全文获取类型
收费全文 | 15894篇 |
免费 | 1375篇 |
国内免费 | 404篇 |
专业分类
电工技术 | 142篇 |
技术理论 | 1篇 |
综合类 | 388篇 |
化学工业 | 6446篇 |
金属工艺 | 841篇 |
机械仪表 | 359篇 |
建筑科学 | 175篇 |
矿业工程 | 334篇 |
能源动力 | 2643篇 |
轻工业 | 609篇 |
水利工程 | 26篇 |
石油天然气 | 407篇 |
武器工业 | 37篇 |
无线电 | 998篇 |
一般工业技术 | 2812篇 |
冶金工业 | 388篇 |
原子能技术 | 113篇 |
自动化技术 | 954篇 |
出版年
2024年 | 32篇 |
2023年 | 1113篇 |
2022年 | 527篇 |
2021年 | 594篇 |
2020年 | 1154篇 |
2019年 | 960篇 |
2018年 | 523篇 |
2017年 | 845篇 |
2016年 | 930篇 |
2015年 | 884篇 |
2014年 | 1163篇 |
2013年 | 1131篇 |
2012年 | 1032篇 |
2011年 | 808篇 |
2010年 | 735篇 |
2009年 | 728篇 |
2008年 | 362篇 |
2007年 | 787篇 |
2006年 | 803篇 |
2005年 | 417篇 |
2004年 | 212篇 |
2003年 | 260篇 |
2002年 | 298篇 |
2001年 | 297篇 |
2000年 | 142篇 |
1999年 | 207篇 |
1998年 | 99篇 |
1997年 | 45篇 |
1996年 | 91篇 |
1995年 | 79篇 |
1994年 | 58篇 |
1993年 | 53篇 |
1992年 | 41篇 |
1991年 | 50篇 |
1990年 | 48篇 |
1989年 | 64篇 |
1988年 | 79篇 |
1982年 | 8篇 |
1981年 | 2篇 |
1951年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 63 毫秒
21.
《Carbon》2015
Fe2O3 nanorod/carbon nanofiber (CNF) composites were prepared by the electrochemical deposition of Fe2O3 on a web of CNFs, which was then used as a free-standing anode. The conductive, three-dimensional structure of the CNF web allowed for the electrodeposition of the Fe2O3 nanorods, while its high conductivity made it possible to use the composite as a free-standing electrode in lithium-ion batteries. In addition, it was easy and cheap to fabricate by a simplification of a process of cell preparation. The nanorod-like Fe2O3 structures could only be electrodeposited on the CNFs; flake-like Fe2O3 was formed on flat conductive glass substrates. It can be attributed to the different growth mechanism of Fe2O3 on the CNFs because of the large number of reaction sites on the CNFs, differences in the precursor concentration and diffusivity within the CNF web. The formation of aggregates of the Fe2O3 particles on thicker CNFs also indicated that the CNFs had determined the Fe2O3 growth mechanism. The synthesised Fe2O3/CNF composite electrode exhibited stable rate capacities at different current densities. This suggested that CNF-based composite did not exhibit the intrinsic disadvantages of Fe2O3. Finally, carbon coatings were deposited on the Fe2O3/CNF composites to further improve their electronic conductivity and rate capability. 相似文献
22.
Huizhu Cai Bingbing Chen Xiao Zhang Yuchen Deng Dequan Xiao Ding Ma Chuan Shi 《Nano Research》2021,14(1):122-130
Over recent years,catalytic materials of Fe-N-C species have been recognized being active for oxygen reduction reaction(ORR).However,the identification of active site remains challenging as it generally involves a pyrolysis process and mixed components being obtained.Herein Fe3C/C and Fe2N/C samples were synthesized by temperature programmed reduction of Fe precursors in 15%CH4/H2and pure NH3,respectively.By acid leaching of Fe2N/C sample,only single sites of FeN4species were presented,providing an ideal model for identification of catalytic functions of the single sites of FeN4in ORR.A correlation was conducted between the concentration of FeⅡN4in low spin state by Mossbauer spectra and the kinetic current density at 0.8 V in alkaline media,and such a structure-performance correlation assures the catalytic roles of low spin FeⅡN4 species as highly active sites for the ORR. 相似文献
23.
《International Journal of Hydrogen Energy》2020,45(57):32856-32864
The electrode ionomer is a key factor that significantly affects the catalyst layer morphology and fuel cell performance. Herein, sulfonated poly(arylene ether sulfone)-based electrode ionomers with polymers of various molecular weights and alcohol/water mixtures were prepared, and those comprising the alcohol/water mixture showed a higher performance than the ones prepared using higher boiling solvents, such as dimethylacetamide; this is owing to the formation of the uniformly dispersed ionomer catalyst layer. The relation between ionomer molecular weight for the same polymer structure and the sulfonation degree was investigated. Because the chain length of polymer varies with molecular weight and chain entanglement degree, its molecular weight affects the electrode morphology. As the ionomer covered the catalyst, the agglomerates formed were of different morphologies according to their molecular weight, which could be deduced indirectly through dynamic light scattering and scanning electron microscopy. Additionally, the fuel cell performance was confirmed in the current-voltage curve. 相似文献
24.
