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71.
72.
Hugo B. C. Kleikamp Yue Mei Lin Duncan G. G. McMillan Jeanine S. Geelhoed Suzanne N. H. Naus-Wiezer Peter van Baarlen Chinmoy Saha Rogier Louwen Dimitry Y. Sorokin Mark C. M. van Loosdrecht Martin Pabst 《Chemical science》2020,11(11):3074
Nonulosonic acids, commonly referred to as sialic acids, are a highly important group of nine-carbon sugars common to all domains of life. They all share biosynthetic and structural features, but otherwise display a remarkable chemical diversity. In humans, sialic acids cover all cells which makes them important for processes such as cellular protection, immunity and brain development. On the other hand, sialic acids and other nonulosonic acids have been associated with pathological processes including cancer and viral infections. In prokaryotes, nonulosonic acids are commonly associated with pathogens, which developed through molecular mimicry a strategy to circumvent the host''s immune response. However, the remarkably large chemical diversity of prokaryotic nonulosonic acids challenges their discovery, and research on molecular characteristics essential for medical applications are often not feasible. Here, we demonstrate a novel, universal large-scale discovery approach that tackles the unmapped diversity of prokaryotic nonulosonic acids. Thereby, we utilize selective chemical labelling combined with a newly established mass spectrometric all-ion-reaction scanning approach to identify nonulosonic acids and other ulosonic acid-like sugars. In doing so, we provide a first molecular-level comparative study on the frequency and diversity across different phyla. We not only illustrate their surprisingly wide-spread occurrence in non-pathogenic species, but also provide evidence of potential higher carbon variants. Many biomedical studies rely on synthetic routes for sialic acids, which are highly demanding and often of low product yields. Our approach enables large-scale exploration for alternative sources of these highly important compounds.A novel large-scale survey approach for microbial nonulosonic acids (sialic acids) including a first molecular level comparative study is presented. 相似文献
73.
Guy Bouchoux Jeanine Tortajada Jacques Dagaut Joëlle Fillaux 《Journal of mass spectrometry : JMS》1987,22(7):451-457
The metastable molecular ion of 2-hexanone loses a methyl radical mainly (~80%) from positions C(4) and C(6), in equal proportions, as indicated by 13C labelling. The necessary skeletal rearrangement of the butyl chain is interpreted in terms of a 1,2-[enol-olefin] +˙ shift. The results and the mechanisms concerning the minor eliminations of C2H4, C2H5˙, C3H5˙ and C3H6 neutrals are also discussed. 相似文献
74.
Z--acetamidocinnamate esters were hydrogenated with neutral rhodium(I) complexes containing (1R,2R)-trans-1,2-bis(diphenylphosphinomethyl)cyclobutane. Increasing the steric bulk of the alcohol moiety in the unsaturated esters had little influence upon the optical purity of the N-acetylphanylalanine ester products. In the series Me, Et, i-Pr, and t-Bu the optical purity decreased from 44 % ee-(R) [Me] to 40 % ee-(R) [t-Bu]. The chiral cyclobutane diphosphine appears to be only slightly more effective than the heterocyclic DIOP when ring-substituted Z--acetamidocinnamic acids are hydrogenated with neutral rhodium(I) complexes without the addition of triethylamine. Addition of triethylamine to the solvent blend seems to be more beneficial to the cyclobutane analogue than to DIOP. 相似文献
75.
76.
