全文获取类型
收费全文 | 4945篇 |
免费 | 243篇 |
国内免费 | 457篇 |
专业分类
电工技术 | 226篇 |
综合类 | 303篇 |
化学工业 | 691篇 |
金属工艺 | 332篇 |
机械仪表 | 267篇 |
建筑科学 | 292篇 |
矿业工程 | 159篇 |
能源动力 | 71篇 |
轻工业 | 330篇 |
水利工程 | 131篇 |
石油天然气 | 236篇 |
武器工业 | 28篇 |
无线电 | 534篇 |
一般工业技术 | 1362篇 |
冶金工业 | 145篇 |
原子能技术 | 97篇 |
自动化技术 | 441篇 |
出版年
2024年 | 68篇 |
2023年 | 195篇 |
2022年 | 264篇 |
2021年 | 313篇 |
2020年 | 165篇 |
2019年 | 196篇 |
2018年 | 168篇 |
2017年 | 93篇 |
2016年 | 109篇 |
2015年 | 146篇 |
2014年 | 183篇 |
2013年 | 184篇 |
2012年 | 481篇 |
2011年 | 598篇 |
2010年 | 216篇 |
2009年 | 194篇 |
2008年 | 407篇 |
2007年 | 304篇 |
2006年 | 295篇 |
2005年 | 215篇 |
2004年 | 137篇 |
2003年 | 77篇 |
2002年 | 99篇 |
2001年 | 91篇 |
2000年 | 66篇 |
1999年 | 72篇 |
1998年 | 56篇 |
1997年 | 60篇 |
1996年 | 54篇 |
1995年 | 38篇 |
1994年 | 26篇 |
1993年 | 9篇 |
1992年 | 18篇 |
1991年 | 7篇 |
1990年 | 5篇 |
1989年 | 6篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1986年 | 4篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 13篇 |
1981年 | 2篇 |
1965年 | 1篇 |
排序方式: 共有5645条查询结果,搜索用时 15 毫秒
41.
43.
目前,将信息科技融入机械专业课程建设中已成为机械专业学科的主要趋势,如何在机械专业基础课程教学中培养学生的理论知识和实际应用能力,并将信息化资源良好的利用在专业课程上,是当前机械类教育工作者面对的主要课题。本文通过分析机械专业的教学现状,从教学定位课程体系和学生素质能力培养等方面,提出了信息化资源在学科建设的实际应用问题,以确保机械专业教学面向实际、面向应用,服务于社会发展, 相似文献
44.
A hybrid multiphase model is developed to simulate the simultaneous momentum, heat and mass transfer and heterogeneous catalyzed reaction in structured catalytic porous materials. The approach relies on the combination of the volume of fluid (VOF) and Eulerian–Eulerian models, and several plug-in field functions. The VOF method is used to capture the gas–liquid interface motion, and the Eulerian–Eulerian framework solves the temperature and chemical species concentration equations for each phase. The self-defined field functions utilize a single-domain approach to overcome convergence difficulty when applying the hybrid multiphase for a multi-domain problem. The method is then applied to investigate selective removal of specific species in multicomponent reactive evaporation process. The results show that the coupling of catalytic reaction and interface species mass transfer at the phase interface is conditional, and the coupling of catalytic reaction and momentum transfer across fluid–porous interface significantly affects the conversion rate of reactants. Based on the numerical results, a strategy is proposed for matching solid catalyst with operating condition in catalytic distillation application. 相似文献
45.
Organic–inorganic halide perovskite solar cells(PSCs)have delivered power conversion efficiency(PCE)on par with that of crystalline silicon solar cells,due to the considerable effort on the optimization of perovskite materials and devices[1].The three-dimensional(3D)perovskite-based PSCs with the standard n–i–p architecture gave a certified PCE of25.5%[2].However,the poor device stability under operating conditions remains an obstacle to commercialization.The 3D hybrid perovskite materials are susceptible to oxygen,UV light,humidity,heat,and electric fields[3].To improve device stability,two main strategies are applied:(1)improving the intrinsic stability[4];(2)providing sufficient protection. 相似文献
46.
