全文获取类型
收费全文 | 280篇 |
免费 | 19篇 |
国内免费 | 3篇 |
专业分类
化学工业 | 39篇 |
金属工艺 | 26篇 |
机械仪表 | 10篇 |
建筑科学 | 9篇 |
能源动力 | 19篇 |
轻工业 | 25篇 |
水利工程 | 2篇 |
石油天然气 | 4篇 |
无线电 | 25篇 |
一般工业技术 | 64篇 |
冶金工业 | 30篇 |
原子能技术 | 1篇 |
自动化技术 | 48篇 |
出版年
2023年 | 3篇 |
2022年 | 5篇 |
2021年 | 10篇 |
2020年 | 16篇 |
2019年 | 8篇 |
2018年 | 19篇 |
2017年 | 12篇 |
2016年 | 8篇 |
2015年 | 10篇 |
2014年 | 19篇 |
2013年 | 31篇 |
2012年 | 18篇 |
2011年 | 21篇 |
2010年 | 16篇 |
2009年 | 18篇 |
2008年 | 16篇 |
2007年 | 12篇 |
2006年 | 10篇 |
2005年 | 11篇 |
2004年 | 4篇 |
2003年 | 2篇 |
2002年 | 2篇 |
2001年 | 1篇 |
2000年 | 3篇 |
1999年 | 2篇 |
1998年 | 5篇 |
1997年 | 5篇 |
1996年 | 2篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1991年 | 1篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1983年 | 1篇 |
1979年 | 2篇 |
排序方式: 共有302条查询结果,搜索用时 218 毫秒
91.
Metin Gencten Hurmus Gursu Yucel Sahin 《International Journal of Hydrogen Energy》2017,42(40):25598-25607
In this study, the effect of α-alumina (α-Al2O3) and γ-alumina (γ-Al2O3) on the precipitation of the positive electrolyte, which is one of the most important problems in vanadium redox battery (VRB) systems, was investigated. α-Al2O3 and γ-Al2O3 were used as additive materials to improve the thermal stability of V(V) ion and the performance of VRB at high temperatures. Cyclic voltammetry and electrochemical impedance spectroscopy were used to determine the properties of positive electrolyte systems. The optimum amount of additives was identified as wt% 0.004 and 0.010 for α-Al2O3 and γ-Al2O3, respectively. The surface morphology and composition of electrodes were investigated by scanning electron microscopy and energy-dispersive X-ray analysis. A plausible reaction mechanism was also proposed for redox reaction occurring on the positive electrode of a VRB. The adsorption of V(V) ions to the electrode surface from the solution increased by the time additives were added into the system. γ-Al2O3 showed the best anti-precipitation effects for the V(V) ion at 40 °C and 60 °C in the precipitation tests. In the battery test, the discharge capacity of γ-Al2O3 with a positive electrolyte, was the highest at 87.2 mAh. According to thermal and electrochemical studies, γ-Al2O3 can be a useful additive for the positive electrolyte of a VRB. 相似文献
92.
Open cell lead foams with the porosities between 48 and 74 % were prepared by means of powder metallurgical and casting routes, using ammonium bicarbonate particles, silica beads, and sodium chloride salt particles as space holder. The resulting foam samples structure closely resembled open cell foam structure: each cell had few interconnections with neighboring cells. Small-sized lead (II) fluoride precipitates were microscopically observed in the interior of cells in the foam samples prepared using silica beads as space holder, resulting from the reaction between silica and hydrofluoric acid in the space holder dissolution step. The compression stress–strain curve of foam samples prepared by powder metallurgical route showed brittle deformation behavior following the initial elastic deformation region, while the foam samples prepared by casting route showed characteristic foam deformation behavior: cell edge crushing on the bent cell walls, and cell wall tearing. The collapse stresses, densification strains, and elastic moduli of the prepared foams were further fitted with scaling relations. 相似文献
93.