Vivier V Aguey F Fournier J Lambert JF Bedioui F Che M 《The journal of physical chemistry. B》2006,110(2):900-906
UV-visible and Raman spectroscopies as well as electrochemical techniques have been used to characterize cis- and trans-[Co(III)(en)2Cl2]Cl (en=ethylenediamine) complexes and the gamma-alumina-supported cis-Co((III)) complex. It is shown that the electrochemical reduction of these complexes occurs according to a multistage mechanism involving two electrochemical steps, with the formation of a dimer that was characterized by UV-visible spectroscopy (intervalence band at 670 nm). The apparent standard redox potential for each step has been determined, and experimental results reveal that cis and trans complexes present similar electrochemical characteristics. It is also shown that the deposition of trans-[Co(III)(en)2Cl2]+ on gamma-alumina leads to an inner-sphere complex (ISC) in a cis configuration in which Cl- ligands are substituted by OH or O- surface groups of alumina. These changes in the coordination sphere of the complex induce a substantial decrease of its apparent redox potential since it is -0.63 V/SCE (saturated calomel electrode) for the gamma-alumina-supported cis-Co(III) complex, whereas values of -0.17 and -0.35 V/SCE were determined in dimethyl sulfoxide (DMSO) for the trans and cis precursor complexes, respectively. 相似文献
77.
Jean‐Yves Salpin Dr. Sébastien Guillaumont Dr. Jeanine Tortajada Prof. Luke MacAleese Dr. Joël Lemaire Dr. Philippe Maitre Dr. 《Chemphyschem》2007,8(15):2235-2244
The gas-phase structures of protonated uracil, thymine, and cytosine are probed by using mid-infrared multiple-photon dissociation (IRMPD) spectroscopy performed at the Free Electron Laser facility of the Centre Laser Infrarouge d'Orsay (CLIO), France. Experimental infrared (IR) spectra are recorded for ions that were generated by electrospray ionization, isolated, and then irradiated in a quadrupole ion trap; the results are compared to the calculated infrared absorption spectra of the different low-lying isomers (computed at the B3LYP/6-31++G(d,p) level). For each protonated base, the global energy minimum corresponds to an enolic tautomer, whose infrared absorption spectrum matched very well with the experimental IRMPD spectrum, with the exception of a very weak IRMPD signal observed at about 1800 cm(-1) in the case of the three protonated bases. This signal is likely to be the signature of the second-energy-lying oxo tautomer. We thus conclude that within our experimental conditions, two tautomeric ions are formed which coexist in the quadrupole ion trap. 相似文献
78.
Salpin JY Mormann M Tortajada J Nguyen MT Kuck D 《European journal of mass spectrometry (Chichester, England)》2003,9(4):361-376
The hitherto unknown gas-phase basicity and proton affinity of 1,3,5-cycloheptatriene (CHT) have been determined by Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. Several independent techniques were used in order to exclude ambiguities due to proton-induced isomerisation of the conjugate cyclic C(7)H(9)(+) ions, [CHT + H](+). The gas-phase basicity obtained by the thermokinetic method, GB(CHT) = 799 +/- 4 kJ mol(-1), was found to be identical, within the limits of experimental error, with the values measured by the equilibrium method starting with protonated reference bases, and with the values resulting from the measurements of the individual forward and reverse rate constants, when corrections were made for the isomerised fraction of the C(7)H(9)(+) population. The experimentally determined gas-phase basicity leads to the proton affinity of cycloheptatriene, PA(CHT) = 833 +/- 4 kJ mol(-1), and the heat of formation of the cyclo-C(7)H(9)(+) ion, deltaH(f)(0)([CHT + H](+)) = 884 +/- 4 kJ mol(-1). Ab initio calculations are in agreement with these experimental values if the 1,2-dihydrotropylium tautomer, [CHT + H((1))](+), generated by protonation of CHT at C-1, is assumed to be the conjugate acid, resulting in PA(CHT) = 825 +/- 2 kJ mol(-1) and deltaH(f)(0)(300)([CHT + H((1))](+)) = 892 +/- 2 kJ mol(-1). However, the calculations indicate that protonation of cycloheptatriene at C-2 gives rise to transannular C-C bond formation, generating protonated norcaradiene [NCD + H](+), a valence tautomer being 19 kJ mol(-1) more stable than [CHT + H((1))](+). The 1,4-dihydrotropylium ion, [CHT + H((3))](+), generated by protonation of CHT at C-3, is 17 kJ mol(-1) less stable than [CHT + H((1))](+). The bicyclic isomer [NCD + H](+) is separated by relatively high barriers, 70 and 66 kJ mol(-1) from the monocyclic isomers, [CHT + H((1))](+) and [CHT + H((3))](+), respectively. Therefore, the initially formed 1,2-dihydrotropylium ion [CHT + H((1))](+) does not rearrange to the bicyclic isomer [NCD + H](+) under mild protonation conditions. 相似文献
79.
