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排序方式: 共有176条查询结果,搜索用时 15 毫秒
21.
Yunho Hwang Dae-Hyun Jin Reinhard Radermacher 《International Journal of Refrigeration》2007,30(4):633-641
To help provide a clear understanding of the relative performance potential of HFCs (R-404A and R-410A) as compared to R-290 for walk-in refrigeration systems representing direct expansion commercial refrigeration systems with small charge, an experimental evaluation of the three refrigerants was investigated. To compare the environmental impact of refrigerants over the entire life cycle of fluid and equipment, including power consumption, the life cycle climate performance (LCCP) of the three refrigerants were evaluated based on measured data. The estimated LCCPs at various emission rates indicate that the LCCP of R-290 is always lower than that of R-404A. The LCCP of R-410A is lower than that of R-290 as long as the annual emission is kept below 10%. It was concluded that R-410A has less or equivalent environmental impact as compared to R-290 when safety (toxicity and flammability), environmental impact (climate change), cost and performance (capacity and COP) are considered. 相似文献
22.
A cone concentrator combined with a solar cavity receiver is presented and its performance compared to a single cavity receiver. For both cases the available heat sink within the receiver is calculated. The cone concentrator suffers from a high amount of rejected rays if the exit aperture is made too small. A larger exit aperture on the other hand increases the thermal losses of the cavity. The optimum cone geometry therefore has to be found taking also into account a model of the cavity. Different operating temperatures and different values of absorption coefficients of the cavity walls are considered. A cone concentrator was built and tested at the solar furnace in Cologne. It transmits 97 percent of the rays entering the entrance aperture, which is in exact agreement with the theoretical predictions. 相似文献
23.
Eunil Hahm Ahla Jo Eun Ji Kang Sungje Bock Xuan-Hung Pham Hyejin Chang Bong-Hyun Jun 《International journal of molecular sciences》2021,22(21)
To study the distance-dependent electromagnetic field effects related to the enhancement and quenching mechanism of surface-enhanced Raman scattering (SERS) or fluorescence, it is essential to precisely control the distance from the surface of the metal nanoparticle (NP) to the target molecule by using a dielectric layer (e.g., SiO2, TiO2, and Al2O3). However, precisely controlling the thickness of this dielectric layer is challenging. Herein, we present a facile approach to control the thickness of the silica shell on silver nanoparticle-assembled silica nanocomposites, SiO2@Ag NPs, by controlling the number of reacting SiO2@Ag NPs and the silica precursor. Uniform silica shells with thicknesses in the range 5–40 nm were successfully fabricated. The proposed method for creating a homogeneous, precise, and fine silica coating on nanocomposites can potentially contribute to a comprehensive understanding of the distance-dependent electromagnetic field effects and optical properties of metal NPs. 相似文献
24.
Ki-Yong Choi Sang-Ki Moon Se-Young Chun Jong-Kuk Park Dae-Hyun Hwang Won-Pil Baek 《传热工程》2013,34(8):685-694
Critical heat flux (CHF) tests in a three-rod bundle were carried out, and a CHF database was established in order to obtain an operational license for the three-pin fuel test loop (FTL) in HANARO (High-flux Advanced Neutron Application Reactor). Two kinds of CHF tests are currently being performed for the CANDU and PWR-type fuel test loop. In this study, an experimental work on the CHF tests for the CANDU-type fuel test loop is explained, and a new CHF prediction methodology is proposed. In all, 108 experimental data points have been obtained, and the data are analyzed and compared with the available CHF correlations for a bundle or an annulus geometry. The 1986 AECL look-up table with a bundle correction factor and the Doerffer's correlation for annuli are compared with the present CHF data. It is found that the 1986 AECL look-up table with a bundle correction factor results in a better prediction than the Doerffer's correlation for annuli geometry. A three-pin correction factor is developed to account for the geometric effects of the three-rod bundle and to improve the prediction accuracy. It is concluded that the best estimate thermal hydraulic system code, MARS 3.0, which uses the same look-up table for a CHF prediction, can be used for a safety analysis of the CANDU-type three-pin FTL to obtain a license if it is corrected by the developed three-pin correction factor. 相似文献
25.
Brent J. Carey Prabir K. Patra Myung Gwan Hahm Pulickel M. Ajayan 《Advanced functional materials》2013,23(23):3002-3007
In the pursuit of advanced polymer composites, nanoscale fillers have long been championed as promising candidates for structural reinforcement. Despite progress, questions remain as to how these diminutive fillers influence the distribution of stresses within the matrix and, in turn, influence bulk mechanical properties. The dynamic mechanical behavior of elastomer‐impregnated forests of carbon nanotubes (CNTs) has revealed distinct orientation‐dependent behavior that sheds light on these complicated interactions. When compressed along the axis of the fillers, the composite will mimic open‐cell foams and exhibit strain softening for increasing amplitudes due to the collective Euler buckling of the slender nanotubes. In contrast, the same material will behave similarly to the neat polymer when compressed orthogonal to the alignment direction of the nanotubes. However, in this orientation the material is incapable of achieving the same ultimate compressive strain due to the role that the embedded nanotubes play in augmenting the effective cross‐link density of the polymer network. Both of these responses are recoverable, robust, and show little dependency on the diameter and wall‐number of the included CNTs. Such observations give insight into the mechanics of polymer/nanoparticle interactions in nanocomposite structures under strain, and the thoughtful control of such coordinated buckling behavior opens the possibility for the development of foam‐like materials with large Poisson ratios. 相似文献
26.
