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   499篇
  免费   15篇
  国内免费   8篇
电工技术   14篇
化学工业   117篇
金属工艺   5篇
机械仪表   3篇
建筑科学   7篇
能源动力   25篇
轻工业   33篇
水利工程   10篇
石油天然气   2篇
无线电   52篇
一般工业技术   144篇
冶金工业   65篇
原子能技术   5篇
自动化技术   40篇
  2023年   12篇
  2022年   17篇
  2021年   16篇
  2020年   11篇
  2019年   12篇
  2018年   18篇
  2017年   18篇
  2016年   15篇
  2015年   11篇
  2014年   15篇
  2013年   44篇
  2012年   13篇
  2011年   11篇
  2010年   9篇
  2009年   7篇
  2008年   14篇
  2007年   12篇
  2006年   7篇
  2005年   11篇
  2004年   12篇
  2003年   10篇
  2002年   12篇
  2001年   4篇
  2000年   5篇
  1999年   10篇
  1998年   15篇
  1997年   13篇
  1996年   14篇
  1995年   10篇
  1994年   15篇
  1993年   9篇
  1992年   11篇
  1991年   11篇
  1990年   4篇
  1989年   9篇
  1988年   6篇
  1987年   4篇
  1986年   7篇
  1985年   5篇
  1984年   5篇
  1983年   6篇
  1982年   8篇
  1981年   5篇
  1980年   5篇
  1978年   7篇
  1977年   3篇
  1976年   4篇
  1975年   3篇
  1972年   2篇
  1931年   2篇
排序方式: 共有522条查询结果,搜索用时 15 毫秒
81.
This paper deals with the problem of designing a controller for a class of discrete-time nonlinear systems which is represented by discrete-time polynomial fuzzy model. Most of the existing control design methods for discrete-time fuzzy polynomial systems cannot guarantee their Lyapunov function to be a radially unbounded polynomial function, hence the global stability cannot be assured. The proposed control design in this paper guarantees a radially unbounded polynomial Lyapunov functions which ensures global stability. In the proposed design, state feedback structure is considered and non-convexity problem is solved by incorporating an integrator into the controller. Sufficient conditions of stability are derived in terms of polynomial matrix inequalities which are solved via SOSTOOLS in MATLAB. A numerical example is presented to illustrate the effectiveness of the proposed controller.  相似文献   
82.
Temporal variation of ‘surface energy balance’ was quantified on tropical lowland rice for 4 years (2013–2016). High response (10 Hz) eddy covariance system was used to estimate real time data on net radiation (NR), sensible heat (Hs), latent heat (LE), air and soil temperature. Annual, monthly, diurnal as well as phenological crop stage wise variation were analysed. Majority of radiation received from sun was partitioned into latent heat (LE, 44–73%) followed by soil heat (G, 13–42%) and sensible heat (Hs 3–16%) in dry cropping season. This was primarily due to presence of stagnant water in this ecology throughout the cropping period except few days during harvesting. Average Hs was negative in the month of April because of higher evapotranspiration during full grown crop at its reproductive stage as well as stagnant water in field. LE was the major contributor of energy balance and consistently increased from active tillering to grain filling stages then gradually decreased in harvesting. Hs contributing more at the initial stages of rice. Diurnal variation showed maximum Hs during 12:00 to 13:00 hours, whereas, highest LE and G were noticed during 13:00 and 11:30–12:00 hours, respectively. LE and G regressed well than Hs with air temperature and NR.  相似文献   
83.
Wireless Personal Communications - Worldwide interoperability for Microwave Access (WiMAX) is an advanced wireless broadband access technology for delivering high speed voice, video and multimedia...  相似文献   
84.

Every year thousands of urban and industrial fires occur, which leads to the destruction of infrastructure, buildings, and loss of lives. One of the reasons behind this is the delayed transmission of information to the fire station and the nearer hospitals for ambulance service as the transmission of information is dependent on observer at the location where the fire is caught and cellular network. This paper proposed an automated routing protocol for the urban vehicular ad-hoc network to send the information from the location where the fire is caught to the nearest fire stations and hospitals with optimum service time. This transmission of information involves Road Side Unit (RSU) at the junction and the vehicles present in the transmission path. Selection of route to transmit faulty vehicle information from the RSU to the required faulty vehicle is based on a parameter called path value. The computation of path value is done by the attributes such as expected End To End (E2E) delay, the shortest distance to destination, the density of vehicle between the junctions, and attenuation. From the current junction, the selection of the next junction is based on minimum path value. The proposed routing protocol considers the performance parameters such as E2E delay, total service time (TST), number of network fragments or network gaps, number of hops, and attenuation for the propagation path for the evaluation of the proposed methodology. The proposed routing algorithm is implemented through OmNet++ and SUMO. Results obtained for the proposed routing protocol is compared with three existing VANET protocols (GSR, A-STAR, and ARP) in terms of End To End delay, number of hops, number of vehicular gaps, and Total Service Time (TST).

