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   618篇
  免费   10篇
  国内免费   2篇
电工技术   15篇
综合类   14篇
化学工业   59篇
金属工艺   89篇
机械仪表   34篇
建筑科学   16篇
矿业工程   1篇
能源动力   5篇
轻工业   204篇
水利工程   4篇
无线电   34篇
一般工业技术   105篇
冶金工业   10篇
原子能技术   8篇
自动化技术   32篇
  2021年   6篇
  2020年   7篇
  2019年   2篇
  2018年   5篇
  2017年   4篇
  2016年   7篇
  2015年   3篇
  2014年   26篇
  2013年   94篇
  2012年   36篇
  2011年   52篇
  2010年   26篇
  2009年   44篇
  2008年   17篇
  2007年   25篇
  2006年   19篇
  2005年   19篇
  2004年   23篇
  2003年   10篇
  2002年   8篇
  2001年   4篇
  2000年   5篇
  1999年   5篇
  1998年   10篇
  1997年   44篇
  1996年   18篇
  1995年   13篇
  1994年   11篇
  1993年   7篇
  1991年   3篇
  1990年   5篇
  1989年   5篇
  1988年   6篇
  1987年   11篇
  1986年   3篇
  1985年   4篇
  1984年   3篇
  1983年   4篇
  1982年   2篇
  1981年   2篇
  1980年   2篇
  1979年   6篇
  1978年   4篇
  1976年   4篇
  1975年   5篇
  1973年   3篇
  1972年   1篇
  1971年   2篇
  1970年   1篇
  1968年   1篇
排序方式: 共有630条查询结果,搜索用时 821 毫秒
1.
After the remarkable increase of Internet users and broadband Internet subscribers at the end of the 20th century, the size of Korean Internet and e-commerce market steadily increased but the growth rate has been either stagnant or decreased. Trends of Korean Internet and e-commerce market are summarized in this paper the trends on Internet usage are introduced. Trends of online games, blogs and wireless Internet are introduced. The trends of Korean Internet market may have implications for China and Japan.  相似文献   
2.
The concept of directional binding energy (DBE) is proposed to describe the binding energy of the crystal and the ideal direction of the antiaction force against the surface tension, which derives the grain-boundary energy and also energy ratio (γgbs). It may provide a simple and lucid way to analyse the surface energy, grain-boundary energy and energy ratio from the correlative view point. It has been found that the grain-boundary energy can be derived only from the conceptual approach of DBE, irrespective of the dislocation model, which also makes it possible to determine the energy ratio with the misorientation angle. That is, the energy ratio (γgbs) is proportional to the misorientation angle, 2 sin (k′θ/2) where k′ is a constant and θ is the misorientation angle. This revised version was published online in November 2006 with corrections to the Cover Date.  相似文献   
3.
Much SO2, another perilous air pollutant, was emitted during the oxidative regeneration of sulfided sorbent by H2S. In order to prevent emission of SO2, we carried out oxidative regeneration with the physical mixture of CaO and sulfided sorbent and investigated the effect of regeneration temperature and oxygen concentration on the reactivity of CaO with S02. The effluent gases were analyzed by G.C. and the properties of sorbent were characterized by XRD. SEM, TG/DTA and EPMA. Deterioration of reactivity of CaO with S02 resulted in increment of emission of SO12 due to the structural changes of CaO above 750°C and that at 850°C was more severe. Furthermore EPMA and XRD analysis revealed that product layer diffusion through the solid product, CaSO4, was the rate limiting step for CaO sulfidation. The reaction of CaO w:.th SO2 was first order approximately and that was accelerated by high O2 concentration.  相似文献   
4.
5.
The effects of various stearic-palmitic acid blend concentrations in films, storage temperatures and storage times on potato chip quality were evaluated using Response Surface Methodology. Storage temperature and time affected the quality of potato chips. The maximum storage times for acceptable potato chip quality were: 30 to 43 days, 23 to 25 days, and 11 to 12 days for storage temperatures of 15, 25 and 35°C, respectively. Results were independent of stearic-palmitic acid blend concentrations.  相似文献   
6.
