全文获取类型
收费全文 | 3561篇 |
免费 | 118篇 |
国内免费 | 17篇 |
专业分类
电工技术 | 249篇 |
综合类 | 10篇 |
化学工业 | 978篇 |
金属工艺 | 121篇 |
机械仪表 | 85篇 |
建筑科学 | 69篇 |
能源动力 | 166篇 |
轻工业 | 361篇 |
水利工程 | 3篇 |
石油天然气 | 4篇 |
无线电 | 236篇 |
一般工业技术 | 722篇 |
冶金工业 | 344篇 |
原子能技术 | 83篇 |
自动化技术 | 265篇 |
出版年
2023年 | 20篇 |
2022年 | 42篇 |
2021年 | 63篇 |
2020年 | 35篇 |
2019年 | 45篇 |
2018年 | 60篇 |
2017年 | 58篇 |
2016年 | 67篇 |
2015年 | 58篇 |
2014年 | 103篇 |
2013年 | 243篇 |
2012年 | 153篇 |
2011年 | 234篇 |
2010年 | 186篇 |
2009年 | 193篇 |
2008年 | 206篇 |
2007年 | 176篇 |
2006年 | 155篇 |
2005年 | 152篇 |
2004年 | 133篇 |
2003年 | 117篇 |
2002年 | 109篇 |
2001年 | 82篇 |
2000年 | 62篇 |
1999年 | 59篇 |
1998年 | 121篇 |
1997年 | 106篇 |
1996年 | 79篇 |
1995年 | 57篇 |
1994年 | 74篇 |
1993年 | 48篇 |
1992年 | 36篇 |
1991年 | 31篇 |
1990年 | 30篇 |
1989年 | 34篇 |
1988年 | 27篇 |
1987年 | 22篇 |
1986年 | 17篇 |
1985年 | 30篇 |
1984年 | 17篇 |
1983年 | 32篇 |
1982年 | 18篇 |
1981年 | 14篇 |
1980年 | 9篇 |
1979年 | 11篇 |
1978年 | 10篇 |
1977年 | 11篇 |
1976年 | 15篇 |
1975年 | 8篇 |
1974年 | 7篇 |
排序方式: 共有3696条查询结果,搜索用时 15 毫秒
1.
Takeshi Kondo Hiroyuki Ito Kazuhide Kusakabe Kazuhiro Ohkawa Kensuke Honda Yasuaki Einaga Akira Fujishima Takeshi Kawai 《Diamond and Related Materials》2008,17(1):48-54
The effect of CF4 plasma etching on diamond surfaces, with respect to treatment time, was investigated using scanning electron microscopy (SEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and electrochemical measurements. SEM observations and Raman spectra indicated an increase in surface roughening on a scale of 10–20 nm, and an increase in crystal defect density was apparent with treatment time in the range of 10 s to 30 min. In contrast, alteration of the diamond surface terminations from oxygen to fluorine was found to be rather rapid, with saturation of the F/C atomic ratio estimated from XPS analysis after treatment durations of 1 min and more. The redox kinetics of Fe(CN)63−/4− was also found to be significantly modified after 10 s of CF4 plasma treatment. This behavior shows that C–F terminations predominantly affect the redox kinetics compared to the effect on the surface roughness and crystal defects. The double-layer capacitance (Cdl) of the electrolyte/CF4 plasma-treated boron-doped diamond interface was found to show a minimum value at 1 min of treatment. These results indicate that a short-duration CF4 plasma treatment is effective for the fabrication of fluorine-terminated diamond surfaces without undesirable surface damage. 相似文献
2.
3.
4.
Wakabayashi R. Kawakami H. Sato G. Amano T. Suzuki Y. 《Vehicular Technology, IEEE Transactions on》1998,47(2):392-405
A VHF omnidirectional radio range (VOR) is a navigation aid radio beacon facility, which provides aircraft with azimuth information relative to the VOR station in question as the origin. In Japan, two types of VOR-the conventional type (referred to as a CVOR) and the Doppler type (referred to as a DVOR)-are currently in use. An element known as the Alford loop antenna (ALA), which changes the loading reactance, is used for the VOR because the horizontally polarized wave and nondirectivity in the horizontal plane are preferred. A VOR antenna consists of a carrier antenna and a sideband antenna-an aircraft receives separate signals from these two antennas and compares them to obtain azimuth information. The mutual coupling between the elements forming the carrier and the sideband antenna affects the directivity of the single elements, resulting in errors in azimuth information. With the mutual coupling between the antenna elements being taken into consideration, a quantitative calculation was made by using the moment method-the results of the calculation made it clear that a loading reactance value of -320 Ω is better to make not mutually coupled elements nondirectional while a loading reactance value of -600 Ω is optimum to minimize the azimuth error of a CVOR 相似文献
5.