  相似文献   
85.

Most of the researches on error rate analysis of direct sequence spread spectrum (DSSS-CDMA) systems assume that the synchronization is perfect. However, in practice, the synchronization is often imperfect due to various effects of channel parameters such as noise and fading. The degree of imperfection further increases due to jamming attacks. The present study, therefore, derives new expressions to compute the probability of error in DSSS-CDMA systems under imperfect synchronisation. It is assumed that the channel is wideband and is subjected to various jamming attacks. A new parameter, called as probability of successful synchronization, was introduced which includes the effects of both the probability of false alarm and detection under fast and slow jammers. Monte Carlo simulations were conducted in MATLAB to establish the validity of the derived mathematical expressions.

  相似文献   
86.
A range of carbon coatings with different hardness and modulus was compared for wear and frictional behaviours using one-side-carbon-coated Ti-6Al-4V alloy couples tested under conditions of combined impact and sliding contact. Carbon films with hardness over 10 GPa were found to cause far greater volume loss of the uncoated counterpart, and the volume loss was approximately proportional to the extent of hardness deviation above 10 GPa. The coefficient of friction was shown to correlate positively with coating hardness. The tendency of a softer coating to possess a greater sp2 or graphite-like content provides more effective solid lubrication in a wet environment, hence minimising both wear and friction. The corresponding low film modulus also provides an optimal structural integrity of the composite system by minimising the elastic modulus mismatch between the film and the underlying substrate.  相似文献   
87.
The separation of Y(III) from Eu(III) using a hollow fiber-supported liquid membrane with 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (EHPNA) as an extractant was studied. The effects of HCl and metal concentrations in the feed solution, the EHPNA concentration in the membrane, and the HCl concentration in the stripping solution on the initial fluxes of the two metals and the separation factor were investigated. The optimum conditions for selective recovery of Y(III) from an equimolar solution of Y(III) and Eu(III) chlorides (0.001?mol?L?1 each) were as follows: HCl concentration in the feed solution, 0.1?mol?L?1; EHPNA dimer concentration in the organic phase in the membrane, 0.1?mol?L?1; and HCl concentration in the stripping solution, 4?mol?L?1. Under these conditions, complete Y(III) extraction was achieved after 1 ks of operation, and the Y(III) purity in the stripping solution was 84%.  相似文献   
88.
Ionization rate coefficients and saturation drift velocities for electrons and holes are the vital material parameters in determining the performance of an IMPATT diode. We have performed a sensitivity analysis of the millimeter wave characteristics of 4H-SiC and 6H-SiC IMPATT diodes with reference to the above mentioned material data and an operating frequency of 220 GHz. The effect of a small variation in the ionization rate and drift velocity on the device characteristics like break down voltage, efficiency, noise measure and power output has been presented here.  相似文献   
89.
The effect of annealing on vertically aligned TiO2 NWs deposited by glancing angle deposition (GLAD) method on Si substrate using pressed and sintered TiO2 pellets as source material is studied.The FE-SEM images reveal the retention of vertically aligned NWs on Si substrate after annealing process.The EDS analysis of TiO2 NWs sample annealed at 600℃ in air for 1 h shows the higher weight percentage ratio of~2.6(i.e.,72.27% oxygen and 27.73% titanium).The XRD pattern reveals that the polycrystalline nature of anatase TiO2 dominates the annealed NWs sample.The electrical characteristics of Al/TiO2-NWs/TiO2-TF/p-Si (NW device) and Al/TiO2-TF/p-Si (TF device) based on annealed samples are compared.It is riveting to observe a lower leakage current of~1.32×10-7 A/cm2 at+1 V with interface trap density of~6.71×1011 eV-1cm-2 in NW device compared to~2.23×10-7 A/cm2 in TF device.The dominant leakage mechanism is investigated to be generally Schottky emission;however Poole-Frenkel emission also takes place during high reverse bias beyond 4 V for NWs and 3 V for TF device.  相似文献   
90.
In the present study, performance and emission analysis are done in a twin cylinder four-stroke dual-fuel diesel engine in two cases of operation. In the first case, the engine is tested using diesel, K10 (10% neat oil+90% diesel) and K20 (20% neat oil+80% diesel) in single mode and in the dual-fuel mode with an optimum producer gas flow rate of 21.49 kg/h under different load conditions. In the second case, the engine is tested using the same test fuels in the dual-fuel mode at different gas flow rates under a constant load of 10 kW. The study reveals that the dual-fuel operation of all test fuels shows a lower engine performance and better control of smoke and oxide of nitrogen emission compared with their single-mode operation under all load conditions. Whereas other emission parameters such as carbon monoxide, carbon dioxide and hydrocarbon are at a higher level.  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