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   578篇
  免费   32篇
  国内免费   7篇
电工技术   15篇
综合类   2篇
化学工业   134篇
金属工艺   22篇
机械仪表   18篇
建筑科学   12篇
能源动力   32篇
轻工业   76篇
水利工程   8篇
石油天然气   3篇
武器工业   1篇
无线电   60篇
一般工业技术   123篇
冶金工业   14篇
原子能技术   6篇
自动化技术   91篇
  2024年   1篇
  2023年   10篇
  2022年   27篇
  2021年   49篇
  2020年   35篇
  2019年   50篇
  2018年   35篇
  2017年   32篇
  2016年   43篇
  2015年   15篇
  2014年   45篇
  2013年   60篇
  2012年   49篇
  2011年   41篇
  2010年   25篇
  2009年   15篇
  2008年   13篇
  2007年   11篇
  2006年   11篇
  2005年   8篇
  2004年   3篇
  2003年   6篇
  2002年   5篇
  2001年   3篇
  1997年   2篇
  1996年   2篇
  1995年   1篇
  1994年   2篇
  1993年   5篇
  1992年   4篇
  1988年   1篇
  1987年   1篇
  1983年   2篇
  1982年   1篇
  1977年   1篇
  1975年   1篇
  1973年   1篇
  1967年   1篇
排序方式: 共有617条查询结果,搜索用时 19 毫秒
1.
Fuzzy geographic information systems is a newly emerging field of computational intelligence. It combines fuzzy logic with spatial context. Most of the natural phenomena are fuzzy in nature. They show a degree of uncertainty or vagueness in their extent and attribute, which cannot be expressed by a crisp value. Agriculture is one of the fields of the spatial domain that needs to be described in fuzzy terms. Fertilizer is a key input for the agriculture sector. In this article, the spatial surfaces of fertilizers are developed for the wheat crop using a fuzzy decision support system. The algorithm of our system takes soil nutrients and cropping time as input, applies fuzzy logic on the input values, defuzzifies the fuzzy output to crisp value, and generates a fertilizer surface. The resultant output surface of fertilizer describes the amount of fertilizer needed to cultivate a specific crop in a specified area. The complexity of our algorithm is \(O(mnr)\) , where \(m\) is the height of the raster, \(n\) is the width of the raster, and \(r\) is the number of expert rules.  相似文献   
2.
In this work, multi-wall carbon nanotube (MWCNT) was successfully modified using aqueous solution of Oxone as a new oxidant. The effect of oxidation temperature on various characteristics of the treated MWCNTs was also investigated. FTIR and titration analysis proved the formation of carboxyl, carbonyl and epoxide groups at the surface of MWCNTs. The concentration of the functional groups increased as the modification temperature increased. The presence of such oxygen containing groups at the surface of MWCNTs justified the long time stability of the treated MWCNTs suspensions in water and methanol. The modified MWCNTs showed higher entanglement compared to row MWCNT due to the cross-links adjacent effect of pendant functional groups. Finally, it was concluded that Oxone oxidation process destroys the structure of the MWCNTs, but not severe enough to unzip the MWCNTs.  相似文献   
3.
4.
Context:How can quality of software systems be predicted before deployment? In attempting to answer this question, prediction models are advocated in several studies. The performance of such models drops dramatically, with very low accuracy, when they are used in new software development environments or in new circumstances.ObjectiveThe main objective of this work is to circumvent the model generalizability problem. We propose a new approach that substitutes traditional ways of building prediction models which use historical data and machine learning techniques.MethodIn this paper, existing models are decision trees built to predict module fault-proneness within the NASA Critical Mission Software. A genetic algorithm is developed to combine and adapt expertise extracted from existing models in order to derive a “composite” model that performs accurately in a given context of software development. Experimental evaluation of the approach is carried out in three different software development circumstances.ResultsThe results show that derived prediction models work more accurately not only for a particular state of a software organization but also for evolving and modified ones.ConclusionOur approach is considered suitable for software data nature and at the same time superior to model selection and data combination approaches. It is then concluded that learning from existing software models (i.e., software expertise) has two immediate advantages; circumventing model generalizability and alleviating the lack of data in software-engineering.  相似文献   
5.
