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971.
Prukała D Prukała W Khmelinskii I Sikorski M 《Physical chemistry chemical physics : PCCP》2011,13(15):6981-6991
Absorption and steady-state fluorescence spectra of nine N-p-(m- and o-) chlorobenzyl substituted (E)-2'-(3' and 4')-hydroxy-4-stilbazolium chlorides belonging to the hemicyanine class of compounds were studied in extra dry alcohols of different polarity. Derivatives with 2'-hydroxy or 4'-hydroxy substituent in the benzene moiety of stilbazol molecule displayed negative solvatochromizm. On the other hand, the excited state decay of compounds with a 3'-hydroxy group in the benzene moiety was dominated by non-radiative processes in protic solvents. Solutions of each of the compounds are yellow in extra dry solvents, red in solvents with small amount of water and yellow again if more water is added. The absorbance and steady-state fluorescence methods were used to explain the protonation/deprotonation processes for N-p-chlorobenzyl-(E)-4'-hydroxy-4-stilbazolium chloride and its zwitterionic or quinoid form in 2-propanol responsible for these phenomena. 相似文献
972.
973.
We present the first results of the quantitative and qualitative gas chromatographic and isotope ratio mass spectrometric analysis of monosaccharides derived from acid hydrolysis of α-cellulose extracted from annual pine tree-rings. The conifers investigated in this study grew in the Niepolomice Forest in Poland, and the annual rings covered the time span from 1940 to 2000 AD. The main components of the α-cellulose samples were two saccharides: glucose and mannose. The amount of glucose in the annual rings varied between 17 and 44%. The δ(13)C of glucose was found to be less negative than that of α-cellulose and the δ(18)O values in glucose were less positive than those in α-cellulose. The content of monosaccharides in the α-cellulose samples has an influence on the isotope fractionation factors. The values of the carbon isotope fractionation factor increase with an increase in the monosaccharides concentration in α-cellulose, while the values of the oxygen isotope fractionation factor decrease with an increase in monosaccharides concentration in α-cellulose. The challenge is to establish, with respect to climate changes and environmental conditions, the significance of the interannual variations in the observed monosaccharide concentration. 相似文献
974.
Rivillas-Acevedo L Grande-Aztatzi R Lomelí I García JE Barrios E Teloxa S Vela A Quintanar L 《Inorganic chemistry》2011,50(5):1956-1972
The prion protein (PrP(C)) is implicated in the spongiform encephalopathies in mammals, and it is known to bind Cu(II) at the N-terminal region. The region around His111 has been proposed to be key for the conversion of normal PrP(C) to its infectious isoform PrP(Sc). The principal aim of this study is to understand the role of protons and methionine residues 109 and 112 in the coordination of Cu(II) to the peptide fragment 106-115 of human PrP, using different spectroscopic techniques (UV-vis absorption, circular dichroism, and electron paramagnetic resonance) in combination with detailed electronic structure calculations. Our study has identified a proton equilibrium with a pK(a) of 7.5 associated with the Cu(II)-PrP(106-115) complex, which is ascribed to the deprotonation of the Met109 amide group, and it converts the site from a 3NO to a 4N equatorial coordination mode. These findings have important implications as they imply that the coordination environment of this Cu binding site at physiological pH is a mixture of two species. This study also establishes that Met109 and Met112 do not participate as equatorial ligands for Cu, and that Met112 is not an essential ligand, while Met109 plays a more important role as a weak axial ligand, particularly for the 3NO coordination mode. A role for Met109 as a highly conserved residue that is important to regulate the protonation state and redox activity of this Cu binding site, which in turn would be important for the aggregation and amyloidogenic properties of the protein, is proposed. 相似文献
975.
Cerveny S Arrese-Igor S Dolado JS Gaitero JJ Alegría A Colmenero J 《The Journal of chemical physics》2011,134(3):034509
The behavior of water dynamics confined in hydrated calcium silicate hydrate (C-S-H) gel has been investigated using broadband dielectric spectroscopy (BDS; 10(-2)-10(6) Hz) in the low-temperature range (110-250 K). Different water contents in C-S-H gel were explored (from 6 to 15 wt%) where water remains amorphous for all the studied temperatures. Three relaxation processes were found by BDS (labeled 1 to 3 from the fastest to the slowest), two of them reported here for the first time. We show that a strong change in the dielectric relaxation of C-S-H gel occurs with increasing hydration, especially at a hydration level in which a monolayer of water around the basic units of cement materials is predicted by different structural models. Below this hydration level both processes 2 and 3 have an Arrhenius temperature dependence. However, at higher hydration level, a non-Arrhenius behavior temperature dependence for process 3 over the whole accessible temperature range and, a crossover from low-temperature Arrhenius to high-temperature non-Arrhenius behavior for process 2 are observed. Characteristics of these processes will be discussed in this work. 相似文献
976.
Primo A Marino T Corma A Molinari R García H 《Journal of the American Chemical Society》2011,133(18):6930-6933
When irradiated with visible light (λ > 400 nm) 1 wt % gold-supported ceria nanoparticles generate oxygen from water (10.5 μmol·h(-1)) more efficiently than the standard WO(3) (1.7 μmol·h(-1)) even under UV irradiation (9.5 μmol·h(-1)). This remarkable photocatalytic activity arises from a novel preparation method to reduce the particle size of ceria (5 nm) by means of electrostatic binding of Ce(4+) to alginate gel, subsequent supercritical CO(2) drying, and calcination. The low loading of Au is crucial for the observed high catalytic activity. 相似文献
977.
