首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:从到   被引次数:从到   他引次数:从到 提示：输入*表示无穷大
全文获取类型
  收费全文   1293篇
  免费   25篇
  国内免费   13篇
专业分类
电工技术   2篇
综合类   17篇
化学工业   391篇
金属工艺   58篇
机械仪表   24篇
建筑科学   44篇
矿业工程   95篇
能源动力   271篇
轻工业   27篇
水利工程   10篇
石油天然气   8篇
无线电   35篇
一般工业技术   232篇
冶金工业   63篇
原子能技术   13篇
自动化技术   41篇
出版年
  2024年   32篇
  2023年   133篇
  2022年   45篇
  2021年   43篇
  2020年   129篇
  2019年   122篇
  2018年   25篇
  2017年   36篇
  2016年   38篇
  2015年   53篇
  2014年   65篇
  2013年   48篇
  2012年   16篇
  2011年   15篇
  2010年   34篇
  2009年   43篇
  2008年   7篇
  2007年   32篇
  2006年   37篇
  2005年   24篇
  2004年   16篇
  2003年   27篇
  2002年   26篇
  2001年   15篇
  2000年   14篇
  1999年   22篇
  1998年   11篇
  1996年   12篇
  1995年   12篇
  1994年   7篇
  1993年   7篇
  1992年   6篇
  1991年   5篇
  1990年   6篇
  1988年   11篇
  1987年   34篇
  1986年   29篇
  1985年   4篇
  1984年   6篇
  1983年   4篇
  1979年   6篇
  1976年   4篇
  1975年   7篇
  1974年   11篇
  1973年   4篇
  1972年   4篇
  1971年   6篇
  1967年   4篇
  1966年   6篇
  1964年   4篇
排序方式： 共有1331条查询结果，搜索用时 0 毫秒
101.
    
The alkylation of benzene with long chain α-olefins is a crucial process in the production of fine chemicals, which requires the upgrading from traditional homogeneous catalysis to heterogeneous catalysis involving zeolites. However, the application of zeolite catalysts has been limited by their fast deactivation due to constrained diffusion resulting from the sole micropores. To address this challenge, a desilication and secondary-crystallization strategy has been employed to fabricate hierarchically structured mesoporous Beta zeolites. The resultant mesoporous Beta zeolites demonstrate excellent catalytic activity and stability in the alkylation of benzene with 1-dodecene, arising from the exposed acid sites and enhanced internal diffusion. Importantly, the internal diffusion limitations for these mesopore Beta zeolites are negligible, which significantly extends their lifetime and improves their regeneration performance. To achieve these benefits, the degree of mesopores must be deliberately controlled. Overall, this approach provides a promising solution for achieving efficient and environmentally friendly alkylation processes.  相似文献   
102.
    
A rapid and low-cost carbon/carbon (C/C) composites preparation method is proposed: graphite prepreg-coated carbon fiber fabric (CFF) is formed by hot pressing, followed by hot isostatic pressing and high temperature graphitization, to prepare C/C composite with low porosity and high crystallinity. In this method, the carbon fiber (CF) mass fraction can be precisely regulated in the range of 40–95% by the impregnation process conditions of CFF in graphite prepreg. The graphite particles in the preform were graphitized and bonded with CFF by high temperature graphitization. Finally, a ZrO2 anti-ablative layer was applied using sol-gel method. The results show that when the CF mass fraction is 50%, the C/C composite with a crystallinity of 92.21 and a porosity of 3.47% can be obtained, with mass ablation rate of 0.23 mg/s and density of 1.62 g/m3. The method can prepare C/C composites with uniform density and high ablation resistance.  相似文献   
103.
    
