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991.
The temperature dependence of the molar heat capacities of the tellurites
PbTeO3, Pb2Te3O8
and Ge(TeO3)2 are determined.
By statistical manipulation of the values obtained, the parameters in the
equations for the corresponding compounds showing this dependence are determined
using the least-squares method. These equations and the standard molar entropies
are used to determine the thermodynamic functions Δ0
T
S
m
0
, ΔT
T
H
m
0 and (Φm
0+Δ0
T
H
m
0/T) for T'=298.15
K. 相似文献
992.
Yung P. Koh Gregory B. McKenna Sindee L. Simon 《Journal of polymer science. Part A, Polymer chemistry》2006,44(24):3518-3527
The absolute heat capacity and glass transition temperature (Tg) of unsupported ultrathin films were measured with differential scanning calorimetry with the step-scan method in an effort to further examine the thermodynamic behavior of glass-forming materials on the nanoscale. Films were stacked in layers with multiple preparation methods. The absolute heat capacity in both the glass and liquid states decreased with decreasing film thickness, and Tg also decreased with decreasing film thickness. The magnitude of the Tg depression was closer to that observed for films supported on rigid substrates than that observed for freely standing films. The stacked thin films regained bulk behavior after the application of pressure at a high temperature. The effects of various preparation methods were examined, including the use of polyisobutylene as an interleaving layer between the polystyrene films. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3518–3527, 2006 相似文献
993.
The sorption mechanism of Al3+ on chelating resins by means of mathematical analysis of sorption isotherms using nonlinear mean square software was studied. This method should yield more detailed information than classical thermodynamics and should be more flexible than the statistical-mechanical method, so that it would make it possible to obtain fairly easily relations directly applicable in practice. This model defined the specific potential ΦAlR for the ion in a resin (which depends on properties of resin and ion). On the basis of this model, N and PO isotherms were derived. To study the sorption mechanism, the Freundlich, Langmuir, N and PO equations (models) of isotherms were used. It was estimated that the functional groups (8-hydroxyquinoline and salicylate) in the studied chelating resins influence ΦAlR and thus their mechanism and sorption capacity. 相似文献
994.
When the sodium ion (Na+) concentration is increased above 0.5 mol-dm−3 (M), the concentrations of dissolved silica in aqueous sodium chloride (NaCl) and sodium nitrate (NaNO3) solutions decrease because of the salting out effect. On the other hand, the concentration of the dissolved silica in aqueous sodium sulfate (Na2SO4) solutions increases monotonously as the concentration of Na+ is increased above 0.5 M. The purpose of this study is to determine the reasons why the salting-out effect is not observed in Na2SO4 solutions. FAB-MS (Fast Atom Bombardment Mass Spectrometry) was used to sample directly the silica species dissolved in aqueous Na2SO4, NaCl, and NaNO3 solutions. In the FAB-MS spectra of these solutions, the peak intensity ratios of the linear tetramer to the cyclic tetramer largely increased for Na+ concentrations between (0.1 and 1) M. This shows that some characteristics of the Na2SO4 solutions are similar to those of the NaCl and NaNO3 solutions. In Na2SO4 solutions, however, when the concentration of Na+ is higher than 1 M, the peak intensity of the dimer is much higher than those of the other silicate complexes. In Na2SO4 solutions, the SO42− ion undergoes partial hydrolysis to form HSO−4 and OH− is produced. In particular, in the range where the concentration of SO42− is high, the pH of the solution increases slightly. This higher pH yields more dimers from the hydrolysis of silicate complexes. This increase in dimer production agrees with the observation that silica dissolves in sodium hydroxide (NaOH) solutions mainly as a dimer when the concentration of NaOH is less than 0.1 M. In Na2SO4 solutions at high concentrations, a salting-out effect is not observed for silica. This is due to the increase in the concentration of OH−, which accelerates the hydrolysis of silica and results in dimer formation. 相似文献
995.
