全文获取类型
收费全文 | 1875篇 |
免费 | 194篇 |
国内免费 | 77篇 |
专业分类
电工技术 | 48篇 |
综合类 | 92篇 |
化学工业 | 465篇 |
金属工艺 | 70篇 |
机械仪表 | 88篇 |
建筑科学 | 63篇 |
矿业工程 | 24篇 |
能源动力 | 109篇 |
轻工业 | 168篇 |
水利工程 | 39篇 |
石油天然气 | 13篇 |
武器工业 | 5篇 |
无线电 | 194篇 |
一般工业技术 | 230篇 |
冶金工业 | 19篇 |
原子能技术 | 2篇 |
自动化技术 | 517篇 |
出版年
2024年 | 4篇 |
2023年 | 95篇 |
2022年 | 57篇 |
2021年 | 98篇 |
2020年 | 85篇 |
2019年 | 77篇 |
2018年 | 54篇 |
2017年 | 92篇 |
2016年 | 101篇 |
2015年 | 85篇 |
2014年 | 95篇 |
2013年 | 118篇 |
2012年 | 179篇 |
2011年 | 194篇 |
2010年 | 181篇 |
2009年 | 173篇 |
2008年 | 110篇 |
2007年 | 111篇 |
2006年 | 101篇 |
2005年 | 37篇 |
2004年 | 23篇 |
2003年 | 14篇 |
2002年 | 13篇 |
2001年 | 16篇 |
2000年 | 8篇 |
1999年 | 10篇 |
1998年 | 7篇 |
1997年 | 5篇 |
1996年 | 3篇 |
排序方式: 共有2146条查询结果,搜索用时 31 毫秒
71.
The multistage hybrid flow shop (HFS) scheduling problems are considered in this paper. Hybrid flowshop scheduling problems were proved to be NP-hard. A recently developed cuckoo search (CS) metaheuristic algorithm is presented in this paper to minimize the makespan for the HFS scheduling problems. A constructive heuristic called NEH heuristic is incorporated with the initial solutions to obtain the optimal or near optimal solutions rapidly in the improved cuckoo search (ICS) algorithm. The proposed algorithm is validated with the data from a leading furniture manufacturing company. Computational results show that the ICS algorithm outperforms many other metaheuristics. 相似文献
72.
This research is a response to the universal use of social media by students for academic-related purposes. It bridges a gap in knowledge in relation to the value and use of social media as effective teaching and learning tool in higher education in developing countries. A pre-tested questionnaire survey was self-administered to faculty members in the eight public Egyptian higher institutions offering tourism and hotel management programs. The results showed that social media have a great value for academic-related purposes, particularly as teaching and learning tool; however, the actual use by faculty was at a minimal level. In-depth interviews were conducted to identify the perils, barriers and concerns for the minimal use. Several barriers were identified with some specific to developing countries' context. Nonetheless, there was consensus by faculty that if these barriers were overcome, social media could be developed as an innovative and effective tool for teaching and learning. Implications for researchers and policy makers are discussed. 相似文献
73.
AbstractThis review collects recent five-year publications on low bandgap semiconducting polymers, which are composed of electron donor (D) and electron acceptor (A) units, exhibiting the power conversion efficiency (PCE) higher than 6%. When the photovoltaic performances of different types of D−A semiconducting copolymers are compared after the copolymers are classified into several categories according to the type of A-units, it is realized that diketopyrrolopyrrole (DPP)-based copolymers exhibit high JSCs owing to low bandgaps and low VOCs due to high-lying HOMO levels, while thienopyrroledione (TPD)-based copolymers exhibit high VOCs due to their deep HOMO levels and low JSCs because of wide bandgaps. Benzothiadiazole- and thienothiophene-based copolymers show intermediate values of VOC and JSC between DPP- and TPD-based ones. For further enhancement of photovoltaic performance, DPP-based copolymers may be designed to have deeper HOMO level with the minimum widening of bandgap while TPD-based polymers may be designed to have lower bandgap with the minimum rise of HOMO level. Hence, the energy level tuning must be considered so as to minimize the adverse effect. 相似文献
74.
Mobile phone technology is thought to have developed in huge demand in the next few years, it exists. 5 G and related techniques, better data transmission rates, improved productivity, low latency, and high-quality services such as a number of major goals, can be solved. To analyze the cultural characteristics of the performance, explaining the characteristics of thinking of positioning principles and modern clothing brand. From the perspective of expressionism and print advertising, literary support, case studies and image analysis, Self-Organizing Map (SOM) network training analysis, summarizing the relationship with the method of painting, the influence of expressionism Conceptual picture summaries, modes, compositions and colors are represented in recent international clothing brand print advertisements. Evaluated and suitable for communication methods such as discontinuous carrier aggregation, centralized processing, and 5 G waveform coexistence Field Programmable Gate Array (FPGA) baseband processing architecture. Cost-effectiveness, and support for5G waveform candidates. Design details, key technologies, and how to actually implement a smart clothing system. A typical application for smart clothing. It still highlights some design challenges and open issues that need to be addressed to make smart clothes for a wide range of applications. 相似文献
75.
