全文获取类型
收费全文 | 749篇 |
免费 | 31篇 |
国内免费 | 5篇 |
专业分类
电工技术 | 19篇 |
综合类 | 2篇 |
化学工业 | 252篇 |
金属工艺 | 20篇 |
机械仪表 | 15篇 |
建筑科学 | 11篇 |
矿业工程 | 1篇 |
能源动力 | 18篇 |
轻工业 | 29篇 |
石油天然气 | 2篇 |
无线电 | 67篇 |
一般工业技术 | 231篇 |
冶金工业 | 49篇 |
原子能技术 | 23篇 |
自动化技术 | 46篇 |
出版年
2023年 | 4篇 |
2022年 | 7篇 |
2021年 | 8篇 |
2020年 | 8篇 |
2019年 | 15篇 |
2018年 | 11篇 |
2017年 | 15篇 |
2016年 | 14篇 |
2015年 | 16篇 |
2014年 | 20篇 |
2013年 | 39篇 |
2012年 | 40篇 |
2011年 | 50篇 |
2010年 | 34篇 |
2009年 | 39篇 |
2008年 | 34篇 |
2007年 | 31篇 |
2006年 | 33篇 |
2005年 | 45篇 |
2004年 | 27篇 |
2003年 | 30篇 |
2002年 | 15篇 |
2001年 | 17篇 |
2000年 | 18篇 |
1999年 | 18篇 |
1998年 | 29篇 |
1997年 | 14篇 |
1996年 | 12篇 |
1995年 | 7篇 |
1994年 | 16篇 |
1993年 | 7篇 |
1992年 | 11篇 |
1991年 | 9篇 |
1990年 | 9篇 |
1989年 | 6篇 |
1988年 | 12篇 |
1987年 | 9篇 |
1986年 | 6篇 |
1985年 | 7篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 7篇 |
1981年 | 4篇 |
1980年 | 8篇 |
1979年 | 3篇 |
1978年 | 5篇 |
1977年 | 3篇 |
1974年 | 1篇 |
1969年 | 1篇 |
1968年 | 1篇 |
排序方式: 共有785条查询结果,搜索用时 0 毫秒
1.
A simple template‐free high‐temperature evaporation method was developed for the growth of crystalline Si microtubes for the first time. As‐grown Si microtubes were characterized using X‐ray diffraction, scanning electron microscopy, transmission electron microscopy, and room‐temperature photoluminescence. The lengths of the Si tubes can reach several hundreds of micrometers; some of them have lengths on the order of millimeters. Each tube has a uniform outer diameter along its entire length, and the typical outer diameter is ≈ 2–3 μm. Most of the tubes have a wall thickness of ≈ 400–500 nm, though a considerable number of them exhibit a very thin wall thickness of ≈ 50 nm. Room‐temperature photoluminescence measurement shows the as‐synthesized Si microtubes have two strong emission peaks centered at ≈ 589 nm and ≈ 617 nm and a weak emission peak centered at ≈ 455 nm. A possible mechanism for the formation of these Si tubes is proposed. We believe that the present discovery of the crystalline Si microtubes will promote further experimental studies on their physical properties and smart applications. 相似文献
2.
D. Golberg P.S. Dorozhkin Y. Bando M. Mitome C.C. Tang 《Diamond and Related Materials》2005,14(11-12):1857
Various multi-walled nanotubes in the B–C–N system are thoroughly investigated using a JEOL-3100FEF high-resolution field emission transmission electron microscope operating at 300 kV and equipped with an in-column built Omega filter. Spatially-resolved B, C and N elemental maps of the nanotubes are constructed. It is realized that a wide variety of tubular arrays composed of B, C and N atoms may exist in the system. Sandwich-like BN-rich and C-rich alternating tubular shells, graphitic C layers inside and outside of pure BN shells induced either by surface contamination, or electron beam irradiation, separation of C-rich and BN-rich tubes and/or BN particles within tubular bunches may take place. One should carefully take these effects into account while analyzing nanotube physical properties, e.g., electrical or optical, rather than simply rely on electron energy loss spectra typically collected from B, C and N containing nanostructures as a whole. Striking dependence of an individual nanotube electrical conductivity on tubular shell chemistry is demonstrated using I–V curve recording in an atomic force microscope. 相似文献
3.
Akihiko Sakurai Mina Masuda Mikio Sakakibara 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2003,78(9):952-958
The removal of phenol by peroxidase‐catalysed polymerization was examined using Coprinus cinereus peroxidase in the presence of surfactants. The non‐ionic surfactants with poly(oxyethene) residues, Triton X‐100, Triton X‐405 and Tween 20, enhanced the phenol removal efficiency at a level similar to high relative molecular mass poly(ethylene glycol) (relative molecular mass 3000). Although the improvement in the removal efficiency was less than that of Triton X‐100, Span 20, sodium lauryl sulfate (SDS) and lauryl trimethylammonium bromide (DTAB) also enhanced the removal efficiency. The requirement of the enzyme for almost 100% removal of 100 mg dm?3 phenol decreased to one‐fourth by the addition of 30 mg dm?3 Triton X‐100. Triton X‐100, Triton X‐405, Tween 20 and DTAB could reactivate the enzyme precipitated with the phenol polymer, leading to the restarting of the phenol removal reaction. Copyright © 2003 Society of Chemical Industry 相似文献
4.
