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81.
Shin Y Choy N Turner TR Balachandran R Madiraju C Day BW Curran DP 《Organic letters》2002,4(25):4443-4446
[structure: see text] Two hybrid analogues of discodermolide and dictyostatin (3, 26) have been designed and synthesized. These are the first macrocyclic analogues of discodermolide and biological activities were evaluated and compared with linear discodermolide analogues. 相似文献
82.
Sandeep Ghumaan Biprajit Sarkar Mahendra P. Patil Jan Fiedler Raghavan B. Sunoj Wolfgang Kaim Goutam Kumar Lahiri 《Polyhedron》2007
The complexes (μ3-L1/L2)[Ru(acac)2]3, acac− = 2,4-pentanedionato, L1 = 2,3,8,9,14,15-hexachlorodiquinoxalino[2,3-a:2′,3′-c]phenazine and L2 = 2,3,8,9,14,15- hexamethyldiquinoxalino[2,3-a:2′,3′-c]phenazine, undergo stepwise one-electron oxidation involving a total of three electrons and stepwise one-electron reduction with three (L2) or four electrons (L1). All reversibly accessible states were characterized by UV–Vis–NIR spectroelectrochemistry. Oxidation leads to mixed-valent intermediates {(μ3-L)[Ru(acac)2]3}+ and {(μ3-L)[Ru(acac)2]3}2+ of which the RuIIIRuIIRuII combinations exhibit higher comproportionation constants Kc than the RuIIIRuIIIRuII states – in contrast to a previous report for the unsubstituted parent systems {(μ3-L3)[Ru(acac)2]3}+/2+, L3 = diquinoxalino[2,3-a:2′,3′-c]phenazine. No conspicuous inter-valence charge transfer absorptions were observed for the mixed-valent intermediates in the visible to near-infrared regions. The monocations and monoanions were characterized by EPR spectroscopy, revealing rhombic ruthenium(III) type signals for the former. Electron addition produces ruthenium(II) complexes of the reduced forms of the ligands L, a high resolution EPR spectrum with 14N and 35,37Cl hyperfine coupling and negligible g anisotropy was found for {(μ3-L1)[Ru(acac)2]3}−. DFT calculations of (μ3-L1)[Ru(acac)2]3 confirm several ligand-centered low-lying unoccupied MOs for reduction and several metal-based high-lying occupied MOs for electron withdrawal, resulting in low-energy metal-to-ligand charge transfer (MLCT) transitions. 相似文献
83.
Huang X Terech P Raghavan SR Weiss RG 《Journal of the American Chemical Society》2005,127(12):4336-4344
The kinetics and mode of nucleation and growth of fibers by 5alpha-cholestan-3beta-yl N-(2-naphthyl)carbamate (CNC), a low-molecular-mass organogelator (LMOG), in n-octane and n-dodecane have been investigated as their sols were transformed isothermally to organogels. The kinetics has been followed in detail by circular dichroism, fluorescence, small-angle neutron scattering, and rheological methods. When treated according to Avrami theory, kinetic data from the four methods are self-consistent and describe a gelation process involving one-dimensional growth and "instantaneous nucleation". As expected from this growth model, polarized optical micrographs of the self-assembled fibrillar networks (SAFINs) show fibrous aggregates. However, their size and appearance change abruptly from spherulitic to rodlike as temperature is increased. This morphological change is attended by corresponding excursions in static and kinetic CD, fluorescence and rheological data. Furthermore, the rheological measurements reveal an unusual linear increase in viscoelastic moduli in the initial stages of self-assembly. Each of the methods employed becomes sensitive to changes of the system at different stages of the transformation from single molecules of the LMOG to their eventual SAFINs. This study also provides a methodology for investigating aggregation phenomena of some other self-assembling systems, including those of biological and physiological importance. 相似文献
84.