A new standard mercury manometer has been developed to calibrate low vacuum gauges in the range from atmospheric pressure to 1 mbar. It consists of a cistern that is a small stainless steel container used as mercury reservoir and also as the first Hg column connected to a long glass tube used as the second Hg column. Manometer scale covers the difference in Hg heights in two columns up to the length equivalent to 1000 mbars. This is a novel low cost manometer with simple design, compact fabrication, better accuracy, easy operation, low vibration, and thermal stability. In order to evaluate the performance of the equipment, its generated pressures are compared with those of secondary standard, i.e., calibrated capacitance diaphragm gauge, giving the average correction factor 0.998. Different uncertainties of the generated pressures are discussed in detail along with the evaluation of correction factors. The relative uncertainty in the higher pressure side is found to be in the range of 10(-4) which is within the limit (approximately 10(-4)).  相似文献   
6.
7.
Two-sourced evaporation technique is used to prepare hard ZnSe films by controlling the evaporation rates of both Zn and Se at substrate temperature of 400 °C. The films are doped with Cu by immersion in the Cu(NO3)2-H2O solution for different periods of time. The XRD has not shown a drastic change in the film structure while the electrical resistivity of the deposited film dropped from 109 Ω-cm to about 1.6 Ω-cm for solution immersed films after heat treatment. Optical properties of deposited and doped films, such as film thickness, absorption coefficient and optical band gap have been calculated from the normal transmission spectra in the range of 300-2200 nm.The optical results show a decrease of the transmission and an increase of the refractive index and a slight shift in the optical band gap. Chemical composition of the Cu is determined by using absorption of immersed films. The composition of Cu is also compared with the composition detected by electron microprobe analyzer (EMPA).  相似文献   
8.
Journal of Materials Science: Materials in Electronics - A photoelectrochemical (PEC) water splitting ability of pure ZnO and manganese-incorporated ZnO thin films fabricated via a simple...  相似文献   
9.
Superconductivity has been improved by partial substitution of slightly higher electronegative (M=Bi, Hg) elements at Tl sites in (Cu0.5Tl0.5?x M x )Ba2O4??? (x=0,0.25) charge reservoir layer of (Cu0.5Tl0.5?x M x )Ba2Ca2Cu3O10??? superconductor. These samples were characterized by X-ray diffractometry, dc-resistivity, ac-susceptibility, FTIR absorption spectroscopy, and fluctuation-induced conductivity (FIC) analysis. The FIC analysis has been carried out in the light of Aslamasov?CLarkin (AL) theory on the resistivity versus temperature curves of (Cu0.5Tl0.5?x M x )Ba2Ca2Cu3O10??? superconductor. The microscopic parameters such as cross-over temperature (T o ), zero-temperature coherence length ?? c (0), inter-layer coupling (J), and critical exponents (?? 2D and ?? 3D) have been determined from FIC analysis of these samples and tried to correlate them to the superconductivity order parameters. A?direct correlation between the cross-over temperatures (T o ) and zero resistivity critical temperature {T c (R=0)} and carrier concentration in these samples has been observed. The improvement in T c (R=0) and the shift of 3D AL region to higher temperature values with the doping of Bi and Hg have also been observed.  相似文献   
10.
JH Kwon  K Akram  KC Nam  B Min  EJ Lee  DU Ahn 《Journal of food science》2012,77(9):C1000-C1004
Abstract: Hydrocarbons, gas compounds, and off‐odor volatiles were determined for irradiated (0 or 5 kGy) commercial sausages with different fat contents (16% and 29%) during a 60‐d storage period at 4 °C. Total of 4 hydrocarbons (C14:1, C15:0, C16:2, and C17:1) were detected only in irradiated sausages: the amount of C16:2 was the highest, followed by C17:1, C14:1, and C15:0. The concentrations of hydrocarbons decreased significantly (P < 0.05) with storage, but were still detectable at the end of 60‐d storage. Irradiated sausages produced significantly higher amounts of CO than the nonirradiated ones. CH4 was detected only in irradiated sausages. Dimethyl disulfide was detected only in irradiated sausages and its concentration decreased significantly (P < 0.05) with storage. Fat content of sausages showed a significant effect on the production and retention of hydrocarbons, gas compounds, and sulfur volatiles in irradiated sausages during storage. Some hydrocarbons (C16:2, C17:1, C14:1, and C15:0), CH4, and dimethyl disulfide were only found in irradiated sausages indicating that these compounds can be used as potential markers for irradiated sausages.  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