全文获取类型
收费全文 | 27792篇 |
免费 | 2499篇 |
国内免费 | 1013篇 |
专业分类
电工技术 | 3993篇 |
综合类 | 2355篇 |
化学工业 | 2416篇 |
金属工艺 | 1133篇 |
机械仪表 | 2210篇 |
建筑科学 | 2574篇 |
矿业工程 | 1558篇 |
能源动力 | 787篇 |
轻工业 | 1377篇 |
水利工程 | 823篇 |
石油天然气 | 1789篇 |
武器工业 | 327篇 |
无线电 | 2373篇 |
一般工业技术 | 1386篇 |
冶金工业 | 1433篇 |
原子能技术 | 549篇 |
自动化技术 | 4221篇 |
出版年
2024年 | 63篇 |
2023年 | 207篇 |
2022年 | 449篇 |
2021年 | 636篇 |
2020年 | 661篇 |
2019年 | 513篇 |
2018年 | 485篇 |
2017年 | 688篇 |
2016年 | 764篇 |
2015年 | 909篇 |
2014年 | 1803篇 |
2013年 | 1741篇 |
2012年 | 2226篇 |
2011年 | 2176篇 |
2010年 | 1623篇 |
2009年 | 1555篇 |
2008年 | 1516篇 |
2007年 | 1955篇 |
2006年 | 1856篇 |
2005年 | 1659篇 |
2004年 | 1367篇 |
2003年 | 1228篇 |
2002年 | 1068篇 |
2001年 | 907篇 |
2000年 | 692篇 |
1999年 | 550篇 |
1998年 | 371篇 |
1997年 | 323篇 |
1996年 | 298篇 |
1995年 | 254篇 |
1994年 | 193篇 |
1993年 | 132篇 |
1992年 | 101篇 |
1991年 | 96篇 |
1990年 | 54篇 |
1989年 | 58篇 |
1988年 | 35篇 |
1987年 | 25篇 |
1986年 | 10篇 |
1984年 | 7篇 |
1983年 | 5篇 |
1982年 | 15篇 |
1981年 | 8篇 |
1980年 | 3篇 |
1979年 | 6篇 |
1962年 | 1篇 |
1959年 | 1篇 |
1958年 | 1篇 |
1955年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
电路板在我们的日常生活中非常常见,这就使得印刷电路板的缺陷检测显得尤为重要。AOI作为新兴的检测PCB板缺陷的系统,在生产实际中正在被大家熟知并且应用。相较于传统的检测方式,AOI系统比较灵活,无论是在检测时间还是系统运算上,或者是对相关技术人员的要求相较于传统方式都比较有优势,本文就AOI系统在实际中的应用展开讨论,分析并且介绍了在实际应用中的具体细则。 相似文献
2.
3.
4.
5.
6.
7.
Chuangang Yao Jixing Yang Haixia Zhang Sigeng Chen Jian Meng Kedi Cai 《Ceramics International》2021,47(17):24589-24596
Bismuth doped La2-xBixNiO4+δ (x = 0, 0.02 and 0.04) oxides are investigated as SOFC cathodes. The effects of Bi doping on the phase structure, thermal expansion, electrical conduction behavior as well as electrochemical performance are studied. All the samples exist as a tetragonal Ruddlesden-Popper structure. Bi-doped LBNO-0.02 and LBNO-0.04 have good chemical and thermal compatibility with LSGM electrolyte. The average TEC over 20–900°С was 13.4 × 10?6 and 14.2 × 10?6 K?1 for LBNO-0.02 and LBNO-0.04, respectively. The electrical conductivity was decreasing with the rise of Bi doping content. EIS measurement indicates Bi doping can decrease the ASR values. At 750 °C, the obtained ASR for LBNO-0.04 is 0.18 Ωcm2, which is 56% lower than that of the sample without Bi doping, suggesting Bi doping is beneficial to the electrochemical catalytic activity of LBNO cathodes. 相似文献
8.
