全文获取类型
收费全文 | 576篇 |
免费 | 17篇 |
国内免费 | 47篇 |
专业分类
化学 | 190篇 |
晶体学 | 1篇 |
力学 | 90篇 |
数学 | 29篇 |
物理学 | 246篇 |
综合类 | 84篇 |
出版年
2024年 | 4篇 |
2023年 | 4篇 |
2022年 | 7篇 |
2021年 | 9篇 |
2020年 | 15篇 |
2019年 | 38篇 |
2018年 | 12篇 |
2017年 | 10篇 |
2016年 | 18篇 |
2015年 | 9篇 |
2014年 | 22篇 |
2013年 | 31篇 |
2012年 | 15篇 |
2011年 | 47篇 |
2010年 | 33篇 |
2009年 | 75篇 |
2008年 | 39篇 |
2007年 | 54篇 |
2006年 | 23篇 |
2005年 | 39篇 |
2004年 | 17篇 |
2003年 | 18篇 |
2002年 | 8篇 |
2001年 | 10篇 |
2000年 | 6篇 |
1999年 | 10篇 |
1998年 | 8篇 |
1997年 | 4篇 |
1996年 | 7篇 |
1995年 | 2篇 |
1994年 | 9篇 |
1993年 | 5篇 |
1992年 | 9篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1989年 | 5篇 |
1988年 | 3篇 |
1987年 | 4篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1968年 | 2篇 |
排序方式: 共有640条查询结果,搜索用时 15 毫秒
71.
72.
Driss Laraqui Olivier Allgaier Cornelius Schönnenbeck Gontrand Leyssens Jean-François Brilhac Ricardo Lomba Clément Dumand Olivier Guézet 《Proceedings of the Combustion Institute》2019,37(3):3175-3184
This work presents a study of a magnesium/air combustion process in the context of innovative zero carbon dioxide (CO2) energy carriers for reducing global warming effects. In order to analyze more deeply the confined combustion of magnesium under fluctuating overpressure conditions (0 to 24 hPa) and the generated gaseous by-products, magnesium/air flames have been realized in a combustion chamber with a conical bluff-body as flame holder and different contraction ratios diaphragms at the exit duct. Sieved magnesium samples with two size-fractions were tested: 20–50?µm and 50–70?µm. The gaseous emissions of nitrogen oxides (NOx) and dioxygen (O2) were analyzed with on-line infrared, ultraviolet and paramagnetic analyzers. A flame pulsating behavior was clearly observed from light emission intensity (monitored by a photodiode) and pressure fluctuations (monitored by a pressure sensor); the frequencies obtained ranged between 3 and 10?Hz. The frequency of the pulsation exhibited strong dependence on the geometric configuration of the chamber: a contraction diaphragm divided by two the frequency level of the fluctuations in the studied range of maximum overpressure. Such fluctuations may probably be the consequence of periodic perturbations of the recirculation zone behind the bluff-body. These periodic perturbations are themselves caused by strong periodic overpressure variations due to stiff contraction downstream responding to gas velocity fluctuations. This feed-back-loop mechanism was considered in this study. NOx emissions produced through the thermal pathway were analyzed for equivalence ratios ranging from 0.29 to 1. The representation of NOx versus equivalence ratio exhibited a parabolic shape with a maximum for an equivalence ratio of 0.4. Moreover, NOx emissions of this metal combustor have shown a similar order of magnitude than current internal combustion engines. 相似文献
73.
Daniel Fernández-Galisteo Vadim N. Kurdyumov 《Proceedings of the Combustion Institute》2019,37(2):1937-1943
The stability of a planar flame front propagating between two parallel adiabatic plates inclined at an arbitrary angle is investigated in the frame of narrow-channel approximation. It is demonstrated that buoyancy forces can suppress the hydrodynamic (Darrieus–Landau) and cellular (diffusive-thermal) instabilities for sufficiently large value of the gravity parameter for the case of downward-propagating flames. The stability analysis reveals that in the case of oscillatory diffusive-thermal instability, the flame front cannot be stabilized in the similar way. Finally, the stability results are compared satisfactorily with unsteady numerical simulations. 相似文献
74.
