全文获取类型
收费全文 | 18428篇 |
免费 | 2500篇 |
国内免费 | 1576篇 |
专业分类
电工技术 | 1004篇 |
综合类 | 1242篇 |
化学工业 | 2980篇 |
金属工艺 | 1907篇 |
机械仪表 | 1596篇 |
建筑科学 | 1358篇 |
矿业工程 | 292篇 |
能源动力 | 812篇 |
轻工业 | 1280篇 |
水利工程 | 343篇 |
石油天然气 | 745篇 |
武器工业 | 23篇 |
无线电 | 1471篇 |
一般工业技术 | 2655篇 |
冶金工业 | 377篇 |
原子能技术 | 595篇 |
自动化技术 | 3824篇 |
出版年
2024年 | 133篇 |
2023年 | 554篇 |
2022年 | 1012篇 |
2021年 | 928篇 |
2020年 | 935篇 |
2019年 | 797篇 |
2018年 | 757篇 |
2017年 | 737篇 |
2016年 | 771篇 |
2015年 | 947篇 |
2014年 | 1419篇 |
2013年 | 1622篇 |
2012年 | 2020篇 |
2011年 | 2077篇 |
2010年 | 1524篇 |
2009年 | 1455篇 |
2008年 | 887篇 |
2007年 | 1097篇 |
2006年 | 865篇 |
2005年 | 342篇 |
2004年 | 184篇 |
2003年 | 138篇 |
2002年 | 153篇 |
2001年 | 126篇 |
2000年 | 104篇 |
1999年 | 128篇 |
1998年 | 60篇 |
1997年 | 46篇 |
1996年 | 56篇 |
1995年 | 38篇 |
1994年 | 41篇 |
1993年 | 47篇 |
1992年 | 43篇 |
1991年 | 41篇 |
1990年 | 35篇 |
1989年 | 20篇 |
1988年 | 65篇 |
1987年 | 102篇 |
1986年 | 109篇 |
1985年 | 25篇 |
1984年 | 16篇 |
1983年 | 17篇 |
1982年 | 5篇 |
1980年 | 8篇 |
1979年 | 4篇 |
1976年 | 2篇 |
1959年 | 9篇 |
1951年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Fine-grained few-shot learning is a difficult task in image classification. The reason is that the discriminative
features of fine-grained images are often located in local areas of the image, while most of the existing few-shotlearning image classification methods only use top-level features and adopt a single measure. In that way, the localfeatures of the sample cannot be learned well. In response to this problem, ensemble relation network with multi-level measure (ERN-MM) is proposed in this paper. It adds the relation modules in the shallow feature space tocompare the similarity between the samples in the local features, and finally integrates the similarity scores from thefeature spaces to assign the label of the query samples. So the proposed method ERN-MM can use local details andglobal information of different grains. Experimental results on different fine-grained datasets show that the proposedmethod achieves good classification performance and also proves its rationality. 相似文献
2.
Shuhai Liu Ming Han Xiaolong Feng Qiuhong Yu Long Gu Longfei Wang Yong Qin Zhong Lin Wang 《Advanced functional materials》2021,31(17):2010339
Utilizing inner-crystal piezoelectric polarization charges to control carrier transport across a metal-semiconductor or semiconductor–semiconductor interface, piezotronic effect has great potential applications in smart micro/nano-electromechanical system (MEMS/NEMS), human-machine interfacing, and nanorobotics. However, current research on piezotronics has mainly focused on systems with only one or rather limited interfaces. Here, the statistical piezotronic effect is reported in ZnO bulk composited of nanoplatelets, of which the strain/stress-induced piezo-potential at the crystals’ interfaces can effectively gate the electrical transport of ZnO bulk. It is a statistical phenomenon of piezotronic modification of large numbers of interfaces, and the crystal orientation of inner ZnO nanoplatelets strongly influence the transport property of ZnO bulk. With optimum preferred orientation of ZnO nanoplatelets, the bulk exhibits an increased conductivity with decreasing stress at a high pressure range of 200–400 MPa, which has not been observed previously in bulk. A maximum sensitivity of 1.149 µS m−1 MPa−1 and a corresponding gauge factor of 467–589 have been achieved. As a statistical phenomenon of many piezotronic interfaces modulation, the proposed statistical piezotronic effect extends the connotation of piezotronics and promotes its practical applications in intelligent sensing. 相似文献
3.
