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排序方式: 共有121条查询结果,搜索用时 343 毫秒
1.
W. H. Klink 《Czechoslovak Journal of Physics》1987,37(3):329-337
A procedure for constructing scattering amplitudes for production processes that is exactly unitary, preserves the bosonic character of the many-particle states, and is invariant with respect to an underlying symmetry group is given. Two simple models, dealing with isospin internal symmetry and the two-dimensional Euclidean space group are presented which illustrate how scattering amplitudes can be represented as matrix elements of groups whose action commutes with the action of the invariance group on the relevant Fock space.Invited talk presented at the International Conference Selected Topics in Quantum Field Theory and Mathematical Physics, Bechyn, Czechoslovakia, June 23–27, 1986.Work supported in part by the Department of Energy. 相似文献
2.
3.
Synthesis and Catalytic Properties of Di- and Trinuclear Palladium Complexes with PCP-Pincer Ligands
Beletskaya I. P. Chuchuryukin A. V. van Koten G. Dijkstra H. P. van Klink G. P. M. Kashin A. N. Nefedov S. E. Eremenko I. L. 《Russian Journal of Organic Chemistry》2003,39(9):1268-1281
Linear and branched conjugated pincer ligands having Ph2P groups were synthesized: 3,3',5,5'- tetrakis(diphenylphosphinomethyl)diphenylacetylene, 3,3',5,5'-tetrakis(diphenylphosphinomethyl)diphenyldi- acetylene, 1,3,5-tris[3,5-bis(diphenylphosphinomethyl)phenylethynyl]benzene, and hexakis[3,5-bis(diphenylphosphinomethyl)phenylethynyl]benzene. Palladation of these ligands by heating with Pd(BF4)2(MeCN)4 in boiling acetonitrile gave the corresponding di- and trinuclear ionic pincer palladium complexes. No individual complex was obtained from hexakis[3,5-bis(diphenylphosphinomethyl)phenylethynyl]benzene. The ionic com- plexes were converted into the corresponding chloride complexes by treatment with sodium chloride in a mixture of water with methylene chloride. The structure of the ionic palladium complex with 3,3',5,5'-tetrakis(diphenylphosphinomethyl)diphenylacetylene was established by X-ray analysis. The obtained palladium complexes exhibited a considerable catalytic activity in the Heck reaction of iodobenzene with ethyl acrylate and in the Michael addition of ethyl cyanoacetate with methyl vinyl ketone. The catalytic activity per palladium atom decreases as the number of palladium atoms in the complex increases. 相似文献
4.
Serenella Medici Marcella Gagliardo ScottB. Williams PrestonA. Chase Serafino Gladiali Martin Lutz AnthonyL. Spek GerardP.M. vanKlink Gerard vanKoten 《Helvetica chimica acta》2005,88(3):694-705
Achiral P‐donor pincer‐aryl ruthenium complexes ([RuCl(PCP)(PPh3)]) 4c , d were synthesized via transcyclometalation reactions by mixing equivalent amounts of [1,3‐phenylenebis(methylene)]bis[diisopropylphosphine] ( 2c ) or [1,3‐phenylenebis(methylene)]bis[diphenylphosphine] ( 2d ) and the N‐donor pincer‐aryl complex [RuCl{2,6‐(Me2NCH2)2C6H3}(PPh3)], ( 3 ; Scheme 2). The same synthetic procedure was successfully applied for the preparation of novel chiral P‐donor pincer‐aryl ruthenium complexes [RuCl(P*CP*)(PPh3)] 4a , b by reacting P‐stereogenic pincer‐arenes (S,S)‐[1,3‐phenylenebis(methylene)]bis[(alkyl)(phenyl)phosphines] 2a , b (alkyl=iPr or tBu, P*CHP*) and the complex [RuCl{2,6‐(Me2NCH2)2C6H3}(PPh3)], ( 3 ; Scheme 3). The crystal structures of achiral [RuCl(equation/tex2gif-sup-3.gifPCP)(PPh3)] 4c and of chiral (S,S)‐[RuCl(equation/tex2gif-sup-6.gifPCP)(PPh3)] 4a were determined by X‐ray diffraction (Fig. 3). Achiral [RuCl(PCP)(PPh3)] complexes and chiral [RuCl(P*CP*)(PPh3)] complexes were tested as catalyst in the H‐transfer reduction of acetophenone with propan‐2‐ol. With the chiral complexes, a modest enantioselectivity was obtained. 相似文献
5.
Retrobiosynthetic analysis of the allergenic sesquiterpene lactone, anthecotuloide, suggested that this natural product could be formed either by head to head condensation of geranyl diphosphate with dimethylallyl diphosphate, or from farnesyl diphosphate (FPP), the accepted regular sesquiterpene precursor via the rearrangement of a germacranolide precursor. Isotopic labelling of anthecotuloide has now been achieved by feeding [1-(13)C]-glucose, [U-13C6]-glucose and [6,6-(2)H2]-glucose to aseptically grown plantlets of Anthemis cotula(family Asteraceae). Analysis of labelling patterns and absolute 13C abundances using quantitative 13C NMR spectroscopy showed that the isoprene building blocks of this sesquiterpene are formed exclusively via the MEP terpene biosynthetic pathway. This was supported by results from an experiment using [U-13C6]-glucose. A deuterium labelling experiment using [6,6-(2)H2]-glucose supported the original proposal and showed that anthecotuloide is formed from a non FPP precursor. Isotope ratio mass spectrometry suggested that there were two pathways for sesquiterpene biosynthesis in A. cotula. 相似文献
6.