Hong Fang Lihai Wang Weijie Kuai Juan Du Guicheng Jiang Xiaoyan Lu Minglei Zhao Chunming Wang Wenbin Su Limei Zheng Chunying Wang Chunlei Wang 《Journal of the American Ceramic Society》2020,103(5):3257-3264
Domain wall motions mainly affect all kinds of properties of ferroelectric materials, such as piezoelectricity, dielectric response, and mechanical loss, and the extrinsic contributions associated with domain wall motions have always been an important issue. In this study, the reversible and irreversible extrinsic contributions to the dielectric properties of [011]C-oriented 0.27Pb(In1/2Nb1/2)O3-0.46Pb(Mg1/3Nb2/3)O3-0.27PbTiO3:Mn single crystals have been extracted by the Rayleigh analysis. We found that in the unpoled samples, the extrinsic contributions of reversible and irreversible domain wall motions to dielectric properties significantly reduced, whereas after poling, only the irreversible extrinsic contribution decreased. The pinning effect in the 2R domain structure is much weaker than that in the 4R domain structure, leading to the low enhancement of Qm and a slight decrease in piezoelectricity caused by acceptor doping in 2R domain structure. This study explores the domain wall dynamics of acceptor-doped single crystals and mainly guides on further performance optimization in PbTiO3-based relaxor single crystals. 相似文献
76.
《International Journal of Hydrogen Energy》2021,46(55):28043-28052
Constructing heterojunction structure is a feasible way to realize an efficient and durable photocatalysts. Herein, a novel Z-scheme zero/three dimensional (0D/3D) ZnIn2S4/Ag6Si2O7 (ZIS/ASO) composite was rationally designed, synthesized and analyzed. ZIS/ASO composite possesses a layer structure for increasing light response, a special 0D/3D structure for reducing the photo-induce carriers migration path, and numerous active sites for absorbing H2O and producing H2. This composite retains the high oxidation and reduction ability by facilitating separation and migration as well as limiting recombination of photo-induced carriers via the intimate interface between ZIS and ASO. Undoubtedly, the synthesized ZIS/ASO photocatalyst achieved a high photocatalytic H2 activity, and the optimum sample shows a satisfactory H2 evolution rate of 590.56 μmol g−1 h−1, distinctly better than that of pure ZIS. More importantly, this composite exhibits high stability and recyclability and is expected to be applied in practical application. Based on the H2 evolution experimental results and electrochemical tests, the Z-scheme heterostructure construction of the composite was confirmed. This work expects to inspire a unique protocol for synthesizing Z-scheme photocatalysts for water splitting under visible light irradiation. 相似文献
77.
《Ceramics International》2016,42(9):10593-10598
The optimized sintering conditions for a 3.5 wt% magnesia partially stabilized zirconia (Mg-PSZ) refractory were proposed in our recent research. The influence of the sintering temperature on the development of phase composition, microstructure, densification, thermal expansion and mechanical strength was studied in detail by X-ray diffraction (XRD), scanning electron microscope (SEM), He-pycnometer, high temperature dilatometry and three-point bending test. The samples sintered at 1670 °C had the highest bend strength, the maximum densification, the lowest thermal expansion coefficient (CTE), a homogeneous microstructure and a linear change in thermal expansion. 相似文献
78.
《International Journal of Hydrogen Energy》2022,47(17):9895-9904
Exploiting efficient catalysts is of interest for solar-driven water splitting. Herein, a novel NiWO4/CdS nanosheets-on-nanorods direct Z-Scheme heterostructure was developed by using a facile in-situ approach. The optimized NiWO4/CdS heterostructure shows a H2 evolution rate of 26.43 mmol g?1 h?1 exceeding that of bare CdS by more than 75 folds. Systematic investigations reveal the nanostructures with numerous active sites, intimate contact interface, and enhanced charge separation rate synergistically account for the outstanding performance of the NiWO4/CdS. Moreover, the band structures were detailedly analyzed and the tentative photocatalytic mechanism was proposed, which could contribute to deeply understanding the catalytic process and guide the synthesis of the efficient heterostructure. These findings and strategies may have great significance in promoting the development of highly efficient and low-cost photocatalysts. 相似文献
79.
80.
Utilising logging residues (termed brash in the UK) for energy production has become a focus for energy providers since the development of specialist baling machinery to improve the logistical and financial potential of this material. To explore a farm-scale operations scenario, brash from a mixed conifer, temperate zone forest was baled and chipped with commercial machinery to produce fuel-grade woodchip. Clear-fell logging procedures presented a range of brash configurations to facilitate baling machinery to produce compacted, tied, regular sized bales. Average hourly bale production and fresh weight tonnage output was 28 ± 2 bales/h and 12.4 t/h respectively. Extraction of bales and stacking along access road verges achieved an average 24 ± 2 bales/h. Woodchipping output averaged 11.8, 13.7 and 13.0 green t/h respectively for whole bale, log only and bale-log composite woodchip. Chipping production efficiency was affected by bale condition, handling and machinery performance but chiefly by site transport accessibility and logistical planning. The average total cost of in-farm delivered fuel quality woodchip product from brash bales was £25.22 (€29.67) per green tonne. Brash bale chips contained more than double the percentage of fines <6.3 mm compared to round log woodchips and also had significantly higher gross energy and nutrients content. Brash bale moisture content was observed to fluctuate widely and nutrients and energy content reduced during the 3-yr monitoring period. In conclusion, the combination of equipment and the confined production scenario was a viable process that provided fuel-grade woodchip at relatively low cost. 相似文献