全文获取类型
收费全文 | 284篇 |
免费 | 3篇 |
专业分类
化学 | 149篇 |
力学 | 2篇 |
数学 | 12篇 |
物理学 | 124篇 |
出版年
2014年 | 2篇 |
2013年 | 18篇 |
2012年 | 12篇 |
2011年 | 13篇 |
2010年 | 4篇 |
2009年 | 6篇 |
2008年 | 6篇 |
2007年 | 4篇 |
2006年 | 5篇 |
2005年 | 5篇 |
2003年 | 5篇 |
2002年 | 5篇 |
2001年 | 6篇 |
2000年 | 12篇 |
1999年 | 6篇 |
1998年 | 2篇 |
1997年 | 6篇 |
1996年 | 5篇 |
1995年 | 2篇 |
1994年 | 5篇 |
1993年 | 8篇 |
1992年 | 9篇 |
1991年 | 5篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1988年 | 6篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 5篇 |
1981年 | 11篇 |
1980年 | 7篇 |
1979年 | 3篇 |
1978年 | 10篇 |
1977年 | 3篇 |
1976年 | 5篇 |
1975年 | 5篇 |
1974年 | 5篇 |
1973年 | 7篇 |
1972年 | 7篇 |
1971年 | 5篇 |
1942年 | 2篇 |
1936年 | 4篇 |
1933年 | 2篇 |
1928年 | 2篇 |
1924年 | 2篇 |
1920年 | 2篇 |
1893年 | 1篇 |
排序方式: 共有287条查询结果,搜索用时 203 毫秒
21.
Solvent isotope effects for H2O---D2O mixtures and for ionic hydration equilibria in such mixtures can be calculated from the structure difference between D2O and H2O and that between HDO and H2O and the relative amounts of the three waters. The behavior of acids in H2O---D2O mixtures is considered in detail. Dissociation constants of acetic acid are calculated over the complete range of deuterium concentrations and found to agree with the experimentally determined ones. The Gross equation for the dependence of isotope effect on mole fraction of deuterium for acid-catalyzed reaction of substrates S proceeding via SL+ transition states (L=H or D) is derived from first principles. 相似文献
22.
The infrared spectra of eight complexes of general formula [ML2(NCS)2] (M = Co, Ni, Cu, Zn; L = aniline or p-toluidine) have been determined over the range 4000–4150 cm?1. Colour, magnetic moments and IR spectra are consistent with polymeric octahedral coordination in the Co(II) and Ni(II) complexes and polymeric tetragonal coordination in the Cu(II) complexes, while the Zn(II) complexes are assigned polymeric octahedral (L = aniline) and tetrahedral (L = p-toluidine) structure on the basis of their IR spectra. Independent 15N-labelling of the nitrogen atoms of the amino and isothiocyanate groups yields assignments for the internal vibrations of both groups and enables the metal-amine and metal—isothiocyanate stretching vibrations (vM-NH2 and vM-NCS) to be distinguished. Both vM-NH2 and vM-NCS are metal ion dependent in the Irving-Williams sequence (Co < Ni < Cu > Zn) expected from their proposed structures while the vN-H and vN-CS vibrations are inversely related to the masses of the coordinated metal ions. 相似文献
23.
The IR. spectra of α-thenoyl-trifluoroacetone (HTTA) and seventeen of its chelates with metal(II) and -(III) ions of the first transition series have been determined. Three series of complexes are represented: the anhydrous metal(II) species, [M(TTA)2]n (M ? Ca, Mn, Co, Ni, Cu, Zn); metal(II) dihydrates, [M(TTA)2(H2O)2] (M ? Mn, Fe, Co, Ni, Zn); and the metal(III) chelates, [M(TTA)3] (M ? Sc, V, Cr, Mn, Fe, Ga). For each metal(II) complex, the spectra of the anhydrous and hydrated compounds are practically identical, suggesting that the anhydrous complexes have the polynuclear octahedral structure established for the corresponding acetylacetonates. Magnetic moment determinations reveal that complexes of the 3d4?3d7 ions all have spin-free configuration. Several vibrational bands with frequencies < 700 cm?1 are found to exhibit a frequency variation with d-orbital population which is consistent with the order of crystal field stabilization energies and hence with their assignment as coupled metal-oxygen stretching modes. Unique features of the spectra of [Cu(TTA)2] and [Mn(TTA)3] are ascribed to structural differences arising from Jahn-Teller distortion. Tentative assignments for the majority of the ligand vibrations are given. 相似文献
24.
