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排序方式: 共有399条查询结果,搜索用时 265 毫秒
51.
R. Brandelik W. Braunschweig K. Gather F.J. Kirschfink K. Lübelsmeyer H.-U. Martyn G. Peise J. Rimkus H.G. Sander D. Schmitz D. Trines W. Wallraff H. Boerner H.M. Fischer H. Hartmann E. Hilger W. Hillen G. Knop G. Zobernig 《Physics letters. [Part B]》1982,113(6):499-508
The ration R = σ(e+e? → hadrons)σμμ was measured between 12.0 and 36.7 GeV c.m. energy W with a precision of typically ± 5.2%. R is found to be constant with an average R = 4.01 ± 0.03 (stat) ± (syst.) for W ? 14 GeV. Quarks are found to be point-like, the mass parameter describing a possible quark form-factor being larger than 186 GeV. Fits including QCD corrections and a weak neutral-current contribution are presented. 相似文献
52.
Martyn C.R. Symons Robert C. Selby Ian G. Smith Stephen W. Bratt 《Chemical physics letters》1977,48(1):100-102
Rigid solution spectra for C6F?6 and C4F?8 are compared, and it is concluded that C6F]t-6 cannot have the planar, σ* structure previously postulated. Instead, a puckered-ring structure with σ and pseudo π delocalisation is postulated. 相似文献
53.
Earle MJ Hakala U Hardacre C Karkkainen J McAuley BJ Rooney DW Seddon KR Thompson JM Wahala K 《Chemical communications (Cambridge, England)》2005,(7):903-905
Chloroindate(III) ionic liquids are versatile reaction media for Friedel-Crafts acylation reactions; the system is catalytic and totally recyclable, using an aqueous workup, with no leaching of the indium into the product phase. 相似文献
54.
Oren P. Anderson Stephen A. Fieldhouse Charles E. Forbes Martyn C.R. Symons 《Journal of organometallic chemistry》1976,110(2):247-255
Exposure of (CO)5MnPbPh3 to 60Co γ-ray at 77 K gave one major paramagnetic species detectable by ESR spectroscopy. This exhibited an anisotropic hyperfine interaction with 55Mn, near free-spin g-values, and a small, almost isotropic coupling to 207Pb. The form of the A(55Mn) and g-tensor components suggest an orbital of dz2 symmetry on manganese for the unpaired electron, but this cannot be directed along the MnPb bond since the 207Pb hyperfine coupling indicates a very low spin-density on lead. We suggest that the centre is formed by electron addition to manganese to give a formal d7 centre, with concomitant loss of one equatorial carbonyl ligand. We defind z as the direction of the lost ligand. A second centre, detected at high gain, having a large hyperfine coupling to 207Pb and a 31 G coupling to 55Mn is tentatively identified as the parent cation.In marked contrast, the molecule (CO)4CoPbPh3 gave a single centre having comparable 59Co hyperfine and g-tensor components, but also a very large hyperfine coupling to 207Pb (ca. 3300 G). Thus, in this case, an electron gain centre (d9) has been formed, the electron being accomodated in the highest MO having a large dz2 component on cobalt (z being now the CoPb direction).Reasons for the adoption of these different structures are discussed. 相似文献
55.
Bruno SM Monteiro B Balula MS Lourenço C Valente AA Pillinger M Ribeiro-Claro P Gonçalves IS 《Molecules (Basel, Switzerland)》2006,11(4):298-308
The tetrahedral triphenylsiloxy complex MoO(2)(OSiPh(3))(2) (1) and its Lewis base adduct with 2,2'-bipyridine, MoO(2)(OSiPh(3))(2)(bpy) (2), were prepared and characterised by IR/Raman spectroscopy, and thermogravimetric analysis. Both compounds catalyse the epoxidation of cis-cyclooctene at 55 degrees C using tert-butylhydroperoxide (t-BuOOH) is decane as the oxidant, giving 1,2-epoxycyclooctane as the only product. The best results were obtained in the absence of a co-solvent (other than the decane) or in the presence of 1,2-dichloroethane, while much lower activities were obtained when hexane or acetonitrile were added. With no co-solvent, catalyst 1 (initial activity 272 mol x molMo(-1) x h(-1)for a catalyst:substrate: oxidant molar ratio of 1:100:150) is much more active than 2(initial activity 12 mol x molMo(-1) x h(-1)). The initial reaction rates showed first order dependence with respect to the initial concentration of olefin. With respect to the initial amount of oxidant, the rate order dependence for 1 (1.9) was higher than that for 2 (1.6).The dependence of the initial reaction rate on reaction temperature and initial amount of catalyst was also studied for both catalysts. The lower apparent activation energy of 1 (11 kcal x mol(-1)) as compared with 2 (20 kcal x mol(-1)) is in accordance with the higher activity of the former. 相似文献
56.
The contribution made by triply-excited and quadruply-excited configurations to electron correlation energies in closed-shell systems is examined in detail. Many-body perturbation theory is used to calculate the contribution of these configurations to the correlation energies in 25 atoms and molecules. Calculations are performed for the nitrogen, carbon monoxide and carbon monosulphide molecules for a range of nuclear geometries. 相似文献
57.
Ab initio CI calculations are presented for potential curves for the valence states of HCl, for the vertical electronic spectrum and for the potential curve for the B 1Σ+ state. The valence 1Π, 3Π and 3Σ+ states are found to be repulsive. Calculated vertical excitation energies are in good agreement with experiment. The B 1Σ+ curve is predicted to have a double minimum. 相似文献
58.
59.
Ryan J. Schwamm Mathew D. Anker Matthias Lein Martyn P. Coles 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(5):1503-1507
The potassium aluminyl complex K[Al(NONAr)] (NON=NONAr=[O(SiMe2NAr)2]2?, Ar=2,6‐iPr2C6H3) reacts with 1,3,5,7‐cyclooctatetraene (COT) to give K[Al(NONAr)(COT)]. The COT‐ligand is present in the asymmetric unit as a planar μ2‐η2:η8‐bridge between Al and K, with additional K???π‐aryl interactions to neighboring molecules that generate a helical chain. DFT calculations indicate significant aromatic character, consistent with reduction to [COT]2?. Addition of 18‐crown‐6 causes a rearrangement of the C8‐carbocycle to form the isomeric 9‐aluminabicyclo[4.2.1]nona‐2,4,7‐triene anion. 相似文献
60.
Dimitra Vernardou Charalampos Drosos Andreas Kafizas Martyn E. Pemble Emmanouel Koudoumas 《Molecules (Basel, Switzerland)》2020,25(23)
The need for clean and efficient energy storage has become the center of attention due to the eminent global energy crisis and growing ecological concerns. A key component in this effort is the ultra-high performance battery, which will play a major role in the energy industry. To meet the demands in portable electronic devices, electric vehicles, and large-scale energy storage systems, it is necessary to prepare advanced batteries with high safety, fast charge ratios, and discharge capabilities at a low cost. Cathode materials play a significant role in determining the performance of batteries. Among the possible electrode materials is vanadium pentoxide, which will be discussed in this review, due to its low cost and high theoretical capacity. Additionally, aqueous electrolytes, which are environmentally safe, provide an alternative approach compared to organic media for safe, cost-effective, and scalable energy storage. In this review, we will reveal the industrial potential of competitive methods to grow cathodes with excellent stability and enhanced electrochemical performance in aqueous media and lay the foundation for the large-scale production of electrode materials. 相似文献