The combustion generated soot contamination effect on a single diesel droplet ignition and burning was investigated experimentally for the first time. Diesel droplet flame was used to contaminate the droplet to be investigated prior to ignition. Distinct differences in lifetime and stability of the burning of the neat and contaminated droplet samples were observed in their heating, boiling and disruptive phases. For a soot-contaminated droplet surface, the evaporation rate became weaker as a result of slower mass transfer thus contracted the flame formation. Contrary to the burning rate enhancement of droplet with stable and uniform suspension of particles observed by other researchers, the slightest contamination of soot particles in a fuel droplet surface can significantly reduce the burning rate. Denser agglomeration of soot can form a shell on the droplet surface which blocks the flow of gas escaping through the surface thus distort the droplet even further. At late combustion stage, bubbles are observed to rapture on the surface of the soot-contaminated droplet. Strong ejections of volatile liquid and vapour that would explode shortly after parting from the droplet are observed. It seems that the explosion and burning of ejected mixture have little interactions with the enveloped flame surrounding the primary droplet. Enhanced visualisation of droplet liquid-phase has clearly indicated the cause of declining trend in the burning rate and flame stand-off ratio of soot-contaminated diesel droplet. These insights are of significance for understanding the effect of fuel droplet contamination by combustion generated soot particles. 相似文献
75.
Guillaume Vignat Daniel Durox Kevin Prieur Sébastien Candel 《Proceedings of the Combustion Institute》2019,37(4):5205-5213
Combustion instabilities depend on a variety of parameters and operating conditions. It is known, especially in the field of liquid rocket propulsion, that the pressure loss of an injector has an effect on its dynamics and on the coupling between the combustion chamber and the fuel manifold. However, its influence is not well documented in the technical literature dealing with gas turbine combustion dynamics. Effects of changes in this key design parameter are investigated in the present article by testing different swirlers at constant thermal power on a broad range of injection velocities in a well controlled laboratory scale single injector swirled combustor using liquid fuel. The objective is to study the impact of injection pressure losses on the occurrence and level of combustion instabilities by making use of a set of injectors having nearly the same outlet velocity profiles, the same swirl number and that establish flames that are essentially identical in shape. It is found that combustion oscillations appear on a wider range of operating conditions for injectors with the highest pressure loss, but that the pressure fluctuations caused by thermoacoustic oscillations are greatest when the injector head loss is low. Four types of instabilities coupled by two modes may be distinguished: the first group features a lower frequency, arises when the injector pressure loss is low and corresponds to a weakly coupled chamber-plenum mode. The second group appears in the form of a constant amplitude limit cycle, or as bursts at a slightly higher frequency and is coupled by a chamber mode. Spontaneous switching between these two types of instabilities is also observed in a narrow domain. 相似文献
76.
Liuhao Ma Zhen Wang Kin-Pang Cheong Hongbo Ning Wei Ren 《Proceedings of the Combustion Institute》2019,37(2):1329-1336
We present the first demonstration of heterodyne phase-sensitive dispersion spectroscopy (HPSDS) for in situ, non-intrusive and quantitative CO2 concentration measurements in flames. Dispersion spectroscopy retrieves gas properties by measuring the refractive index in the vicinity of a molecular resonance. The HPSDS scheme features a significant diagnostic advantage of the intrinsic immunity to laser power fluctuations caused by beam steering, thermal radiation and soot scattering in combustion environments, and thus no extra calibration process is required. In this work, we described the spectroscopic fundamentals for measuring heterodyne phase signals in flames. As a proof of principle, we used a mid-infrared interband cascade laser (ICL) near 4183?nm to exploit the strong CO2 transitions in the R-branch of the v3 fundamental band. The HPSDS signals of four CO2 lines, R(76), R(78), R(80) and R(82), were measured in CH4/air flames to obtain CO2 concentrations at different equivalence ratios (Φ?=?0.8–1.2), yielding a good agreement with the simultaneous laser absorption measurements using the same ICL. With its immunity to laser power fluctuations verified experimentally, the HPSDS sensor was successfully implemented to measure CO2 concentrations in C2H4/air sooting flames (Φ?=?1.78–2.38). Laser dispersion spectroscopy proves to be a promising and alternative diagnostic tool for combustion measurements. 相似文献
77.
