全文获取类型
收费全文 | 237篇 |
免费 | 9篇 |
专业分类
化学 | 162篇 |
晶体学 | 5篇 |
力学 | 2篇 |
数学 | 36篇 |
物理学 | 41篇 |
出版年
2023年 | 1篇 |
2022年 | 6篇 |
2021年 | 7篇 |
2020年 | 8篇 |
2019年 | 9篇 |
2018年 | 9篇 |
2017年 | 13篇 |
2016年 | 14篇 |
2015年 | 7篇 |
2014年 | 9篇 |
2013年 | 23篇 |
2012年 | 18篇 |
2011年 | 21篇 |
2010年 | 16篇 |
2009年 | 16篇 |
2008年 | 13篇 |
2007年 | 16篇 |
2006年 | 10篇 |
2005年 | 7篇 |
2004年 | 4篇 |
2003年 | 4篇 |
2002年 | 1篇 |
2001年 | 1篇 |
1994年 | 1篇 |
1992年 | 1篇 |
1990年 | 1篇 |
1983年 | 2篇 |
1976年 | 3篇 |
1975年 | 1篇 |
1973年 | 1篇 |
1970年 | 1篇 |
1956年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有246条查询结果,搜索用时 15 毫秒
141.
Muvaffak Seyhan 《Monatshefte für Chemie / Chemical Monthly》1955,86(3):545-548
Zusammenfassung Es wird die Darstellung einiger koordinativ ungesättigter Nickelkomplexe der heterocyclischen Formazylreihe beschrieben. 相似文献
142.
Ronald J. Baker David C. Lankin Pesi P. Umrigar Gary W. Griffin Seyhan N. Ege Katherine S. Ragone Louis M. Trefonas 《Journal of heterocyclic chemistry》1983,20(3):559-563
The stereochemical assignment of molecular geometry for α-arylidene carbonyl compounds and spirooxirane derived from them have continued to be a challenging problem for which the most satisfactory solution continues to be an x-ray diffraction structure determination. In that regard, the title compound (a spirooxirane) has been found to crystallize in the monoclinic space group P21/c with cell dimensions of a = 5.989(1)Å, b = 27.625(4)Å, c = 9.374(2)Å, β = 99.06(1)°. The structure of the compound has been determined, with the refinement to R = 0.059. The previous, tentative assignment of structure has been confirmed substantiating our prediction that the oxidation of the enone system proceeds with rotation of the phenyl group on the β-carbon away from the carbonyl group, minimizing adverse steric interactions and allowing orbitals of the carbonyl group to overlap with those of the carbanionic center during the closure of the oxirane ring. The agreement between predictions based on nmr data and the x-ray diffraction determination will support a stronger reliance on the nmr data predictions in subsequent studies. 相似文献
143.
Let G be a locally compact group, let be a 2‐cocycle, and let () be a complementary pair of strictly increasing continuous Young functions. We continue our investigation in [14] of the algebraic properties of the Orlicz space with respect to the twisted convolution ? coming from Ω. We show that the twisted Orlicz algebra posses a bounded approximate identity if and only if it is unital if and only if G is discrete. On the other hand, under suitable condition on Ω, becomes an Arens regular, dual Banach algebra. We also look into certain cohomological properties of , namely amenability and Connes‐amenability, and show that they rarely happen. We apply our methods to compactly generated group of polynomial growth and demonstrate that our results could be applied to variety of cases. 相似文献
144.
Lütfiye Dumlu Asli Seyhan Ciggin Stefan Ru
man N. Altnay Perendeci 《Molecules (Basel, Switzerland)》2021,26(14)
Pretreatment and codigestion are proven to be effective strategies for the enhancement of the anaerobic digestion of lignocellulosic residues. The purpose of this study is to evaluate the effects of pretreatment and codigestion on methane production and the hydrolysis rate in the anaerobic digestion of agricultural wastes (AWs). Thermal and different thermochemical pretreatments were applied on AWs. Sewage sludge (SS) was selected as a cosubstrate. Biochemical methane potential tests were performed by mixing SS with raw and pretreated AWs at different mixing ratios. Hydrolysis rates were estimated by the best fit obtained with the first-order kinetic model. As a result of the experimental and kinetic studies, the best strategy was determined to be thermochemical pretreatment with sodium hydroxide (NaOH). This strategy resulted in a maximum enhancement in the anaerobic digestion of AWs, a 56% increase in methane production, an 81.90% increase in the hydrolysis rate and a 79.63% decrease in the technical digestion time compared to raw AWs. On the other hand, anaerobic codigestion (AcoD) with SS was determined to be ineffective when it came to the enhancement of methane production and the hydrolysis rate. The most suitable mixing ratio was determined to be 80:20 (Aws/SS) for the AcoD of the studied AWs with SS in order to obtain the highest possible methane production without any antagonistic effect. 相似文献
145.
ABSTRACTThis article examines patterns of classroom organisation and interaction associated with the use of a particular type of digital technology – the dynamic software GeoGebra – in the lessons of an opportunity sample of three English secondary-school mathematics teachers. The concept of activity structure is used to organise this study, further informed by the concept of instrumental orchestration. While the case study analysis identifies structures already reported in those earlier papers, it also draws attention to the prevalence of a Predict-and-test format in tasks carried out by students at the computer. This study also shows how synthesising the activity structure and instrumental orchestration frameworks may be productive. 相似文献
146.