Jiandong Zhang Rui Dong Xiaoxiao Yang Lili Gao Chaofeng Zhang Fan Ren Jing Li Honghong Chang 《中国化学工程学报》2022,47(7):145-154
Enantiopure vicinal diols are important building blocks used in the synthesis of fine chemicals and pharmaceutical compounds. Diol dehydrogenase (DDH) mediated stereoselective oxidation of racemic vicinal is an efficient way to prepare enantiopure vicinal diols. In this study, four new bacterial DDHs (AnDDH from Anoxybacillus sp. P3H1B, HcDDH from Hazenella coriacea, GzDDH from Geobacillus zalihae and LwDDH from Leptotrichia wadei) were mined from the GenBank database and expressed in E. coli T7. The four DDHs were purified and biochemically characterized for oxidation activity toward (R)-1-phenyl-1,2-ethanediol, with the optimal reaction condition of pH9.0 (AnDDH), 10.0 (HcDDH) and 11.0 (GzDDH and LwDDH) and the temperatures at 40℃ (AnDDH), 50℃ (HcDDH) and 60℃ (GzDDH and LwDDH), respectively. The four enzymes were stable at the pH from 7.0 to 9.0 and below 40℃. Kinetic parameters of four DDHs showed that the HcDDH from Hazenella coriacea had high activity toward a broad range of vicinal diols. A series of racemic vicinal diols were successfully resolved by recombinant E. coli (HcDDH-NOX) resting cells co-expression of an NADH oxidase (NOX), affording (S)-diols and (1S, 2S)-trans-diols in ≥ 99% ee. The synthetic potential of HcDDH was proved by E. coli (HcDDH-NOX) via kinetic resolution of racemic trans-1,2-indandiol on a 100 ml scale reaction, (S, S)-trans-1,2-indandiol was prepared in 46.7% yield and >99% ee. In addition, asymmetric reduction of four α-hydroxy ketones (10-300 mmol·L-1) by E. coli (HcDDH-GDH) resting cells resulted in >99% ee and 69-98% yields of (R)-vicinal diols. The current research expands the toolbox of DDHs to synthesize chiral vicinal diols and demonstrated that the mined HcDDH is a potential enzyme in the synthesis of a broad range of chiral vicinal diols. 相似文献
47.
Mg-Zn-Nd alloy is a promising biodegradable metal material for surgical staples during the reconstruc-tion of digestive tract due to its good biocompatibility and suitable mechanical properties.However,its deformation property and corrosion resistance should be improved to make better safety and effective-ness of staples.In the present study,bi-direction drawing was adopted to maintain the initial texture characteristics,and improve mechanical property and corrosion resistance of Mg-2Zn-0.5Nd alloy.The results showed that the microstructure after bi-direction did not change too much,but the texture could maintain its initial characteristics.The ductility of the alloy with 60 % accumulative area reduction after bi-direction drawing was increased by 70 %,indicating that an outstanding deformation property of Mg-Zn-Nd alloy can be obtained by bi-direction drawing.The corrosion resistance was also improved after bi-direction drawing compared with that under single direction drawing. 相似文献
48.
Suisui Zhang Jingying Li Yan Nie Luyao Qiang Boyang Bai Zhiwei Peng Xiaoxun Ma 《中国化学工程学报》2022,42(2):236-244
HFC-134a is a widely used environment-friendly refrigerant. At present, China is the largest producer of HFC-134a in the world. The production of HFC-134a in China mainly adopts the calcium carbide acetylene route. However, the production route has high resource and energy consumption and large waste emission, and few of the studies addressed on the environmental performance of its production process. This study quantified the environmental performance of HFC-134a production by calcium carbide route via carrying out a life cycle assessment (LCA) using the CML 2001 method. And uncertainty analysis by Monte-Carlo simulation was also carried out. The results showed that electricity had the most impact on the environment, followed by steam, hydrogen fluoride and chlorine, and the impact of direct CO2 emissions in calcium carbide production stage on the global warming effect also could not be ignored. Therefore, the clean energy (e.g., wind, solar, biomass, and natural gas) was used to replace coal-based electricity and coal-fired steam in this study, showing considerable environmental benefits. At the same time, the use of advanced production technologies could also improve environmental benefits, and the environmental impact of the global warming category could be reduced by 4.1% via using CO2 capture and purification technology. The Chinese database of HFC-134a production established in this study provides convenience for the relevant study of scholars. For the production of HFC-134a, this study helps to better identify the specific environmental hotspots and proposes useful ways to improve the environmental benefits. 相似文献
49.
50.
正GB/T 3003-20061 Scope This standard specifies the terms,definitions,classifications,brands,technical requirements,test methods,quality appraisal procedure,packing,marking,transportation,storage and quality certificate of 相似文献