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   517篇
  免费   24篇
  国内免费   1篇
电工技术   6篇
综合类   1篇
化学工业   88篇
金属工艺   26篇
机械仪表   23篇
建筑科学   28篇
矿业工程   2篇
能源动力   31篇
轻工业   47篇
水利工程   4篇
石油天然气   14篇
无线电   35篇
一般工业技术   135篇
冶金工业   25篇
原子能技术   3篇
自动化技术   74篇
  2023年   7篇
  2022年   7篇
  2021年   26篇
  2020年   11篇
  2019年   20篇
  2018年   29篇
  2017年   23篇
  2016年   23篇
  2015年   15篇
  2014年   18篇
  2013年   45篇
  2012年   38篇
  2011年   23篇
  2010年   26篇
  2009年   36篇
  2008年   22篇
  2007年   26篇
  2006年   14篇
  2005年   12篇
  2004年   9篇
  2003年   10篇
  2002年   6篇
  2001年   8篇
  2000年   2篇
  1998年   4篇
  1997年   6篇
  1996年   4篇
  1995年   4篇
  1994年   5篇
  1992年   2篇
  1991年   3篇
  1990年   2篇
  1988年   5篇
  1985年   3篇
  1984年   2篇
  1983年   1篇
  1982年   3篇
  1981年   3篇
  1979年   1篇
  1978年   1篇
  1977年   4篇
  1976年   1篇
  1975年   3篇
  1974年   2篇
  1973年   5篇
  1972年   5篇
  1971年   6篇
  1969年   1篇
  1967年   3篇
  1966年   2篇
排序方式: 共有542条查询结果,搜索用时 15 毫秒
81.
This paper presents constraint programming models that aim to solve scheduling and tool assignment problems in parallel machine environments. There are a number of jobs to be processed on parallel machines. Each job requires a set of tools, but limited number of tools are available in the system due to economic restrictions. The problem is to assign the jobs and the required tools to machines and to determine the schedule so that the makespan is minimised. Three constraint programming models are developed and compared with existing methods described in the literature.  相似文献   
82.
The Impedance Group Laboratories of National Metrology Institute of Turkey previously developed a new method for the characterization of Agilent 16380A-type four-terminal-pair air dielectric capacitance standards ranged from 1 to 1,000 pF up to 30 MHz. This method is based on obtaining all resonance frequencies of standard capacitors using a vector network analyzer in order to calculate inductive residual parameters of the standards. As a continuation of the study, this paper gives a detailed uncertainty analysis for the method.  相似文献   
83.
The Fused Modified Grasshopper Optimization Algorithm has been proposed, which selects the most specific feature sets from images of the disease of plant leaves. The Proposed algorithm ensures the detection of diseases during the early stages of the diagnosis of leaf disease by farmers and, finally, the crop needed to be controlled by farmers to ensure the survival and protection of plants. In this study, a novel approach has been suggested based on the standard optimization algorithm for grasshopper and the selection of features. Leaf conditions in plants are a major factor in reducing crop yield and quality. Any delay or errors in the diagnosis of the disease can lead to delays in the management of plant disease spreading and damage and related material losses. Comparative new heuristic optimization of swarm intelligence, Grasshopper Optimization Algorithm was inspired by grasshopper movements for their feeding strategy. It simulates the attitude and social interaction of grasshopper swarm in terms of gravity and wind advection. In the decision on features extracted by an accelerated feature selection algorithm, popular approaches such as ANN and SVM classifiers had been used. For the evaluation of the proposed model, different data sets of plant leaves were used. The proposed model was successful in the diagnosis of the diseases of leaves the plant with an accuracy of 99.41 percent (average). The proposed biologically inspired model was sufficiently satisfied, and the best or most desirable characteristics were established. Finally, the results of the research for these data sets were estimated by the proposed Fused Modified Grasshopper Optimization Algorithm (FMGOA). The results of that experiment were demonstrated to allow classification models to reduce input features and thus to increase the precision with the presented Modified Grasshopper Optimization Algorithm. Measurement and analysis were performed to prove the model validity through model parameters such as precision, recall, f-measure, and precision.  相似文献   
84.
