全文获取类型
收费全文 | 985篇 |
免费 | 62篇 |
国内免费 | 15篇 |
专业分类
化学 | 624篇 |
晶体学 | 6篇 |
力学 | 41篇 |
数学 | 124篇 |
物理学 | 267篇 |
出版年
2024年 | 7篇 |
2023年 | 15篇 |
2022年 | 34篇 |
2021年 | 101篇 |
2020年 | 43篇 |
2019年 | 52篇 |
2018年 | 53篇 |
2017年 | 36篇 |
2016年 | 82篇 |
2015年 | 63篇 |
2014年 | 76篇 |
2013年 | 75篇 |
2012年 | 84篇 |
2011年 | 60篇 |
2010年 | 38篇 |
2009年 | 28篇 |
2008年 | 34篇 |
2007年 | 26篇 |
2006年 | 24篇 |
2005年 | 18篇 |
2004年 | 12篇 |
2003年 | 8篇 |
2002年 | 12篇 |
2001年 | 6篇 |
2000年 | 4篇 |
1999年 | 2篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1996年 | 2篇 |
1995年 | 5篇 |
1994年 | 7篇 |
1993年 | 8篇 |
1992年 | 3篇 |
1991年 | 4篇 |
1990年 | 7篇 |
1989年 | 2篇 |
1988年 | 5篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 5篇 |
1980年 | 2篇 |
1976年 | 2篇 |
1968年 | 1篇 |
1966年 | 1篇 |
1965年 | 2篇 |
排序方式: 共有1062条查询结果,搜索用时 109 毫秒
61.
Let G be a fnite group and P a subgroup of order 3. In this paper we proved some results about the soluble subgroups generated by three conjugates of P and we use these results to produce some properties of the group G. 相似文献
62.
Takayoshi Kimura Sekai Iwama Satoko Kido Mohammad Abdullah Khan 《The Journal of chemical thermodynamics》2009,41(10):1170-1177
Enthalpies of mixing and the densities of ethanol solution of R- and S-enantiomers of camphor, 10-camphorsulfonamide, 10-camphorsulfonic acid, camphorquinone, and 10-camphorsulfonyl chloride have been measured for a wide range of mole fractions of heterochiral components at 298.15 K. Enthalpies of mixing were exothermic for all concentrations and heterochiral solutions were more stable than each of the homochiral solutions. Enthalpic stabilization of mixing of heterochiral solutions was increased with a decreasing concentration of all the camphor derivatives measured. The sequence of enthalpic stabilization on mixing was 10-camphorsulfonyl chloride, 10-camphorsulfonic acid, 10-camphorsulfonamide, camphor, and camphorquinone. Apparent molar volumes were determined and excess volumes of mixing of heterochiral solutions were small and negative. Enthalpic stabilizations were found to be dependent on dipole–dipole interaction between solutes and solvents. 相似文献
63.
64.
POOL — Listing service in game theory no. 17 相似文献
65.
Abdullah S. AlRamadan Moez Ben Houidi Julien Sotton Marc Bellenoue Bengt Johansson S. Mani Sarathy 《Proceedings of the Combustion Institute》2021,38(4):5539-5548
One approach to enhancing the thermal efficiency of combustion systems is to burn fuels at ultra-lean conditions (equivalence ratio below 0.5). It has been recently reported that the auto-ignition of some hydrocarbon fuels, under specific temperature, pressure, and mixture conditions, releases heat in three distinctive stages. The three auto-ignition stages can be divided as a first low-temperature auto-ignition stage with conventional low temperature, and a high-temperature stage separated into two sub-stages. This study presents ignition delay time measurements of n-heptane and methyl-cyclohexane (MCH) mixtures in a flat piston rapid compression machine (RCM) under ultra-lean conditions. It provides experimental evidence of three-stage auto-ignition. This phenomenon of delayed high-temperature heat release is seldom reported in the literature and this is the first time to be reported for these types of fuels. The experiments cover two binary n-heptane/MCH mixtures of 15/85 and 70/30 by volume, pressures of 11 bar and 16 bar, temperature range of 700 to 900 K, and equivalence ratio of 0.4. The RCM optical access was utilized for high-speed chemiluminescence imaging. Detailed chemical kinetic simulations in a homogenous batch reactor with variable volume were conducted to further interrogate the three-stage auto-ignition phenomenon. Chemiluminescence shows that three-stage auto-ignition occurs in the adiabatically compressed end-gas, which indicates that this phenomenon is chemically-driven and is not induced by a thermal stratification in the RCM experiments. The model predicts the features of three-stage auto-ignition, which were experimentally observed at temperatures approximately below 750 K. As expected, significant discrepancies are observed in the ignition delays of experiment and simulation in the negative temperature coefficient (NTC) region. The simulation of the n-heptane/MCH 70/30 mixture shows better agreement with experiments in the Positive Temperature Coefficient (PTC) region compared to the 15/85 mixture. 相似文献
66.