Abstract The vibrational and electronic spectra of eleven complexes of copper(II) succinimide [CuSu2Am2] (Su = succinimide ion; Am = variously substituted primary aliphatic amines) show that metal-imide co-ordination occurs through the imide nitrogen atom. The electronic effects of the amine substituents on the carbonyl stretching frequencies and on the electronic spectra are used to infer the probable mechanism of metal-imide bonding. 相似文献
25.
Bharathi Avula Babu L. Tekwani Narayan D. Chaurasiya NP Dhammika Nanayakkara Yan‐Hong Wang Shabana I. Khan Vijender R. Adelli Rajnish Sahu Mahmoud A. Elsohly James D. McChesney Ikhlas A. Khan Larry A. Walker 《Journal of mass spectrometry : JMS》2013,48(2):276-285
Therapeutic efficiency and hemolytic toxicity of primaquine (PQ), the only drug available for radical cure of relapsing vivax malaria are believed to be mediated by its metabolites. However, identification of these metabolites has remained a major challenge apparently due to low quantities and their reactive nature. Drug candidates labeled with stable isotopes afford convenient tools for tracking drug‐derived metabolites in complex matrices by liquid chromatography‐tandem mass spectrometry (LC‐MS‐MS) and filtering for masses with twin peaks attributable to the label. This study was undertaken to identify metabolites of PQ from an in vitro incubation of a 1:1 w/w mixture of 13C6‐PQ/PQ with primary human hepatocytes. Acquity ultra‐performance LC (UHPLC) was integrated with QTOF‐MS to combine the efficiency of separation with high sensitivity, selectivity of detection and accurate mass determination. UHPLC retention time, twin mass peaks with difference of 6 (originating from 13C6‐PQ/PQ), and MS‐MS fragmentation pattern were used for phenotyping. Besides carboxy‐PQ (cPQ), formed by oxidative deamination of PQ to an aldehyde and subsequent oxidation, several other metabolites were identified: including PQ alcohol, predictably generated by oxidative deamination of PQ to an aldehyde and subsequent reduction, its acetate and the alcohol's glucuronide conjugate. Trace amounts of quinone‐imine metabolites of PQ and cPQ were also detected which may be generated by hydroxylation of the PQ/cPQ quinoline ring at the 5‐position and subsequent oxidation. These findings shed additional light on the human hepatic metabolism of PQ, and the method can be applied for identification of reactive PQ metabolites generated in vivo in preclinical and clinical studies. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
26.
Robert M. Przeslawski Suzanne Newman Edward R. Thornton Madeleine M. Joullié 《合成通讯》2013,43(19):2975-2980
The commercially available α-ketoxime of camphorquinone (1) was reduced to the corresponding exo,exo-amino alcohol (2) in a two-step, one-pot procedure using sodium borohydride and nickel(II) chloride hexahydrate. 相似文献
27.
Malcolm A. Halcrow Colin A. Kilner Mark Thornton‐Pett 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(12):1425-1426
The title compound, [Zn(C29H29N5)2](ClO4)2·2CH3NO2, contains a ZnII ion showing only small deviations from local D2d symmetry. The lower rhombicity exhibited by this complex compared with that of its CuII congener suggests that the highly rhombic stereochemistry exhibited by the latter is largely imposed by the stereoelectronic preferences of the CuII ion. 相似文献
28.
29.
The infrared spectra (700–150 cm?1) of twenty-six complexes of 2-aminomethylpyridine (amp) with first transition series metal(II) ions are discussed. The complexes include the tris(amp) complexes [M(amp)3]2+ the bis(amp) compounds M(amp)2X2 and the mono(amp) complexes M(amp)X2. Assignments of the NH2 rocking modes, v(M-NH2), v(M-py) and ligand modes are based on the effects of isotopic labelling of the amino group and the effects of substitution of the metal ion and halide. The structural implications of the spectra are discussed. 相似文献
30.
We analyze phase separation in ternary systems in the asymptotic hydrodynamic regime when the volume fractions and concentrations are constant. The multiphase Navier-Stokes equations are solved using a level set method. A new projection method was developed to treat multiple junctions for systems with more than two phases. It is found that surface tension ratios can alter the growth mechanism of a minority phase in the presence of two majority phases. When the minority phase wets the interface of the majority phases the domain growth rate of all three phases is initially similar to that of a symmetric binary fluid but slows down at later times. 相似文献