An outbreak of Cryptosporidiosis occurred over three months in a British Columbia community, peaking in December 1990. Results of the case-control study and illness surveys support the hypothesis that transmission occurred in a public children's pool at the local recreation centre. Analysis using lab-confirmed cases revealed a matched odds ratio of 4.5 [95% CI 0.97, 20.83], and using clinical cases an unmatched odds ratio of 12.8 [95% CI 3.68, 46.77], associated with swimming in the children's pool within two weeks prior to onset of illness. Other risk factors were not significant. Attack rates in various groups of children's pool users ranged from 8% to 78%. The children's pool was closed for steam cleaning and disinfection. Unusually frequent defecations including liquid stools had occurred before and during the outbreak. Improvements were instituted for removal of feces and superchlorination of pool water. 相似文献
6.
Hiroshi Ito Takehiko Ishiguro Tokutaro Komatsu Nozomu Matsukawa Gunzi Saito Hiroyuki Anzai 《Journal of Superconductivity and Novel Magnetism》1994,7(3):667-669
The superconducting transition of the organic compoundsκ-(BEDT-TTF)2 X is studied by resistive measurement in a magnetic field up to 10 T applied normal to the conducting plane. For the salts withX=Cu[N(CN)2]Br andX=CuCN[N(CN)2] the transition shows fanshaped broadening caused by superconductivity fluctuation. For theX=Cu(NCS)2 salt the resistivity shows a peak in the transition region in a magnetic field below 4 T.This phenomenon is suppressed in defect-reduced samples for intralayer conduction. We discuss this peak in relation to the thermal fluctuation on the Josephson junction structures in this salt. 相似文献
7.
We investigated Au catalysts supported on TiO2, Fe2O3, and ZnO for their preferential oxidation of CO in a H2-rich atmosphere. Both full conversion and selectivity were achieved over Au/Fe2O3 and Au/ZnO around room temperature, but at higher temperatures the CO conversion was suppressed due to competition between CO and H2. 相似文献
8.
Remarkably rapid nitriding which is independent of diffusion theory based on the thermal activation process, was observed during nitriding of austenitic Fe-Ni-Cr steels containing 16 and 19 mass% chromium. Increase of the chromium content in the alloys yielded increasing thickness of the nitrided layer, i.e. the internal nitriding theory did not hold in the nitriding. No rapid nitriding was observed in steels containing less than 13 mass% chromium. Hence the limiting concentration of chromium for the rapid nitriding will lie between 13 and 16 mass% chromium. A solution to the problem of abnormalities arising during nitriding of practical austenitic stainless steels which have been investigated since 1972, has been presented experimentally by nitriding various chromium-containing steels. Based on the experimental results, the origin of the rapid nitriding is discussed in connection with the free-energy function of Cr2N and CrN to temperature. In particular, a plateau of nitrogen concentration measured in the nitrided layers leads to the conclusion that a forced nitrogen diffusion in the layer resulted in the rapid nitriding. 相似文献
9.
Poly(L-ornithine)s having various azo-contents in the side chains were synthesized by the water-soluble carbodiimide procedure. The photochemical properties of the polypeptides poly[Nδ-p-(phenylazo)benzoyl-L-ornithine] (PPABLO) containing 3–77 mol% azobenzene were investigated by absorption and circular dichroism spectroscopy in hexafluoro-2-propanol (HFIP) or water, and in HFIP-water or methanol-water solvent mixtures. The photochromism of the dichroic bands of the PPABLOs containing 20–77 mol% azobenzene in the visible and ultraviolet wavelength regions was found to be mostly reversible as a function of irradiation time at different wavelengths due to the photostationary state (above 80% trans-cis photoisomerization) of the azo aromatic moieties. The PPABLO containing 3.2 mol% azobenzene in water exhibited conformational changes from random coil to helix by the addition of methanol or sodium dodecyl sulphate (SDS). The photo-induced conformational change was observed in HFIP-water-SDS solvent mixtures, while no conformational change was seen in water and HFIP-water solvent mixtures. 相似文献
10.