全文获取类型
收费全文 | 19098篇 |
免费 | 1548篇 |
国内免费 | 1535篇 |
专业分类
电工技术 | 3780篇 |
综合类 | 1031篇 |
化学工业 | 4260篇 |
金属工艺 | 1624篇 |
机械仪表 | 789篇 |
建筑科学 | 674篇 |
矿业工程 | 372篇 |
能源动力 | 677篇 |
轻工业 | 789篇 |
水利工程 | 1472篇 |
石油天然气 | 310篇 |
武器工业 | 76篇 |
无线电 | 1931篇 |
一般工业技术 | 2568篇 |
冶金工业 | 549篇 |
原子能技术 | 721篇 |
自动化技术 | 558篇 |
出版年
2024年 | 67篇 |
2023年 | 426篇 |
2022年 | 704篇 |
2021年 | 783篇 |
2020年 | 752篇 |
2019年 | 658篇 |
2018年 | 669篇 |
2017年 | 785篇 |
2016年 | 752篇 |
2015年 | 703篇 |
2014年 | 1072篇 |
2013年 | 1141篇 |
2012年 | 1242篇 |
2011年 | 1495篇 |
2010年 | 1005篇 |
2009年 | 1084篇 |
2008年 | 1130篇 |
2007年 | 1162篇 |
2006年 | 1077篇 |
2005年 | 886篇 |
2004年 | 803篇 |
2003年 | 647篇 |
2002年 | 530篇 |
2001年 | 473篇 |
2000年 | 389篇 |
1999年 | 334篇 |
1998年 | 256篇 |
1997年 | 233篇 |
1996年 | 161篇 |
1995年 | 159篇 |
1994年 | 105篇 |
1993年 | 102篇 |
1992年 | 93篇 |
1991年 | 78篇 |
1990年 | 44篇 |
1989年 | 47篇 |
1988年 | 38篇 |
1987年 | 18篇 |
1986年 | 15篇 |
1985年 | 9篇 |
1984年 | 7篇 |
1983年 | 12篇 |
1982年 | 9篇 |
1981年 | 10篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1976年 | 2篇 |
1959年 | 2篇 |
1958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
51.
Cheul-Ro Lee 《Journal of Electronic Materials》2002,31(4):327-331
We have investigated the growth characteristics of n-Al0.15Ga0.85N:Si/GaN and the electronic properties of Au/n-Al0.15Ga0.85N:Si diode structures grown by metal-organic chemical vapor deposition (MOCVD) with various Si incorporations. The Al0.15Ga0.85N:Si layers were grown on undoped GaN/sapphire (0001) epitaxial layers in a horizontal MOCVD reactor at the reduced pressure
of 300 torr. The mirrorlike surface, free of defects, such as cracks or hillocks, can be seen in the undoped Al0.15Ga0.85N epilayer, which was grown without any intentional flow of SiH4. However, many cracks are observed in the n-Al0.15Ga0.85N:Si, which was grown with Si incorporation above 1.0 nmol/min. While Au/n-Al0.15Ga0.85N:Si diodes having low incorporation of Si showed retively good rectifying behavior, the samples having high Si incorporation
exhibited leaky current-voltage (I-V) behavior. Particularly, the Au/n-Al0.15Ga0.85N:Si structure grown with Si incorporation above 1.0 nmol/min cannot be used for electrical rectification. Both added tunneling
components and thermionic emission influence the current transport at the Au/n-Al0.15Ga0.85N:Si barrier when Si incorporation becomes higher. 相似文献
52.
53.
通过对镍氢电池性能的研究,给出了一个应用ISA总线技术构建的、基于DELPHI编程平台的镍氢电池管理系统的设计方案,重点介绍了该系统的软件技术和实现方法。 相似文献
54.
Gasification of polyethylene (PE) pellet was studied using atmospheric argon-steam plasma generated by microwave discharge and the feasibility of the process was examined. The experimental results showed that additional steam to argon plasma promoted the weight decrease of PE and enhanced the production of H2, CO, CO2 and CH4. The results confirmed that the treatment of plastics with the steam plasma was effective to obtain synthesis gas. 相似文献
55.
Roberto Leoni Bruno Buonomo Gabriella Castellano Francesco Mattioli Guido Torrioli Luciana Di Gaspare Florestano Evangelisti 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》2004,520(1-3):44-47
We discuss the performance, of a normal metal hot electron bolometer (NHEB) that we have measured at 0.3 K. We found that the noise equivalent power was limited by the amplifier noise. To improve the NHEB power response and to make it more robust and reliable we propose to substitute the normal metal with heavily doped silicon. The heavily doped silicon behaves like a metal with lower carrier concentration and has a smaller electron–phonon thermal coupling. We have fabricated superconductor-doped silicon-superconductor contacts (S-Sm-S) and we have used them as thermometers and coolers. 相似文献
56.
Y.H. Sun 《Materials Research Bulletin》2004,39(9):1247-1255
Effects of Ca and Zr substitution upon the dielectric properties of Ba5LaTi3Ta7O30 ceramics were investigated together with the structural characterization. All the samples of Ba5La(ZrxTi1−x)3Ta7O30 formed a filled tungsten-bronze structures, whereas the solid solution limit was determined as x=0.25 in (CaxBa1−x)5LaTi3Ta7O30. Beyond this limit secondary phase of CaTa2O6 was detected and it would become the major phase for the Ca-rich compositions. The temperature coefficient of dielectric constant was improved with increasing Zr content while the dielectric constant decreased and the low dielectric loss varied little (in the order of 10−4). In the case of (CaxBa1−x)5LaTi3Ta7O30, small temperature coefficient of dielectric constant could be obtained with increasing Ca content while the dielectric constant decreased significantly, and a small amount substitution of Ca for Ba induced decrease in dielectric loss. 相似文献
57.
BBN (BaBi2Nb2O9) is very interesting and promising lead free material with relaxor properties in capacitors, sensors and actuators. 相似文献
58.
59.
60.
Chihiro J. Uchibori Y. Ohtani T. Oku Naoki Ono Masanori Murakami 《Journal of Electronic Materials》1997,26(4):410-414
Significant reduction of the contact resistance of In0.7Ga0.3As/Ni/W contacts (which were previously developed by sputtering in our laboratory) was achieved by depositing a W2N barrier layer between the Ni layer and W layer. The In0.7Ga0.3 As/Ni/W2N/W contact prepared by the radio-frequency sputtering technique showed the lowest contact resistance of 0.2 Ωmm after annealing
at 550°C for 10 s. This contact also provided a smooth surface, good reproducibility, and excellent thermal stability at 400°C.
The polycrystalline W2N layer was found to suppress the In diffusion to the contact surface, leading to improvement of the surface morphology and
an increase in the total area of the InxGa−As between metal and the GaAs substrate. These improvements are believed to reduce the contact resistance. 相似文献