Mohamed E. Mostafa 《Proceedings of the Combustion Institute》2019,37(3):3053-3060
Fluorescence interference in Raman spectrum is a big barrier for rapid and precise analysis of coal structures by Raman spectroscopy. Dealing with fluorescence interference suitably is one of the key tasks before efficient application of Raman spectroscopy in coal assessment. In this study, Raman spectra and coal combustion characteristics of 32 kinds of Chinese coals were respectively obtained in a micro-Raman spectrometer and Thermal Gravimetric Analyzer. The degree of fluorescence interference in Raman spectrum was firstly defined and quantified as the drift coefficient α using a simple method without curve-fitting the spectrum. The correlations between the degree of fluorescence interference and coal property, coal combustion characteristics were set up and multivariable analysis was done. The results indicate that the degree of fluorescence interference is well related to the coal structures, and it is synthetically determined by volatile, moisture and ash content in coal. With the increase of volatile, moisture content in coal, the fluorescence interference increases continuously, and it can be reduced but not eliminated by drying the moisture in coals. Significant mathematical relations between the drift coefficient α and volatile, moisture content, coal combustion characteristic temperatures have been found. Coal with more evident fluorescence interference in Raman spectrum usually has lower degree of coalification, more polar functional groups, and burns at a lower temperature. The drift coefficient α can act as an efficient probe for coal property and coal combustion characteristics. This study provided a new and simple approach for evaluating coal property and coal combustion characteristics by fluorescence interference in Raman spectrum. 相似文献
78.
采用密度泛函理论计算和实验研究形貌可控制备氧化铁作为高效载氧体用于化学链燃烧的可行性. 首先从理论上对比分析Fe2O3高指数晶面[104]和低指数晶面[001]的反应活性及深层还原反应机理. 表面反应结果显示, Fe2O3[104]氧化CO的反应活性远高于Fe2O3[001], Fe2O3[104]被还原成为低价的铁氧化物或单质, 这些低价的铁氧化物或单质可被O2氧化再生. 载氧体和CO深层反应结果显示Fe2O3[104]可被CO彻底还原成Fe单质, Fe2O3[104]释放氧能力强, 反应活性高; 而Fe2O3[001]还原到一定程度后反应能垒高, 抑制表面进一步还原, 释放氧能力有限. 最后, 实验结果进一步证明了Fe2O3[104]作为载氧体用于化学链燃烧的高反应活性及稳定性. 相似文献
79.
Xiaofeng Peng 《Applied Surface Science》2009,255(8):4384-4388
A novel approach is presented for nanohole 3D-size tailoring. The process starts with a monolayer of polystyrene (PS) beads spun coat on silicon wafer as a template. The holes can be directly prepared through combustion of PS beads by oxygen plasma during metal or oxide thin film deposition. The incoming particles are prevented from adhering on PS beads by H2O and CO2 generated from the combustion of the PS beads. The hole depth generally depends on the film thickness. The hole diameter can be tailored by the PS bead size, film deposition rate, and also the combustion speed of the PS beads. In this work, a series of holes with depth of 4-24 nm and diameter of 10-36 nm has been successfully prepared. The hole wall materials can be selected from metals such as Au or Pt and oxides such as SiO2 or Al2O3. These templates could be suitable for the preparation and characterization of novel nanodevices based on single quantum dots or single molecules, and could be extended to the studies of a wide range of coating materials and substrates with controlled hole depth and diameters. 相似文献
80.
G.M. Dutro R.A. Yetter G.A. Risha S.F. Son 《Proceedings of the Combustion Institute》2009,32(2):1921-1928
The effect of stoichiometry on the combustion behavior of the nanoscale aluminum molybdenum trioxide (nAl/MoO3) thermite was studied in a burn tube experiment by characterizing the propagation velocity and pressure output of the reaction. Changing the stoichiometry affects the combustion through changes in the product temperature, phase, and composition. The mixture ratios of the composites were varied over an extremely wide range (5% nAl (95% MoO3)–90% nAl (10% MoO3)). Results revealed three separate combustion regimes: a steady high speed propagation (100 to 1000 m/s) from approximately 10% to 65% nAl, an oscillating and accelerating wave near 70% nAl, and a steady-slow speed propagation (0.1–1 m/s) from approximately 75% to 85% nAl. Propagation was observed to fail both <10% nAl and >85% nAl. This is the first known observation of such limits for a nanoscale thermite in a tube geometry. The instrumented tube tests revealed peak pressures over 8 MPa near stoichiometric conditions in the steady high speed propagation region, no measurable pressure rise at low speed propagation, and building pressures for accelerating waves. The results suggest the propagation mode to be a supersonic convective wave for near stoichiometric mixtures and a conductive deflagration for extremely fuel-rich mixtures. The implications of these results for microscale combustion applications are discussed. 相似文献