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1.
Following recent studies which showed that the most stable structures for (ZnS)(n) clusters (n= 10-47) are the so-called "bubble clusters", in which all the atoms are three-coordinated, we have used simulated annealing techniques to find the most stable structure for a larger cluster, (ZnS)(60). We find an onion-like structure, with one small cluster enclosed inside a bigger one. The inner cluster has the structure of a sodalite cage. Bonding between the inner and the outer clusters creates a network of four-coordinated atoms. 相似文献
2.
Michael I. Bruce Andrew Catlow Mark G. Humphrey George A. Koutsantonis Michael R. Snow Edward R.T. Tiekink 《Journal of organometallic chemistry》1980,338(1):59-80
A reinvestigation of the reaction between C2(CO2Me)2 and RuH(PPh3)2(η-C5H5) and some related complexes is reported. Initial cis addition is followed by conversion into the trans isomer. In the case of the bis-(PPh3) complex, isomerisation is followed by chelation of the ester CO group with concomitant displacement of one PPh3ligand. The resulting chelate complex reacts with CO or CNBut to give the (Z)-RuC(CO2Me)CH(CO2Me) complexes; the (E)-isomer of the carbonyl complex is obtained by addition of C2(CO2Me)2to RuH(CO)(PPh3)(η-C5H5). The 1Hand 13C NMR spectra are not a reliable guide to assignment of the stereochemistry of the vinyl group. Other products isolated from the initial reaction are the bis-insertion product CH(CO2Me)} -(PPh3)(η-C5H5) and the 1/2 PPh3/C2(CO2Me)2 adduct. The molecular structures of Ru{(Z)-C(CO2Me)CH(CO2Me)}(CO)(PPh3(η-C5H5) · 0.5EtOH, Ru{(E)-C(C2Me)CH(CO2Me)}(dppe)(η-C5H5) and CH(CO2Me)}(PPh3)(η-C5H5) have been determined. The cis isomer is monoclinic, space group P21,with a 9.328(8), b 17.385(10), c 10.356(7) Å, β 101.78(3)° and Z = 2; 2107 data with I ≥ 2.5σ(I) were refined to R = 0.076 Rw = 0.085. The trans isomer is triclinic, space group P, with a 10.404(7) b 11.221(6), c 13.230(9) Å, α 92.67(5), β 110.56(5), γ 106.21(5)° and Z = 2; 2520 data with I ≥ 2.5σ(I) were refined to R = 0.055 Rw = 0.068. The butadienyl complex is monoclinic, space group P21/a, with a 19.655(8), b 8.674(4), c 21.060(5) Å, β 116.22(3)° and Z = 4; 2724 data with I ≥ 2.5σ(I) were refined to R = 0.042, Rw = 0.047. 相似文献
3.
Ohsuna T Slater B Gao F Yu J Sakamoto Y Zhu G Terasaki O Vaughan DE Qiu S Catlow CR 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(20):5031-5040
High-resolution electron microscopy (HREM) has been used to image the surface structure of nano- and micrometer-sized synthetic crystals of zeolite-Linde-L (LTL). Columnar holes and rotational, nano-sized, wheel-like defects were observed within the crystals, where the hole has a minimum size equal to that of the rotational defect. Predictions of surface structure from atomistic computer simulation concur with the observations from HREM and provide insight into the crystal growth mechanism of perfect and defective LTL. Analysis of the energetics of the formation of rotational defect structures reveals that the driving force for defect creation is thermodynamic and furthermore, the rotational defects could be created in high concentrations. Formation of a columnar hole is found to be slightly energetically unfavourable and therefore we speculate that the incidence of both rotational and nano-sized vacancy defects is strongly dependent on kinetic factors and reaction conditions. The morphology of nano- and microcrystalline LTL is contradistinct and we use insights from simulation to propose an explanation of the disparity in crystal shape. 相似文献
4.
Pereira J.C.G. Catlow C.R.A. Price G.D. Almeida R.M. 《Journal of Sol-Gel Science and Technology》1997,8(1-3):55-58
Density Functional Theory is used to study water, methanol, ethanol, TMOS, and TEOS molecules and the most important silica
clusters participating in sol-gel processes. Calculated bond lengths, bond angles and electric dipole moments compare well
with experimental data. The energy of these molecules is reported and used to discuss the energetics of the hydrolysis and
condensation reactions. Molecular Dynamics is employed to simulate liquid water, methanol, ethanol, TMOS, TEOS and experimental
sol-gel solutions. Calculated densities and enthalpies of vaporisation compare well with experimental data. Preliminary results
are presented for MD simulations of sol-gel solutions. 相似文献
5.
S. A. Catlow G. L. Troyer D. R. Hansen R. A. Jones 《Journal of Radioanalytical and Nuclear Chemistry》2005,263(3):599-603
Summary Long-term risk assessment of residual and disposed nuclear fuel reprocessing waste requires good knowledge of component isotopes with long half-lives. For example, the accuracy of the accepted 126Sn half-life of approximately 100,000 years is insufficient for desired risk assessments. From modeling and sampling, 126Sn is known to exist in Hanford nuclear waste. Excess portions of waste characterization samples were used to isolate 126Sn for measurement of its half-life. Isolation was performed with ion-exchange resins. The resulting 126Sn was gamma-assayed with a hyperpure germanium spectrometer for decay photon identification and activity values. An inductively coupled plasma/mass spectrometer was used to measure the atom quantity of the isolated 126Sn. The separation chemistry, observed gamma energies, and calculated half-life are presented. The half-life of 126Sn estimated in this work is (2.33±0.10) . 105 years. 相似文献
6.
7.
Alfredsson M Catlow CR Paulidou A Nix RM 《Chemical communications (Cambridge, England)》2002,(18):2128-2129
By performing first-principles Molecular Dynamics simulations at 300 K, we show that water dissociates on the A-La2O3(001) surface giving rise to one exclusive type of hydroxyl-group, which is associated with a surface reconstruction, incorporating an additional oxygen ion into the oxide subsurface, yielding a surface structure that is oxygen rich. 相似文献
8.
9.
G.V. Lewis C.R.A. Catlow A.N. Cormack 《Journal of Physics and Chemistry of Solids》1985,46(11):1227-1233
We present the results of a computer simulation study of the defect formation and migration energies in Fe3O4. Calculated Frenkel and Schottky energies are found to be similar in magnitude and both are considerably reduced by screening due to electron redistribution around the charged-defect species. The calculations also suggest that cation diffusion is mainly effected by a colinear interstitialcy mechanism at low Po2 and by a simple octahedral vacancy mechanism at higher Po2. 相似文献
10.