全文获取类型
收费全文 | 300篇 |
免费 | 8篇 |
专业分类
化学 | 178篇 |
晶体学 | 1篇 |
力学 | 10篇 |
数学 | 40篇 |
物理学 | 79篇 |
出版年
2023年 | 7篇 |
2021年 | 3篇 |
2020年 | 17篇 |
2019年 | 13篇 |
2018年 | 5篇 |
2017年 | 4篇 |
2016年 | 6篇 |
2015年 | 6篇 |
2014年 | 7篇 |
2013年 | 16篇 |
2012年 | 13篇 |
2011年 | 13篇 |
2010年 | 8篇 |
2009年 | 7篇 |
2008年 | 22篇 |
2007年 | 10篇 |
2006年 | 6篇 |
2005年 | 5篇 |
2004年 | 9篇 |
2003年 | 4篇 |
2002年 | 9篇 |
2001年 | 5篇 |
2000年 | 5篇 |
1998年 | 3篇 |
1997年 | 2篇 |
1996年 | 5篇 |
1995年 | 4篇 |
1994年 | 4篇 |
1993年 | 5篇 |
1992年 | 4篇 |
1990年 | 3篇 |
1989年 | 5篇 |
1987年 | 4篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1981年 | 5篇 |
1980年 | 4篇 |
1979年 | 5篇 |
1978年 | 4篇 |
1977年 | 7篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1973年 | 5篇 |
1970年 | 2篇 |
1966年 | 2篇 |
1954年 | 2篇 |
1934年 | 2篇 |
排序方式: 共有308条查询结果,搜索用时 15 毫秒
111.
112.
113.
From the essential oil of myrrh (Commiphora molmol ENGLER) three new furanogermacrens have been isolated and their structures elucidated to , and . 相似文献
114.
Use of gas chromatography/mass spectrometry selected-ion recording for sterol content pattern recognition in fungal classification 总被引:1,自引:0,他引:1
Chemotaxonomic studies are frequently limited by the volume of data obtained and the difficulty of reducing this to statistically interpretable results. This paper describes the use of a straightforward procedure for relating the pattern of occurrence of sterols in fungi, analysed by mass spectrometry, to their classification. 相似文献
115.
116.
The electronic absorption and circular dichroism (CD) spectra of the complexes produced by the one, two, and three electron reduction of Delta-[Ru(bipy)(3)](2+) and Delta-[Os(bipy)(3)](2+) are reported. The CD spectra give unequivocal proof that the added electrons are localized on individual bipiridine ligands and thus that the complexes are correctly formulated [M(bipy)(2)(bipy(-))](+), [M(bipy)(bipy(-))(2)](0), and [M(bipy(-))(3)](-). The absorption spectra of the triply reduced species [M(bipy(-))(3)](-) (M = Ru, Os) are compared to those of the Fe(II) and Ir(III) analogs. The luminescence spectra of the two triply reduced complexes [Ru(bipy(-))(3)](-) and [Os(bipy(-))(3)](-). are also presented. The MLCT luminescence found in the parent complexes is completely quenched and is replaced by a weak luminescence attributed to the pi(10) --> pi(7) transition of the (coordinated) [bipy](-) ion. 相似文献
117.
Finotello A Bara JE Narayan S Camper D Noble RD 《The journal of physical chemistry. B》2008,112(8):2335-2339
This study focuses on the solubility behaviors of CO2, CH4, and N2 gases in binary mixtures of imidazolium-based room-temperature ionic liquids (RTILs) using 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C2mim][Tf2N]) and 1-ethyl-3-methylimidazolium tetrafluoroborate ([C2mim][BF4]) at 40 degrees C and low pressures (approximately 1 atm). The mixtures tested were 0, 25, 50, 75, 90, 95, and 100 mol % [C2mim][BF4] in [C2mim][Tf2N]. Results show that regular solution theory (RST) can be used to describe the gas solubility and selectivity behaviors in RTIL mixtures using an average mixture solubility parameter or an average measured mixture molar volume. Interestingly, the solubility selectivity, defined as the ratio of gas mole fractions in the RTIL mixture, of CO2 with N2 or CH4 in pure [C2mim][BF4] can be enhanced by adding 5 mol % [C2mim][Tf2N]. 相似文献
118.