In an era of globalized trade relations where food and pharmaceutical products cross borders effortlessly, consumers face counterfeit and deteriorated products at elevated rates. This paper presents multifunctional, biodegradable hydrogel microparticles that can provide information on the authenticity and the potential deterioration of the tagged food or pharmaceutical formulations. These microparticles integrate spatially patterned authenticity code with two sensors—the first one detects possible presence of pathogenic microbes through monitoring pH while the second one identifies products stored above optimal temperatures via optical monitoring of the microparticle degradation. Particles are synthesized from a biocompatible polymer and a photoinitiator, dextran modified with 2‐hydroxyethylmethacrylate and riboflavin, respectively, using a continuous, high throughput method stop‐flow lithography. The proposed synthesis approach also enables crosslinking with visible light bringing about additional flexibility to flow lithography. Model liquid and solid food and pharmaceutical products are successfully labeled with microparticles and the functionality of the sensors in aqueous solutions is demonstrated.  相似文献   
85.
The manipulation of single magnetic molecules may enable new strategies for high-density information storage and quantum-state control. However, progress in these areas depends on developing techniques for addressing individual molecules and controlling their spin. Here, we report success in making electrical contact to individual magnetic N@C(60) molecules and measuring spin excitations in their electron tunnelling spectra. We verify that the molecules remain magnetic by observing a transition as a function of magnetic field that changes the spin quantum number and also the existence of non-equilibrium tunnelling originating from low-energy excited states. From the tunnelling spectra, we identify the charge and spin states of the molecule. The measured spectra can be reproduced theoretically by accounting for the exchange interaction between the nitrogen spin and electron(s) on the C(60) cage.  相似文献   
86.
Water vapour permeability (WVP) and mechanical properties were assessed in edible films prepared from methylcellulose (MC) and MC–whey protein isolate (WPI) or MC–whey protein concentrate (WPC). Glycerol (Gly) was used as the plasticizer. Two MC–WP films were formulated. For Group I films, the mass ratio of WP : Gly was constant, whereas for Group II films the mass ratio of polymer (MC + WP) : Gly was constant. The WVP of MC–Gly film decreased with increasing MC concentration, while the tensile strength (TS) and percent elongation (E) increased. The WVP of Group I and Group II films decreased erratically and TS increased when the MC concentration was increased. Group I films had higher TS values than Group II films at the same MC : WP ratios. E of both groups increased with increasing MC concentration (p < 0.05), excluding the films with the highest MC : WP ratio tested (0.8) in Group I films. Group I films had lower E values than Group II films at the same MC : WP ratios. MC effectively governed WVP, TS and E of the WP films. Generally, MC–WP films of this work showed lower WVP than that of MC‐ and WP‐based edible films in the literature. This can potentially make MC–WP films a suitable film material for moisture‐sensitive food products. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   
87.
S. Yildirim  D. Deger  I. Turhan 《Vacuum》2005,77(3):329-335
The dielectric constant and the dielectric loss of tantalum pentoxide (Ta2O5) thin films, produced by sol-gel spin-coated process on Corning glass substrates, have been investigated in the frequency range of 20-105 Hz and the temperature range of 183-403 K, using ohmic Al electrodes. The frequency and temperature dependence of relaxation time has also been determined. The capacitance and loss factor were found to decrease with increasing frequency and increase with increasing temperature. The activation energy values were evaluated and a good agreement between the activation energy values obtained from capacitance and dielectric loss factor measurements were observed.  相似文献   
88.
We carried out an experimental investigation of free convective heat transfer on a vertical plate subjected to a constant heat flux in the presence of one or several rectangular steps. Temperature fields were investigated with the help of a Mach-Zehnder interferometer. During the experiment the Rayleigh number changed from zero to Ra=2.8·103. The flow was observed by the method of track visualization by means of a laser knife. Durectly behind a step we observed a circulating free convective flow having the shape of two oppositely rotating vortices.Academic Scientific Complex A. V. Luikov Heat and Mass Transfer Institute of the Academy of Sciences of Belarus, Minsk, Belarus. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 67, Nos. 3–4, pp. 190–196, September–October, 1994.  相似文献   
89.
Nondestructive testing (NDT) methods are widely used for the performance evaluation of flexible pavements. Falling weight deflectometer (FWD), which measures time-domain deflections resulting from applied impulse loads, is the most popular technique among all NDT methods. The evaluation of the FWD data requires the inversion of mechanical pavement properties using a backcalculation tool that includes both a forward pavement response model and an optimization algorithm. Neural networks (NNs) have also emerged as alternative tools that can be employed for pavement backcalculation problems relative to their real-time processing abilities. However, there have been no comprehensive analyses in previous studies that focus on the learning algorithm and the architecture of a NN model, which considerably affect backcalculation results. In this study, 284 different NN models were developed using synthetic training and testing databases obtained by layered elastic theory. Results indicated that both the learning algorithm and network architecture play important roles in the performance of the NN based backcalculation process.  相似文献   
90.
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