《International Journal of Hydrogen Energy》2020,45(38):19720-19732
The need to reduce PEMFC systems cost as well as to increase their durability is crucial for their integration in various applications and especially for transport applications. A new simplified architecture of the anode circuit called Alternating Fuel Feeding (AFF) offers to reduce the development costs. Requiring a new stack concept, it combines the simplicity of Dead-End Anode (DEA) with the operation advantages of the hydrogen recirculation. The three architectures (DEA, recirculation and AFF) are compared in terms of performance on a 5-kW test bench in automotive conditions, through a sensitivity analysis. A gain of 17% on the system efficiency is observed when switching from DEA to AFF. Moreover, similar performances are obtained both for AFF and for recirculation after an accurate optimization of the AFF tuning parameters. Based on DoE data, a gain of 25% on the weight of the anodic line has been identified compared to pulsed ejector architecture and 43% with the classic recirculation architecture with blower only (Miraï). 相似文献
25.
26.
《Ceramics International》2020,46(12):20163-20172
A double-layer coating composed of MoSi2–SiO2–SiC/ZrB2–MoSi2–SiC was designed and successfully constructed by a novel combination of precursor pyrolysis assisted sintering and rapid sintering to improve the ablation resistance of SiOC ceramic modified carbon fiber needled felt preform composites (CSs). The ZrB2–MoSi2–SiC inner layer coating was in relatively uniform distribution in the zone of 0–3 mm from the surface of CSs through the slurry/precursor infiltration in vacuum and SiOC precursor pyrolysis assisted sintering, which played a predominant role in improving oxidation and ablation resistance and maintaining the morphology of CSs. The MoSi2–SiO2–SiC outer layer coating was prepared by the spray and rapid sintering to further protect CSs from high-temperature oxidation. The ablation resistance of CSs coated with double-layer coating was evaluated by an oxygen-acetylene ablation test under the temperature of 1600–1800 °C with different ablation time of 1000 and 1500 s. The results revealed that the mass recession rates increased with the rise of ablation temperature and extension of ablation time, ranging from 0.47 g/(m2·s) to 0.98 g/(m2·s) at 1600–1800 °C for 1000 s and from 0.72 g/(m2·s) to 0.86 g/(m2·s) for 1000–1500 s at 1700 °C, while the linear recession rates showed negative values at 1700 °C due to the formation of oxides, such as SiO2 and ZrO2. The ablation mechanism of the double-layer coating was analyzed and found that a SiO2–ZrO2–Mo4.8Si3C0.6 oxidation protection barrier would be formed during the ablation process to prevent the oxygen diffusion into the interior CSs, and this study provided a novel and effective way to fabricate high-temperature oxidation protective and ablation resistant coating. 相似文献
27.
《Journal of the European Ceramic Society》2020,40(8):2896-2906
The brittleness of MoSi2 ceramic and the thermal mismatch between MoSi2 coating and C / C composite lead to brittle cracking of the coating at 900−1200 °C. This problem has been overcome in this studyby introducing submicron-SiB6 into the coating. The pre-fabricated cracks and a kinetics model of hot-pressed SiB6-MoSi2 ceramic could quantitatively predict the glass growth and crack healing. As expected, enhancing temperature and SiB6 content increased the growth rate of the borosilicate glass and the crack healing ability of MoSi2 ceramic, which was ascribed to the lower oxidation activation energy and larger specific surface area of submicron-SiB6. For the plasma sprayed coating, SiB6 with submicron structure was benefit for cracking inhibition and formation of borosilicate glass during oxidation, reducing the oxygen permeability and the consumption of inner coating. Hence, the 15 % SiB6-MoSi2 coatings raised the protection times to 84 and 120 h at 900 and 1200 °C respectively, presenting favorable oxidation protective performance. 相似文献
28.
29.
The results of formation of the high density effective scintillation ceramics consisting of two compounds of the cubic symmetry, LuAG:Ce and Lu2O3 (LuAG:Ce + Lu2O3), are described. Powders of a novel material LuAG:Ce + Lu2O3 were synthesized by co-precipitation method. The introduction of Lu2O3 into LuAG:Ce was shown to increase the density of the ceramics obtained and modify its scintillation properties. 相似文献
30.
Surface-modified δ-MnO2 with a hierarchical structure was synthesized via a hydrothermal redox reaction between toluene and KMnO4. Toluene is oxidized to produce benzoic acid which rapidly adsorbs onto the surface of δ-MnO2. The δ-MnO2 sample prepared with toluene exhibited a much higher catalytic activity for the Fenton-like oxidation of methylene blue in aqueous solution than that prepared without toluene. The enhanced catalytic activity might be attributed to the surface-bound persistent free radicals produced from the electron transfer from the adsorbed C6H5–COO− to Mn(IV). 相似文献