A SAPO-34 membrane separated CO2/H2 and H2/CH4 mixtures at feed pressures up to 1.7 MPa. Strong CO2 adsorption inhibited H2 adsorption and decreased H2 permeances significantly, especially at low temperatures, so that CO2 preferentially permeated and CO2/H2 selectivities were higher at low temperatures. At 253 K, CO2/H2 separation selectivities were greater than 100 with CO2 permeances of 3 × 10−8 mol m−2 s−1 Pa−1. The CO2/H2 separation exceeded the upper bounds (selectivity–permeability plot) for polymer membranes. The SAPO-34 membrane separated H2 from CH4 because CH4 is close to the SAPO-34 pore size and has a lower diffusivity than H2. The H2/CH4 separation selectivity had a small maximum with temperature, and decreased slightly with feed pressure and CH4 feed concentration. 相似文献
119.
Jason E. Bara Christopher J. Gabriel Evan S. Hatakeyama Trevor K. Carlisle Sonja Lessmann Richard D. Noble Douglas L. Gin 《Journal of membrane science》2008
Solid, polymer membranes fabricated from room-temperature ionic liquid monomers containing oligo(ethylene glycol) or nitrile-terminated alkyl substituents tethered to imidazolium cations were found to exhibit ideal CO2/N2 and CO2/CH4 separation factors significantly greater than those with comparable length n-alkyl substituents, with similar CO2 permeability. Polymers containing these functional groups exhibited CO2/N2 gas separation performance exceeding the “upper bound” of a “Robeson Plot”. 相似文献
120.
Comba P Gahan LR Haberhauer G Hanson GR Noble CJ Seibold B van den Brenk AL 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(14):4393-4403
The copper(II) coordination chemistry of westiellamide (H(3)L(wa)), as well as of three synthetic analogues with an [18]azacrown-6 macrocyclic structure but with three imidazole (H(3)L(1)), oxazole (H(3)L(2)), and thiazole (H(3)L(3)) rings instead of oxazoline, is reported. As in the larger patellamide rings, the N(heterocycle)-N(peptide)-N(heterocycle) binding site is highly preorganized for copper(II) coordination. In contrast to earlier reports, the macrocyclic peptides have been found to form stable mono- and dinuclear copper(II) complexes. The coordination of copper(II) has been monitored by high-resolution electrospray mass spectrometry (ESI-MS), spectrophotometric and polarimetric titrations, and EPR and IR spectroscopies, and the structural assignments have been supported by time-dependent studies (UV/Vis/NIR, ESI-MS, and EPR) of the complexation reaction of copper(II) with H(3)L(1). Density functional theory (DFT) calculations have been used to model the structures of the copper(II) complexes on the basis of their spectroscopic data. The copper(II) ion has a distorted square-pyramidal geometry with one or two coordinated solvent molecules (CH(3)OH) in the mononuclear copper(II) cyclic peptide complexes, but the coordination sphere in [Cu(H(2)L(wa))(OHCH(3))](+) differs from those in the synthetic analogues, [Cu(H(2)L)(OHCH(3))(2)](+) (L = L(1), L(2), L(3)). Dinuclear copper(II) complexes ([Cu(II) (2)(HL)(mu-X)](+); X = OCH(3), OH; L = L(1), L(2), L(3), L(wa)) are observed in the mass spectra. While a dipole-dipole coupled EPR spectrum is observed for the dinuclear copper(II) complex of H(3)L(3), the corresponding complexes with H(3)L (L = L(1), L(2), L(wa)) are EPR-silent. This may be explained in terms of strong antiferromagnetic coupling (H(3)L(1)) and/or a low concentration of the dicopper(II) complexes (H(3)L(wa), H(3)L(2)), in agreement with the mass spectrometric observations. 相似文献