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61.
Zusammenfassung Optisch aktive Methylcymantren-- und--carbonsäuren wurden durch Racematspaltung ihrer Phenäthylaminsalze erhalten. Bei der Umwandlung in die entsprechenden Acetyl- bzw. Vinyl-methylcymantrene treten charakteristische Drehwertänderungen auf. Aus diesen, vor allem aber aus der Rotationsdispersion, ließ sich auf Grund von Konformationsanalysen und Vergleichen zwischen offenkettigen und cyclischen Verbindungen sowie mit analogen Methylferrocenderivaten für die -substituierten Produkte mit großer Sicherheit die absolute Konfiguration ableiten: (1S) für (+)-Methylcymantren--carbonsäure und ihre Folgeprodukte. Dieser Befund wurde durch kinetische Racematspaltung des Anhydrides der racem. Säure mit (–)--Phenäthylamin gestützt.
Mit 3 Abbildungen 相似文献
Optically active methylcymantrene-- and--carboxylic acids were obtained by resolution of their salts with -phenethylamine. Upon transformation into the corresponding acetyl and vinyl methylcymantrenes, characteristic shifts of the optical rotation are observed. From these data, and especially from the rotatory dispersions, on the basis of conformational analyses and comparisons between open chain and cyclic compounds as well as with analogous methylferrocene derivatives, the absolute configurations of the -substituted products could be deduced with reasonable probability: (1S) for (+)-methylcymantrenecarboxylic acid and its subsequent products. This result was supported by kinetic resolution of the anhydride of the racemic carboxylic acid with (–)--phenethylamine.
Mit 3 Abbildungen 相似文献
62.
Sjöde A Alriksson B Jönsson LJ Nilvebrant NO 《Applied biochemistry and biotechnology》2007,137(1-12):327-337
Industrial production of bioethanol from fibers that are unusable for pulp production in pulp mills offers an approach to product diversification and more efficient exploitation of the raw material. In an attempt to utilize fibers flowing to the biological waste treatment, selected fiber sludges from three different pulp mills were collected, chemically analyzed, enzymatically hydrolyzed, and fermented for bioethanol production. Another aim was to produce solid residues with higher heat values than those of the original fiber sludges to gain a better fuel for combustion. The glucan content ranged between 32 and 66% of the dry matter. The lignin content varied considerably (1-25%), as did the content of wood extractives (0.2-5.8%). Hydrolysates obtained using enzymatic hydrolysis were found to be readily fermentable using Saccharomyces cerevisiae. Hydrolysis resulted in improved heat values compared with corresponding untreated fiber sludges. Oligomeric xylan fragments in the solid residue obtained after enzymatic hydrolysis were identified using matrix-assisted laser desorption ionization-time of flight and their potential as a new product of a pulp mill-based biorefinery is discussed. 相似文献
63.
Molten salt hydrates proved to be alternative solvents to cellulose. Toinvestigate the reasons for this dissolving ability, information about thesolvent–cellulose interactions is essential. As well as 13CHR NMR, 7Li NMR was used to obtain further insight into thisproblem.After comparing several molten salt hydrates, the 7Li NMR spectrarevealed a smaller shielding of the lithium cation for not dissolving than fordissolving and swelling cellulose systems. In most solvent systems theshieldingat the 7Li nuclei increases with the cellulose concentration. 2D7Li-1H HOESY NMR was successfully applied to verify thepresence of cellobiose, used as a model compound for cellulose, in the firstco-ordination sphere of the lithium cation. 相似文献
64.
