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91.
Intramolecular 6-exolendo-trig and 5-exo-trig cyclisations of aryl radical intermediates to the alpha-, beta- and gamma-carbons of pyridine have been shown to be facile processes at neutral pH. The tether conjoining the radical donor to the pyridine plays an important role in determining the outcome of the reaction. When a Z-alkene is used as a tether, ortho-cyclisation proceeds in good yield. A more complex course is followed when a saturated two carbon tether is employed, leading to products derived from hydrogen atom abstraction, ipso-cyclisation and ortho-cyclisation pathways. All attempts to effect 5-exolendo-trig cyclisations failed. Tributyltin hydride, tris(trimethylsilyl)silane, tris(trimethylsilyl)germane and, in part, samarium(II) iodide can each be employed as mediators of the reaction. 相似文献
92.
A. Patterson G. J. Sutton B. J. Tighe 《Journal of polymer science. Part A, Polymer chemistry》1973,11(9):2343-2355
The thermal degradation of two β-chlorinated versions of poly(isopropylidene carboxylate) has been studied by the combined thermogravimetric and gas evolution techniques described previously. Poly(3-chloro-2-methyl-2-hydroxypropionic acid) was found to decompose by a predominantly first-order process which was characterized by kinetic parameters similar to those obtained for poly(isopropylidene carboxylate). These are interpreted in terms of an intramolecular ester-exchange process. As the reaction proceeds intermolecular elimination of hydrogen chloride leads to crosslinking and ultimately to the formation of a carbonaceous char. This process is much more marked in the randomly β-chlorinated analog of poly(isopropylidene carboxylate). With this polymer, drastic deviation from first-order behavior is observed in thermogravimetric results, even in the early stages of reaction. Gas evolution analysis, being more influenced by degradation fragments having an appreciable vapor pressure, yields reasonable first-order data and indicates that the intramolecular interchange mechanism is still an important process. In general, the introduction of β-chlorine atoms is seen to reduce the rate of thermal decomposition of poly-α-esters. 相似文献
93.
Chen Z Sutton LR Moran D Hirsch A Thiel W Schleyer Pv 《The Journal of organic chemistry》2003,68(23):8808-8814
Density functional theory energies, geometries, and population analyses as well as nucleus-independent chemical shifts (NICS) have been used to investigate the structural and magnetic evidence for cyclic CnSn(2-) and CnSn (n = 3-6) electron delocalization. Localized molecular orbital contributions to NICS, computed by the individual gauge for localized orbitals method, dissect pi effects from the sigma single bonds and lone pair influences. CnSn(2-) (n = 3-5) structures in Dnh symmetry are minima. Their aromaticity decreases with increasing ring size. C3S3(2-) is both sigma and pi aromatic, while C4S4(2-) and C5S5(2-) are much less aromatic. NICS(0)pi, the C-C(pi) contribution to NICS(0) (i.e., at the ring center), decreases gradually with ring size. In contrast, cyclic C6S6(2-) prefers D2h symmetry due to the balance between aromaticity, strain energy, and the S-S bond energies and is as aromatic as benzene. The theoretical prediction that C6S6(6-) has D6h minima was confirmed by X-ray structure analysis. Comparisons between thiocarbons and oxocarbons based on dissected NICS analysis show that CnSn(2-) (n = 3-5) and C6S6(6-) are less aromatic in Dnh symmetry than their oxocarbon analogues. 相似文献
94.
Mark J. Sarsfield Andrew D. Sutton Francis R. Livens Iain May Robin J. Taylor 《Acta Crystallographica. Section C, Structural Chemistry》2003,59(6):i45-i46
The title compound, AgTcO4, contains close Ag—O contacts, and Raman spectroscopy shows a reduction in the Tc—O stretching frequencies on changing the pertechnetate counter‐cation from K+ to Ag+. 相似文献
95.
E. G. Yanes S. R. Gratz R. M. C. Sutton A. M. Stalcup 《Analytical and bioanalytical chemistry》2001,369(5):412-417
The enantioseparation capabilities of three different functionalized β-cyclodextrins, two sulfated β-cyclodextrins with 4 and 15 nominal degrees of substitution and a phosphated β-cyclodextrin with 8 degrees of substitution, were compared. While anodic detection was used with both sulfated cyclodextrins, the phosphated cyclodextrin required cathodic detection suggesting either lower ionization of the phosphated cyclodextrin or generally lower affinity of the analytes for the phosphated cyclodextrin. The effects of several experimental parameters were evaluated with respect to enantioseparation. The degrees of substitution of the cyclodextrin, pH of the background electrolyte as well as the concentration of the functionalized β-cyclodextrin, each had a significant influence on the successful enantiomeric separation of the chiral drugs investigated. 相似文献
96.
