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91.
The surface free energy of a monolithic silica xerogel treated at 1000°C has been measured by inverse gas chromatography in the temperature range 25–150°C using n-alkanes. Values of the dispersive component, S
D, vary from 49.07 mJ·m–2 at 25°C to 17.20 mJ·m–2 at 150°C. The S
D value obtained at 25°C is lower than that found for amorphous and crystalline silicas but higher than that found for glass fibres meaning that the heat treatment at 1000°C changes drastically the structure of the silica xerogel showing a surface similar to a glass. However, the higher value of S
D in comparison to glass fibres can be attributed to the mesoporous structure present in the silica xerogel. In the temperature range of 60–90°C there exists an abrupt change of the S
D values as well as in the dispersive component of the surface enthalpy, h
S
D. Such abrupt change can be attributed to an entropic contribution of the surface free energy. 相似文献
92.
C. Y. Zhu R. M. Izatt J. S. Bradshaw N. K. Dalley 《Journal of inclusion phenomena and macrocyclic chemistry》1992,13(1):17-27
Equilibrium constant (K), enthalpy change (H), and entropy change (S) values have been determined calorimetrically at 25°C in 90%MeOH 10%H2O (v/v) for the interactions of pyridino-18-crown-6 (P18C6) and diketopyridino-18-crown-6 (K2P18C6) with perchlorate salts of ammonium, benzylammonium,-phenylethylammonium,-phenylethylammonium, and-(1-naphthyl)ethyl-ammonium cations. The crystal structure of the complex of P18C6 with benzylammonium perchlorate was determined by X-ray crystallography. The1H 1D and 2D NMR spectra of some of these complexes were used to elucidate their structural features in solution. The logK values for the interaction of the ammonium cations with P18C6 are larger than those with K2P18C6, probably due to the higher degree of structural flexibility of P18C6. Ligand K2P18C6 displays appreciable - interaction with the-(1-naphthyl)ethylammonium cation, but not with the-phenylethylammonium cation.- interaction between ligand and cationSupplementary Data relating to this article are deposited with the British Library as Supplementary Publication No SUP 00000 (22 pages) 相似文献
93.
E. T. Denisov 《Russian Chemical Bulletin》2005,54(4):914-923
Interatomic distances in the reaction centers of the addition reactions of (i) H· to the C=C, C=O, N≡C, and C≡C bonds, (ii) ·CH3 radical to the C=C, C=O, and C≡C bonds, and (iii) alkyl, aminyl, and alkoxyl radicals to olefin C=C bonds were determined
using a new semiempirical method for calculating transition-state geometries of radical reactions. For all reactions of the
type X· + Y=Z → X— Y—Z· the r
#
X...Y distance in the transition state is a linear function of the enthalpy of reaction. Parameters of this dependence were determined
for seventeen classes of radical addition reactions. The bond elongation, Δr
#
X...Y, in the transition state decreases as the triplet repulsion, electronegativity difference between the atoms X and Y in the
reaction center, and the force constant of the attacked multiple bond increase.
__________
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 894–902, April, 2005. 相似文献
94.
Z. H. Zhang Z. J. Ku H. R. Li Y. Liu S. S. Qu 《Journal of Thermal Analysis and Calorimetry》2005,79(1):169-173
The solid-state ternary complex of terbium chloride with L-tyrosine and glycine, [Tb(Tyr)(Gly)3Cl3·3H2O], was synthesized and characterized. Using a solution-reaction isoperibol calorimeter, the enthalpy of reaction for the following reaction, TbCl3·6H2O(s)+Tyr(s)+3Gly(s)=Tb(Tyr)(Gly)3Cl3·3H2O(s)+3H2O(l), was determined to be (5.1±0.6) kJ mol-1. The standard enthalpy of formation of Tb(Tyr)(Gly)3Cl3-3H2O at T=298.15 K has been derived as -(4267.3±2.3) kJ mol-1. The thermal decomposition kinetics of the complex was studied by non-isothermal thermogravimetry in the temperature range of 325-675 K. Two main mass loss stages existed in the process of the decomposition of the complex, the kinetic parameters for the second stage were analyzed by means of differential and integral methods, respectively. Comparing the results of differential and integral methods, mechanism functions of the thermal decomposition reaction for its second stage were proposed. The kinetic equation can be expressed as: d/dt=Aexp(-E/RT)(1-)2. The average values of the apparent activation energy E and pre-exponential factor A were 213.18 kJ mol-1 and 2.51·1020 s-1, respectively. 相似文献
95.