Equilibrium studies in aqueous solution are reported for dimethyltin(IV) complexes of the zwitterionic buffers “Good’s buffer”, such as Mes and Mops (L). Stoichiometry and stability constants for the complexes formed were determined at different temperature and ionic strength 0.1 M NaNO3. The results showed the best fit of the titration curves were obtained when complexes ML, MLH−1, MLH−2, and MLH−3 were expected beside the hydrolysis products of the dimethyltin(IV) cation. The thermodynamic parameters ΔH°, ΔS° and ΔG° calculated from the temperature dependence of the formation constant of the dimethyltin(IV)-Mes complex was investigated. The effect of dioxane as a solvent on the formation constants of dimethyltin(IV)-Mes complex was discussed. The concentration distribution of the various complex species was evaluated as a function of pH. The bonding sites of the dimethyltin(IV) complexes in solid state with Mes and Mops were characterized by means of elemental analyses and FTIR. The NMR (1H, 13C) spectra of the DMT-Mes complex exhibits the strongly distorted octahedron geometry around tin atom. Also, thermal analyses (TGA and DTA) were discussed. Thermodynamic parameters such as activation energy (Ea), pre-exponential factor (A), entropy of activation (ΔS∗) and free energy of activation (ΔG∗) have been calculated for each step, employing integral method Coats and Redfern. The reaction enthalpy (ΔH) is obtained from DTA data. 相似文献
996.
The temperature dependence of heat capacity of C70 fullerene was studied by calorimetry in the range between 6 and 390 K. Phase transitions were established and their thermodynamic
characteristics were determined. From the experimental data obtained, the thermodynamic functionsH
o
(T)-H
o(0),S
o(T),G
o(T)-H
o(0) for temperatures between 0 and 390 K were calculated. The results were used to calculate the standard values of Δf
S
o, Δf
G
o, and logK
f
o
for the formation of C70 from graphite.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 647–650, April, 1998. 相似文献
997.
Katsutoshi Tamura Sachio Murakami Masato Fukumori Yoshimasa Akagi Yoshikane Kawasaki 《Journal of solution chemistry》1994,23(9):989-996
Excess isobaric heat capacities C
p
E
, densities and speeds of sound u of HMPA+heptane and+benzene were measured at 25°C. C
p
E
of both mixtures were positive in the range of small x and negative in the other region. The mixture containing benzene showed higher C
p
E
than the heptane mixture. They both exhibited considerably smaller C
V
E
than C
p
E
. VE was positive for HMPA+heptane and negative for HMPA+benzene. The compressibilities K
s
E
and K
p
E
of both mixtures were negative. In both mixtures, non-random mixing is expected and [(CH3)2N]3PO molecules are inhomogeneously distributed. 相似文献
998.
Bei-Ping Liu Zhi-Cheng Tan Xiao-Zheng LanHua-Guang Yu Da-Shun ZhangLi-Xian Sun 《Thermochimica Acta》2003,401(2):233-238
Two solid-state coordination compounds of rare earth metals with glycin, [Gd4/3Y2/3(Gly)6(H2O)4](ClO4)6·5H2O and [ErY(Gly)6(H2O)4](ClO4)6·5H2O were synthesized. The low-temperature heat capacities of the two coordination compounds were measured with an adiabatic calorimeter over the temperature range from 78 to 376 K. [Gd4/3Y2/3(Gly)6(H2O)4](ClO4)6·5H2O melted at 342.90 K, while [ErY(Gly)6(H2O)4](ClO4)6·5H2O melted at 328.79 K. The molar enthalpy and entropy of fusion for the two coordination compounds were determined to be 18.48 kJ mol−1 and 53.9 J K−1 mol−1 for [Gd4/3Y2/3(Gly)6(H2O)4](ClO4)6·5H2O, 1.82 kJ mol−1 and 5.5 J K−1 mol−1 for [ErY(Gly)6(H2O)4](ClO4)6·5H2O, respectively. Thermal decompositions of the two coordination compounds were studied through the thermogravimetry (TG). Possible mechanisms of the decompositions are discussed. 相似文献
999.
V. A. Drebushchak Yu. A. Kovalevskaya I. E. Paukov E. V. Boldyreva 《Journal of Thermal Analysis and Calorimetry》2006,85(2):485-490
Heat capacity of α-glycylglycine was measured
using adiabatic calorimetry (6 to 304 K) and DSC (264 to 443 K), and then
thermodynamic functions were calculated. Heat capacity has no anomalies. The
molecular crystal melts at 493 K (enthalpy of melting is about 62 kJ mol–1).
The melting is accompanied by decomposition.
C
P(T) function for glycylglycine is very similar to
those of three glycine polymorphs. The ‘universal’ curve consists
of two parts: low-temperature Debye-like function (from 0 to about 120 K)
and a straight line (up to the melting point). At very low temperatures rigid
molecules oscillate as a whole, and the Debye temperature is proportional
to the molecular mass to the power of 3/2. 相似文献
1000.