González Álvarez J Blanco Gomis D Arias Abrodo P Díaz Llorente D Busto E Ríos Lombardía N Gotor Fernández V Gutiérrez Álvarez MD 《Analytical and bioanalytical chemistry》2011,400(5):1209-1216
Two ionic liquids (ILs), namely (S,S)-1-butyl-3-(2'-hydroxy-cyclohexyl)-3H-imidazol-1-ium tetrafluoroborate and (S,S)-1-butyl-3-(2'-acetyl-cyclohexyl)-3H-imidazol-1-ium tetrafluoroborate have been employed as stationary phases in capillary gas chromatography. These new phases exhibit a column efficiency of 1,600 and 2,100 plates m(-1) for IL 1 and IL 2, respectively, a wide operating temperature range and good thermal stability (bleeding temperature of 250 °C for IL 1 and 160 °C for IL 2). Inverse gas chromatography (GC) analyses were used to study the solvation properties of these ILs through a linear solvation energy model. The application of these ILs as new GC stationary phases was studied. These stationary phases exhibited unique selectivity for many organic substances, such as alkanes, ketones, esters, and aromatic compounds. The efficient separation of several mixtures containing compounds of different polarities and the good separation of fatty acid methyl esters (FAMEs) and cis/trans isomers indicate that these ILs may be applicable as a new type of GC stationary phases. 相似文献
978.
de Llanos AM Espinosa-Mansilla A Cañada-Cañada F de la Peña AM 《Journal of separation science》2011,34(11):1283-1292
A simple liquid chromatographic method has been developed to achieve the complete separation and determination of a wide range of pteridinic compounds and creatinine (CREA) in urine samples, in just one run. The influences of mobile phase composition and buffer pH have been studied. The optimized mobile phase was composed of a Tris-HCl buffer (15 mmol/L) at pH 6.10 solution (eluent A) and a Tris-HCl buffer (15 mmol/L) at pH 6.40 solution (eluent B), in gradient mode. Analytes were determined by fluorimetric detection, exciting at 272 nm, and measuring the fluorescence emission at three wavelengths, 410, 445 and 465 nm. CREA, as a reference of metabolites excretion in urine, was determined by photometric detection at 230 nm. Pteridines detection limits varied from 0.2 to 6.1 ng/mL, and 0.2 g/mL for CREA. Calculated precision values expressed as RSD (%) varied from 1.1 to 5.9. Two different oxidation procedures for urine samples were optimized. The neopterin/biopterin ratios found were 0.98 and 0.86 for adults and children, respectively, by means of the alkaline iodide/iodine oxidation and 0.45 and 0.57 using neutral KMnO(4) oxidation. 相似文献
979.
Campuzano S Pedrero M García JL García E García P Pingarrón JM 《Analytical and bioanalytical chemistry》2011,399(7):2413-2420
A disposable magnetogenosensor for the rapid, specific and sensitive detection of Streptococcus pneumoniae is reported. The developed procedure involves the use of streptavidin-modified magnetic beads, a specific biotinylated capture
probe that hybridizes with a specific region of lytA, the gene encoding the pneumococcal major autolysin, and appropriate primers for asymmetric polymerase chain reaction (PCR)
amplification. Capture probes and amplicons specific for S. pneumoniae were selected by a careful analysis of all lytA alleles available. The selected primers amplify a 235-bp fragment of pneumococcal lytA. A detection limit (LOD) of 5.1 nM was obtained for a 20-mer synthetic target DNA without any amplification protocol, while
the LOD for the asymmetric PCR amplicon was 1.1 nM. A RSD value of 6.9% was obtained for measurements carried out with seven
different genosensors for 1.1-nM aPCR product. The strict specificity of the designed primers was demonstrated by aPCR amplification
of genomic DNA prepared from different bacteria, including some closely related streptococci. Direct asymmetric PCR (daPCR),
using cells directly from broth cultures of S. pneumoniae, showed that daPCR products could be prepared with as few as 2 colony-forming units (CFU). Furthermore, this methodology
did not show any cross-reaction with closely related streptococci such as Streptococcus mitis (or Streptococcus pseudopneumoniae) even when present in the culture at concentrations up to 105 times higher than that of S. pneumoniae. Preliminary data for rapid detection of pneumococcus directly in clinical samples has shown that it is possible to discriminate
between non-inoculated blood and urine samples and samples inoculated with only 103 CFU mL−1
S. pneumoniae. 相似文献
980.
Aparicio S Alcalde R Dávila MJ García B Leal JM 《The journal of physical chemistry. B》2008,112(36):11361-11373
This work reports on the properties and structure of N-methyl-2-pyrrolidone in binary and ternary liquid mixtures with water and/or methanol. A comprehensive set of thermophysical properties have been measured at 298.15 K and 0.1 MPa over the whole composition range. On the basis of the derived excess and mixing properties, the fluid structure was analyzed by looking into the forces and geometry factors that effectively control the mixture behavior. Application of the inverted Kirkwood-Buff theory provides a reasonable link between the macroscopic properties and the microscopic features. A density functional theory computation was carried out to analyze the structure and energy features of the hydrogen bonded complexes formed between the components. Use of semiempirical models in the framework of molecular-based equations of state according to the PC-SAFT approach led to unsatisfactory predicted thermophysical properties. The conclusions arrived at give away the existence of strong heteroassociations and hydrogen bonding self-associations that determine the complex nature of the fluid structure. 相似文献