Yu H. G. Yu Dong J. X. Qin C. Q. Liu Y. Qu S. S. 《Journal of Thermal Analysis and Calorimetry》2004,75(3):807-813
The energy of combustion of crystalline 3,4,5-trimethoxybenzoic acid in oxygen at T=298.15 K was determined to be -4795.9±1.3 kJ mol-1 using combustion calorimetry. The derived standard molar enthalpies of formation of 3,4,5-trimethoxybenzoic acid in crystalline
and gaseous states at T=298.15 K, ΔfHm
Θ (cr) and ΔfHm
Θ (g), were -852.9±1.9 and -721.7±2.0 kJ mol-1, respectively. The reliability of the results obtained was commented upon and compared with literature values.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
96.
I. Zięborak-Tomaszkiewicz 《Journal of Thermal Analysis and Calorimetry》2006,83(3):611-615
The energies of combustion
in fluorine of gallium nitride and indium nitride in wurzite crystalline structure
have been measured in a two-compartment calorimetric bomb, and new standard
molar enthalpies of formation have been calculated: ΔfHm0(GaN(cr)
298.15 K)= –(163.7±4.2) kJ mol–1
and ΔfHm0(InN(cr) 298.15 K)= –(146.5±4.6) kJ mol–1
. Comparison with the recommended values of the ΔfHm0 nitrides
from the literature is also presented. 相似文献
97.
M. Fujiwara T. Okano T. -H. Nakashima A. A. Nakamura G. Sugihara 《Colloid and polymer science》1997,275(5):474-479
For a sodium salt of α-sulfonatomyristic acid methyl ester (14SFNa), one of the α-SFMe series surfactants, critical micellization
concentration (CMC), solubility and degree of counterion binding (β) were determined by means of electrocon-ductivity measurements
at different temperatures (at every 5 °C) ranging from 15 to 50 °C. The phase diagram of 14SFNa in pure water was constructed
from the CMC- and solubility-temperature data, in which the Krafft temperature (critical solution temperature) was found around
0 °C. The changes in the Gibbs energy, ΔG
0
m, enthalpy, ΔH
0
m, and entropy, ΔS
0
m, upon micelle formation as a function of temperature were evaluated taking βvalues into calculation.
Received: 28 August 1996 Accepted: 5 November 1996 相似文献
98.
A pure calcium borate Ca2[B2O4(OH)2]·0.5H2O has been synthesized under hydrothermal condition and characterized by XRD, FT-IR and TG as well as by chemical analysis. The molar enthalpy of solution of Ca2[B2O4(OH)2]·0.5H2O in HC1·54.582H2O was determined. From a combination of this result with measured enthalpies of solution of H3BO3 in HC1·54.561H2O and of CaO in (HCl + H3BO3) solution, together with the standard molar enthalpies of formation of CaO(s), H3BO3(s) and H2O(l), the standard molar enthalpy of formation of −(3172.5 ± 2.5) kJ mol−1 of Ca2[B2O4(OH)2]·0.5H2O was obtained. 相似文献
99.
Enthalpies of solution of sodium benzoate, potassium benzoate, and potassium halo-substituted benzoates are reported at 298.15°K
in water and in nine water-tert-butyl alchol mixtures. Transfer enthalpies from water to the mixed solvent go through a maximum for about 0.055 mole fraction
of alcohol. Additivity of ionic contributions in the enthalpies of transfer is verified. Substituent effects on the transfer
enthalpies of benzoates are discussed in terms of size of the solutes and cohesion of the solvent mixtures.
For Part V, see ref. 1. 相似文献
100.
The hydrogen peroxide-oxidation of o-phenylenediamine (OPD) catalyzed by horseradish peroxidase (HRP) at 37 °C in 50 mM phosphate buffer (pH 7.0) was studied by calorimetry. The apparent molar reaction enthalpy with respect to OPD and hydrogen peroxide were −447 ± 8 kJ mol−1 and −298 ± 9 kJ mol−1, respectively. Oxidation of OPD by H2O2 catalyzed by HRP (1.25 nM) at pH 7.0 and 37 °C follows a ping-pong mechanism. The maximum rate Vmax (0.91 ± 0.05 μM s−1), Michaelis constant for OPD Km,S (51 ± 3 μM), Michaelis constant for hydrogen peroxide Km,H2O2 (136 ± 8 μM), the catalytic constant kcat (364 ± 18 s−1) and the second-order rate constants k+1 = (2.7 ± 0.3) × 106 M−1 s−1 and k+5 = (7.1 ± 0.8) × 106 M−1 s−1 were obtained by the initial rate method. 相似文献