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31.
The nonlocal contribution of the pi-electrons to the 1H-chemical shifts in the annulenoid systems 1–12 is calculated within the HMO theory from which information is gained about the change of the annulenoid character of (4n) and (4n + 2)-annulenes by different annelated groups. The predicted trends are then compared with experimental data. Calculated ground state stabilization energies and aromaticity indices based on the uniformization of bond lengths show no correlation with the chemical shifts. 相似文献
32.
Eva Rentschler Werner Massa Stefan Vogler Kurt Dehnicke Dieter Fenske Gerhard Baum 《无机化学与普通化学杂志》1991,592(1):59-72
Halogeno-Nitrosyl Complexes of Molybdenum and Tungsten. Crystal Structures of [Na2(15-Crown-5)2(CH3CN)][MoCl4(NO)2] and [Na(15-Crown-5)]2[MoF4Cl(NO)] MoCl2(NO)2 and WCl2(NO)2, respectively, react with excess sodium fluoride in acetonitrile at room temperature and in the presence of 15-crown-5 to give crystalline mixtures, which consist of the title compounds, respectively of [Na(15-crown-5)]2[WCl4(NO)2] and [Na(15-crown-5)]2[WF4Cl(NO)], and which can be separated by selection. The complexes are characterized by their i.r. spectra, the molybdenum compounds additionally by crystal structure determinations. [Na2(15-crown-5)2(CH3CN)][MoCl4(NO)2]: Space group P21, Z = 2, 5415 independent unique reflexions, R = 0.039. Lattice dimensions at ?10°C: a = 984.3, b = 1231.1, c = 1483.0 pm, β = 105.67°. The compound consists of cations [Ne(l5-crown-5)(CH3CN)]+, in which the sodium ion is surrounded by the five O-atoms of the crown ether and by the N-atom of the acetonitrile molecule, as well as of anions, which form an ion pair {Na(15-crown-5)[MoCl4(NO)2]}?. In the in pairs the sodium ion is coordinated by the five oxygen atoms of the crown ether and by two chlorine atoms of the [MoCI4(NO)2]2? unit. The nitrosyl ligands take the cis-position a t the molybdenum atom which is in a distorted octahedrally fashion. [Na(15-crown-5)]2[MoF4Cl(NO)]. Space group C2/c, Z = 4, 1933 independent unique reflexions, R = 0.078. Lattice dimensions at ?7O°C: D : 1.585.8, b = 1171.5, c = 1771.5 pm, β = 114.91°. The compound forms an ion triple, in which the sodium ions are linked to five oxygen atoms each of the crown ether molecules, and to two F-atoms of the [MoF4Cl(NO)]2? unit. The F-atom which is arranged in trans-position to the nitrosyl ligand coordinates with both sodium ions; thus an unusual T-shaped arrangement results for this F-atom. The sole terminal F-Atom and the Cl-atom are disordered in two positions. 相似文献
33.
Sharon M. Molnar Glen E. Jensen Lisa M. Vogler Sumner W. Jones Leroy Laverman Jon S. Bridgewater Mark M. Richter Karen J. Brewer 《Journal of photochemistry and photobiology. A, Chemistry》1994,80(1-3):315-322
We have prepared a series of mixed-metal trimetallic complexes of the form {[(bpy)2Ru(BL)]2MCl2}n+(bpy 2,2′-bipyridine; BL 2,3-bis(2-pyridyl)pyrazine (dpp), 2,3-bis(2-pyridyl)quinoxaline (dpq) or 2,3-bis(2-pyridyl)-benzoquinozaline (dpb); M Ir(III), Rh(III) or Os(II). This new class of trimetallic complexes can be prepared with a good yield, often as high as 95%, using our building block strategy. The central rhodium and iridium fragments of these trimetallic, namely [M(BL)2Cl2]+, have been shown in our laboratory to be capable of delivering multiple electrons, “stored” on the bridging ligand π* orbitals, to a substrate as they functioned as electrocatalysts for the reduction of carbon dioxide to formate. The two terminal ruthenium metals are good light absorbers designed to give rise to photochemical activity. These bichromophoric systems should be capable of absorbing two photons of light, each giving rise to a desired photochemical reaction, namely excited-state electron transfer. Thus these systems form the basis of a molecular device for photoinitiated electron collection. The properties of these supramolecular complexes have been tuned by variation in the central metal and bridging ligand. Comparison of this array of nine complexes is described herein. 相似文献
34.
