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:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   2096篇
  免费   103篇
  国内免费   13篇
电工技术   36篇
综合类   7篇
化学工业   396篇
金属工艺   57篇
机械仪表   50篇
建筑科学   104篇
矿业工程   1篇
能源动力   142篇
轻工业   149篇
水利工程   22篇
石油天然气   25篇
无线电   302篇
一般工业技术   343篇
冶金工业   196篇
原子能技术   9篇
自动化技术   373篇
  2024年   6篇
  2023年   47篇
  2022年   95篇
  2021年   125篇
  2020年   86篇
  2019年   74篇
  2018年   96篇
  2017年   75篇
  2016年   100篇
  2015年   48篇
  2014年   86篇
  2013年   159篇
  2012年   102篇
  2011年   149篇
  2010年   98篇
  2009年   108篇
  2008年   89篇
  2007年   84篇
  2006年   68篇
  2005年   48篇
  2004年   46篇
  2003年   45篇
  2002年   31篇
  2001年   29篇
  2000年   8篇
  1999年   24篇
  1998年   34篇
  1997年   23篇
  1996年   26篇
  1995年   20篇
  1994年   19篇
  1993年   17篇
  1992年   16篇
  1991年   14篇
  1990年   17篇
  1989年   10篇
  1988年   9篇
  1987年   12篇
  1986年   7篇
  1985年   5篇
  1984年   6篇
  1983年   5篇
  1982年   7篇
  1981年   4篇
  1980年   5篇
  1978年   3篇
  1977年   6篇
  1976年   5篇
  1975年   3篇
  1972年   3篇
排序方式: 共有2212条查询结果,搜索用时 15 毫秒
971.
Single crystals of 9,10-anthraquinone having dimensions 5 mm × 5 mm × 1.5 mm were grown from the melt using the Bridgeman technique. The starting material was purified by sublimation and zone-refining techniques in specially, designed crystal-growth tubes. The crystals were transparent and yellow in colour, and could be cleaved easily along ab-, bc-planes and poorly along the ac-planes of the crystal. Thin layer chromatography of the final crystals was performed, and no impurity was detected in these crystals by this technique. The cleaved crystals were found to have a surface photocurrent of 10–11 A, which increased non-linearly with the increasing voltage at room temperature. This is attributed to the formation of triplets in the bulk of the crystal which migrate and dissociate at the surface of the crystal. The optical absorption spectrum in benzene and ether solutions were found to exhibit similar behaviour in the visible range, i.e. 320–450 nm. From the optical absorbance data, the optical band gap was found to be 3.4 eV.  相似文献   
972.
The authors report on the kinetics, pseudo first-order model, pseudo second-order model, and intraparticle diffusion mechanism. Thus, the experimental data of the adsorption of thiophene, benzothiophene, and dibenzothiophene on a material of carbon nanotubes-titania were fitted to the kinetics and intraparticle diffusion models. The kinetics parameters of qe and correlation coefficient indicated that the data are not fitted with the pseudo first-order model while they are well fitted to the pseudo second-order model with R2 of more than 0.99 and the maximum adsorption capacities qe calculated from the pseudo second order model are in accordance with the experimental values for the three sulfur compounds in a model fuel. The results indicated that the adsorbent has a higher adsorption efficiency toward DBT over the other two sulfur compounds. Fitting the data to the intraparticle diffusion model indicated the intraparticle diffusion was not only rate-controlling step and hence it can be suggested that the surface adsorption and intraparticle diffusion were concurrently operating. The experimental results demonstrate that the combining of titania and carbon nanotubes is a promising material, which can be used in desulfurization.  相似文献   
973.
Channel‐based radio‐frequency fingerprinting such as a channel impulse response (CIR), channel transfer function (CTF), and frequency coherence function (FCF) have been recently proposed to improve the accuracy at the physical layer; however, their empirical performance, advantages, and limitations have not been well reported. This paper provides a comprehensive empirical performance evaluation of RF location fingerprinting, focusing on a comparison of received‐signal strength, CIR‐, CTF‐, and FCF‐based fingerprinting using the weighted k‐nearest neighbor pattern recognition technique. Frequency domain channel measurements in the IEEE 802.11 band taken on a university campus were used to evaluate the accuracy of the fingerprinting types and their robustness to human‐induced motion perturbations of the channel. The localization performance was analyzed, and the results are described using the spatial and temporal radio propagation characteristics. In particular, we introduce the coherence region to explain the spatial properties and investigate the impact of the Doppler spread in time‐varying channels on the time coherence of RF fingerprint structures.  相似文献   
974.