M Ramakrishna Prasad G Kamalakar S. J Kulkarni K. V Raghavan 《Journal of molecular catalysis. A, Chemical》2002,180(1-2):109-123
Mesoporous aluminosilicates (Al-containing NaMCM-41) were applied as catalyst supports for oxidative coupling of β-naphthol and substituted β-naphthols due to their remarkable features such as surface area, ordered mesopores and high thermal stability. The NaMCM-41 supported copper catalysts prepared by impregnation method, and Cu-NaMCM-41 was prepared by incorporating copper during synthesis. Oxidative coupling of β-naphthol reaction was studied using molecular oxygen as oxidant. The copper supported NaMCM-41 catalysts were prepared with different Si/Al ratios and calcined from 120 to 420 °C were observed to show varied product selectivity. The NaMCM-41 supported copper catalysts and Cu-NaMCM-41 were more active than the corresponding Cu/Fe supported on NaY zeolite. The catalysts were characterized by X-ray diffraction (XRD), temperature programmed reduction (TPR), UV–DRS, ICPMS and BET surface area techniques and the reaction products were confirmed by 1H-NMR, FTIR and HRMS. An attempt has been made to explain the product selectivity of the catalysts discussed with the above techniques. The high dispersion of Cu+2 species observed in the catalysts having high Si/Al ratios in NaMCM-41 support and catalysts that are calcined at low temperatures, i.e. less than 420 °C, yielded an unexpected product perylene diol. A comparatively low dispersion of Cu+2 species, noticed in catalysts having low Si/Al ratios and calcined at high temperatures, yielded binapthol as the coupled product. The effect of the variation of catalyst and the solvent are also studied. 相似文献
85.
Determination of hexavalent chromium by on-line dialysis ion chromatography in a matrix of strong colourants and trivalent chromium 总被引:3,自引:0,他引:3
Ganeshjeevan R Chandrasekar R Yuvaraj S Radhakrishnan G 《Journal of chromatography. A》2003,988(1):151-159
Hexavalent chromium detection in the presence of a high load of colourants without any false positive and in-procedure oxidation of Cr(III) is an important area of study. Colourants are a class of interfering substances in many spectroscopic analyses and chromatographic separations and detection. A purification method using an on-line dialysis technique for ion chromatography (IC) has been developed to remove water-soluble anionic dyes and particulate colourants and other substances to facilitate Cr(VI) quantification and the method is discussed. The dialysis was optimized with Cr(VI) standard solutions for quantification. The efficacy of the procedure for the removal of anionic dyes and detection of Cr(VI) was checked with a Cr(VI) spiked synthetic preparation containing a water-soluble dye and trivalent chromium. Soluble Cr(VI) extracted with organic dyes from environmental samples was analyzed. The method has a detection limit of 5 microg/l, recovery rate of 100% and analysis time less than 20 min. 相似文献
86.
M. Asai T. Aziz J. F. Bailly J. F. Baland S. Banerjee W. Bartl A. Batunin C. Caso F. Diez-Medo B. Epp A. Ferrando F. Fontanelli S. N. Ganguli V. G. Gavrjusev T. Gemesy P. Girtler A. Gurtu R. Hamatsu P. Herquet J. Hrubec Y. Iga V. Khalatyan E. Kistenev J. M. Kohli J. Mac Naughton J. C. Marin M. Markytan L. Montanet G. Neuhofer G. Pinter P. Porth R. Raghavan T. Rodrigo J. M. Salicio J. B. Singh S. Squarcia K. Takahashi L. A. Tikhonova U. Trevisan T. Tsurugai V. Yarba G. Zholobov S. Zotkin EHS-RCBC Collaboration 《Zeitschrift fur Physik C Particles and Fields》1987,34(4):429-435
Production properties and correlations forK s 0 K s 0 ,K s 0 Λ,K s 0 ¯Λ and Λ¯Λ systems in 360 GeV/cpp interactions are presented. All rapidity gap distributions are observed to peak at Δy=0 and the azimuthal angular distributions between the two particles are consistent with being flat. Experimental results are compared with the quark fusion and Lund models of particle production. 相似文献
87.
Lyxo-phytosphingosine and erythro-sphingosine have been elaborated from a common intermediate. The key step in the reaction sequence involves stereo- and regiospecific functionalization of an olefin by intramolecular nucleophilic sulfinyl group participation. 相似文献
88.
The time dependent performance of extended surfaces subjected to fouling is addressed in this work. Where fins are used for
augmenting boiling heat transfer, the interaction of local values of temperature excess, fouling resistance and surface characteristics
of the deposit can be quite complex. Taking typical asymptotic fouling growth parameters from literature for reverse solubility
salts, three kinds of fin geometry are analysed – rectangular, triangular and annular. For various values of the fin parameter
mL, the temperature distribution and variation of fouling resistance are obtained as a function of time. To interpret the
performance of a fouled fin, a new term `cleanliness efficiency' is introduced. The necessity of choosing an optimal value
of mL for the fin is also highlighted here. It is shown that for all three fin configurations, cleanliness efficiency differs
little, thus simplifying the geometry dependence. The approach set out in this work will help in the design of finned heat
exchangers subjected to fouling and thereby minimise their overdesign.
Received on 12 July 2000 相似文献
89.
90.