Nilvebrant Nils-Olof Reimann Anders Larsson Simona Jönsson Leif J. 《Applied biochemistry and biotechnology》2001,91(1-9):35-49
Lignocellulose hydrolysates contain fermentation inhibitors causing decreased ethanol production. The inhibitors include phenolic
compounds, furan aldehydes, and aliphatic acids. One of the most efficient methods for removing inhibiting compounds prior
to fermentation is treatment of the hydrolysate with ion-exchange resins. The performance and detoxification mechanism of
three different resins were examined: an anion exchanger, a cation exchanger, and a resin without charged groups (XAD8). A
dilute acid hydrolysate of spruce was treated with the resins at pH 5.5 and 10.0 prior to ethanolic fermentation with Saccharomyces cerevisiae. In addition to the experiments with hydrolysate, the effect of the resins on selected model compounds, three phenolics (vanillin,
guaiacol, and coniferyl aldehyde) and two furan aldehydes (furfural and hydroxymethyl furfural), was determined. The cation
exchanger increased ethanol production, but to a lesser extent than XAD-8, which in turn was less effective than the an ion
exchanger. Treatment at pH 10.0 was more effective than at pH 5.5. At pH 10.0, the anion exchanger efficiently removed both
anionic and uncharged inhibitors, the latter by hydrophobic interactions. The importance of hydrophobic interactions was further
indicated by a substantial decrease in the concentration of model compounds, such as guaiacol and furfural, after treatment
with XAD-8. 相似文献
65.
66.
LiTiCl3 is obtained as one example within an ample solid solution, Li24–2nTinCl24 (?4?n?10), by synpropotionation of TiCl3 and Ti in the presence of LiCl (2:1:3 molar ratio) in sealed tantalum tubes at 750°C. It crystallizes with the inverse spinel-type structure according to (Li0.67)[4](Li0.67Ti1.33)[4]Cl4 with, at 25°C, a = 1048.62(4) pm, space group Fd3m. Thermal expansion is linear with α = 4.85 × 10?5K?1 up to about 300°C and thereafter, when the migration of Li+ from tetrahedral to octahedral interstices becomes increasingly important, it exhibits a relative decrease resulting, finally, in the phase transition to a NaCl-type structure that is observed for the first time at about 575°C. 相似文献
67.
68.
69.
Batlle R Carlsson H Holmgren E Colmsjö A Crescenzi C 《Journal of chromatography. A》2002,942(1-2):73-82
An investigation into the selectivity of an iminodiacetic acid (IDA) modified silica gel column for transition and heavy metal ions using non-chelating inorganic eluents has been carried out. A number of eluent parameters were investigated to determine the exact retention mechanism taking place and to control selectivity. The parameters studied were eluent ionic strength and the nature of the inorganic salt used, eluent pH and eluent temperature. The results obtained showed how despite certain metal ions exhibiting similar stability constants with the bonded IDA groups, careful control of each of the above parameters, in particular eluent chloride ion concentration and eluent temperature, could result in large changes in selectivity. Optimal conditions for the isocratic and gradient separation of Mg(II), Ca(II), Mn(II), Cd(II), Co(II), Zn(II) and Pb(II) were determined. An isocratic method using a 0.035 M KCl, 0.065 M KNO3 (pH 2.5) eluent was successfully applied to the determination of Mn(II), Cd(II), Co(II) and Zn(II) at concentrations between 20 and 121 microg/l in a freshwater certified reference material (NIST 1640). 相似文献
70.
Benedikt Nowak Oskar Karlström Peter Backman Anders Brink Maria Zevenhoven Severin Voglsam Franz Winter Mikko Hupa 《Journal of Thermal Analysis and Calorimetry》2013,111(1):183-192
In order to determine the intrinsic reactivity behavior from thermogravimetry studies, the experimental conditions should be such that the reactions are not mass transfer limited. Biomass char usually has a higher reactivity than coal chars. Therefore, mass transfer limitations may be more problematic when studying biomass char reactivity. Chemical reaction kinetics and mass transfer processes present in thermogravimetry are used for modeling the overall reaction rate for spruce bark CO2 gasification. Thermogravimetric experiments are carried out between 700 and 900 °C, and the CO2 concentration is varied between 10 and 90 vol%. The intrinsic activation energy is found to be 120 kJ mol?1. The transition temperature between regimes I and II is here defined when the fraction apparent to true activation energy equals 0.75. Higher external mass transfer (e.g., by decreasing the diffusion path through the crucible’s freeboard), decreasing the sample amounts, and higher CO2 partial pressures for the Langmuir–Hinshelwood reaction type increase the transition temperature. The results show that the transition temperature between regimes I and II conditions is approx. 1,030 °C for 90 vol% CO2. 相似文献