Ultraviolet Radiation Effects on a Microscopic Green Alga and the Protective Effects of Natural Dissolved Organic Matter 总被引:1,自引:0,他引:1
L. Jeanine A. West Bruce M. Greenberg Ralph E. H. Smith 《Photochemistry and photobiology》1999,69(5):536-544
Abstract— The population and photosynthetic responses of a microscopic green alga ( Selenastrum capricornutum ) to realistic levels of UV radiation (UVA and UVB) were assessed in natural lake waters of different dissolved organic carbon (DOC) concentration. Specific growth rates and photosynthetic competence (as reflected by Fv /Fm [measure of maximal quantum efficiency of photosystem II] and t1/2 [estimate of electrons transported to the plastoquinone pool] measured by in vivo variable chlorophyll a fluorescence) were compared between two exposure levels of UVR and two concentrations of DOC (2.5 mg C L−1 7.7 mg C L−1 ). Exposure periods of 6–9 days (five to nine generations) were used. Exposure to UVA primarily affected the efficiency of photosystem II, as evidenced by significant decreases of Fv /Fm but not growth rates or t1/2 Exposure to UVB, in the presence of UVA, did not cause significant additional decreases of Fv /Fm but did diminish growth rates. In the low DOC water, t1/2 was also diminished, suggesting different proximate sites of action from those for UVA. The high DOC water decreased the effective exposure to both UVA and UVB and diminished the negative impact of UV radiation on the cells, but the apparent protection was not explicable solely by the shading action of the DOC. Control values for Fv /Fm , growth rates and t1/2 were all lower in the high DOC water, suggesting a negative side effect to the apparent protective action of the DOC against UVB. 相似文献
80.
T. Zerguerras B. Blank Y. Blumenfeld T. Suomijärvi D. Beaumel B. A. Brown M. Chartier M. Fallot J. Giovinazzo C. Jouanne V. Lapoux I. Lhenry-Yvon W. Mittig P. Roussel-Chomaz H. Savajols J. A. Scarpaci A. Shrivastava M. Thoennessen 《The European Physical Journal A - Hadrons and Nuclei》2004,20(3):389-396
Light proton-rich bound and unbound nuclei were produced by means of stripping reactions of secondary beams of 20Mg and 18Ne. The decays of the unbound nuclei 18,19Na have been measured by detecting their decay products 17,18Ne and one proton and by performing an invariant-mass reconstruction. For 18Na, the present work is the first measurement of its decay. As the decay scheme of this nucleus could not be determined, two possible scenarios are proposed and discussed. In addition, the decay of excited states in 17Ne via two-proton emission was observed. The proton-proton angular distribution is isotropic for the first two-proton-emitting states, whereas higher-lying states seem to decay by a correlated two-proton emission, consistent with a 2He emission pattern for part of the decay strength.Received: 30 September 2003, Revised: 27 November 2003, Published online: 2 June 2004PACS:
21.10.-k Properties of nuclei; nuclear energy levels - 23.40.-s
decay; double
decay; electron and muon capture - 23.50. + z Decay by proton emissionM. Chartier: Present address: Physics Department, University of Liverpool, Liverpool, UK.M. Fallot: Present address: SUBATECH, Ecole des Mines, BP 20722, F-44307 Nantes Cedex, France.A. Shrivastava: Permanent address: Bhabha Atomic Research Center, Mumbai, India.Experiment performed at the GANIL facility, Caen, France. 相似文献