Using a photon-particle delayed coincidence method the energy distributions of H +H(2p) and H++H(2p) fragment pairs have been measured arising from collisional dissociation of 10 keV H 2 + ions incident on various target gases. H fragments in their 2p state are identified by the Lymanα radiation emitted. The distribution of H+H(2p) fragment pairs arising from dissociative charge exchange reveals a sharp increase below 0.2 eV in the center-of-mass frame of the H 2 + ion. This is ascribed to predissociation of vibrational levels of higher H2 Rydberg states close above then=2 dissociation limit by those H2 Rydberg states which separate into H+H(2p) fragments. Only direct transitions into the continuum of theGK 1 ∑ g + state may compete. Some structure at 0.3–0.5 eV is attributed to the three statesI 1 П g,i 3 П g, andh 3 bE g + having potential barriers of this height. The distributions for H++H(2p) have maxima at 3.4, 3.8, and 4.2 eV for a H2, Ar, and He target, respectively, indicating that the 2pπ u state as well as the 3dσ g state ofH 2 + is excited. The H+H(2p) process has a greater probability than the H++H(2p) process for Ar and H2 targets, though all electronic H2 states under consideration are bound. 相似文献
35.
P. Würtz T. Gericke A. Vogler F. Etzold H. Ott 《Applied physics. B, Lasers and optics》2010,98(4):641-645
Imaging ultracold atoms by means of scanning electron microscopy involves several aspects that are different from standard
optical imaging techniques. The quality of the images depends on the properties of the electron beam, and the signal depends
on the details of the ionization process and subsequent detection strategy. We discuss the alignment and characterization
procedure of the electron beam, the handling of different charge states that are produced upon electron impact, and correction
algorithms to compensate for relative drifts between the field of view of the electron beam and the atomic target. 相似文献
36.
37.
38.
H. Vogler 《Tetrahedron》1985,41(22):5383-5386
Simple MO theory of induced ring currents is used in order to rationalise the observed diatropism of neutral [4m+2]annulenes and their tetraanions and the paratropism of the corresponding dianions. 相似文献
39.
The geometries and the 1H chemical shifts of dihydropyrene and its benzannelated derivatives – have been studied by means of semiempirical quantum chemical procedures. The calculated bond lengths of and proton shifts of – are in good accord with the corresponding experimental values. We show that monobenzannelation in – causes considerable bond length alternation in the [14] perimeter and hence reduced diatropocity. The same is true for the phenanth-fused dibenzannelated compounds and . On the other hand we report evidence that anth-fused dibenzannelated dihydropyrenes , , and should be characterized by symmetric geometrical structures without significant bond length alternation thus leading to enhanced diatropicity. 相似文献
40.
Two classes of synthetically useful bimetallic complexes of the form [(tpy)M(tpp)RuCl(3)](PF(6)) and [(tpy)M(tpp)Ru(tpp)](PF(6))(4) have been prepared and their spectroscopic and electrochemical properties investigated (tpy = 2,2':6',2"-terpyridine, tpp = 2,3,5,6-tetrakis(2-pyridyl)pyrazine, and M = Ru(II) or Os(II)). Synthetic methods have been developed for the stepwise construction of tpp-bridged systems using a building block approach. In all four complexes, the tpp that serves as the bridging ligand is the site of localization of the lowest unoccupied molecular orbital (LUMO). The nature of the HOMO (highest occupied molecular orbital) varies depending upon the components present. In the systems of the type [(tpy)M(tpp)RuCl(3)](PF(6)), the ruthenium metal coordinated to tpp and three chlorides is the easiest to oxidize and is the site of localization of the HOMO. In contrast, for the [(tpy)M(tpp)Ru(tpp)](PF(6))(4) systems, the HOMO is based on the metal, M, that is varied, either Ru or Os. This gives rise to systems which possess a lowest lying excited state that is always a metal-to-ligand charge transfer state involving tpp but can be tuned to involve Os or Ru metal centers in a variety of coordination environments. The synthetic variation of the components within this framework has allowed for understanding the spectroscopic and electrochemical properties. Bimetallic systems incorporating this tpp ligand have long-lived excited states at room temperature (lifetimes of ca. 100 ns). The bimetallic system [(tpy)Ru(tpp)Ru(tpp)](PF(6))(4) has a longer excited state lifetime than the monometallic system from which it was constructed, [(tpy)Ru(tpp)](PF(6))(2). Details of the spectroscopic and electrochemical studies are reported herein. 相似文献