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:从到   被引次数:从到   他引次数:从到 提示：输入*表示无穷大
全文获取类型
  收费全文   46篇
  免费   0篇
  国内免费   1篇
专业分类
电工技术   3篇
化学工业   3篇
金属工艺   2篇
机械仪表   1篇
建筑科学   6篇
能源动力   6篇
轻工业   4篇
无线电   9篇
一般工业技术   6篇
冶金工业   1篇
自动化技术   6篇
出版年
  2023年   2篇
  2022年   1篇
  2021年   4篇
  2020年   2篇
  2019年   3篇
  2018年   3篇
  2017年   1篇
  2016年   4篇
  2015年   2篇
  2014年   2篇
  2013年   5篇
  2012年   2篇
  2011年   2篇
  2010年   2篇
  2009年   1篇
  2008年   2篇
  1999年   1篇
  1997年   1篇
  1992年   2篇
  1991年   1篇
  1987年   1篇
  1982年   1篇
  1974年   1篇
  1973年   1篇
排序方式： 共有47条查询结果，搜索用时 0 毫秒
31.
Contents In this paper systematic study of the temperature and doping dependences of the energy gap, the diffusion length, the lifetime and the emitter-Gummel number is presented. Based on a special transistor structure, the above parameters could be measured. The doping concentration in the base varies from 1016/cm3 to 4×1018/cm3 while the temperature changes from 100 K to 340 K. It is found that the band gap narrowing is smaller than that published in some literature while it agrees with that recently published by del Alamo and Swanson [25]. This result is fully discussed and explained in the text. The diffusion length is nearly independent of temperature, which is interesting for device modeling. On the other hand, the diffusion length decreases with the doping concentrationN A . The measured lifetime is inversely proportional to doping concentration with powerm wherem=0.6–0.2 depending on temperature. The results show an exponential increase of the emitter Gummel-number with temperature and an increase with doping concentration in the base.
Die Abhängigkeit der Diffusionslänge, der Trägerlebensdauer und der Emitter-Gummelzahl von der Temperatur und der Dotierungskonzentration
Übersicht Die Arbeit gibt eine systematische Studie wieder über die Temperatur- und Dotierungsabhängigkeit des Bandabstandes, der Diffusionslänge, der Trägerlebensdauer sowie der Emitter-Gummelzahl. An einer speziell präparierten Transistor-Struktur konnten diese Parameter gemessen werden. Die Dotierungskonzentration in der Basis variierte von 1016 cm–3 bis 4×1018 cm–3, während sich die Temeraturänderung über den Bereich von 100 K bis 340 K erstreckte. Es zeigt sich, daß die Verminderung des Bandabstandes kleiner ist als in einem Teil der Literatur publiziert, daß sic aber übereinstimmt mit dem von del Alamo und Swanson [25] kürzlich veröffentlichten Wert. Dieses Ergebnis wird ausführlich diskutiert und erklärt. Die Diffusionslänge ist annähernd unabhängig von der Temperatur, was für die Bauelemente-Modellierung von Interesse ist. Andererseits nimmt die Diffusionslänge mit wachsender DotierungskonzentrationN A ab. Die gemessene Ladungsträgerlebensdauer ist proportionalN A –m , wobeim=0,6–0,2 beträgt, abhängig vom Temperaturbereich. Die Ergebnisse zeigen einen exponentiellen Anstieg der Emitter-Gummelzahl mit der Temperatur und eine Zunahme mit der Dotierungskonzentration der Basiszone.
  相似文献   
32.
  相似文献   
33.
    