运用计算流体力学方法,采用ANSYS CFX软件对发夹式换热器的壳侧流场进行了三维数值模拟。流场计算中采用多孔介质模型对管束区域进行简化,分析了壳侧流场的速度分布,结果表明:直管段部分的流体湍流强度大于弯管段,且外层管束所在区域为高流速区,受流体冲刷严重。结合流场信息,通过功率谱生成随机激振力,采用ABAQUS软件模拟计算了湍流激振下管束的振动响应,结果显示管束的面外均方根位移远大于面内位移,且弯管部分的振动位移最大。该研究结果可为发夹式换热器的性能分析和优化设计提供参考和依据。 相似文献
9.
Mostafa Dellahi Hattab Maker Guillermo Botella Enrique Alameda-Hernandez Azeddine Mouhsen 《International Journal of Circuit Theory and Applications》2020,48(6):887-905
The three-phase four-wire shunt active power filter (SAPF) was developed to suppress the harmonic currents generated by nonlinear loads, and for the compensation of unbalanced nonlinear load currents, reactive power, and the harmonic neutral current. In this work, we consider instantaneous reactive power theory (PQ theory) for reference current identification based on the following two algorithms: the classic low-pass filter (LPF) and the second-order generalized integrator (SOGI) filter. Furthermore, since an important process in SAPF control is the regulation of the DC bus voltage at the capacitor, a new controller based on the Lyapunov function is also proposed. A complete simulation of the resultant active filtering system confirms its validity, which uses the SOGI filter to extract the reference currents from the distorted line currents, compared with the traditional PQ theory based on LPF. In addition, the simulation performed also demonstrates the superiority of the proposed approach, for DC bus voltage control based on the Lyapunov function, compared with the traditional proportional-integral (PI) controller. Both novel approaches contribute towards an improvement in the overall performance of the system, which consists of a small rise and settling time, a very low or nonexistent overshoot, and the minimization of the total harmonic distortion (THD). 相似文献
10.
Seyedeh Nooshin Banitaba Dariush Semnani Elahe Heydari‐Soureshjani Behzad Rezaei Ali A Ensafi Ahmadreza Taghipour‐Jahromi 《Polymer International》2020,69(8):675-687
In this study, solvent‐free nanofibrous electrolytes were fabricated through an electrospinning method. Polyethylene oxide (PEO), lithium perchlorate and ethylene carbonate were used as polymer matrix, salt and plasticizer respectively in the electrolyte structures. Keggin‐type hetero polyoxometalate (Cu‐POM@Ru‐rGO, Ni‐POM@Ru‐rGO and Co‐POM@Ru‐rGO (POM, polyoxometalate; rGO, reduced graphene oxide)) nanoparticles were synthesized and inserted into the PEO‐based nanofibrous electrolytes. TEM and SEM analyses were carried out for further evaluation of the synthesized filler structures and the electrospun nanofibre morphologies. The fractions of free ions and crystalline phases of the as‐spun electrolytes were estimated by obtaining Fourier transform infrared and XRD spectra, respectively. The results showed a significant improvement in the ionic conductivity of the nanofibrous electrolytes by increasing filler concentrations. The highest ionic conductivity of 0.28 mS cm?1 was obtained by the introduction of 0.49 wt% Co‐POM@Ru‐rGO into the electrospun electrolyte at ambient temperature. Compared with solution‐cast polymeric electrolytes, the electrospun electrolytes present superior ionic conductivity. Moreover, the cycle stability of the as‐spun electrolytes was clearly improved by the addition of fillers. Furthermore, the mechanical strength was enhanced with the insertion of 0.07 wt% fillers to the electrospun electrolytes. The results implied that the prepared nanofibres are good candidates as solvent‐free electrolytes for lithium ion batteries. © 2020 Society of Chemical Industry 相似文献