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71.
Bernardes CE Minas da Piedade ME Amaral LM Ferreira AI Ribeiro da Silva MA Diogo HP Costa Cabral BJ 《The journal of physical chemistry. A》2007,111(9):1713-1720
The energetics of the C-F, C-Cl, C-Br, and C-I bonds in 2-haloethanols was investigated by using a combination of experimental and theoretical methods. The standard molar enthalpies of formation of 2-chloro-, 2-bromo-, and 2-iodoethanol, at 298.15 K, were determined as Delta(f)H(degree)m(CH2CH2OH, l) = -315.5 +/- 0.7 kJ.mol-1, Delta(f)H(degree)mBrCH2CH2OH, l) = -275.8 +/- 0.6 kJ.mol-1, Delta(f)H(degree)m(ICH2CH2OH, l) = -207.3 +/- 0.7 kJ.mol-1, by rotating-bomb combustion calorimetry. The corresponding standard molar enthalpies of vaporization, Delta(vap)H(degree)m(ClCH2CH2OH) = 48.32 +/- 0.37 kJ.mol-1, Delta(vap)H(degree)m(BrCH2CH2OH) = 54.08 +/- 0.40 kJ.mol-1, and Delta(vap)H(degree)m(ICH2CH2OH) = 57.03 +/- 0.20 kJ.mol-1 were also obtained by Calvet-drop microcalorimetry. The condensed phase and vaporization enthalpy data lead to Delta(f)H(degree)m(ClCH2CH2OH, g) = -267.2 +/- 0.8 kJ.mol-1, Delta(f)H(degree)m(BrCH2CH2OH, g) = -221.7 +/- 0.7 kJ.mol-1, and Delta(f)H(degree)m(ICH2CH2OH, g) = -150.3 +/- 0.7 kJ.mol-1. These values, together with the enthalpy of selected isodesmic and isogyric gas-phase reactions predicted by density functional theory (B3LYP/cc-pVTZ) and CBS-QB3 calculations were used to derive the enthalpies of formation of gaseous 2-fluoroethanol, Delta(f)H(degree)m(FCH2CH2OH, g) = -423.6 +/- 5.0 kJ.mol-1, and of the 2-hydroxyethyl radical, Delta(f)H(degree)m(CH2CH2OH, g) = -28.7 +/- 8.0 kJ.mol-1. The obtained thermochemical data led to the following carbon-halogen bond dissociation enthalpies: DHo(X-CH2CH2OH) = 474.4 +/- 9.4 kJ.mol-1 (X = F), 359.9 +/- 8.0 kJ.mol-1 (X = Cl), 305.0 +/- 8.0 kJ.mol-1 (X = Br), 228.7 +/- 8.1 kJ.mol-1 (X = I). These values were compared with the corresponding C-X bond dissociation enthalpies in XCH2COOH, XCH3, XC2H5, XCH=CH2, and XC6H5. In view of this comparison the computational methods mentioned above were also used to obtain Delta(f)H(degree)m-594.0 +/- 5.0 kJ.mol-1 from which DHo(F-CH2COOH) = 435.4 +/- 5.4 kJ.mol-1. The order DHo(C-F) > DHo(C-Cl) > DHo(C-Br) > DHo(C-I) is observed for the haloalcohols and all other RX compounds. It is finally concluded that the major qualitative trends exhibited by the C-X bond dissociation enthalpies for the series of compounds studied in this work can be predicted by Pauling's electrostatic-covalent model. 相似文献
72.
Historical nomenclature has not always been unequivocally associated with the botanical origin of natural resins. The availability
of natural resins has changed throughout the centuries and so have their trade names. Furthermore, adulterations and lack
of knowledge have led to variations in the composition of the products traded under the same name. This investigation aims
at a new understanding of the interrelation between the historical and modern terms for natural resins. Different Pinaceae
and Pistacia resins, mastic, sandarac, copaiba balm and burgundy pitch from Vigani’s Cabinet, a 300-year-old pharmaceutical collection
owned by Queens’ College, Cambridge (UK) were investigated. Related reference materials from modern collections were analysed
together with natural resins derived from reliable botanical sources. The analytical method was gas chromatography/mass spectrometry
(GC-MS) with and without derivatisation with trimethylsulfonium hydroxide. This technique provided detailed molecular compositions
of the studied materials, which in turn led to particular data profiles of the materials. Marker molecules of Copaifera, Pinaceae, Cupressaceae and Pistacia resins were identified. By comparing the GC-MS data profiles to the reference samples, a clearer picture of the connection
between nomenclature and botanical origin was obtained. With the aid of the marker molecules and data profiles, it was then
possible to clarify the nomenclature of the aged resins sampled from Vigani’s Cabinet. 相似文献
73.
Sumida K Brown CM Herm ZR Chavan S Bordiga S Long JR 《Chemical communications (Cambridge, England)》2011,47(4):1157-1159
The hydrogen storage properties of Mg(2)(dobdc) (dobdc(4-) = 2,5-dioxido-1,4-benzenedicarboxylate), a metal-organic framework possessing hexagonal one-dimensional channels decorated with unsaturated Mg(2+) coordination sites, have been examined through low- and high-pressure adsorption experiments, infrared spectroscopy, and neutron scattering studies. 相似文献
74.