The present numerical study focuses on the cooling by natural convection and surface radiation of two electronic components generating two different and uniform volumetric powers. These components are modeled by two square bodies placed inside a closed square cavity with a cold straight wall. Two configurations are analyzed based on the position of the two heat-generating bodies. In the first one (horizontal position configuration), the two bodies are located at the same height of the cavity, while they are placed at different heights in the second case (vertical position configuration). The effects of two Rayleigh numbers ( 0 ≤ ( Ra 1 , Ra 2 ) ≤ 10 6 $0le ({{Ra}}_{1},{{Ra}}_{2})le {10}^{6}$ ), the conductivity ratio ( 0.01 ≤ K ≤ 100 $0.01le Kle 100$ ), and the emissivity ( 0 ≤ ε ≤ 1 $0le varepsilon le 1$ ) on the heat transfer characteristics and the flow structure are analyzed. The data is displayed as streamlines, isotherms, velocity, and maximum temperature profiles, and local heat transfer on the active wall. The obtained results indicate that the choice of the appropriate configuration depends mainly on the deviation between the two Rayleigh numbers. Furthermore, the maximum temperature of a specific block decreases as the quantity of heat generated by the other block rises. We can also see that the maximum temperature of the two blocks decreases by about 50 % $50 % $ with the increase in the emissivity (from 0 $0$ to 1 $1$ ) or the conductivity ratio (from 0.1 $0.1$ to 1 $1$ ).  相似文献   
34.
    
The purpose of this study is to determine the thermal conductance of concrete hollow bricks, which is necessary for the evaluation of the energy efficiency of a building. The three varieties of hollow concrete bricks that are often used to build walls in Morocco are the subject of this study. A computational model created using the finite volume method is used to evaluate the conjugate heat transfer through concrete hollow bricks. According to the results, the use of hollow brick type Ah3 reduces the heat flux by approximately 86% compared with type Ah1. It is undeniable that hollow bricks type Ah3 with a thermal conductivity of 1 W/m K can improve the thermal characteristics of building walls.  相似文献   
35.
    
The development of hybrid algorithms is becoming an important topic in the global optimization research area. This article proposes a new technique in hybridizing the particle swarm optimization (PSO) algorithm and the Nelder–Mead (NM) simplex search algorithm to solve general nonlinear unconstrained optimization problems. Unlike traditional hybrid methods, the proposed method hybridizes the NM algorithm inside the PSO to improve the velocities and positions of the particles iteratively. The new hybridization considers the PSO algorithm and NM algorithm as one heuristic, not in a sequential or hierarchical manner. The NM algorithm is applied to improve the initial random solution of the PSO algorithm and iteratively in every step to improve the overall performance of the method. The performance of the proposed method was tested over 20 optimization test functions with varying dimensions. Comprehensive comparisons with other methods in the literature indicate that the proposed solution method is promising and competitive.  相似文献   
36.
    
Most of the methods that generate decision trees for a specific problem use the examples of data instances in the decision tree–generation process. This article proposes a method called RBDT‐1—rule‐based decision tree—for learning a decision tree from a set of decision rules that cover the data instances rather than from the data instances themselves. The goal is to create on demand a short and accurate decision tree from a stable or dynamically changing set of rules. The rules could be generated by an expert, by an inductive rule learning program that induces decision rules from the examples of decision instances such as AQ‐type rule induction programs, or extracted from a tree generated by another method, such as the ID3 or C4.5. In terms of tree complexity (number of nodes and leaves in the decision tree), RBDT‐1 compares favorably with AQDT‐1 and AQDT‐2, which are methods that create decision trees from rules. RBDT‐1 also compares favorably with ID3 while it is as effective as C4.5 where both (ID3 and C4.5) are well‐known methods that generate decision trees from data examples. Experiments show that the classification accuracies of the decision trees produced by all methods under comparison are indistinguishable.  相似文献   
37.
    
