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   983篇
  免费   29篇
  国内免费   3篇
电工技术   34篇
化学工业   183篇
金属工艺   43篇
机械仪表   31篇
建筑科学   6篇
能源动力   50篇
轻工业   67篇
水利工程   2篇
石油天然气   2篇
无线电   97篇
一般工业技术   250篇
冶金工业   157篇
原子能技术   8篇
自动化技术   85篇
  2023年   10篇
  2022年   22篇
  2021年   24篇
  2020年   20篇
  2019年   21篇
  2018年   28篇
  2017年   33篇
  2016年   45篇
  2015年   11篇
  2014年   32篇
  2013年   87篇
  2012年   34篇
  2011年   61篇
  2010年   49篇
  2009年   48篇
  2008年   42篇
  2007年   38篇
  2006年   45篇
  2005年   36篇
  2004年   22篇
  2003年   20篇
  2002年   23篇
  2001年   18篇
  2000年   18篇
  1999年   14篇
  1998年   33篇
  1997年   16篇
  1996年   21篇
  1995年   12篇
  1994年   17篇
  1993年   10篇
  1992年   17篇
  1991年   9篇
  1990年   9篇
  1989年   5篇
  1988年   10篇
  1987年   10篇
  1986年   3篇
  1985年   5篇
  1984年   4篇
  1983年   2篇
  1982年   5篇
  1981年   2篇
  1980年   6篇
  1979年   2篇
  1978年   3篇
  1976年   4篇
  1973年   3篇
  1972年   2篇
  1969年   1篇
排序方式: 共有1015条查询结果,搜索用时 15 毫秒
991.
Machine?Cpart cell formation is used in cellular manufacturing in order to process large varieties, improve quality, and lower work-in-process levels, reducing manufacturing lead time and customer response time while retaining flexibility for new products. This paper presents a new and novel approach for obtaining machine cells and part families. In cellular manufacturing, the fundamental problem is the formation of part families and machine cells. The present paper deals with the self-organizing map (SOM) method, an unsupervised learning algorithm in artificial intelligence which has been used as a visually decipherable clustering tool of machine?Cpart cell formation. The objective of the paper is to cluster the binary machine?Cpart matrix through visually decipherable cluster of SOM color coding and labeling via the SOM map nodes in such a way that the part families are processed in that machine cell. The U-matrix, component plane, principal component projection, scatter plot, and histogram of SOM have been reported in the present work for the successful visualization of the machine?Cpart cell formation. Computational result with the proposed algorithm on a set of group technology problems available in the literature is also presented. The proposed SOM approach produced solutions with a grouping efficacy that is at least as good as any results earlier reported in the literature and improved the grouping efficacy for 70% of the problems and was found to be immensely useful to both industry practitioners and researchers.  相似文献   
992.
Solar energy as the principle source has become very attractive, as it is abundantly available, can be tapped locally, pollution free and commercially viable over a period. Solar energy may be converted to other forms of higher-grade energy through one of several methods such as photothermal, photochemical, photoelectrochemical and photovoltaic (PV). Among these, as noted above the cleanest and most direct and efficient and of converts to electrical power is with the help of PV or solar cell devices. Photovoltaics are one of the hottest areas of research today. Nowadays organic material finds greater importance in the PV cell fabrications. Among the available organic materials ZincPhthalocyanine is a promising candidate for the solar cell applications, because of its easy synthesization and non-toxic to the environment. The major part of incident light in the visible region effectively contributes to photocarrier generation and the excited ZnPc molecules play an important role in PV effect. In this paper, we have reported electrical transport properties of flash evaporated ZincPhthalocyanine thin films have been reported. DC conduction mechanism in these films (Al–ZnPc–Al structure) was studied at different temperatures. The field dependence behaviour on activation energy and possible conduction mechanism in the ZnPc films under DC field has been discussed.  相似文献   
993.
The X-ray diffraction analysis of vacuum-evaporated cadmium telluride (CdTe) films reveals that the structure of the films is polycrystalline in nature for the samples prepared at higher substrate temperatures. The crystallite size (D), dislocation density (δ) and strain () were calculated. The composition analysis was made by the energy dispersive X-ray analysis. It confirmed the equal distribution of Cd and Te elements in the CdTe films. The fundamental optical parameters like band gap and extinction coefficient are calculated from the transmission spectra. The possible optical transition in these films is found to be direct and allowed. The charge transport phenomenon appears to be space charge limited conduction. Various electrical parameters were determined from the IV analysis.  相似文献   
994.
