全文获取类型
收费全文 | 126篇 |
免费 | 4篇 |
国内免费 | 1篇 |
专业分类
化学 | 76篇 |
晶体学 | 2篇 |
数学 | 35篇 |
物理学 | 18篇 |
出版年
2022年 | 3篇 |
2021年 | 1篇 |
2020年 | 5篇 |
2019年 | 3篇 |
2018年 | 3篇 |
2017年 | 1篇 |
2016年 | 6篇 |
2014年 | 1篇 |
2013年 | 11篇 |
2012年 | 6篇 |
2011年 | 6篇 |
2010年 | 4篇 |
2009年 | 3篇 |
2008年 | 10篇 |
2007年 | 2篇 |
2006年 | 3篇 |
2005年 | 8篇 |
2004年 | 5篇 |
2003年 | 6篇 |
2002年 | 7篇 |
2001年 | 4篇 |
2000年 | 3篇 |
1999年 | 5篇 |
1998年 | 2篇 |
1997年 | 1篇 |
1996年 | 2篇 |
1995年 | 3篇 |
1994年 | 1篇 |
1993年 | 3篇 |
1991年 | 1篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1986年 | 1篇 |
1984年 | 1篇 |
1981年 | 2篇 |
1968年 | 1篇 |
1967年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有131条查询结果,搜索用时 46 毫秒
1.
Gamil A. Al-Hazmi Mohammed S. El-Shahawi Ahmed A. El-Asmy 《Transition Metal Chemistry》2005,30(4):464-470
The redox properties of the title mono- and binuclear copper(II) chelates have been investigated by cyclic voltammetry in DMF at a working platinum electrode. The cathodic reduction and anodic oxidation of the investigated chelates produced the corresponding electrochemical CuI and CuIIIspecies stable only in the voltammetric time scale, The effects of substituents on E1/2, redox properties and stability towards oxidation of the complexes were related to the electron-withdrawing or releasing ability of the substituents on the C=N1[H, CH3 or C6H5] and/or N4H [H, C2H5, C6H5 or pClC6H4] groups, The electron attracting substituents stabilize the Cu(II) complexes while electron-donating groups favor oxidation to Cu(III). Changes in the E1/2 for the complexes due to remote substituent effects could be related to changes in basicity of N4H.Thus, variation in N41-J has more influence on E1/2 than changes in C=N1. The correlation between E1/2 of the complexes and pKa of the ligands has been attributed to the spherical potential generated by the electron density of the donor atoms at the antibonding d orbitals. 相似文献
2.
Stephen Bell Xiaodong Zhu Gamil A. Guirgis James R. Durig 《Journal of Molecular Structure》2002,616(1-3):135-158
The infrared spectra (3500–50 cm−1) of the gas and solid and the Raman spectra (3500–50 cm−1) of the liquid and solid have been recorded for 2-hexyne, CH3–CC–CH2CH2CH3. Variable temperature studies of the infrared spectrum (3500–400 cm−1) of 2-hexyne dissolved in liquid krypton have also been recorded. Utilizing four anti/gauche conformer pairs, the anti(trans) conformer is found to be the lower energy form with an enthalpy difference of 74±8 cm−1 (0.88±0.10 kJ/mol) determined from krypton solutions over the temperature range −105 to −150 °C. At room temperature it is estimated that there is 42% of the anti conformer present. Equilibrium geometries and energies of the two conformers have been determined by ab initio (HF and MP2) and hybrid DFT (B3LYP) methods using a number of basis sets. Only the HF and DFT methods predict the anti conformer as the more stable form as found experimentally. A vibrational assignment is proposed based on the force constants, relative intensities, depolarization ratios from the ab initio and DFT calculations and on rotational band contours obtained using the calculated equilibrium geometries. From calculated energies it is shown that the CH3 group exhibits almost completely free rotation which is in agreement with the observation of sub-band structure for the degenerate methyl vibrations from which values of the Coriolis coupling constants, ζ, have been determined. The results are compared to similar properties of some corresponding molecules. 相似文献
3.
The sensitivity of an enzyme to its environment has provoked much interest both for its immediate relevance to biochemistry and for the use of enzymes in chemical synthesis. The intercellular or extracellular environment in which an enzyme naturally operates is crowded with macromolecular, small-molecule, and ionic solutes and hence is markedly different from the dilute aqueous buffer solutions commonly cited for comparisons of biochemical processes. We report the results of a kinetic study into the effects of such a crowded solution on the rate of an enzyme-mediated process-the trypsin-catalyzed hydrolysis of a nonnatural substrate ester. The catalytic rate constant decreases linearly with solvent polarity, but substrate binding is independent of the concentration of added crowding agent up to 395 g/L. 相似文献
4.
