全文获取类型
收费全文 | 530篇 |
免费 | 19篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 1篇 |
化学工业 | 123篇 |
金属工艺 | 10篇 |
机械仪表 | 18篇 |
建筑科学 | 28篇 |
能源动力 | 14篇 |
轻工业 | 34篇 |
水利工程 | 2篇 |
石油天然气 | 2篇 |
无线电 | 28篇 |
一般工业技术 | 131篇 |
冶金工业 | 76篇 |
原子能技术 | 4篇 |
自动化技术 | 79篇 |
出版年
2024年 | 1篇 |
2023年 | 7篇 |
2022年 | 11篇 |
2021年 | 13篇 |
2020年 | 11篇 |
2019年 | 8篇 |
2018年 | 18篇 |
2017年 | 19篇 |
2016年 | 21篇 |
2015年 | 15篇 |
2014年 | 24篇 |
2013年 | 46篇 |
2012年 | 15篇 |
2011年 | 39篇 |
2010年 | 22篇 |
2009年 | 24篇 |
2008年 | 32篇 |
2007年 | 23篇 |
2006年 | 19篇 |
2005年 | 17篇 |
2004年 | 17篇 |
2003年 | 14篇 |
2002年 | 11篇 |
2001年 | 10篇 |
2000年 | 4篇 |
1999年 | 14篇 |
1998年 | 21篇 |
1997年 | 13篇 |
1996年 | 10篇 |
1995年 | 5篇 |
1994年 | 7篇 |
1993年 | 2篇 |
1992年 | 4篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 6篇 |
1987年 | 1篇 |
1985年 | 5篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 7篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1963年 | 1篇 |
排序方式: 共有550条查询结果,搜索用时 0 毫秒
101.
As proven by the success of OFDM, multicarrier modulation has been recognized as an efficient solution for wireless communications. Waveform bases other than sine functions could similarly be used for multicarrier systems in order to provide an alternative to OFDM. In this paper, we study the performance of wavelet packet transform modulation (WPM) for transmission over wireless channels. This scheme is shown to be overall quite similar to OFDM but with some interesting additional features and improved characteristics. A detailed analysis of the system's implementation complexity as well as an evaluation of the influence of implementation‐related impairments are also reported. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
102.
Lead zirconate titanate thick film with molecular formula PbZr0.52Ti0.42O3 (PZT) was prepared by a modified conventional sol–gel method through seeding and high-energy ball milling, resulting in perovskite phase formation at lower temperatures. The ball-milling time was optimized by keeping the seed particle loading (5 wt.%) constant in the sol–gel solution. This methodology helped in reduction of the crystalline phase formation temperature to 300°C, which is much lower than that reported in the literature (450°C). The well-established perovskite phase was confirmed by x-ray diffraction (XRD) analysis. Scanning electron microscopy (SEM) of PZT films revealed uniform and crystalline microstructure. Film prepared by this methodology showed higher spontaneous polarization (2.22 μC/cm2), higher capacitance (1.17 nF), and low leakage current density (18 μA/cm2). The results obtained from ferroelectric characterization showed a strong correlation with the XRD and SEM results. 相似文献
103.
The optimization of multiple responses (or performance characteristics) has received increasing attention over the last few years in many manufacturing organizations. Many Taguchi practitioners have employed past experience and engineering knowledge or judgement when dealing with multiple responses. This approach brings an element of uncertainty to the decision-making process and therefore is not recommended for optimization of multiple responses. The approach presented in this paper takes advantage of both the Taguchi method and a fuzzy-rule based inference system, which forms a robust and practical methodology in tackling multiple response optimization problems. The paper also presents a case study to illustrate the potential of this powerful integrated approach for tackling multiple response optimization problems. The variance analysis is also an integral part of the study, which identifies the most critical and statistically significant parameters. 相似文献
104.
The analytic hierarchy process (AHP) is a powerful multiple-criteria decision analysis technique for dealing with complex problems. Traditional AHP forces decision-makers to converge vague judgements to single numeric preferences in order to estimate the pairwise comparisons of all pairs of objectives and decision alternatives required in the AHP. The resultant rankings of alternatives cannot be tested for statistical significance and it lacks a systematic approach that addresses managerial/soft aspects. To overcome the above limitations, the present paper presents a modified analytic hierarchy process, which incorporates probabilistic distributions to include uncertainty in the judgements. The vector of priorities is calculated using Monte Carlo simulation. The final rankings are analysed for rank reversal using analysis of variance, and managerial aspects (stake holder analysis, soft system methods, etc.) are introduced systematically. The focus is on the actual methodology of the modified analytic hierarchy process, which is illustrated by a brief account of a case study. 相似文献
105.
Autoclave cure simulation of composite structures applying implicit and explicit FE techniques 总被引:1,自引:0,他引:1
Gasser F. Abdelal Antony Robotham Wesley Cantwell 《International Journal of Mechanics and Materials in Design》2013,9(1):55-63
Simulation of the autoclave manufacturing technique of composites can yield a preliminary estimation of induced residual thermal stresses and deformations that affect component fatigue life, and required tolerances for assembly. In this paper, an approach is proposed to simulate the autoclave manufacturing technique for unidirectional composites. The proposed approach consists of three modules. The first module is a thermo-chemical model to estimate the temperature and the degree of cure distributions in the composite part during the cure cycle. The second and third modules are a sequential stress analysis using FE-implicit and FE-explicit respectively. User-material subroutine is used to model the viscoelastic properties of the material based on theory of micromechanics. 相似文献
106.
