全文获取类型
收费全文 | 7597篇 |
免费 | 661篇 |
国内免费 | 606篇 |
专业分类
电工技术 | 516篇 |
综合类 | 754篇 |
化学工业 | 1743篇 |
金属工艺 | 772篇 |
机械仪表 | 128篇 |
建筑科学 | 423篇 |
矿业工程 | 166篇 |
能源动力 | 306篇 |
轻工业 | 733篇 |
水利工程 | 175篇 |
石油天然气 | 214篇 |
武器工业 | 22篇 |
无线电 | 883篇 |
一般工业技术 | 1134篇 |
冶金工业 | 227篇 |
原子能技术 | 262篇 |
自动化技术 | 406篇 |
出版年
2024年 | 39篇 |
2023年 | 246篇 |
2022年 | 340篇 |
2021年 | 395篇 |
2020年 | 347篇 |
2019年 | 324篇 |
2018年 | 279篇 |
2017年 | 286篇 |
2016年 | 291篇 |
2015年 | 254篇 |
2014年 | 372篇 |
2013年 | 495篇 |
2012年 | 454篇 |
2011年 | 537篇 |
2010年 | 413篇 |
2009年 | 437篇 |
2008年 | 382篇 |
2007年 | 419篇 |
2006年 | 403篇 |
2005年 | 367篇 |
2004年 | 342篇 |
2003年 | 241篇 |
2002年 | 233篇 |
2001年 | 211篇 |
2000年 | 156篇 |
1999年 | 116篇 |
1998年 | 78篇 |
1997年 | 72篇 |
1996年 | 60篇 |
1995年 | 43篇 |
1994年 | 42篇 |
1993年 | 42篇 |
1992年 | 27篇 |
1991年 | 22篇 |
1990年 | 20篇 |
1989年 | 22篇 |
1988年 | 15篇 |
1987年 | 6篇 |
1986年 | 6篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1981年 | 7篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1965年 | 1篇 |
1960年 | 1篇 |
1959年 | 2篇 |
1958年 | 1篇 |
1956年 | 1篇 |
排序方式: 共有8864条查询结果,搜索用时 31 毫秒
21.
22.
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
23.
24.
25.
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
26.
27.
会计集中核算制度是财政体制改革的一项重要举措,它对改变现行财政资金分散收付方式发挥了很大的作用.应在会计集中核算的基础上建立行业财务管理中心,并作为会计集中核算改革的进一步深入和补充.探讨了建立行业财务管理中心的重要性和必要性以及行业财务管理中心的模式,并在行业财务管理中心引入融资理念. 相似文献
28.
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
29.
基底元素表面富集与扩散阻档层 总被引:1,自引:0,他引:1
根据An-Ag系统以及An-Cu系统的扩散系数计算,提出了扩散阻挡层模型。利用这个模型对Au-Ag系统进行有关实验,得利了较好的验证。 相似文献
30.
A one-dimensional fluid model for homogeneous atmospheric pressure barrier discharges in helium is presented by considering elementary processes of excitation and ionization including a metastable atom effect. Using this model we investigate the behaviours of the helium metastable atoms in discharges as well as their influence on the discharge characteristics. It is shown that the metastable atoms with a relatively high concentration during the discharge are mainly produced in the active phase of the discharge and dissolved in the off phase. It is also found that the metastable atom collisions can not only provide seed electrons for discharges but also influence the concentration of ions. A reduction of matestable atom density results in a drop in the charged particle densities and causes a qualitative change in the discharge patterns. 相似文献