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81.
Cristina López Moreno Pedro Cañada Rudner José Manuel Cano García José Manuel Cano Pavón 《Mikrochimica acta》2004,148(1-2):93-98
A sequential injection analysis method is developed for the determination of the total polyphenol index in wines. The determination is based on the Folin-Ciocalteu reaction, which is monitored spectrophotometrically. Interactions between experimental variables and their optimal levels were investigated using factorial designs. The proposed system is fully computerised and is able to monitor polyphenol index in real samples of white, sweet and red wines. The calibration graph is linear from 5 to 200mg·L–1 using Tannic acid as standard, with a detection limit of 3.2mg·L–1. Interferences are studied. For validation purposes the proposed methodology was applied to the determination of the total polyphenol index in different types of wines and compared with earlier alternatives in order to assess their performance. 相似文献
82.
Cháfer-Pericás C Herráez-Hernández R Campíns-Falcó P 《Journal of chromatography. A》2004,1042(1-2):219-223
The selective determination of trimethylamine (TMA) in air by liquid chromatography is reported. Sampling is effected by flushing air through C18-packed solid-phase extraction (SPE) cartridges at a flow rate of 15 mL/min for 15 min. Next, TMA is desorbed from the cartridges and injected into the chromatographic system. The analyte is then selectively retained on a precolumn (20 mm x 2.1 mm i.d., packed with 30 microm, Hypersil C18 phase), and derivatized on-line by injecting 9-fluorenylmethyl chloroformate (FMOC). Finally, the TMA-FMOC derivative is transferred to the analytical column (125 mm x 4 mm i.d., LiChrospher 100 RP18, 5 microm), and monitored at 262 nm. The method was applied to the measurement of TMA in air in the 0.25-2.5 microg interval (equivalent to concentrations of TMA of 1.1-11 mg/m3), providing good linearity, reproducibility and accuracy. The mean recovery of TMA was (96 +/- 7%) (n = 12), and the limit of detection was 0.05 microg. The proposed procedure allows the selective determination of TMA in the presence of other primary and secondary short-chain aliphatic amines. 相似文献
83.
We present extensive molecular dynamics simulations of the motion of a single linear rigid molecule in a two-dimensional random array of fixed overlapping disklike obstacles. The diffusion constants for the center of mass translation, D(CM), and for rotation, D(R), are calculated for a wide range of the molecular length, L, and the density of obstacles, rho. The obtained results follow a master curve Drho(micro) approximately (L(2)rho)(-nu) with an exponent micro=-3/4 and 1/4 for D(R) and D(CM), respectively, that can be deduced from simple scaling and kinematic arguments. The nontrivial positive exponent nu shows an abrupt crossover at L(2)rho=zeta(1). For D(CM) we find a second crossover at L(2)rho=zeta(2). The values of zeta(1) and zeta(2) correspond to the average minor and major axis of the elliptic holes that characterize the random configuration of the obstacles. A violation of the Stokes-Einstein-Debye relation is observed for L(2)rho>zeta(1), in analogy with the phenomenon of enhanced translational diffusion observed in supercooled liquids close to the glass transition temperature. 相似文献
84.
Picquart M. López T. Gómez R. Torres E. Moreno A. Garcia J. 《Journal of Thermal Analysis and Calorimetry》2004,76(3):755-761
Sol-gel zirconia was characterized using high-resolution thermogravimetry (Hi-Res TG) and differential scanning calorimetry
(DSC) and compared with X-ray diffraction, Raman scattering, and UV-Vis spectroscopy. ZrO2-x(OH)2x·yH2O annealed below 400°C show typical behavior of amorphous material. As the annealing temperature is increased, the tetragonal
and monoclinic phases crystallize. Typical Hi-Res TG curve shows that the samples are continuously dehydrated in a long temperature
range, between room temperature and 600°C. The total mass loss relative to the initial mass is of about 29%. The DSC analysis
coupled with TG and structural information, indicate that the exothermic processes about 355 and 447°C can be related to the
nucleation process of the formation of tetragonal zirconia, with bulk crystallization at 447°C.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
85.
R. J. C. Lima E. C. Santos-Junior A. J. D. Moreno P. F. Façanha-Filho P. T. C. Freire M. I. Yoshida 《Journal of Thermal Analysis and Calorimetry》2013,111(1):627-631
In this study l-alanine, l-threonine, and taurine crystals were characterized through dilatometric technique and thermogravimetric and differential thermal analysis. The dilatometric analysis shows that the thermal expansion of the crystals is correlated with the strengths of local hydrogen bonding in the amino acid structures at room temperature. Thermogravimetric analysis and differential thermal analysis of the l-alanine, taurine, and l-threonine crystals have been performed at high temperatures. No clear correlation between the hydrogen bonding strengths and endothermic peak positions was observed. 相似文献
86.
87.
Alejandro Marcó Ramón Compañó Roser Rubio Pilar Domènech Albert Palangues Miguel Maestro 《Mikrochimica acta》2002,140(1-2):131-139
Four inter-comparison exercises on organic elemental analysis were carried out between 1997 and 2001 by the Department of
Analytical Chemistry of the University of Barcelona, together with the Microanalysis Service and the Institute of the Marine
Sciences, which both belong to the CSIC in Barcelona, and the University of A Coru?a. More than sixty laboratories participated
in these exercises. Here we describe the design and characteristics of the trials, the samples and the homogeneity tests applied.
We report the results obtained for the analysis of carbon, hydrogen, nitrogen, sulphur and oxygen, their statistical analysis,
and the most relevant aspects of the technical discussion meetings.
Received December 20, 2001; accepted March 18, 2002; published online July 22, 2002 相似文献
88.
89.
Moreno M. M. Torres Santos R. H. A. Gambardella M. T. P. Camargo A. J. da Silva A. B. F. Trsic M. 《Structural chemistry》1998,9(5):365-373
The crystal and molecular structures of the following molecules have been determined: 1-acetyl-indoline, 1-acetyl-5-nitro-indoline, l-acetyl-5-nitro-7-bromo-indoline, 1-acetyl-5-bromo-7-nitroindoline, and l-acetyl-5-bromo-7-nitro-indol. Molecular orbital calculations are performed for these compounds and two related species. 相似文献
90.
Four new ternary complexes of CuII with l-methionine and the nucleotides 5AMP (adenosine 5-phosphate), 5GMP (guanosine 5-phosphate) and 5IMP (inosine 5-phosphate), and with l-tryptophan and 5AMP, were synthesized and characterized by elemental analysis and i.r. spectroscopy. One ternary complex of NII with l-cysteine and 5IMP was also prepared and characterized. The study of the three ternary compounds of CuII, of general formulae Cu-5NMP-l-methionine, indicates coordination of the phosphate group and of N(7) of the purinic ring. l-Methionine is bound by the carboxylic and amino groups. The ternary complex obtained from a mixture of Cu-5AMP and l-tryptophan is a dimer in which the nucleotide bridges the two copper atoms. In the complex of Ni-5IMP and l-cysteine, the nucleotide seems to bind the metal through the N(7) of the heterocyclic ring, and the l-cysteine is coordinated as a bidentate chelate by the carboxyl and thiol groups. E.s.r. spectra of the copper complexes are in good agreement with the low symmetry structure proposed. The one-electron reduction potentials Ec(Fc+/Fc) (V) of CuII to CuI were established for the four copper complexes from cyclic voltammetry studies. The one-electron oxidation potential Ea(Fc+/Fc+) (V) of NiII to NiIII was also measured for the nickel complex. 相似文献