Gasser F. Abdelal Jonathan E. Cooper Antony J. Robotham 《International Journal of Mechanics and Materials in Design》2013,9(1):1-9
Throughout design development of satellite structure, stress engineer is usually challenged with randomness in applied loads and material properties. To overcome such problem, a risk-based design is applied which estimates satellite structure probability of failure under static and thermal loads. Determining probability of failure can help to update initially applied factors of safety that were used during structure preliminary design phase. These factors of safety are related to the satellite mission objective. Sensitivity-based analysis is to be implemented in the context of finite element analysis (probabilistic finite element method or stochastic finite element method (SFEM)) to determine the probability of failure for satellite structure or one of its components. 相似文献
107.
J. Antony 《The International Journal of Advanced Manufacturing Technology》2001,17(2):134-138
Taguchi methods have proved to be successful over the last fifteen years or so for the improvement of product quality and
process performance. Most Taguchi experiments are concerned with the optimisation of a single quality characteristic. Optimisation
of multiple quality characteristics in manufacturing processes is not common and has received very little attention among
the Taguchi practitioners. Many engineers using Taguchi methods have employed pure engineering judgement when dealing with
multiple quality characteristics in manufacturing process optimisation. This approach is very subjective and therefore always
brings an element of uncertainty to the decision-making process. This paper presents an alternative approach for tackling
such optimisation problems using Taguchi’s quality loss function analysis. The paper also presents a case study to illustrate
the potential of the proposed methodology. 相似文献
108.
109.
There are many circumstances in science where the process of measuring the properties of a system alters the system. An imaging process can exert an inadvertent effect on the object being observed. Consequently, what we observe does not necessarily represent what had been present before the observation. Normally, this effect can be ignored if the consequence of such a change is believed not to be significant. The expansion of nanostructured materials has made high-resolution transmission electron microscopy one of the indispensable tools for probing the characteristics of nanomaterials. Modification of nanoparticles by the electron beam during their imaging has been widely noticed and this is generally believed to be due to electron beam-induced heating effect, defect formation in the particles, charging of the particle, or excitation of surrounding gases. However, an explicit experimental identification of which process dominates is often very hard to establish. We report the thickening of native oxide layer on iron nanoparticle under electron beam irradiation. Based on atomic level imaging, electron diffraction, and computer simulation, we have direct evidence that the protecting oxide layer formed on Fe nanoparticle at room temperature in air or oxygen continues to grow during an electron beam bombardment in the vacuum system typical of most TEM systems. Typically, the oxide layer increases from approximately 3 to approximately 6 nm following approximately 1h electron beam exposure typically with an electron flux of 7 x 10(5)nm(-2)s(-1) and an vacuum of approximately 3 x 10(-5)Pa. Partial illumination of a nanoparticle and observation of the shell thickening conclusively demonstrates that many of the mechanisms postulated to explain such processes are not occurring to a significant extent. The observed growth is not related to the electron beam-induced heating of the nanoparticle, or residual oxygen ionization, or establishment of an electrical field, rather it is related to electron beam-facilitated mass transport across the oxide layer (a defect-related process). The growth follows a parabolic growth law. 相似文献
110.
Judit Sztáray Antony Memboeuf László Drahos Károly Vékey 《Mass spectrometry reviews》2011,30(2):298-320
The present article reviews the mass spectrometric fragmentation processes and fragmentation energetics of leucine enkephalin, a commonly used peptide, which has been studied in detail and has often been used as a standard or reference compound to test novel instrumentation, new methodologies, or to tune instruments. The main purpose of the article is to facilitate its use as a reference material; therefore, all available mass spectrometry‐related information on leucine enkephalin has been critically reviewed and summarized. The fragmentation mechanism of leucine enkephalin is typical for a small peptide; but is understood far better than that of most other compounds. Because ion ratios in the MS/MS spectra indicate the degree of excitation, leucine enkephalin is often used as a thermometer molecule in electrospray or matrix‐assisted laser desorption ionization (ESI or MALDI). Other parameters described for leucine enkephalin include collisional cross‐section and energy transfer; proton affinity and gas‐phase basicity; radiative cooling rate; and vibrational frequencies. The lowest‐energy fragmentation channel of leucine enkephalin is the MH+ → b4 process. All available data for this process have been re‐evaluated. It was found that, although the published Ea values were significantly different, the corresponding Gibbs free energy change showed good agreement (1.32 ± 0.07 eV) in various studies. Temperature‐ and energy‐dependent rate constants were re‐evaluated with an Arrhenius plot. The plot showed good linear correlation among all data (R2 = 0.97), spanned over a 9 orders of magnitude range in the rate constants and yielded 1.14 eV activation energy and 1011.0 sec?1 pre‐exponential factor. Accuracy (including random and systematic errors, with a 95% confidence interval) is ±0.05 eV and 10±0.5 sec?1, respectively. The activation entropy at 470 K that corresponds to this reaction is ?38.1 ± 9.6 J mol?1 K?1. We believe that these re‐evaluated values are by far the most accurate activation parameters available at present for a protonated peptide and can be considered as “consensus” values; results on other processes might be compared to this reference value. © 2010 Wiley Periodicals, Inc., Mass Spec Rev 30:298–320, 2011 相似文献