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71.
Aqueous suspension of carbon nanotubes via non-covalent functionalization with oligothiophene-terminated poly(ethylene glycol) 总被引:1,自引:0,他引:1
A new polymeric amphiphilic molecule for dispersing carbon nanotubes (CNTs) in water, oligothiophene-terminated poly(ethylene glycol) (TN-PEG), was synthesized and its ability to stabilize aqueous CNT dispersions was examined by UV-Vis spectroscopy and transmission electron microscopy. It was observed that the TN-PEGs were strongly adsorbed onto the nanotube surface via a strong π-π interaction, and thus only gentle sonication causes exfoliation of CNT ropes and bundles into well-separated individual objects and small bundles comprising 2-10 tubes. The dispersion ability of the TN-PEGs and the long-term stability of their resulting dispersions were much better than commercial surfactants. 相似文献
72.
In an online data stream, the composition and distribution of the data may change over time, which is a phenomenon known as concept drift. The occurrence of concept drift can affect considerably the performance of a data stream mining method, especially in relation to mining accuracy. In this paper, we study the problem of mining frequent patterns from transactional data streams in the presence of concept drift, considering the important issue of mining accuracy preservation. In terms of frequent-pattern mining, we give the definitions of concept and concept drift with respect to streaming data; moreover, we present a categorization for concept drift. The concept of streaming data is considered the relationships of frequency between different patterns. Accordingly, we devise approaches to describe the concept concretely and to learn the concept through frequency relationship modeling. Based on concept learning, we propose a method of support approximation for discovering data stream frequent patterns. Our analyses and experimental results have shown that in several studied cases of concept drift, the proposed method not only performs efficiently in terms of time and memory but also preserves mining accuracy well on concept-drifting data streams. 相似文献
73.
Amide‐Catalyzed Phase‐Selective Crystallization Reduces Defect Density in Wide‐Bandgap Perovskites 下载免费PDF全文
Junghwan Kim Makhsud I. Saidaminov Hairen Tan Yicheng Zhao Younghoon Kim Jongmin Choi Jea Woong Jo James Fan Rafael Quintero‐Bermudez Zhenyu Yang Li Na Quan Mingyang Wei Oleksandr Voznyy Edward H. Sargent 《Advanced materials (Deerfield Beach, Fla.)》2018,30(13)
Wide‐bandgap (WBG) formamidinium–cesium (FA‐Cs) lead iodide–bromide mixed perovskites are promising materials for front cells well‐matched with crystalline silicon to form tandem solar cells. They offer avenues to augment the performance of widely deployed commercial solar cells. However, phase instability, high open‐circuit voltage (Voc) deficit, and large hysteresis limit this otherwise promising technology. Here, by controlling the crystallization of FA‐Cs WBG perovskite with the aid of a formamide cosolvent, light‐induced phase segregation and hysteresis in perovskite solar cells are suppressed. The highly polar solvent additive formamide induces direct formation of the black perovskite phase, bypassing the yellow phases, thereby reducing the density of defects in films. As a result, the optimized WBG perovskite solar cells (PSCs) (Eg ≈ 1.75 eV) exhibit a high Voc of 1.23 V, reduced hysteresis, and a power conversion efficiency (PCE) of 17.8%. A PCE of 15.2% on 1.1 cm2 solar cells, the highest among the reported efficiencies for large‐area PSCs having this bandgap is also demonstrated. These perovskites show excellent phase stability and thermal stability, as well as long‐term air stability. They maintain ≈95% of their initial PCE after 1300 h of storage in dry air without encapsulation. 相似文献
74.
Byung-Soon Chun Dong Hyun Lee Norman Epstein John R. Grace Ah-Hyung Alissa Park Sang Done Kim Jea Keun Lee 《Chemical engineering science》2011,66(14):3180
Water fluidization in a 210 mm diameter semi-cylindrical acrylic column of a binary solids mixture of 3.2 mm polymer beads (ρs=1280 kg/m3) and 0.385 mm glass beads (ρs=2500 kg/m3) at superficial liquid velocities from 18.1 to 43.1 mm/s is shown to generate layer inversion at a superficial liquid velocity, UL, of 33.1 mm/s. Introduction of air with a superficial velocity, Ug, of 1.92 mm/s yielded a layer inversion velocity at UL=30.4 mm/s. The latter is explainable if it is assumed that the determinant of layer inversion is the interstitial liquid velocity and that therefore the main function of the gas in this respect is to occupy space.Mixing of the binary solids, as quantified by a mixing index applied to measured particle compositions at different levels of the fluidized bed, is shown to be greatest at the layer inversion velocity for liquid fluidization and, in general, to increase as co-current gas flow increases at a fixed value of UL. 相似文献
75.
Sang Won Lee Chan Hee Park Jea Keun Hong Jong-Taek Yeom 《Metallurgical and Materials Transactions A》2018,49(12):5913-5918
The mechanism by which α″-martensite decomposes in Ti-4Al-4Fe-0.25Si-0.1O alloy is found to change depending on the aging temperature, with Fe-rich α first transforming in twins of α″-martensite. As the aging temperature increases, Fe is segregated at the boundaries between α″ and α. At temperatures >?773 K, the Fe-segregated boundaries provide a nucleation site for B2-structured TiFe intermetallic compounds. This process of α″-martensite decomposition is described as follows: α″?+?α″Twin?→?α″Fe-rich?+?αFe-rich,V1?→?αFe-lean,V2?+?αFe-lean,V1?+?TiFe. 相似文献