In realistic scenarios of cognitive radio (CR) systems, imperfect channel sensing may occur due to false alarms and miss detections. Channel estimation between the secondary user transmitter and another secondary user receiver is another challenge in CR systems, especially for frequency‐selective fading channels. In this context, this paper presents a study of the effects of imperfect channel sensing and channel estimation on the performance of CR systems. In particular, different methods of channel estimation are analyzed under channel sensing imperfections. Initially, a CR system model with channel sensing errors is described. Then, the expectation maximization (EM) algorithm is implemented in order to learn the channel fading coefficients. By exploiting the pilot symbols and the detected symbols at the secondary user receiver, we can estimate the channel coefficients. We further compare the proposed EM estimation algorithm with different estimation algorithms such as the least squares (LS) and linear minimum mean square error (LMMSE). The expressions of channel estimates and mean squared errors (MSE) are determined, and their dependencies on channel sensing uncertainty are investigated. Finally, to reduce the complexity of EM algorithm, a sub‐optimal algorithm is also proposed. The obtained results show that the proposed sub‐optimal algorithm provides a comparable bit error rate (BER) performance with that of the optimal one yet with less computational complexity.  相似文献   
38.
    
This article presents the design and the implementation of dSPACE DS1104 controller board-based PI and fuzzy logic peak current-mode controllers in the voltage loop and two controllers in the current loop based first on a standard fixed hysteresis band control, followed by a variable hysteresis band control to achieve constant switching frequency for a single-phase active power factor corrector in the continuous conduction mode. All these controllers have been verified via simulation in Simulink and a real-time implementation is performed on an experimental test bench utilising a rapid prototyping tool. The controllers are experimentally compared for steady-state performance and transient response. It is shown that the PI and fuzzy logic controllers give a superior steady-state performance, whereas the fuzzy logic inference based controller can achieve better dynamic response than its PI counterpart under large load disturbance and plant uncertainties. Furthermore, the variable hysteresis band control in the current loop gives a low total harmonic distortion of the input current compared to a standard fixed hysteresis band control.  相似文献   
39.
    
Reverse genetic approaches have been widely applied to study gene function in crop species; however, these techniques, including gel-based TILLING, present low efficiency to characterize genes in soybeans due to genome complexity, gene duplication, and the presence of multiple gene family members that share high homology in their DNA sequence. Chemical mutagenesis emerges as a genetically modified-free strategy to produce large-scale soybean mutants for economically important traits improvement. The current study uses an optimized high-throughput TILLING by target capture sequencing technology, or TILLING-by-Sequencing+ (TbyS+), coupled with universal bioinformatic tools to identify population-wide mutations in soybeans. Four ethyl methanesulfonate mutagenized populations (4032 mutant families) have been screened for the presence of induced mutations in targeted genes. The mutation types and effects have been characterized for a total of 138 soybean genes involved in soybean seed composition, disease resistance, and many other quality traits. To test the efficiency of TbyS+ in complex genomes, we used soybeans as a model with a focus on three desaturase gene families, GmSACPD, GmFAD2, and GmFAD3, that are involved in the soybean fatty acid biosynthesis pathway. We successfully isolated mutants from all the six gene family members. Unsurprisingly, most of the characterized mutants showed significant changes either in their stearic, oleic, or linolenic acids. By using TbyS+, we discovered novel sources of soybean oil traits, including high saturated and monosaturated fatty acids in addition to low polyunsaturated fatty acid contents. This technology provides an unprecedented platform for highly effective screening of polyploid mutant populations and functional gene analysis. The obtained soybean mutants from this study can be used in subsequent soybean breeding programs for improved oil composition traits.  相似文献   
40.
    
The aim of this work is to study the influence of successive weld repairs on the microstructure and the mechanical behavior of the heat-affected zone(HAZ) of an HSLA X70 steel. Detailed microstructural examination combined to grain size measurement showed that beyond the second weld repair, the microstructure of the HAZ undergoes significant change in the grain morphology and grain growth. The results of the X-ray diffraction analyzed using MAUD software indicated an increase in the crystallite size and a decrease in the dislocation density according to the number of weld repair operations. Consequently, a loss of mechanical properties, namely the yield strength and the toughness with the number of weld repairs, was recorded. Beyond the second weld repair operation, the properties of the welded joint do not fulfill the standards applied in piping industry.  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