Natural convection and melting of ice as a phase change material dispersed with copper nanoparticles are numerically investigated. Square cavity filled with nano-mixture (Cu−ice) subjected to sinusoidal temperature distributions from the hot bottom boundary. The phase change process and heat transfer are formulated and solved using the enthalpy-based lattice Boltzmann method. Home-built numerical code is developed and validated. The effect of Rayleigh number (Ra = 104, 105, and 106) and copper nanoparticle concentration (ϕ = 0%, 1%, 3%, and 5%) on the flow characteristics and thermal performance of NePCM during the melting process is examined. According to the numerical results, the melting and charging times decrease by increasing the Rayleigh number. It is also observed that increasing the volume fraction of nanoparticle decrease melting time by up to 10%.  相似文献   
975.
Journal of Applied Electrochemistry - In this work, poly(3,4-propylenedioxythiophene) (PProDOT)-based counter electrode (CE) was elaborated. The PProDOT polymer was electropolymerized by using...  相似文献   
976.
Tuning the parameters of any evolutionary algorithm is considered as a very difficult task. In this paper, we present a new adaptive multi-objective technique which consists of a hybridization between a particular particle swarm optimization approach (Tribes) and tabu search (TS) technique. The main idea behind this hybridization is to combine the rapid convergence of Tribes with the high efficient exploitation of a local search technique based on TS. In addition, we propose three different places where the local search can be applied: TS applied on the particles of the archive, TS applied only on the best particle of each tribe and TS applied on each particle of the swarm. The aim of those propositions is to study the impact of the place where the local search is applied on the performance of our hybridized Tribes. The mechanisms proposed are validated using 10 different functions from specialized literature of multi-objective optimization. The obtained results show that using this kind of hybridization is justified as it is able to improve the quality of the solutions in the majority of cases.  相似文献   
977.
Hybrid nanostructures can be developed with inorganic nanoparticles (NPs) such as zinc oxide (ZnO) and natural antibacterials. ZnO NPs can also exert antibacterial effects, and we used them here to examine their dual action in combination with a natural antibacterial agent, protocatechuic acid (PCA). To produce hybrid nanoformulations, we functionalized ZnO NPs with four types of silane organic molecules and successfully linked them to PCA. Physicochemical assessment confirmed PCA content up to ~18% in hybrid nanoformulations, with a PCA entrapment efficiency of ~72%, indicating successful connection. We then investigated the in vitro release kinetics and antibacterial effects of the hybrid against Staphylococcus aureus. PCA release from hybrid nanoformulations varied with silane surface modification. Within 98 h, only 8% of the total encapsulated PCA was released, suggesting sustained long-term release. We used nanoformulation solutions collected at days 3, 5, and 7 by disc diffusion or log reduction to evaluate their antibacterial effect against S. aureus. The hybrid nanoformulation showed efficient antibacterial and bactericidal effects that also depended on the surface modification and at a lower minimum inhibition concentration compared with the separate components. A hybrid nanoformulation of the PCA prodrug and ZnO NPs offers effective sustained-release inhibition of S. aureus growth.  相似文献   
978.
Studies of the DLR Mediterranean – Concentrated Solar Project indicate Iran can be a part of the Mediterranean renewable power generation chain in 2050 to provide the electrical power demand of Europe. However, Iran as a developing country and due to its large area has some limitations on the number of synoptic stations. Hence, the aim of this study is to determine the theoretical solar irradiation potential in Iran by using an Niroo Research Institute irradiation model based on the geographical and meteorological data. Monthly, seasonal, and annual values of irradiation on the ground surface, and extracted solar energy from different tracking systems, are estimated across the country. A typical photovoltaic system, parabolic trough, and dish concentrator are considered and extracted solar energy of them is illustrated on the map. Results of this study make clear that the presented solar atlas can provide appropriate tools for primary study of solar energy potential and extracted energy in Iran.  相似文献   
979.
Metallurgical and Materials Transactions A - In this study, the effect of ausforming temperature and strain on the bainite transformation in a model alloy containing 0.39 pct C, 2.0 pct Mn, 1.9 pct...  相似文献   
980.
In this paper, we investigated the design and optimization of a proposed radio-frequency identification (RFID)-enabled automated warehousing system in terms of the optimal number of storage racks and collection points that should be established in an efficient and cost-effective approach. To this aim, a fuzzy tri-criterion programming model was developed and used for obtaining trade-off decisions by measuring three conflicting objectives. These are minimization of the warehouse total cost, maximization of the warehouse capacity utilization, and minimization of the travel time of products from storage racks to collection points. To reveal the alternative Pareto optimal solutions using the developed model, a new approach was developed and compared with a recently developed fuzzy approach so-called Selim and Ozkarahan (SO). A decision-making algorithm was used to select the best Pareto optimal solution, and the applicability of the developed model was examined using a case study. Research findings demonstrate that the developed model is capable of generating an optimal solution as an aid for the design of the proposed RFID-enabled automated warehousing system.  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