Alves P Pinto S Kaiser JP Bruinink A de Sousa HC Gil MH 《Colloids and surfaces. B, Biointerfaces》2011,82(2):371-377
The material performance, in a biological environment, is mainly mediated by its surface properties and by the combination of chemical, physical, biological, and mechanical properties required, for a specific application.In this study, the surface of a thermoplastic polyurethane (TPU) material (Elastollan®1180A50) was activated either by plasma or by ultra-violet (UV) irradiation. After surface activation, methacrylic acid (MAA) was linked to the surface of TPU in order to improve its reactivity and to reduce cell adhesion. Grafted surfaces were evaluated by X-ray photoelectron spectroscopy (XPS), by atomic force microscopy (AFM) and by contact angle measurements. Blood compatibility studies and cell adhesion tests with human bone marrow cells (HBMC) were also performed.If was found that UV grafting method led to better results than the plasma activation method, since cell adhesion was reduced when methacrylic acid was grafted to the TPU surface by UV. 相似文献
75.
Several experimental techniques are currently used for the determination of the glass transition temperature, Tg. Thermally stimulated depolarization currents (TSDC) is a thermal analysis technique whose experimental results display a very clean glass transition signature and that, nevertheless, is seldom used as a technique for Tg determination. In the present work we explain how to get the glass transition temperature from TSDC data, and we compare the values obtained for a vast number of glass forming systems (with Tgs in a wide range between ?145 and +180 °C and fragilities between m = 15 and m = 100), with the values obtained by differential scanning calorimetry (DSC) and dielectric relaxation spectroscopy (DRS). We conclude that the Tg determination by TSDC is direct, accurate and reproducible and that the obtained values correlate very well with those obtained by DSC and DRS. This general survey thus suggests TSDC as a valuable alternative technique for determining Tg. 相似文献
76.
77.
78.
Iodide salts of several N-retinylidenedialkylamines were prepared and their UV-VIS spectra recorded. Their lambda max values increased as the number of hydrogen atoms on the carbons alpha to nitrogen increased. In separate experiments, iodide salts of N-retinylidene-n-butylammonium (1) and N-retinylidene-n-butylmethylammonium (2) were prepared, and their excitation energies (delta E) were measured in selected solvents of varying dielectric constant (epsilon). Data from each compound gave a straight line which converged at epsilon = 0. On the other hand, when delta E values of the iodide and bromide of 2 were plotted vs solvent epsilon, parallel rather than convergent lines were obtained. When lambda max values of 1 and 2 were measured in a greater number of solvents, the solvents fell into four main groups. The first group, regular solvents, are rigid, have fixed dipoles, neither donate nor accept H-bonds, and the delta E of 1 and 2 decreases linearly as solvent epsilon increases. This line for 2 is taken as a standard against which other solvents are judged. A second class of solvents that are good H-bond donors like CHCl3, whose dipole moment coincides with the C-H bond axis, is located in an area below the standard line. A third group, nucleophilic solvents like tetrahydrofuran, whose dipole moment is coincident with a strongly nucleophilic oxygen atom are good H-bond acceptors and are found above the standard line. Solvents with unpredictable spectroscopic behavior are classed as anomalous. 相似文献
79.
S. Thomas E. Mohler F. Keilmann L. Genzel 《Applied Physics A: Materials Science & Processing》1984,33(4):247-250
We report changes in the excitonic absorption edge of CuCl caused by intense CO2 laser radiation at 10.6 m, a wavelength which lies in the infrared (ir) transparency region of CuCl. With an ir intensity of 0.4 GW/cm2 we observe a 100% absorption increase for the Kr+ laser probe wavelength of 406.7nm. The effect scales linearly with ir intensity but does not depend on relative polarization. We explain the effect by laser field induced electroabsorption of the exciton. The magnitude of the effect is closely related to electroabsorption induced by static external fields and by internal electric fields from optical phonons. 相似文献
80.
P E Blatz R H Johnson J H Mohler S K al-Dilaimi S Dewhurst J O Erickson 《Photochemistry and photobiology》1971,13(3):237-245
Abstract— –Preliminary examination of the effect of solution environment on the electronic absorption spectrum of N-retinylidene-n-butylamine(I) is reported. It is established that small amounts of CO2 dissolved in certain solvents cause the formation of the conjugate acid of I. This reaction is shown to be dependent on temperature and the concentration of CO2. The pKb of I in aqueous buffer was measured spectrophotometrically and found to be 8.71. Salts of I were prepared in a number of ways and their spectra were determined in selected solvents. The Λmax varies with method of preparation, and only one method gives reproducible results. The Λmnx is a function of the solvent in which the spectrum is determined. It was also found that the absorption maximum in wavenumbers is proportional to the negative logarithm of acid concentration. 相似文献