Do-Kwan Hong Jae-Hak Choi Byung-Chul Woo Dae-Hyun Koo Gyeong-Bae Kim Chan-Woo Ahn 《Journal of Mechanical Science and Technology》2013,27(10):3035-3041
A copper die casting induction motor can obtain an energy saving effect of about 2–3% compared to previous aluminum die casing induction motors. In addition, copper die casting motors can reduce the size of motors and reduce material costs. The critical speed and unbalance response of high speed machines need to be verified by rotordynamic analysis for dynamic stability of the rotors. The critical speed analysis, harmonic analysis and transient analysis by unbalance are performed for dynamic stability. The unbalance analysis results are compared with the experiment considering allowable vibration displacement (API 611) and balancing grade (ISO 1940-1). This paper dealt with the design, analysis and experimental validation of a high speed induction motor. The dynamic stability of the prototype is verified successfully, and two experimental methods by ISO 10816-3 are suitable and reliable for the allowable vibration evaluation of rotating machine. 相似文献
27.
Suk-Hun Lee Jae-Kyu Chun Jae-Jin Hur Jae-Seung Lee Gi-Hong Rue Young-Ho Bae Sung-Ho Hahm Yong-Hyun Lee Jung-Hee Lee 《Electron Device Letters, IEEE》2000,21(6):261-263
This is a first time report of a ruthenium oxide (RuO2) Schottky contact on GaN. RuO2 and Pt Schottky diodes were fabricated and their characteristics compared. When the RuO2 Schottky contact was annealed at 500°C for 30 min, the current-voltage (I-V) and capacitance-voltage (C-V) characteristics of the RuO2 were dramatically improved. The annealed RuO2 /GaN Schottky contact exhibited a reverse leakage current that was at least two or three orders lower in magnitude than that of the Pt/GaN contact along with a very large barrier height of 1.46 eV, which is the highest value ever reported for a GaN Schottky system 相似文献
28.
29.
Dong Hoon Park Joo Wan Kim Hi-Joon Park Dae-Hyun Hahm 《International journal of molecular sciences》2021,22(8)
Atopic dermatitis (AD) is a refractory and relapsing skin disease with a complex and multifactorial etiology. Various congenital malformations and environmental factors are thought to be involved in the onset of the disease. The etiology of the disease has been investigated, with respect to clinical skin symptoms and systemic immune response factors. A gut microbiome–mediated connection between emotional disorders such as depression and anxiety, and dermatologic conditions such as acne, based on the comorbidities of these two seemingly unrelated disorders, has long been hypothesized. Many aspects of this gut–brain–skin integration theory have recently been revalidated to identify treatment options for AD with the recent advances in metagenomic analysis involving powerful sequencing techniques and bioinformatics that overcome the need for isolation and cultivation of individual microbial strains from the skin or gut. Comparative analysis of microbial clusters across the gut–skin axis can provide new information regarding AD research. Herein, we provide a historical perspective on the modern investigation and clinical implications of gut–skin connections in AD in terms of the integration between the two microbial clusters. 相似文献
30.
We analyze the interface between a supplier and an assembly facility, where direct shipments are made from one to the other. The final manufacturing step at the supplier involves multiple components produced on a single machine or production line. The assembly facility uses these components at a constant rate. The supplier incurs a sequence-independent setup cost and/or setup time each time the production line is changed over from one component to another. On the other hand, setup costs and times for the assembly facility are negligible. We consider two types of delivery cost: a fixed charge for each delivery, and a fixed-charge-per-truck cost.
We develop a heuristic procedure to find a 'just-in-time' schedule in which one production run of each product and a subsequent delivery of these products to the assembly facility occur in each cycle. The objective is to find the cycle duration that minimizes the average cost per unit time of transportation, inventory at both the supplier and the assembly facility, and setup costs at the supplier. We also develop an error bound for this procedure, and use some of the insights gained from the analysis to explain how delivery schedules can influence the attractiveness of reductions in production setup costs. 相似文献
We develop a heuristic procedure to find a 'just-in-time' schedule in which one production run of each product and a subsequent delivery of these products to the assembly facility occur in each cycle. The objective is to find the cycle duration that minimizes the average cost per unit time of transportation, inventory at both the supplier and the assembly facility, and setup costs at the supplier. We also develop an error bound for this procedure, and use some of the insights gained from the analysis to explain how delivery schedules can influence the attractiveness of reductions in production setup costs. 相似文献