Ultrasmall mesoporous nanoparticles (<50 nm), a unique porous nanomaterial, have been widely studied in many fields in the last decade owing to the abundant advantages, involving rich mesopores, low density, high surface area, numerous reaction sites, large cavity space, ultrasmall size, etc. This paper presents a review of recent advances in the preparation, functionalization, and applications of ultrasmall inorganic mesoporous nanoparticles for the first time. The soft monomicelles-directed method, in contrast to the hard-template and template-free methods, is more flexible in the synthesis of mesoporous nanoparticles. This is because the amphiphilic micelle has tunable functional blocks, controlled molecule masses, configurations and mesostructures. Focus on the soft micelle directing method, monomicelles could be classified into four types, i.e., the Pluronic-type block copolymer monomicelles, laboratory-synthesized amphiphilic block copolymers monomicelles, the single-molecule star-shaped block copolymer monomicelles, and the small-molecule anionic/cationic surfactant monomicelles. This paper also reviews the functionalization of the inner mesopores and the outer surfaces, which includes constructing the yolkshell structures (encapsulated nanoparticles), anchoring the active components packed on the shell and building an asymmetric Janus architecture. Then, several representative applications, involving catalysis, energy storage, and biomedicines are presented. Finally, the prospects and challenges of controlled synthesis and large-scale applications of ultrasmall mesoporous nanoparticles in the future are foreseen.  相似文献   
104.
    
Two-dimensional molybdenum carbide (2D-Mo2C) is thought to be promising for catalytic hydrogenation of CO2 to CH4, but little is known about its catalytic reaction mechanism. In this work, we investigate the hydrogenation of CO2 to CH4 on 2D-Mo2C using density functional theory. Our calculations show that Mo on the surface can efficiently decompose CO2 to CO and O, and also H2 to H. The hydrogenation of CO produces CHO that is readily deoxygenated to CH, and CH is selectively hydrogenated to produce CH4. Interestingly, the embedded Ir1 on 2D-Mo2C can act as a single-atom promoter to improve the performance of CO2 methanation, while on the other hand maintaining its high selectivity for CH4. This work provides insight into the mechanism of 2D-Mo2C-catalyzed CO2 methanation reactions and suggests a strategy to improve the performance of such catalysts through single-atom promoters.  相似文献   
105.
Construction of composite metal interfaces with synergistic catalysis is an important research field for CO preferential oxidation in H2 steam (CO-PROX). Microwave electromagnetic loss can effectively compensate the thermal action on the active interface derived from metal-organic frameworks (MOFs). Herein, a trimetallic CuCoCe-MOF is derived to construct Cu–Co–Ce oxidation active interface oriented by magnetic, conduction and relaxation loss, which inhibit the high temperature deactivation due to sintering. Equipped with the tandem microwave pyrolysis, the intermediate CuCoCe/C fully exposes electromagnetic characteristic and heterogeneous interfaces. Subsequently, microwave strengthened CuCoCeOx exhibits an excellent CO-PROX activity window with the more than 85% CO conversion within 80–210 °C. Besides, in-situ Raman and in-situ DRIFTs investigations demonstrate that the equilibrium of active interfacial oxygen vacancy via hydrogen is crucial for the temperature window broadening of CO-PROX. This work provides a route for the efficient conversion of microwave electromagnetic energy to enhance the active interface for synergistic catalysis.  相似文献   
106.
    
In this work, the photocatalysts containing oxygen-deficient molybdenum oxide and macroscopic three-dimensional porous graphitic carbon nitride phase composite (MoO3-x/PCN) were prepared by in situ self-assembly method. The crystal phase and structure were characterized by XRD, XPS, FT-IR, SEM, and TEM measurements. Hydrogen production results showed that introducing of MoO3-x resulted in a higher hydrogen production rate of MoO3-x/PCN composite catalyst than that of PCN. Among them, the highest hydrogen production rate of 2336.15 μmol g−1 h−1 was achieved for MoO3-x-10/PCN, which was 2.23 times higher than PCN (1048.00 μmol g−1 h−1). When the reaction system temperature was 100 °C, the photothermal hydrogen production rate of MoO3-x-10/PCN was 8902.00 μmol g−1 h−1, which was 3.81 times higher than that at room temperature. PL spectra, UV–vis spectra and photoelectrochemical measurements showed that the localized surface plasmon resonance (LSPR) effect of MoO3-x effectively enhanced the photo response range and increased the temperature of the reaction system. ESR measurements showed that he composites should follow the Z-scheme charge transfer mechanism, the electrons in the CB of MoO3-x further migrate to the VB of PCN, which hinders the charge complexation in MoO3-x and PCN, improving the hydrogen production activity. This study provides a new idea for constructing a plasma-based photothermal synergistic catalytic hydrogen production strategy.  相似文献   
107.
To improve the DRM reaction performance of the catalysts, a series of Co–Ni/WC-AC catalysts are prepared by impregnation using WC-AC as the support. The structural features of the fresh and spent catalysts are characterized by BET, XRD, H2-TPR, XPS and TG. The results show that the introduction of Ni in the 20Co/WC-AC catalyst promotes the conversion of W species to WC. Further, WC enhances the interaction between the active metal and the support. Thus, the activity and sintering resistance of Co–Ni/WC-AC catalysts are improved. It is also found that the introduction of different ratios of Ni has a significant effect on the chemical environment (oxygen environment) on the catalyst surface.10Co–10Ni/WC-AC catalysts showed high surface Oα and Oβ contents of 26% and 53%, respectively. The catalyst shows excellent catalytic performance. The conversion of CH4 and CO2 is stable at about 84% and 85% at 800 °C.  相似文献   
108.
    