A low energy N2 ? ion beam impinged on a α-Al2O3(0001) single crystal surface in the range of fluence 5×1015/cm2?1×1018/cm2 at room temperature. After ion bombardment, chemical bonding on the modified sapphire surface was investigated by x-ray photoelectron spectroscopy. Below a fluence of 1×1015/cm2, only a non-bonded N1s peak at the binding energy 398.7 eV was found, but further irradiation up to 2×1017/cm2 induced Al?O?N bonding at around 403 eV. The occurrence of Al?N bonding was identified at ion fluence higher than 5×1017/cm2 at 396.6 eV. II–VI ZnO thin films were grown on an untreated/ion-beam-induced sapphire surface by pulsed laser deposition (PLD) for the investigation of the modified-substrate effect on photoluminescence. The ZnO films grown on modified sapphire containing Al?O?N bonding only, and both Al?O?N and Al?N bonding showed a significant reduction of the peak related to deep-level defects in photoluminescence. These results are explained in terms of the formation of Al?N?O and Al?O?N layers and relaxation of the interfacial strain between Al2O3 and ZnO.  相似文献   
7.
This paper investigates an algorithm for robust fault diagnosis (FD) in uncertain robotic systems by using a neural sliding mode (NSM) based observer strategy. A step by step design procedure will be discussed to determine the accuracy of fault estimation. First, an uncertainty observer is designed to estimate the uncertainties based on a first neural network (NN1). Then, based on the estimated uncertainties, a fault diagnosis scheme will be designed by using a NSM observer which consists of both a second neural network (NN2) and a second order sliding mode (SOSM), connected serially. This type of observer scheme can reduce the chattering of sliding mode (SM) and guarantee finite time convergence of the neural network (NN). The obtained fault estimations are used for fault isolation as well as fault accommodation to self-correct the failure systems. The computer simulation results for a PUMA560 robot are shown to verify the effectiveness of the proposed strategy.  相似文献   
8.
The tip vortex cavitation and its relevant noise has been the subject of extensive researches up to now. In most cases of experimental approaches, the accurate and objective decision of cavitation inception is primary, which is the main topic of this paper. Although the conventional power spectrum is normally adopted as a signal processing tool for the analysis of cavitation noise, a faithful exploration cannot be made especially for the cavitation inception. Alternatively, the periodic occurrence of bursting noise induced from tip vortex cavitation gives a diagnostic proof that the repeating frequency of the bursting contents can be exploited as an indication of the inception. This study, hence, employed the Short-Time Fourier Transform (STFT) analysis and the Detection of Envelope Modulation On Noise (DEMON) spectrum analysis, both which are appropriate for finding such a repeating frequency. Through the acoustical measurement in a water tunnel, the two signal processing techniques show a satisfactory result in detecting the inception of tip vortex cavitation.  相似文献   
9.
Tip vortex cavitation noise of marine propeller became primary concerns to reduce hazardous environmental impacts from commercial ship or to keep the underwater surveillance of naval ships. The investigations of the tip vortex and its induced noise are normally conducted through the model test in a water cavitation tunnel. However the Reynolds number of model-test is much smaller than that of the full-scale, which subsequently results in the difference of tip vortex cavitation inception. Hence, the scaling law between model-and full-scales needs to be identified prior to the prediction and assessment of propeller noise in full scale. From previous researches, it is generally known that the incipient caivtation number of tip vortex can be represented as a power of the Reynolds number. However, the power exponent for scaling, which is the main focus of this research, has not been clearly studied yet. This paper deals with the estimation of scaling exponent based on tip vortex cavitation inception test in both full-and model-scale ships. Acoustical measurements as well as several kind of signal processing technique for an inception criterion suggest the scaling exponent as 0.30. The scaling value proposed in this study shows slight difference to the one of most recent research. Besides, extrapolation of model-ship noise measurement using the proposed one predicts the full-scale noise measurement with an acceptable discrepancy.  相似文献   
10.
Carbon nanotube field-effect transistors (CNTFETs) have been studied in recent years as a potential alternative to CMOS devices, because of the capability of ballistic transport. The ambipolar behavior of Schottky barrier CNTFETs limits the performance of these devices. A double gate design is proposed to suppress this behavior. In this structure the first gate located near the source contact controls carrier injection and the second gate located near the drain contact suppresses parasitic carrier injection. To avoid the ambipolar behavior it is necessary that the voltage of the second gate is higher or at least equal to the drain voltage. The behavior of these devices has been studied by solving the coupled Schrödinger-Poisson equation system. We investigated the effect of the second gate voltage on the performance of the device and finally the advantages and disadvantages of these options are discussed.  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