Innus Mohammad JiYoung Mun Amber Onorato Martha D. Morton Abdullah I. Saleh Michael B. Smith 《Tetrahedron letters》2017,58(44):4162-4165
When compared to a long-straight chain terminal alkyne, a long chain terminal alkyne with a distal isopropyl unit (isobranched) isomerizes about two times faster when treated with strong base under identical conditions, and appears to follow pseudo first order kinetics. In both cases, equilibration to a 95–97:5–3 mixture of terminal:internal alkyne accompanies isomerization. The difference in rate may be due to an unusual folding of both long-chain alkynes, bringing the distal substituent close to the carbon-carbon-triple bond moiety. The distal isopropyl moiety may provide unanticipated steric hindrance that disrupts such folding, making the propargylic proton more available for reaction with base. 相似文献
67.
68.
Sofiyev Abdullah Ay Zeki 《Acta Mechanica Solida Sinica》2003,16(1):81-87
The subject of this investigation is to study the buckling of orthotropic cylindricalthin shells under torsion,which is a power function of time.The dynamic stability and compati-bility equations are obtained first.These equations are subsequently reduced to a time dependentdifferential equation with variable coefficient by using Galerkin's method.Finally,the critical dy-namic and static loading,the corresponding wave numbers,the dynamic factors,critical time andcritical impulse are found analytically by applying the Ritz type variational method.Using thoseresults,the effects of the variations of the power of time in the torsion load expression,of theloading parameter,the ratio of the Young's moduli and the ratio of the radius to thickness onthe critical parameters are studied numerically.It is observed that these factors have appreciableeffects on the critical parameters of the problem in the heading. 相似文献
69.
A facile and convenient synthesis of bis(2-(1H-benzo[d]imidazol-2(3H)-ylidene)-3-oxopropanenitrile), bis((3-amino-5-(methylthio)-1H-pyrazol-4-yl)methanone) and bis(2-thioxo-1,2-dihydropyrimidine-5-carbonitrile) derivatives incorporating a thieno- [2,3-b]thiophene moiety via versatile, readily accessible diethyl 3,4-dimethylthieno-[2,3-b]thiophene-2,5-dicarboxylate is described. 相似文献
70.
Abdullah S. Al-Dughaither Ahmed A. Ibrahim Waheed A. Al-Masry 《Journal of Saudi Chemical Society》2010,14(4):331-339
Effects of design parameters on performance of wire-mesh mist eliminators were experimentally investigated in 15 cm bubble column. The demisters performances were evaluated by droplet collection efficiency as a function of wide ranges of operating and design parameters. These parameters include: droplet size exiting the demister (250–380 μm), specific surface area (236–868 m2/m3), void fraction (97–98.3%), wire diameter (0.14–0.28 mm), packing density (130–240 kg/m3), and superficial gas velocity (0.109–0.118 m/s. All demisters were 15 cm in diameter with 10 cm pad thickness, made from 316L stainless steel layered type demister pad wires. Experiments were carried out using air–water system at ambient temperature and atmospheric pressure. The experimental data on the droplet removal efficiency were obtained using Malvern Laser Droplet Sizer. The removal efficiency was found to increase with the increasing the demister specific surface area, packing density, and superficial gas velocity. In contrast, the removal efficiency was found to increase with decreasing the demister void fraction and wire diameter. The separation efficiency is correlated empirically as a function of the design parameters. A good agreement was obtained between the measured values and the correlation predictions with ±5% accuracy. 相似文献