A rapid and specific proton magnetic resonance (PMR) spectroscopic method was developed for determining ranitidine hydrochloride in tablets. 2-Choloroacetophenon was used as the internal standard and DMSO-d6 served as the PMR solvent. The concentration of drug per unit dose was calculated from the integration values for the resonance signals of ranitidine hydrochloride at 4.32 δ ppm and int. st. at 5.19 δ ppm. The method using commercial products gave comparable results to those obtained by the methods of UV spectroscopy and USP XXIII. 相似文献
147.
K. Tsukada P. Achenbach C. Ayerbe Gayoso R. Böhm O. Borodina D. Bosnar V. Bozkurt L. Debenjak M. Distler A. Esser I. Friščić Y. Fujii T. Gogami M. Gomez O. Hashimoto S. Hirose E. Kim A. Margaryan H. Merkel U. Müller S. Nagao S. N. Nakamura J. Pochodzalla C. Rappold J. Reinhold A. Sanchez Lorente T. Saito B. S. Schlimme M. Schoth F. Schulz C. Sfienti S. Širca L. Tang 《Few-Body Systems》2013,54(1-4):375-379
The investigation of light hypernuclei is quite important for understanding the basic YN interaction and the mechanism of hypernuclear structure. We started the commissioning of the decay pion spectroscopy of light hypernuclei at MAMI-C in 2011. In order to realize the K+ tagging efficiently, some detectors on KAOS spectrometer were upgraded or newly installed. The existing and well-studied spectrometers, SpekA, SpekC were used as pion spectrometers. The analysis is ongoing to estimate the detectors performance and develop the spectrometers for future experiments with higher beam intensity. The preliminary results of the particle identification are presented in this article. 相似文献
148.
The temporal variation of chemiluminescence emission from OH?(A2 Σ +) and CH?(A2 Δ) in reacting Ar-diluted H2/O2/CH4, C2H2/O2 and C2H2/N2O mixtures was studied in a shock tube for a wide temperature range at atmospheric pressures and various equivalence ratios. Time-resolved emission measurements were used to evaluate the relative importance of different reaction pathways. The main formation channel for OH? in hydrocarbon combustion was studied with CH4 as benchmark fuel. Three reaction pathways leading to CH? were studied with C2H2 as fuel. Based on well-validated ground-state chemistry models from literature, sub-mechanisms for OH? and CH? were developed. For the main OH?-forming reaction CH+O2=OH?+CO, a rate coefficient of k 2=(8.0±2.6)×1010 cm3?mol?1?s?1 was determined. For CH? formation, best agreement was achieved when incorporating reactions C2+OH=CH?+CO (k 5=2.0×1014 cm3?mol?1?s?1) and C2H+O=CH?+CO (k 6=3.6×1012exp(?10.9 kJ?mol?1/RT) cm3?mol?1?s?1) and neglecting the C2H+O2=CH?+CO2 reaction. 相似文献
149.
Yunus Çelik Esat Bozkurt İbrahim Uçar Bünyamin Karabulut 《Journal of Physics and Chemistry of Solids》2012,73(8):1010-1016
The crystal structures of [Co(4-acpy)2(H2O)4] (sac)2 (1) and [Zn(4-acpy)2(H2O)4] (sac)2 (2) (4-acpy: 4-acetylpyridine, sac: saccharinate) complexes have been investigated by X-ray diffraction techniques. The magnetic environments of Cu2+ doped [Co(4-acpy)2(H2O)4] (sac)2 and [Zn(4-acpy)2(H2O)4] (sac)2 complexes have been identified by electron paramagnetic resonance (EPR) technique. Principal values of g and hyperfine tensors are determined and the ground state wave functions of Cu2+ ions are obtained using EPR parameters. The vibrational spectra were also discussed in relation with the other compounds containing saccharinate and 4-acetylpyridine complexes. 相似文献
150.
Meral G. Babaoğlu Serap Safran Özlem Çiçek Hasan Ağıl Ercan Ertekin Md.Shahriar A. Hossain Ekrem Yanmaz Ali Gencer 《Journal of magnetism and magnetic materials》2012
The effect of aromatic hydrocarbon (benzene, C6H6) addition on lattice parameters, microstructure, critical temperature (Tc), critical current density (Jc) of bulk MgB2 has been studied. In this work only 2 mol% C6H6 addition was found to be very effective in increasing the Jc values, while resulting in slight reduction of the Tc. Jc values of 2 mol% C6H6 added MgB2 bulks reached to 1.83×106 A/cm2 at 15 K and 0 T. Microstructural analyses suggest that Jc enhancement is associated with the substitution of carbon with boron and which also results in the smaller MgB2 grain size. The change in the lattice parameters or the lattice disorder is claimed as a cause of the slight reduction in the Tc by carbon addition. We note that our results show the advantages of C6H6 addition include homogeneous mixing of precursor powders, avoidance of expansive nanoadditives, production of highly reactive C, and significant enhancement in Jc of MgB2, compared to un-doped samples. 相似文献