Zn0.965Cd0.035O/ZnO bilayer film has been developed using pulsed laser deposition (PLD) technique. The film is characterized by X-ray diffraction (XRD), energy dispersion analysis by X-ray (EDAX), UV-Vis and Valence band spectra (VBS). The XRD pattern confirms the single phase crystalline nature of the deposited film. The UV-Vis spectra establish a reduction of band gap (≈ 340 meV) in the ternary alloy film of Zn0.965Cd0.035O/ZnO. The VBS shows shift in the peak corresponding to nonbonding oxygen p states. We also obtained valence band offset of 191 meV in the film showing the rise of valence band. The calculated conduction band offset is found to be −51 meV which confirms the lowering of the conduction band in the ternary alloy film.  相似文献   
995.
Present study concerns assessment of nanomechanical property in the bulk Al65Cu20Ti15 alloy with varying microstructure synthesized by consolidation of mechanically alloyed powder at different temperature. The microstructure after consolidation at room temperature and 500 °C exhibits completely amorphous and nanocrystalline states respectively. Nanoindentation experiments suggest that the maximum strength and hardness values are achieved in the sample sintered at 450 °C. The corresponding microstructure revealed dispersion of nanocrystalline intermetallic phase (<50 nm) in the amorphous matrix.  相似文献   
996.
Chattopadhyay T 《Applied optics》2011,50(32):6049-6056
Logic units are the building blocks of many important computational operations likes arithmetic, multiplexer-demultiplexer, radix conversion, parity checker cum generator, etc. Multifunctional logic operation is very much essential in this respect. Here a programmable Boolean logic unit is proposed that can perform 16 Boolean logical operations from a single optical input according to the programming input without changing the circuit design. This circuit has two outputs. One output is complementary to the other. Hence no loss of data can occur. The circuit is basically designed by a 2×2 polarization independent optical cross bar switch. Performance of the proposed circuit has been achieved by doing numerical simulations. The binary logical states (0,1) are represented by the absence of light (null) and presence of light, respectively.  相似文献   
997.
A coordination polymer, Na2Cd2I6L2(H2O)6 [L = Urotropine] has been employed as sole precursor to synthesize CdO particles. Two different preparation methods viz (i) pyrolysis of the title compound at 700 °C for 2 h and (ii) forming cadmium hydroxide from the title compound followed by pyrolysis at 700 °C for 2 h have been used for the synthesis of nano sized CdO-I and CdO-II, respectively. From powder XRD data the lattice parameters (0.4701 and 0.4696 nm respectively for the two samples) and particle size (~ 77 and 30 nm for CdO-I and CdO-II) have been evaluated. Morphology of the two varieties of CdO is widely different as is evident from their SEM images. The estimated values of the band gap of 2.53 eV and 2.59 eV for CdO-I and CdO-II respectively are obtained from the optical spectral analysis.  相似文献   
998.
The properties of ferromagnetic fluids make them suitable for a wide range of applications, including loudspeakers, magnetic resonance imaging, computer hard drives, magnetic drug delivery, and magnetic hyperthermia. Owing to all such potential applications, the present research work is established to explain the stagnation point flow, heat, and mass transfer of Walters-B liquid in the presence of magnetic dipole, Brownian diffusion, and thermophoresis. To control the nanoparticles concentration at the surface, a passive control condition is employed. Using suitable similarity transformations, the governing equations are converted into nonlinear ordinary differential equations. Noticeable behavior of significant parameters on flow fields is studied graphically. The significant outcomes of the present study are that the increased values of viscoelastic parameter decline the velocity but an inverse trend is seen in heat transfer. The increased values of the Brownian motion parameter decline the heat transfer but a contrary trend is seen for augmented values of the thermophoresis parameter. The heat transfer rate is increased for rising values of radiation parameter and Biot number. The upward values of the thermophoresis parameter decline the rate of mass transfer. The escalating values of ferromagnetic interaction and velocity ratio parameters improve the skin friction.  相似文献   
999.
In this paper, a simple but novel scheme for all optical clocked D flip flop based on single micro-ring resonator with a feedback loop is proposed and prescribed. The GaAs-AlGaAs based micro-ring resonator is modulated through optical pump beam. The proposed clocked D flip flop presents two stable states determined by the phase shift in the ring and will allow synchronization of different optical devices by clock pulse (optical control pump beam). Theoretical model of clocked D flip flop has been developed using single micro-ring resonator and numerical simulation results confirming described methods are given in this paper. The design will be helpful in designing all optical integrated circuit.  相似文献   
1000.
We present the outline of the optical design of a TeraHertz (THz) imager for the detection of shrapnel-loaded improvised explosive devices (IED) devices at “stand-off” distances of 14–26 meters. The system will use 4 antenna-coupled TES detector arrays of 16 by 16 pixels cooled in a cryogen-free system with microwave readout to see beneath clothing at non-lethal detonation distances. A spatial resolution of ∼10 mm and close to video frame rates is anticipated.   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