全文获取类型
收费全文 | 181篇 |
免费 | 10篇 |
专业分类
化学 | 156篇 |
数学 | 2篇 |
物理学 | 33篇 |
出版年
2021年 | 7篇 |
2020年 | 2篇 |
2019年 | 8篇 |
2018年 | 5篇 |
2017年 | 3篇 |
2016年 | 7篇 |
2015年 | 4篇 |
2014年 | 5篇 |
2013年 | 6篇 |
2012年 | 9篇 |
2011年 | 7篇 |
2010年 | 6篇 |
2008年 | 7篇 |
2007年 | 4篇 |
2006年 | 10篇 |
2005年 | 6篇 |
2004年 | 4篇 |
2003年 | 10篇 |
2002年 | 6篇 |
2001年 | 4篇 |
2000年 | 4篇 |
1999年 | 4篇 |
1998年 | 5篇 |
1997年 | 2篇 |
1996年 | 5篇 |
1995年 | 4篇 |
1994年 | 2篇 |
1993年 | 4篇 |
1991年 | 1篇 |
1990年 | 3篇 |
1988年 | 4篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 6篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1973年 | 1篇 |
1969年 | 1篇 |
1967年 | 2篇 |
1966年 | 1篇 |
1965年 | 1篇 |
1961年 | 1篇 |
1960年 | 1篇 |
排序方式: 共有191条查询结果,搜索用时 15 毫秒
61.
Makarieva TN Shubina LK Guzii AG Ivanchina NV Denisenko VA Afiyatullov SS Dmitrenok PS Kalinovsky AI Stonik VA 《Natural product communications》2011,6(5):673-676
A study has been made of the 1H NMR spectra of peracetylated beta-glucopyranosides and alpha-arabinopyranosides obtained by reaction of D- and L-glucoses, and L- and D-arabinoses with either (R)- or (S)-2-octanols. The obtained and literature data show that 1H NMR spectra may be used to determine the absolute configuration of the aglycone moieties of some alicyclic glycosides without the need to synthesize derivatives with chiral reagents, as long as the absolute configuration of their monosaccharide moiety is known or vice versa. Spectra of marine steroid glycosides and their acetates containing glycosylated side chains as alicyclic fragments were also examined. It was shown that analysis of 1H NMR spectra for the determination of the absolute configuration is more applicable in the cases when glycosides have the same substitution in the D-ring of the aglycone moiety. 相似文献
62.
The influence of electron attachment on the stability of the mono- and dihydrogenated buckminsterfullerene C(60) was studied using density functional theory and semiempirical molecular orbital techniques. We have also assessed the reliability of computationally accessible methods that are important for investigating the reactivity of graphenic species and surfaces in general. The B3LYP and M06L functionals with the 6-311+G(d,p) basis set and MNDO/c are found to be the best methods for describing the electron affinities of C(60) and C(60)H(2) . It is shown that simple frontier molecular orbital analyses at both the AM1 and B3LYP/6-31G(d) levels are useful for predicting the most favourable position of protonation of C(60)H(-) , that is, formation of the kinetically controlled product 1,9-dihydro[60]fullerene, which is also the thermodynamically controlled product, in agreement with experimental and previous theoretical studies. We have shown that reduction of exo- and endo-C(60)H makes them more stable in contrast to the reduction of the exo,exo-1,9-C(60)H(2) , reduced forms of which decompose more readily, in agreement with experimental electrochemical studies. However, most other dihydro[60]fullerenes are stabilized by reduction and the regioselectivity of addition is predicted to decrease as the less stable isomers are stabilized more by the addition of electrons than the two most stable ones (1,9 and 1,7). 相似文献
63.