This study aimed to synthesize an iron (II) oxide-zinc oxide (Fe2O3/ZnO) nanocomposite using eco-friendly methods and to evaluate its performance as a catalyst against textile dyes and hydrogen generation. To these means, Fe2O3/ZnO was synthesized from the Thymus vulgaris plant by biogenic methods. The resulting nanocomposite was characterized by Fourier Transmission Infrared Spectroscopy, Transmission Electron Microscopy (TEM), UV–vis spectrometry, and X-Ray diffraction patterns (XRD). According to the obtained TEM characterization results, it was observed that the nanocomposite had an average size of 3.78 nm. According to the XRD results, the nanocomposite's average crystal size was 3.884 nm. In addition, the hydrogen release was investigated by NaBH4 hydrolysis. The turnover frequency, activation energy (Ea), entropy (ΔS), and enthalpy (ΔH) values obtained from hydrogen production studies are 1942.23 h−1 and 15.68 kJ/mol, −127.29 J/mol K, and 13.14 kJ/mol, respectively. In the reusability tests, it was observed that the nanocomposite was 78% effective. The photocatalytic studies using solar energy revealed that the nanocomposite was 79% effective for methylene blue (MB) dye removal. This work demonstrated the potential of transition metals for energy production. It showed that the developed nanocomposite could be a viable solution and, with further development, can be an efficient catalyst for alternative energy production (energy generation) and textile industry wastewater treatment.  相似文献   
109.
    
Stainless steels play an extremely vital role in the field of marine engineering equipment. However, stainless steel products in service are still subject to corrosion from severe environments such as alternating dry/wet condition and damage caused by hydrogen introduced during heat treatment or cathodic protection. Under alternating dry/wet marine environment, the synergistic effect of hydrogen and corrosion can influence the corrosion resistance of stainless steels dramatically. In this work, the corrosion behavior and mechanism of 2205 duplex stainless steel under alternating dry/wet marine environment are investigated before and after hydrogen charging using electrochemical testing, component characterization and morphological observation. The results show that the open circuit potential, film resistance and breakdown potential all reduce and the passive current density increases after 12 h hydrogen charging. The ratio of Fe3+ and O2−/OH− decreases. The components of the hydrogen charged passive film alter and the performance deteriorates. The number of surface pits increases after 12 h hydrogen charging and additional 10 d alternating dry/wet corrosion. The pitting potential drops much lower. Consequently, The synergistic effect of high concentrations of Cl− in the thin liquid film and hydrogen accelerates the destruction of the passive film, further reducing the corrosion resistance of stainless steels.  相似文献   
110.
    
Erbium is widely considered as a promising tritium storage material due to its high capacity and stability. In this work, the influences of the grain size of original erbium and the deuteration conditions on the microstructure of erbium deuteride film were studied by SEM, FIB-TEM and XRD. The results indicate that the erbium films with small grains transformed into large grains after deuteration, whereas those with large grains changed to smaller grains. The lattice expansion after the loading of deuterium was measured, which confirmed that the films possess small grains present a weaker expansion (7.7%) than those with large grains (10.8%). All of the as-prepared erbium deuteride films exhibited a strong (111) preferred orientation and the film with smaller change of grain size during deuteration presents much stronger preferential growth. It is demonstrated that the deuteration temperature and pressure have a significant effect on the grain size of erbium deuteride films, which the higher deuteration temperature and pressure would induce a bigger change of grain size. In final, the underlying cause of the effect of grain size and deuteration conditions is discussed based on the thermodynamic and kinetics. The higher reaction rate under high deuteration temperature and pressure would prefer to increase the internal stress and the transformation of grain size.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号