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31.
32.
Representational analysis is used to examine the interplay between Fermi surface nesting and local moment effects in the formation of the magnetically ordered states of the rare-earth nickel borocarbides, RNi2B2C. We derive compatibility tables for the propagation wavevector k, the local moment anisotropy and the ordered moment direction μ k for materials with this tetragonal crystal structure. The magnetic structures observed in the rare-earth nickel borocarbides are discussed in this context. 相似文献
33.
Victor Adebomi Ryan D. Cohen Rachel Wills Holland Andrew Hays Chavers Gary E. Martin Monika Raj 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(52):19249-19256
Here, we report a novel “CyClick” strategy for the macrocyclization of peptides that works in an exclusively intramolecular fashion thereby precluding the formation of dimers and oligomers via intermolecular reactions. The CyClick chemistry is highly chemoselective for the N‐terminus of the peptide with a C‐terminal aldehyde. In this protocol, the peptide conformation internally directs activation of the backbone amide bond and thereby facilitates formation of a stable 4‐imidazolidinone‐fused cyclic peptide with high diastereoselectivity (>99 %). This method is tolerant to a variety of peptide aldehydes and has been applied for the synthesis of 12‐ to 23‐membered rings with varying amino acid compositions in one pot under mild reaction conditions. The reaction generated peptide macrocycles featuring a 4‐imidazolidinone in their scaffolds, which acts as an endocyclic control element that promotes intramolecular hydrogen bonding and leads to macrocycles with conformationally rigid turn structures. 相似文献
34.
Roy Hodgkinson Václav Jurčík Hans Nedden Andrew Blackaby Martin Wills 《Tetrahedron letters》2018,59(10):930-933
A new route towards a series of tethered η6-arene/Ru(II) catalysts for use in the transfer and pressure hydrogenation of ketones and aldehydes to alcohols is reported. The route proceeds through the formation of an amide from the diamine precursor, followed by reduction, rather than the direct alkylation of the diamine. This has the advantage that dialkylation of the amine is avoided during the synthesis. Through this new route, both racemic and enantiomerically-pure η6-arene/Ru(II) tethered catalysts can be prepared in high yield. 相似文献
35.
36.
A series of catalysts have been prepared for use in the asymmetric transfer hydrogenation of ketones. The complexes were prepared using a [4 + 2] cycloaddition reaction at a key step in the reaction sequence. This provides a means for the synthesis of catalysts with modifications at specific sites. 相似文献
37.
Izod K Wills C Clegg W Harrington RW 《Dalton transactions (Cambridge, England : 2003)》2007,(33):3669-3675
The adducts [[(Me(3)Si)(2){Me(2)P(BH(3))}C]K(L)(n)](m) [L = THF, n = 0.5, m = infinity (2a); L = tmeda (2b), pmdeta (2c), n = 1, m = 2] may be synthesised by treatment of solvent-free [[(Me(3)Si)(2){Me(2)P(BH(3))}C]K](infinity) (2) with the corresponding Lewis base (tmeda = N,N,N',N'-tetramethylethylenediamine; pmdeta = N,N,N',N',N'-pentamethyldiethylenetriamine). X-Ray crystallography reveals that, whereas 2 crystallises with a complex 2-dimensional sheet structure, 2a crystallises as a ribbon-type one-dimensional polymer and both 2b and 2c crystallise as dimers. The corresponding complex with 12-crown-4, [K(12-crown-4)(2)][(Me(3)Si)(2){Me(2)P(BH(3))}C] (2d) crystallises as a separated ion pair. The complexes [[(Me(3)Si)(2){Me(2)P(BH(3))}C]M(pmdeta)](n) [M = Na, n = 1 (6); M = Rb, n = 2 (7)] may be synthesised by treatment of [(Me(3)Si)(2){Me(2)P(BH(3))}C]M with pmdeta. Whereas crystallises as a discrete monomer, compound 7 crystallises as a dimer. Compounds 2, 2a-2d, 6, 7 and the corresponding caesium derivative [[(Me(3)Si)(2){Me(2)P(BH(3))}C]Cs(pmdeta)](2) () provide an opportunity to consider the influence of the ionic radius of the metal and the nature of the co-ligands on the structures of alkali metal complexes of a phosphine-borane-stabilised carbanion. 相似文献
38.
We determine lattice polytopes of smallest volume with a given number of interior lattice points. We show that the Ehrhart
polynomials of those with one interior lattice point have largest roots with norm of order n2, where n is the dimension. This improves on the previously best known bound n and complements a recent result of Braun where
it is shown that the norm of a root of a Ehrhart polynomial is at most of order n2. For the class of 0-symmetric lattice polytopes we present a conjecture on the smallest volume for a given number of interior
lattice points and prove the conjecture for crosspolytopes. We further give a characterisation of the roots of Ehrhart polyomials
in the three-dimensional case and we classify for n ≤ 4 all lattice polytopes whose roots of their Ehrhart polynomials have
all real part -1/2. These polytopes belong to the class of reflexive polytopes. 相似文献
39.
In 1921, Blichfeldt gave an upper bound on the number of integral points contained in a convex body in terms of the volume
of the body. More precisely, he showed that
#(K?\Bbb Zn) £ n! vol(K)+n\#(K\cap{\Bbb Z}^n)\le n! {\rm vol}(K)+n
, whenever
K ì \Bbb RnK\subset{\Bbb R}^n
is a convex body containing n + 1 affinely independent integral points. Here we prove an analogous inequality with respect to the surface area F(K), namely
#(K?\Bbb Zn) < vol(K) + ((?n+1)/2) (n-1)! F(K)\#(K\cap{\Bbb Z}^n) < {\rm vol}(K) + ((\sqrt{n}+1)/2) (n-1)! {\rm F}(K)
. The proof is based on a slight improvement of Blichfeldt’s bound in the case when K is a non-lattice translate of a lattice polytope, i.e., K = t + P, where
t ? \Bbb Rn\\Bbb Znt\in{\Bbb R}^n\setminus{\Bbb Z}^n
and P is an n-dimensional polytope with integral vertices. Then we have
#((t+P)?\Bbb Zn) £ n! vol(P)\#((t+P)\cap{\Bbb Z}^n)\le n! {\rm vol}(P)
.
Moreover, in the 3-dimensional case we prove a stronger inequality, namely
#(K?\Bbb Zn) < vol(K) + 2 F(K)\#(K\cap{\Bbb Z}^n)< {\rm vol}(K) + 2 {\rm F}(K)
. 相似文献
40.
Peter Wills 《Physics letters. [Part B]》1985,150(4):277-281
The one loop, large Higgs mass corrections to the ? parameter are calculated in a manifestly supersymmetric way, in a model with soft breaking in which Yukawa couplings are neglected. We find that the Higgs decouples from ? and, in a phenomenologically viable class of models, which are a subset of the above model, the ? parameter is independent of Higgs mass. 相似文献