Yucel Can Severcan 《International Planning Studies》2015,20(3):251-269
This paper discusses barriers to civic engagement of disadvantaged young people that we observed in the course of a child-friendly city project in Turkey. It also emphasizes the importance of being prepared to overcome such barriers, some of which were quite unexpected. Results show that many of the unexpected issues are the outcome of poverty, illiteracy, lack of ethics, inexperience of project managers, conflicting political interests and sense of insecurity. The paper concludes with suggestions for researchers and policy-makers on how to overcome such unforeseen barriers to child and youth participation in disadvantaged communities. 相似文献
94.
G. Yildirim S. Bal E. Yucel M. Dogruer M. Akdogan A. Varilci C. Terzioglu 《Journal of Superconductivity and Novel Magnetism》2012,25(2):381-390
This study deals with the effect of Mn addition on the structural and superconducting properties of Bi1.8Pb0.4Sr2Mn
x
Ca2.2Cu3.0O
y
ceramics with x=0,0.03,0.06,0.15,0.3 and 0.6 by means of X-ray analysis (XRD), scanning electron microscopy (SEM), electron dispersive X-ray
(EDX), resistivity, and transport critical current density (J
c) measurements. Zero-resistivity transition temperatures (T
c) of the samples produced via the standard solid-state reaction method are estimated from the dc resistivity measurements.
Moreover, the phase fraction and lattice parameters are determined from XRD measurements while the microstructure, surface
morphology and element composition analyses of the samples are investigated by SEM and EDX measurements, respectively. It
is found that T
c values are obtained to decrease from 109 K to 85 K; likewise, J
c values are observed to reduce from 3200 A/cm2 to 125 A/cm2 with increasing Mn addition. According to the refinement of cell parameters done by considering the structural modulation,
the Mn addition is confirmed by both an increase of the lattice parameter a and a decrease of the cell parameter c of the samples in comparison with that of the pure sample (Mn0). SEM measurements show that not only the surface morphology
and grain connectivity are seen to degrade but the grain sizes of the samples are found to decrease with the increase of the
Mn addition as well. The EDX results reveal that the elements used for the preparation of samples distribute homogeneously
and the Mn atoms enter into the crystal structure by replacing Sr and Cu atoms. The possible reasons for the obtained degradation
in microstructural and superconducting properties are also interpreted. 相似文献
95.
In this article, two new highly linear tunable transconductor circuits are proposed. The transconductors employ only six MOS transistors operated in saturation region. The second transconductor is derived from the first one with a slight modification. Transconductance of both transconductors can be tuned by a control voltage. Both of the transconductors do not need any additional bias voltages and currents. Another important feature of the transconductors is their high input and output impedances for cascadability with other circuits. Besides, total harmonic distortions are less than 1.5% for both transconductors. A positive lossless grounded inductor simulator with a grounded capacitor is given as an application example of the transconductors. Simulation and experimental test results are included to show effectiveness of the proposed circuits. 相似文献
96.
Ultrasonic velocity and attenuation measurements (2.25 MHz center frequency) were used to follow bulk crystallization of lactose (43% and 46%) from gelatin (1.5% and 3%) gels at 25 °C, and compared to turbidity (500 nm) and isothermal calorimetric measurements. Ultrasonic velocity decreased slightly (approximately 0.5%) during crystallization while ultrasonic attenuation was low in the absence of lactose crystals and increased progressively during crystallization. The lag time before the onset of crystallization decreased and the maximum rate of increase in attenuation during crystallization increased with increasing lactose supersaturation but was not affected by gelatin concentration (P < 0.05). Similar results were seen in turbidity and isothermal calorimetric measurements. Ultrasonic attenuation measurements have the potential to measure crystallization kinetics in complex food matrices and to be applied on-line. Practical Application: Many foods contain crystals that affect their taste and texture (for example, lactose crystals can give a grainy defect in ice cream). The formation of crystals is often hard to predict so methods to measure the development of crystals inside real foods are useful. In this study, we show that as lactose crystallizes in a gelatin gel the ultrasonic attenuation--capacity to absorb sound--increases and can be related to the amount of crystals present. Ultrasound is easier to apply in real food processing than the existing methodologies. 相似文献
97.