The infrared (3200-40 cm(-1)) spectra of gaseous and solid 1,1-dicyclopropylethene, (c-C3H5)2C=CH2, along with the Raman (3200-40 cm(-1)) spectra of liquid and solid phases, have been recorded. The major trans-gauche (C=C bond trans to one ring with the other ring rotated about 60 degrees from the C=C bond, trivial C(1) symmetry) and gauche-gauche (the two three-membered rings rotated oppositely about 60 degrees from the C=C bond, C2 symmetry) rotamers have been confidently identified in the fluid phases, but no definitive spectroscopic evidence was found for the gauche-gauche' form (the two three-membered rings rotated to the same side about 60 degrees from the C=C bond, Cs symmetry), which is calculated to be present in no more than 6% at ambient temperature. Variable-temperature (-55 to -100 degrees C) studies of the infrared spectra of the sample dissolved in liquid xenon have been carried out. Utilizing six different combinations of pairs of bands from the C1 and C2 conformers, the average enthalpy difference between these two has been determined to be 146 +/- 30 cm(-1) (1.75 +/- 0.36 kJ x mol(-1)), with the C1 form more stable. Given statistical weights of 2:1:1 respectively for the C1, C2, and Cs forms, it is estimated that there are 75 +/- 2% C(1) and 19 +/- 1% C2 conformers present at ambient temperature. By utilizing predicted frequencies, infrared intensities, Raman activities, and band envelopes from scaled MP2(full)/6-31G(d) ab initio calculations, a complete vibrational assignment is made for the C1 form and a number of fundamentals of the C2 conformer have been identified. The structural parameters, dipole moments, and conformational stabilities have been obtained from ab initio calculations at the level of Hartree-Fock (RHF), the perturbation method to second order with full electron correlation (MP2(full)), and hybrid density functional theory (DFT) by the B3LYP method with a variety of basis sets. The predicted conformational stabilities from the MP2 calculations with relatively large basis sets are consistent with the experimental results. Structural parameters are estimated from the MP2(full)/6-311+G(d,p) predictions which are compared to the previously reported electron diffraction parameters. These experimental and theoretical results are compared to the corresponding quantities of some similar molecules. 相似文献
5.
Duffy DJ Quenneville J Baumbaugh TM Kitchener SA McCormick RK Dormady CN Croce TA Navabi A Stidham HD Hsu SL Guirgis GA Deng S Durig JR 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2004,60(3):659-671
Ab initio calculations are reported for three of four possible conformers of 1,3-dichloropropane. The fourth conformer, with Cs symmetry, has a predicted enthalpy difference of more than 1500 cm(-1) from the most stable conformer from each calculation regardless of the basis set used, so there is little chance of observing it. Thus, there is no evidence in the infrared or Raman spectrum of the presence of a fourth conformer. The order of stability given by the ab initio calculations is C2(GG)>C1(AG)>C2v(AA)>Cs(GG'), where A indicates the anti form for one of the CH2Cl groups and G indicates the gauche conformation for the other CH2Cl group relative to the plane of the carbon atoms. Almost every band observed can be confidently assigned to one or another of the conformers. Many observed bands proved to be of a composite nature, with several nearly coincident vibrations of different conformers contributing to the band contour. Nonetheless, a complete assignment of fundamentals is possible for the most stable C2 conformer, and 5 of the fundamentals of the C2v conformer and 13 those of the C1 conformer can be confidently assigned. 相似文献
6.
7.
Gouda A. A. El Sheikh R. El Sayed H. M. Khedr A. M. Al Ezz Sh. Abo Gamil W. Hamdy M. 《Journal of Applied Spectroscopy》2022,89(3):567-578
Journal of Applied Spectroscopy - A new, green, simple, and validated ultrasound-assisted dispersive microsolid-phase extraction method applying unprecedented adsorbent-modified multiwalled carbon... 相似文献
8.
Korany Mohamed Abdel Tawab Moneeb Marwa Said Selim Dina Ahmed Asaad Aya Mohamed El-Sebakhy Nadia Abdel Aziz 《平面色谱法杂志一现代薄层色谱法》2016,29(2):148-154
JPC – Journal of Planar Chromatography – Modern TLC - 相似文献
9.
Fahmy M. Asaad Nazih Latif Nawal Mishriky Ibrahim Zeid 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-2):17-18
Abstract In the present investigation, the authors could obtain a new series of spiranes (1) through the reaction of the high potential quinone tetrachloro-o-benzoquinone with 2-aryl-3-phenyl-3H-quinazoline-4-thiones. Thus, 2,3-diphenyl- (2a), 2-p-tolyl-3-phenyl- (2b) and 2-p-anisyl-3-phenyl- (2c)-3H-quinazoline-4-thiones react readily with tetrachloro-o-benzoquinone, in boiling toluene, to give the corresponding spiro-1,3-benzodioxole-2,4′-(3′H)-quinazolines (1a-c), respectively. 相似文献
10.
Gamil A. Guirgis Mohammad A. Qtaitat Y. A. Pentin C. M. Whang J. F. Sullivan J. R. Durig Peter Klaeboe 《Fresenius' Journal of Analytical Chemistry》1995,352(5):499-507
The Raman (50 to 3200 cm–1) and infrared (50 to 3500 cm–1) spectra of chlorodimethylmethoxysilane, Cl(CH3)2SiOCH3, in the vapor and solid phases have been recorded. Raman spectra of the liquid including depolarization ratios have also been recorded. Optimized geometries and conformational stabilities have been obtained from ab initio calculations utilizing the RHF/3–21G* and RHF/6–31G* basis sets. The calculations from both of these basis sets indicated the gauche conformer to be significantly more stable than the trans conformer. Since the gauche has twice the multiplicity of the trans form it is unlikely that the trans conformer will be detected in the fluid phases at room temperature. This is supported by the fact that no infrared or Raman bands were found to vanish in the spectra of the crystalline solid. The vibrational frequencies have been calculated using appropriate scaling factors, and the vibrational spectra are interpreted in detail. The results have been compared with those obtained for some related molecules.Dedicated to Professor Dr. H. Kriegsmann on the occasion of his 70th birthdayFor part XX, see J Raman Spectrosc 26:in press (1995)Analytical R/D Department, Organic Products Division, Miles Inc., Bushy Park Plant. Charleston, SC 9411, USAChemistry Department, Mu'tah University, P.O.Box 7, Mu'tah-Karak, JordanDepartment of Chemistry, Moscow State University, Moscow, B-234, RussiaDepartment of Ceramic Engineering, Inha University, Nam-Ku, Incheon 160, KoreaDepartment of Chemistry, University of Oslo, P.O.Box 1033, 0315 Oslo, Norway 相似文献