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   1591篇
  免费   80篇
  国内免费   3篇
电工技术   24篇
化学工业   365篇
金属工艺   31篇
机械仪表   45篇
建筑科学   24篇
矿业工程   6篇
能源动力   134篇
轻工业   139篇
水利工程   44篇
石油天然气   4篇
无线电   172篇
一般工业技术   256篇
冶金工业   79篇
原子能技术   9篇
自动化技术   342篇
  2024年   5篇
  2023年   42篇
  2022年   65篇
  2021年   63篇
  2020年   50篇
  2019年   67篇
  2018年   85篇
  2017年   58篇
  2016年   71篇
  2015年   49篇
  2014年   68篇
  2013年   122篇
  2012年   67篇
  2011年   107篇
  2010年   72篇
  2009年   88篇
  2008年   60篇
  2007年   70篇
  2006年   52篇
  2005年   41篇
  2004年   33篇
  2003年   36篇
  2002年   26篇
  2001年   16篇
  2000年   17篇
  1999年   15篇
  1998年   20篇
  1997年   26篇
  1996年   16篇
  1995年   19篇
  1994年   11篇
  1993年   7篇
  1992年   16篇
  1991年   13篇
  1990年   12篇
  1989年   11篇
  1988年   13篇
  1987年   7篇
  1986年   6篇
  1985年   6篇
  1984年   6篇
  1983年   5篇
  1982年   8篇
  1981年   3篇
  1980年   4篇
  1979年   6篇
  1977年   4篇
  1976年   4篇
  1972年   3篇
  1969年   1篇
排序方式: 共有1674条查询结果,搜索用时 15 毫秒
71.
72.
73.
Fast pyrolysis of the crushed Delonix regia seed was carried out in a semi-batch reactor at a temperature ranging from 400 to 650°C with an objective to produce bio-oil. The effect of temperature to obtain an optimum condition for maximum bio-oil yield and the composition of pyrolysis product were investigated. The maximum bio-oil yield was found to be 48?wt% at pyrolysis temperature of 600°C. The chemical composition of bio-oil obtained at optimum condition was analysed using Fourier-transformed infrared spectroscopy and Gas chromatography–mass spectrometry. The chemical analysis of the biofuel showed the presence of hydrocarbons in major, aldehydes, ketones, amides, nitriles, etc. The composition and fuel characteristics of the pyrolysis oil obtained in this work show that it may potentially be used as a renewable fuel and chemical feedstock.  相似文献   
74.
In this paper we propose an efficient and novel technique that handles production discontinuities through a resampling of the production data, eliminating high frequency production details in a transformed domain. The technique also reduces non-monotonic behavior and results in a response more suitable for the GTTI based misfit calculations. Our proposed approach has been applied to an offshore turbidite reservoir with extensive well intervention resulting in highly detailed production responses. The static model contains more than three-hundred-thousand cells, complex sand depositional distribution combined with fault structures, four pairs of injector-producers, deviated producing wells and more than 8 years of production history. Previous history matching attempts using traditional approaches had difficulties matching production response at the individual well level. With our proposed modifications to the GTTI approach, a significant improvement was obtained on the well level match quality. Most importantly, by visualizing the streamlines and the dynamic adjustment of flow paths during history matching, we could easily identify the areas of inconsistency between the geologic model and the production data. The calibrated geologic model and streamline trajectories provided important insight about communication within sand channels, differences in flow paths and barriers that have not been included in the previous geologic and seismic interpretation.  相似文献   
75.
This work deals with the study of hydrothermally synthesized zinc oxide (ZnO) loaded mesoporous SBA‐15 hybrid nanocomposite for relative humidity sensing (RH) at room temperature. The sensor exhibits an excellent ~5 orders impedance change along with excellent linearity, quick response time (17 s), rapid recovery time (18 s), negligible hysteresis (1.2%), good repeatability, and stability (1.8%) in 11%–98% RH range. In addition, complex impedance spectra of the sensor at different RHs were analyzed to understand the humidity sensing mechanism. Our study can open a new way for realizing ZnO/SBA‐15 hybrid nanocomposite for fabrication of high‐performance RH sensors.  相似文献   
76.
The structural, electronic, and elastic properties of pristine and carbon‐doped boron suboxide (B6O) are calculated using density functional theory. The results indicate that it is energetically preferable for a single carbon atom to substitute into an oxygen site rather than a boron site. The lattice parameters and cell volume increase to relieve the residual stress created by the carbon substitution. The interstitial position is not favorable for a single atom substitution. However, if two carbon atoms substitute for two neighboring oxygen atoms, then it becomes energetically favorable to dope an interstitial oxygen, boron, or carbon atom along the C–C chain. If the interstitial dopant is either boron or carbon, a local B4C‐like structure with either a C–B–C or C–C–C chain is created within the boron suboxide unit cell. The resulting structure shows improvements in the bulk modulus at the expense of the shear and Young's moduli. The moduli further improve if an additional carbon is substituted within a polar or equatorial site of the neighboring B12 icosahedron. Based on these calculations, we conclude that carbon doping can either harden or soften B6O depending on the manner in which the substitutions are populated. Furthermore, as B6O samples are often oxygen deficient, C doping can occupy such sites and improve the elastic properties.  相似文献   
77.
In order to reveal the unsteady features of gas–solid flow, the pressure fluctuations were measured at different locations along the length of the pipeline while conveying powders through the pipeline. Power spectral density (PSD) functions were obtained for the analysis of the pressure fluctuation. Two types of powders (fly ash and alumina) were used in this analysis. The PSD analysis was conducted by taking into account different aspects such as flow conditions (dilute or dense), location of transmitter (top and bottom transmitters), location of transmitter along the length of the pipeline (three different locations), material property (fly ash or alumina), etc. Analysis of signals from top and bottom transmitters shows that it is not possible to identify the flow mode at upper and lower portions of pipeline. The magnitude of power is found to be higher for alumina as compared to fly ash. PSD parametric analysis reveals that frequency bandwidth and average power decreases exponentially with increase in solid loading ratio.  相似文献   
78.
79.
Herein, we present the dielectric and electrical conductivity properties of the partially miscible polymer blend prepared using pyrene functionalized polyaniline (pf‐PANI) and poly(vinylidene fluoride‐co‐hexafluoro propylene) (PVDF‐co‐HFP). The blend mostly retains the fluorescent nature of pf‐PANI as well as can be moldable and possesses good damping property. The dielectric properties have been investigated as a function of temperature at three different frequencies and the plausible origin of polarization responsible for dielectric behavior in this blend has been identified. The experimental results of dielectric measurements are compared with theoretical models and discussed. The surface morphology of the samples has been examined with a scanning electron microscope. The electrical conductivity has also been studied as a function of temperature and explained in terms of hopping of charge carriers/interconnected networks. The combined dielectric and conductivity results together with scanning electron microscope micrographs, reveal that there is hindrance to achieve percolation threshold even after pf‐PANI addition of 57 vol % and subsequent thermal treatment. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44077.  相似文献   
80.
Metal Science and Heat Treatment - Composites obtained by powder metallurgy from a mixture of copper powders and graphene nanosheets are studied. The response surface methodology is used to design...  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