Mikio Miyake Katsuyuki Takahashi Jun Higashine Masakatsu Nomura 《Fuel Processing Technology》1992,30(3):205-213
A series of mixtures of Japanese subbituminous Taiheiyo coal and Athabasca oil sand bitumen (AOB) with various coal concentrations (0–100 wt%) was coprocessed in a 70 ml autoclave at 420°C for 1 h in the presence of H2 (50 kg/cm2 at room temperature) and sulfided Ni---Mo/Al2O2 catalyst. The mixture containing 2 wt% coal produced the largest amount of hexane soluble fraction (HS) and the smallest amount of benzene insoluble fraction (BI). Thus, a synergistic liquid production occurred for this mixture with 2 wt% coal by suppressing the retrogressive reactions which proceeded for pure AOB. The HS obtained from mixtures with 2–30 wt% showed higher H/C ratios and lower heteroatom contents than those obtained from pure AOB and the mixtures with more than 30 wt% coal. The amounts of transferable hydrogen contained in the mixtures were estimated using anthracene as a hydrogen acceptor. The mixtures with 2–10 wt% coal contained higher amounts of donor hydrogen than pure AOB. The HS yield from the various mixtures was correlated with the amount of donor hydrogens contained in the mixtures, except for the mixture with 10 wt% coal. Thus, the important factor which results in synergism is suggested to be the amount of donor hydrogens contained in the feed mixtures. 相似文献
5.
UV-Vis spectroscopy was used to directly determine the concentration of Eu(Ⅱ) during electroreduction of Eu(Ⅲ) in hydrochloric acid medium. Electroreduction was carried out in a flow type electrolyzer with glassy carbon cathode at the constant potential of -800 mV vs. Ag/AgCl. The effects of oxygen and concentration of hydrochloric acid on the system were investigated. For 0.01 mol·L-1 hydrochloric acid, calibration curves for Eu(Ⅱ) absorption bands at 248 and 320 nm were constructed. Molar absorption coefficients were estimated to be 2016 and 648 L·mol-1·cm-1, respectively. The absorbance strongly decreased with decrease in pH of the solution, whereas concentration of chloride had only a negligible effect. 相似文献
6.
7.
Hydrogenation of four bituminous coals impregnated with 5 wt% of either mixtures of ZnCl2-MCln (CuCl, CrCl3 and MoCl5) systems or ZnCl2 was carried out using a batch autoclave system at 400° for 3 h at 9.8 MPa of initial hydrogen pressure. The ZnCl2-MoCl5 system showed the highest yield of the hexane-soluble (HS) fraction compared with the other systems irrespective of the coal used. The difference between the yields of HS fractions using the ZnCl2-MoCl5 and other systems was most marked for coals of fairly low volatile matter content, though the conversion was relatively low (47–66%), whilst for coals of high volatile matter content HS yields with the binary melt systems were high (86–91% conversion). Elemental analyses of the HS fractions indicated that the ZnCl2-MoCl5 system is most favourable in decreasing the average molecular weight and the heteroatom content of HS, this characteristic trend being confirmed also with five HS fractions separated by Chromatographic techniques. Both elemental analyses and molecular weights of asphaltene (benzene-soluble materials, BS) indicated that the ZnCl2-MoCl5 system is also most effective in cracking coal structure. 相似文献
8.
The electron-microscopic visualization of acrylic rubber dispersed in a heterogeneous structural resin composition consisting of a rubber-modified two-phase plastic comprising essentially a butyl acrylate rubber phase and an acrylonitrile–styrene copolymer phase, respectively, has been accomplished. This procedure consists of the following: The molded resin specimen is treated with hydrazine hydrate solution to produce the acrylic acid hydrazides. Allow the treated specimen to soak in osmium tetroxide solution. The acrylic rubber may be indirectly fixed and stained. Some micrographs of ultrathin sections of two or three resin compositions, cut by an ultramicrotome, are presented. 相似文献
9.
Noboru Hashimoto Yasushi Sawada Takashi Bando Hiroyoshi Yoden Shigehito Deki 《Journal of the American Ceramic Society》1991,74(6):1282-1286
AIN powder was synthesized from aluminum polynuclear complexes. Basic aluminum chloride and basic aluminum lactate were used as the aluminum polynuclear complexes. These starting materials and glucose were dissolved in water and mixed homogeneously. AIN powder was obtained by calcining after drying and precalcining at 800°C under nitrogen gas flow. Then excess carbon was removed by firing in air. Nitridation in the system was investigated and compared with that in the alumina–carbon black system. It was found that in our reaction system nitridation began and proceeded at lower calcination temperatures above 1200°C than in the alumina–carbon black system. Using aluminum polynuclear complexes, AIN was synthesized through the nitridation of γ-alumina and produced in a very fine and sharp particle size distribution. 相似文献
10.
Jingxian Zhang Mikio Iwasa Dongliang Jiang 《Journal of the American Ceramic Society》2005,88(4):1013-1016
It has been well accepted that polyethylene imine (PEI) is an effective dispersant for silicon carbide (SiC) in aqueous media. However, after the addition of sintering additives (Al2 O3 and Y2 O3 ), this dispersing effect is reduced significantly. In this work, a second dispersant, citric acid, was used to resolve this problem. It was found that citric acid could decrease the slurry viscosity (without sintering additives) and enhance the PEI adsorption on SiC particle surface. The optimal amount of citric acid required to achieve a minimum viscosity for 55 vol% SiC suspensions was equal to ∼0.87 wt% (at pH ∼6.8). With the aid of citric acid, well-stabilized SiC suspensions (containing sintering additives) were realized, which exhibited slight shear thinning rheologies. After tape casting and SPS sintering, dense SiC samples were obtained with a homogeneous fine-crystalline microstructure. Results showed that citric acid was an effective dispersant for improving the dispersion of SiC particles containing sintering additives. 相似文献