MA Freitas SR Dillon RC Dougherty AG Marshall 《Rapid communications in mass spectrometry : RCM》1999,13(15):1622-1625
The self-chemical ionization of diethylzinc is examined by Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry and semiempirical molecular orbital calculations. Electron impact of diethylzinc neutral produces the radical cation, C(4)H(15)Zn(+) (m/z x 122), which reacts further with the neutral (C(2)H(5))(2)Zn to give the following product ions: Zn(+) (m/z x 64), C(2)H(5)Zn(+) (m/z x 93), C(4)H(9)Zn(+) (m/z x 121), C(4)H(11)Zn(2)(+) (m/z x 187), and C(6)H(15)Zn(2)(+) (m/z x 215). To determine the structure and pathways for production of these ions, monoisotopic (12)C(4)H(15)(64)Zn(+), (64)Zn(+) and (12)C(2)H(5)(64)Zn(+) were individually isolated and reacted with the neutral background. We also performed semiempirical molecular orbital calculations (ZINDO/1). The molecular orbital calculations and experimental data are consistent in predicting that the ethyl group on the diethylzinc cation carries the positive charge. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
97.
Peter G. Sutton Christopher F. Harrington Ben Fairman E. Hywel Evans Les Ebdon Tim Catterick 《应用有机金属化学》2000,14(11):691-700
Synthetic methods for the small‐scale laboratory preparation of isotopically enriched dibutyltin dichloride, dibutyltin di‐iodide, tributyltin chloride, tributyltin iodide, diphenyltin dichloride, triphenyltin chloride and triphenyltin iodide have been successfully established. Organotin iodides were prepared from redistribution reactions between tin(IV) iodide and the corresponding tetraorganotin, with the exception of dibutyltin di‐iodide, which was prepared directly from the reaction between tin metal and iodobutane. The development of novel procedures for the dealkylation/dearylation of tetraorganotins by acid hydrolysis produced superior yields of tributyltin chloride and diphenyltin dichloride in comparison with redistribution reactions. Organotin iodide redistribution reaction products were converted to their chloride analogues via the fluoride salts using an aqueous ethanolic solution of potassium fluoride. The insolubility of organotin fluoride salts was exploited to isolate and purify the isotopically enriched compounds, and to prevent losses during the purification procedure. The nuclear magnetic resonance (NMR) spectroscopic study of ‘natural abundance’ and isotopically enriched organotin compounds gave proton (1H) and carbon‐13 (13C) spectra for butyltins, Bu4−nSnXn, and phenyltins, Ph4−nSnXn (X = I, Cl), allowing the assignment of 1H and 13C chemical shifts, and 119Sn–13C and 117Sn–13C coupling constants. The 13C NMR spectroscopic analysis of 117Sn‐enriched organotin compounds has allowed the assignment of certain resonances and tin–carbon coupling constants which were previously unobservable. The spectral patterns show that Δ(1H) and Δ(13C) values are sensitive to structural changes, and that 13C shielding decreases with an increase in the electronegativity of the substituent. The tin–carbon coupling constants are also sensitive to structural changes, and for alkyl and aryl compounds the couplings decrease in the order 1J > 3J > 2J > 4J. The 13C chemical shift values and the magnitude of tin–carbon coupling constants are shown to be solvent‐dependent. The 13C spectra of the isotopically enriched compounds show that the degree of isotopic enrichment and the nature of the isotope used (magnetic or non‐magnetic) are reflected in the spectral pattern obtained. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
98.
A review of X-ray intensity fluctuation spectroscopy 总被引:1,自引:0,他引:1
This article reviews the literature on X-ray fluctuation intensity spectroscopy or, as it is often called, X-ray photon correlation spectroscopy. It highlights measurements using different types of diffuse scattering. To cite this article: M. Sutton, C. R. Physique 9 (2008). 相似文献
99.
Albert Murad Sutton 《International Journal of Theoretical Physics》2007,46(5):1065-1082
There exist classical systems whose canonical quantization yields relativistic wave equations. As a constructive proof, the
classical mechanics of a translating-rotating five-frame is considered. Its quantization yields the Dirac, Weyl, Klein-Gordon,
Maxwell-Proca, and higher spin equations, together with a rotational mass spectrum for the states predicted. 相似文献
100.
Rudd RE Briggs GA Sutton AP Medeiros-Ribeiro G Williams RS 《Physical review letters》2003,90(14):146101
We present a nanostructure diagram for use in designing heteroepitaxial systems of quantum dots. The nanostructure diagram is computed using a new equilibrium statistical physics model and predicts the island size and shape distributions for a range of combinations of growth temperature and amount of deposited material. The model is applied to Ge on Si(001), the archetype for bimodal island growth, and the results compare well with data from atomic force microscopy of Ge/Si islands grown by chemical vapor deposition. 相似文献