Yucel Birol Duygu İsler Mustafa Urgen 《Metallurgical and Materials Transactions A》2011,42(11):3316-3322
Thin hard coatings provide the much needed protection for steel thixoforming tools that must resist wear at high temperatures.
The wear resistance of AlTiN- and AlTiON-coated hot work tool steel was investigated at 1023 K (750 °C), measured to be the
cavity surface temperature shortly after the steel slurry was forced into the thixoforming die. The wear tests were repeated
in exactly the same fashion with uncoated tool steel samples to identify the impact of AlTiN and AlTiON coatings on the high-temperature
wear performance of X32CrMoV33 tool steel. The nature, the thickness, and the adherence of the oxide scales impact the tribological
behavior. The poor adherence and limited ductility of ferrous oxides promote the failure of the oxide scale impairing the
resistance to wear of the hot work tool steel at elevated temperatures. The substantial softening in the X32CrMoV33 hot work
tool steel is also critical in the wear volume loss it suffers. AlTiN and AlTiON coatings, on the other hand, form a stable
and protective oxide surface layer at high temperatures and therefore provide an enhanced resistance to oxidation. The latter
is relatively more resistant to oxidation and is thus the better of the two coatings tested in the present work. 相似文献
98.
Ipek AkinElif Yilmaz Filiz SahinOnuralp Yucel Gultekin Goller 《Ceramics International》2011,37(8):3273-3280
Alumina (Al2O3) and alumina-yttria stabilized zirconia (YSZ) composites containing 3 and 5 mass% ceria (CeO2) were prepared by spark plasma sintering (SPS) at temperatures of 1350-1400 °C for 300 s under a pressure of 40 MPa. Densification, microstructure and mechanical properties of the Al2O3 based composites were investigated. Fully dense composites with a relative density of approximately 99% were obtained. The grain growth of alumina was inhibited significantly by the addition of 10 vol% zirconia, and formation of elongated CeAl11O18 grains was observed in the ceria containing composites sintered at 1400 °C. Al2O3-YSZ composites without CeO2 had higher hardness than monolithic Al2O3 sintered body and the hardness of Al2O3-YSZ composites decreased from 20.3 GPa to 18.5 GPa when the content of ZrO2 increased from 10 to 30 vol%. The fracture toughness of Al2O3 increased from 2.8 MPa m1/2 to 5.6 MPa m1/2 with the addition of 10 vol% YSZ, and further addition resulted in higher fracture toughness values. The highest value of fracture toughness, 6.2 MPa m1/2, was achieved with the addition of 30 vol% YSZ. 相似文献
99.
Didar Sevim Oya Köseoğlu Hasan Ertaş Durmuş Özdemir Mehmet Ulaş Salih Günnaz Veysel Umut Çelenk 《Journal of the American Oil Chemists' Society》2023,100(5):355-367
Isotope ratio mass spectroscopy (IRMS) and nuclear magnetic resonance (NMR) spectroscopy techniques are two of the analytical methods that are used to characterize food products. The aim of this study is to classify extra virgin olive oil (EVOO) samples collected from different regions of Turkey based on 1H and 13C NMR spectra along with IRMS δ13C carbon isotope ratio data by using chemometrics multivariate data analysis methods. A total of 175 EVOO samples were analyzed in 2014/15 and 2015/16 harvest seasons. Multivariate classification and clustering models were used to identify geographical and botanical origins of the EVOOs. IRMS results showed that there was no significant difference in terms of δ13C values between the years in terms of harvest year (p > 0.05), only extraction phase and variety were statistically significant factors (p < 0.05). The interactions of the factors showed that the harvest year × variety interaction is important. The outcomes of this research clearly indicated that considering the partial least squares discriminant analysis result with NMR spectra, the percent success of the model in the South Marmara, North Aegean, and South Aegean region samples were 95%, 95.7%, and 96.4% in the model set, respectively. The results showed that by using classification and clustering models, geographic marking and labeling of these oils can be carried out regardless of differences in year and production systems (2 and 3 phase extraction system) according the NMR analysis. 相似文献
100.