The differences between the molecular structures of the PCP-pincer complex [RuCl{C6H3(CH2P(C6H5)2)2-2,6}(PPh3)] ([RuCl(PCPH)(PPh3)], 1) and its tetrakis-pentafluorophenyl substituted analogue [RuCl{C6H3(CH2P(C6F5)2)2-2,6}(PPh3)] ([RuCl(PCPF20)(PPh3)], 2) have been rationalised by performing calculations on the cations [Ru(PCPH)(PPh3)]+ (1cat) and [Ru(PCPF20)(PPh3)]+ (2cat). The molecular interactions between the chloride ligand and the axial rings, as found in 1 and 2, respectively, have been studied computationally in the model systems [(C6X5PH2)2Cl−] (X = H, F). The calculations on 2cat show that in 2 it is most likely the attractive electrostatic interaction between the chloride ligand and the fluorinated phenyl rings that forces the Cipso atom to occupy an axial position rather than an equatorial one in the observed (X-ray of 2) square pyramidal arrangement. In 1, however, repulsive steric hindrance forces the PPh3 ligand to take the apical position. The applicability of the TD-DFT method for the calculation of the electronic spectra of the PCP-pincer compounds 1 and 2 has been tested. The results indicate that the excitation energies calculated for both complexes are in a reasonable agreement with the experimental absorption maxima. However, for 1, all the calculated transition energies are underestimated. 相似文献
7.
F.?A.?ReuseEmail author K.?Maschke V.?de?Coulon J.?van?der?Klink J.-Ph?Ansermet 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,36(4):573-592
We present a detailed discussion of the evolution of a statistical ensemble of quantum mechanical systems coupled weakly to a bath. The Hilbert space of the full system is given by the tensor product between the Hilbert spaces associated with the bath and the bathed system. The statistical states of the ensemble are described in terms of density matrices. Supposing the bath to be held at some - not necessarily thermal - statistical equilibrium and tracing over the bath degrees of freedom, we obtain reduced density matrices defining the statistical states of the bathed system. The master equations describing the evolution of these reduced density matrices are derived under the most general conditions. On time scales that are large with respect to the bath correlation time
and with respect to the reciprocal transition frequencies of the bathed system, the resulting evolution of the reduced density matrix of the bathed system is of Markovian type. The detailed balance relations valid for a thermal equilibrium of the bath are derived and the conditions for the validity of the fluctuation-dissipation theorem are given. Based on the general approach, we investigate the non-linear response of the bathed subsystem to a time-periodic perturbation. Summing the perturbation series we obtain the coherences and the populations for arbitrary strengths of the perturbation.Received: 26 November 2003, Published online: 30 January 2004PACS:
05.30.-d Quantum statistical mechanics - 33.35. + r Electron resonance and relaxation - 33.25. + k Nuclear resonance and relaxation 相似文献
8.
9.
Bisphosphinoaryl ruthenium(Ⅱ)compounds are synthesized using two distinct synthetic routes.One route,direct cycloruthenation,consists of the reaction of the parent arene compound R-PCHP with [RuCl2(PPh3)3]in chlorinated solvents.However,this route suffers from major drawbacks because HCl is formed as well as free triphenylphoshine.The other route,the transcyclometalation reaction,involves the interconversion of one cyclometalated ligand metal complex,[RuCl(NCN)(PPh3)],into another complex,[RuCl(R-PCP)(PPh3)],with concomitant consumption and formation of the corresponding arenes R-PCHP and NCHN,respectively. 相似文献
10.
O. Hromatka J. Augl E. Flieder R. Klink 《Monatshefte für Chemie / Chemical Monthly》1961,92(1):107-111
Zusammenfassung Durch Überführung der in früheren Arbeiten erhaltenen Hexahydrophenthiazine in die zugehörigen Sulfone wurden die Beziehungen zu den von uns auf anderem Wege synthetisierten Sulfonen hergestellt. Von den beiden 6-Chlor-hexahydrophenthiazinen gibt das niedriger schmelzende das früher durch Synthese erhaltene Sulfon, das höher schmelzende ein Isomeres. Hexahydrophenthiazin vom Schmp. 100o gibt ein zum synthetisch erhaltenen isomeres Sulfon. Wir schließen aus Regelmäßigkeiten der Schmelzpunkte, daß das zum durch frühere Synthesen erhaltenen Sulfon gehörige isomere Hexahydrophenthiazin einen niedrigeren Schmp. hat. Wenn diese niedriger schmelzende Modifikation — wie bei den 6-Chlor-hexahydrophenthiazinen—auch in wesentlich geringerer Ausbeute entsteht, wäre es leicht erklärlich, daß sie bisher noch nicht aufgefunden wurde. 相似文献