for cardiovascular disorders or colitis. Compounds binding at alternative sites could allosterically affect the interaction with the spike protein. Herein, we review biochemical, chemical biology, and structural information on ACE2, including the recent cryoEM structures of full-length ACE2. We conclude that ACE2 is very dynamic and that allosteric drugs could be developed to target ACE2. At the time of the 2020 pandemic, we suggest that available ACE2 inhibitors or activators in advanced development should be tested for their ability to allosterically displace the interaction between ACE2 and the spike protein. 相似文献
59.
本研究针对水泥窑余热发电系统的工作条件,根据耐磨材料的损毁机理,采用高铝矾土、煅烧氧化铝粉、黏土、硅微粉等为原料,以磷酸二氢铝为结合剂,以铝酸钙水泥为促硬剂,通过添加掩蔽剂和优化配料工艺,制备了水泥窑余热发电系统用耐磨材料,并对不同处理温度对耐磨材料的性能影响进行了分析。结果表明增强骨料与基质的结合能力有利于耐磨性的提高,磷酸及磷酸盐与氧化铝之间会随着温度的升高生成不同的磷酸铝相,都能够起到结合作用,比采用水泥结合更有利于提高材料在不同温度下的强度和耐磨性。使用结果表明,制备的耐磨材料施工性能优良,凝结硬化时间适当,强度高,抗冲刷性能好,在水泥窑余热发电系统中取得了良好的使用效果。 相似文献
60.
铝灰渣是铝熔铸过程中产生的废弃物。本文主要介绍了酒钢东兴铝业嘉峪关分公司铝灰渣的产生量、排放、利用情况、化学成分及表面特征,并简要介绍了铝灰渣、铝灰的循环利用途径。 相似文献