Dr. Oleg A. Filippov Dr. Natalia V. Belkova Prof. Lina M. Epstein Prof. Agusti Lledos Prof. Elena S. Shubina 《Chemphyschem》2012,13(11):2677-2687
A theoretical study on two series of electron‐rich group 8 hydrides is carried out to evaluate involvement of the transition metal in dihydrogen bonding. To this end, the structural and electronic parameters are computed at the DFT/B3PW91 level for hydrogen‐bonded adducts of [(PP3)MH2] and [Cp*MH(dppe)] (M=Fe, Ru, Os; PP3=κ4‐P(CH2CH2PPh2)3, dppe= κ2‐Ph2PCH2CH2PPh2) with CF3CH2OH (TFE) as proton donor. The results are compared with those of adduct [Cp2NbH3] ? TFE featuring a “pure” dihydrogen bond, and classical hydrogen bonds in pyridine ? TFE and Me3N ? TFE. Deviation of the H ??? H? A fragment from linearity is shown to originate from the metal participation in dihydrogen bonding. The latter is confirmed by the electronic parameters obtained by NBO and AIM analysis. Considered together, orbital interaction energies and hydrogen bond ellipticity are salient indicators of this effect and allow the MH ??? HA interaction to be described as a bifurcate hydrogen bond. The impact of the M ??? HA interaction is shown to increase on descending the group, and this explains the experimental trends in mechanisms of proton‐transfer reactions via MH ??? HA intermediates. Strengthening of the M ??? H interaction in the case of electron‐rich 5d metal hydrides leads to direct proton transfer to the metal atom. 相似文献
64.
EM Kozinets O Koniev OA Filippov JC Daran R Poli ES Shubina NV Belkova E Manoury 《Dalton transactions (Cambridge, England : 2003)》2012,41(38):11849-11859
Complexes [RhCl(diene)(P,SR)] with chiral ferrocenyl phosphine-thioethers ligands (diene = norbornadiene, NBD, 1(R), or 1,5-cyclooctadiene, COD, 3(R); P,SR = CpFe(1,2-η(5)-C(5)H(3)(PPh(2))(CH(2)SR); R = tBu, Ph, Bz, Et) and the corresponding [Rh(diene)(P,SR)][BF(4)] (diene = NBD, 2(R); COD, 4(R)) have been synthesized from [RhCl(diene)](2) and the appropriate P,SR ligand. The molecular structure of the cationic complexes 2(tBu), 4(Ph) and 4(Bz), determined by single-crystal X-ray diffraction, shows the expected slightly distorted square planar geometry. For the neutral chloride complexes, a combination of experimental IR and computational DFT investigations points to an equally four coordinate square planar geometry with the diene ligand, the chlorine and the phosphorus atoms in the coordination sphere and with a dangling thioether function. However, a second isomeric form featuring a 5-coordinated square planar geometry with the thioether function placed in the axial position is easily accessible in some cases. 相似文献
65.
A. A. Golovatenko M. A. Semina A. V. Rodina T. V. Shubina 《Physics of the Solid State》2017,59(6):1215-1224
We present a comparative study of the influence of the form of a localization potential on the binding energy of the biexciton in spherically symmetric quantum dots based on II–VI compounds. The proposed criterion for the comparison of potentials of different forms—the box potential, the harmonic oscillator, and the Gaussian potential—is based on the identical localization of charge carriers of the same sign in these potentials. Calculations of the biexciton binding energy have been performed using the variational method within the framework of the kp-perturbation theory taking into account additional polarization terms in the wave functions of the electron and hole subsystems, as well as the complex structure of the valence band. The obtained results have demonstrated that the presence of a smoothly varying finite-height potential in Cd(Zn)Se/ZnSe quantum dots can lead to a more efficient localization in the case of the biexciton in comparison with the exciton, which is of interest for the implementation of fast-acting quantum light emitters. 相似文献
66.
67.
林苏榕 《数学物理学报(A辑)》1998,(Z1)
该文研究极限方程在部分边界上为退缩椭圆型(椭圆-抛物)的一类六阶椭圆型方程混合边值问题的奇摄动,在适当的假设下,应用改进了的多重尺度法,求得其解包括边界层和套层在内除了半圆域的两个角点外,在整个半圆域中有任意阶的一致有效的渐近展开式. 相似文献
68.
69.
Yu. V. Shubina D. A. Tikhomirov A. V. Eremeev 《Chemistry of Heterocyclic Compounds》1985,21(5):516-520
On the basis of the results of IR and UV spectroscopy, a considerable decrease in the efficacy of the conjugation of the unshared pair of the nitrogen atom with a carbonyl group in ynaziridines as compared with ynamines has been shown. The difference in the electronic structures of these compounds finds its reflection in their chemical behavior: the electrophilicity of the triple bond in an ynaziridine is higher than that in the analogous ynamine in reactions with amines.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 618–622, May, 1985. 相似文献
70.