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排序方式: 共有136条查询结果,搜索用时 218 毫秒
1.
Robert W. Baker Geoffrey R. Pocock Melvyn V. Sargent Edi Twiss 《Tetrahedron: Asymmetry》1993,4(12):2423-2426
Introduction of a 2-isopropoxycarbonyl or 2-NN-dimethylcarbamoyl group into homochiral 1-p-tolyl- or 1-t-butyl-sulfinylnaphthalenes, via directed metalation reaction, followed by ligand coupling reaction with 1-naphthylmagnesium bromide, furnished atropisomeric 1,1′-binaphthyls in 82–95% enantiomeric excess (e.e.). 相似文献
2.
3.
Melvyn P. Melrose 《Theoretical chemistry accounts》1997,95(3-4):67-79
Algebraic expressions for the vertical Delocalisation Energy (DE) of benzene are derived from non-empirical MO theory. For
comparison with early work in the π-electron approximation, and ultimately with Hückel theory, the results are formulated
in terms of a core resonance integral,β, and π-electronic repulsion integrals. All integral values are inferred from the results ofab initio SCF calculations. Two expressions are derived, which refer to two ways of forming the localised π MOs: one where three pairs
of adjacent atomic orbitals are selected from a set of six orthogonalised orbitals; and another where a non-orthogonal set
of atomic orbitals is used. The first expression is formally similar to an expression originally derived by Pople from a different
point of view and with many approximations. This expression gives too large a magnitude for DE when used with anab initio value ofβ. The second expression gives a result much closer to an empirical value of DE and shows that the main reason for DE being
about 50% of 2β rather than 2β is the stabilising effect of overlap in the localised structure, and that the less important factor is the inclusion of electronic
repulsion. 相似文献
4.
Melvyn H. Wood 《Chemical physics》1974,5(3):471-477
The shake-up peaks which are observed to high binding energy of the main photoionization peak in the high energy photoeletron spectra of CO (carbon and oxygen core holes), H2O and NH3 have been interpreted by an extension of the singly excited configuration interaction method used previously in the study of the low-lying excited states of these molecules. The results obtained provide a good interpretation of the experimental spectra of these molecules in terms of many shake-up states. It is concluded that relaxed orbitals and an extensive basis set, including diffuse functions, should be used in the calculations in order to obtain good results. 相似文献
5.
Melvyn B. Nathanson 《Monatshefte für Mathematik》1980,89(3):219-222
Let
. LetG
m
(R) be the graph whose vertices are the numbers 1, 2, ...,m and whose edges are all pairs {a, b} such thata+br (modm) for somerR. LetC
m
(R) be the number of connected components ofG
m
(R). Letd be the greatest common divisor ofm and the differencesr
j
–r
j
or allr
i
,r
j
R. ThenC
m
(R) is equal to (i) (d+1)/2 ifd is odd, (ii)d/2 ifd is even andr is odd for allrR, or (iii) (d/2)+1 ifd is even andr is even for allrR.This research was supported in part by the National Science Foundation under grant No. MCS78-07908. 相似文献
6.
Melvyn Rowen Churchill Clifford Bueno David A. Young 《Journal of organometallic chemistry》1981,213(1):139-150
The species FeRu3(CO)13(μ-PPH2)2, synthesized from Ru3(CO)12 and Fe(CO)4(Ph2PPPh2),has been characterized both spectroscopically and via a single-crystal X-ray structural analysis. This complex crystallizes in the centrosymmetric triclinic space group P [No. 2, Ci1] with a 10.066(3), b 12.899(3), c 17.003(4) Å, α 111.89(2), β 91.02(2), γ 102.00(2)°, V 1992.7(9) Å3, Z 2, ?(obsd) 1.79(2) g cm-3 and ?(calcd) 1.82 cm-3. Diffraction data were collected with a Syntex P21 automated four-circle diffractometer and the structure was refined to RF 6.0% and RWF 3.6% for all 5213 reflections (RF 3.8%, RWF 3.6% for those 4140 reflections with |Fo|> 3σ(|Fo|).The metal atoms define a planar triangulated rhombus, with atoms Ru(1) and Ru(2) at the bridgehead, and Fe(1) and Ru(3) at the acute apices. Fe(1) is linked to four terminal carbonyl ligands and is associated with the heteronuclear bonds Fe(1)Ru(1) 2.861(1) Å and Fe(1)Ru(2) 2.868(1) Å. The ruthenium atoms are each bonded to three terminal carbonyl groups. The retheniumruthenium distances are Ru(1)Ru(2) 3.098(1), Ru(1)Ru(3) 3.147(1), and Ru(2)Ru(3) 3.171(1) Å. The structure is completed by Ph2P bridges across the Ru(1)Ru(3) and Ru(2)(ru(3) vectors (<Ru(1)P(1)Ru(3) 84.89(5)° and <Ru(2)P(2)Ru(3) 85.56(6)°). 相似文献
7.
8.
J.C. Hart R.D. Baker K.W. Bell J.A. Blissett I.J. Bloodworth T.A. Broome A.L. Lintern V.K. Magon R. Maybury A.G. Parham B.T. Payne D.H. Saxon T.G. Walker H.M. Watson M. Gay 《Nuclear Physics B》1980,166(1):73-83
Differential cross-section and polarization measurements for the reaction π?p → K0Σ0 are presented from 1395 to 2375 MeV/c incident beam momentum. The polarization data from an earlier experiment, from thershold to 1334 MeV/c, have been re-analysed by an improved method leading to a substantial reduction in the errors. 相似文献
9.
Usselman MC 《Ambix》2003,50(1):71-89
Liebig's 1831 paper that describes a new apparatus for the analysis of organic compounds and the results of several analyses using the apparatus is a justly famous contribution to the evolution of modern chemistry. In this paper, I look at the three separate components of Liebig's combustion apparatus that collect the water, carbon dioxide and nitrogen released by the combustion of six alkaloids. Gravimetric data included in the paper reveal that very accurate results could be obtained for water by absorption in a calcium chloride tube, and even better results for carbon dioxide resulted from use of the Kaliapparat. Volumetric measurement of nitrogen gave very poor results despite Liebig's efforts to improve it. Inaccuracies in nitrogen measurement made consistent construction of accurate molecular formulae for nitrogenous substances impossible, and only fortuitous decisions intended to bring molecular formulae into agreement with measured combining weights gave formulae in agreement with modern ones, as in the case for quinine. 相似文献
10.
Melvyn B. Nathanson 《Journal of Number Theory》2003,103(2):214-233
For the quantum integer [n]q=1+q+q2+?+qn−1 there is a natural polynomial multiplication such that [m]q⊗q[n]q=[mn]q. This multiplication leads to the functional equation fm(q)fn(qm)=fmn(q), defined on a given sequence of polynomials. This paper contains various results concerning the construction and classification of polynomial sequences that satisfy the functional equation, as well open problems that arise from the functional equation. 相似文献