《International Journal of Hydrogen Energy》2022,47(49):21261-21272
Utilization of 3D nanostructured Pt cathodes could obviously improve performances of proton exchange membrane fuel cells (PEMFCs) owing to the reduced tortuosity and the bi-continuous nanoporous structure. However, these cathodes usually suffer from the flooding problem ascribed to the ionomer-free and nanoscale pores which are more susceptible to water condensation. In this paper, ultra-thin nanoporous metal films (100 nm) were utilized to construct PEMFC cathodes and independent transport channels were designed separately for water and gas aiming at the flooding problem. Nanoporous gold (NPG) film was used as the model support for loading Pt nanoparticles owing to its controllable and stable structure. After optimizing the polytetrafluoroethylene (PTFE) content and carbon loading in the gas diffusion layer (GDL), plasma treatment under O2 atmosphere was used to pattern the GDL with independent water transport channels. The obtained liquid permeation coefficients and oxygen gains demonstrated the obviously improved water and O2 transport. By using a home-made optimized GDL and a nanoporous film cathode with pore size ~60 nm, the flooding problem could be facilely solved. With a Pt loading of ~16 μg cm?2, this 3D nanostructured cathode exhibits a PEMFC performance of ~957 mW cm?2 at 80 °C. The Pt power efficiency is about 4 times higher than that of the commercial Pt/C cathode (50 μg cm?2, 756 mW cm?2). Obviously, this study provides a simple but effective methodology to solve the water flooding problem in the ultra-thin nanoporous film cathodes which is applicable for other types of 3D nanostructured PEMFC cathodes. 相似文献
4.
既有公共建筑能耗中,围护结构节能潜力巨大。以兰州某既有办公建筑为例,采用DeST-C软件模拟围护结构不同材料厚度、窗型,得出系列负荷,通过对数据分析、比较,得出如下结论:外墙外保温适宜材料为50mm的挤塑板,最大热负荷节能率为45.66%;屋面适宜保温材料为65mm的挤塑板,最大热负荷节能率为4.25%;外窗各个朝向全部更换玻璃,推荐选用内张膜中空玻璃(双膜),最大热负荷节能率为7.36%;单独更换南向外窗材料,推荐选用真空镀膜复合中空玻璃,最大热负荷节能率为1.78%。 相似文献
5.
6.
7.
The top illuminated organic photodetectors (OPDs) with a Dielectric/Metal/Dielectric (DMD) transparent anode are fabricated. The transparent electrode is composed of molybdenum trioxide (MoO3)/silver (Ag)/MoO3 layers and zinc oxide (ZnO)/aluminum (Al) is used for bottom cathode. The optimized DMD electrode has an optical transmittance of 85.7% at the wavelength of 546 nm and sheet resistance of ∼6 Ω/sq. The fabricated OPDs exhibit a high detectivity and wide range linearity. 相似文献
8.
9.
《Intermetallics》2015
An equiatomic CoCrFeNiMn high-entropy alloy was synthesized by mechanical alloying (MA) and spark plasma sintering (SPS). During MA, a solid solution with refined microstructure of 10 nm which consists of a FCC phase and a BCC phase was formed. After SPS consolidation, only one FCC phase can be detected in the HEA bulks. The as-sintered bulks exhibit high compressive strength of 1987 MPa. An interesting magnetic transition associated with the structure coarsening and phase transformation was observed during SPS process. 相似文献
10.
《Ceramics International》2022,48(4):5040-5053
Using tailings as material to prepare glass-ceramic is an excellent way to achieve the resource utilization of solid waste. However, at present, researches on the solidification and migration of heavy metals are limited. Therefore, in this study, ten groups of samples were prepared by controlling sintering temperatures. The solidification, migration, and leaching behavior of non-volatile and volatile heavy metals were studied. The research showed that, with the increase of temperature, the properties of the samples were improved. Fe participated in the phase transformation and evolved into insoluble iron pyroxenes solid solution, while Pb was homogeneously distributed in the glass matrix of glass-ceramics. The leaching concentrations of Fe and Pb in the glass-ceramics were 0.055 mg/L ~0.087 mg/L and 0.074 mg/L ~0.140 mg/L, which were far below the threshold value. The results showed that heavy metals can be effectively solidified in glass-ceramics and have good environmental benefits. 相似文献