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991.
Irina F. Catta Preta Solange K. Sakata G. Garcia J. P. Zimmermann F. Galembeck Claudia Giovedi 《Journal of Thermal Analysis and Calorimetry》2007,87(3):657-659
Polyacrylonitrile
(PAN) polymers are used as precursors for carbon fiber production. This process
requires an oxidative stabilization step, which can be studied by differential
scanning calorimetry (DSC). In this sense, thermal behavior of PAN based terpolymers
by different polymerization processes, compositions and itaconic acid concentrations
in the reaction media were investigated. The obtained results showed that
the addition of itaconic acid and methyl acrylate as comonomers resulted a
lower heat flow during the process comparing to the PAN homopolymer. It suggested
that these comonomers aid the oxidative stabilization stage for all studied
process. The redox system polymerization at 40°C resulted in a lower heat
flow. Itaconic acid decreases slightly initial and peak temperatures of the
terpolymer and heat flow until concentration of 3y. The cyclization temperature
decreases when MAis incorporated into the terpolymer compared to the MMA terpolymer
and increases when MAA is the acidic monomer. Among terpolymers the AN/MA/AA
polymer showed the best thermal behavior for carbon fiber producing. 相似文献
992.
The electronic structure and the spectroscopic properties of [Au2(CS3)2]?2, [Au2(pym‐2‐S)2] (pym = pyrimidethiolate), [Au2(dpm)2]+2 (dpm = bis(diphosphino)methane) were studied using density functional theory (DFT) at the B3LYP level. The absorption spectrum of these binuclear gold(I) complexes was calculated by single excitation time‐dependent (TD) method. All complexes showed a 1(5dσ* → 6pσ) transition associated with a metal–metal charge transfer, which is strongly interrelated with the gold–gold distance. Furthermore, we have calculated the frequency of the gold–gold vibration (νAu2) on the above complexes. The values obtained are theoretically in agreement with experimental range. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 相似文献
993.
In the present work, corrosion resistance of surface-coated galvanized steel was quantitatively determined by an analysis
of the alternating current (AC) impedance spectra measured on the salt-spray-tested specimen. To evaluate the corrosion resistance
of the surface-coated galvanized steel, AC impedance spectroscopy was performed on the salt-spray-tested specimen previously
exposed to salt-sprayed corrosive environment. From the analysis of the impedance spectra, the area fraction transient of
white rust θ
2(t) was theoretically derived from the equivalent circuit equation by using two fitting parameters. The values of the two fitting
parameters were determined by fitting the empirical transient equations to the area fraction of the resin coating layer and
to the total resistance obtained from the impedance spectra measured, respectively. From the analyses of θ
2(t) for four kinds of surface-coated galvanized steels with various resin coating layers, it is indicated that as the values
of the two fitting parameters decrease in the order of CP, GI, OD and OM (commercial trade names) specimens, the corrosion
resistance increases in that order as well. Furthermore, from the quantitative comparison of the two fitting parameters with
the polarization resistance of the upper resin coating layer R
p determined from the potentiodynamic polarization curve, it is suggested that the two fitting parameters decrease in value
as well with increasing R
p. 相似文献
994.
Rollie J. Myers 《Journal of solution chemistry》2007,36(3):395-403
We have measured the second acid dissociation constant, K
2a
, at several ionic strengths for hydrogen telluride (H2Te) using the Charge Transfer to Solvent (CTTS) uv spectra of its anions HTe− and Te2−. Since it is produced in our solutions, we have also determined the spectra of Te2
2− both in the uv and in the visible regions. At 25 ∘C, K
2a
= (1.28 ± 0.02) × 10−12 by extrapolation to zero ionic strength. Its value at an ionic strength equal to 0.5 mol.dm-3 was estimated to be (8.7 ± 0.2) × 10−12. The solution thermodynamics of these species are also discussed and comparisons are made to related acids. 相似文献
995.
FLUORESCENCE QUANTUM YIELDS OF 124-kDa PHYTOCHROME FROM OAT UPON EXCITATION WITHIN DIFFERENT ABSORPTION BANDS 总被引:1,自引:0,他引:1
Claudio G. Colombano Silvia E. Braslavsky Alfred R. Holzwarth Kurt Schaffner 《Photochemistry and photobiology》1990,52(1):19-22
Abstract— A fluorescence quantum yield (emission at650–850 nm) of π= (2.3 ± 0.3)10−3 was measured for the red-absorbing form (Pr) of 124-kDa phytochrome from etiolated oat seedlings ( Avena sativa ) upon excitation in the Soret band at Λexc = 380 nm. The small difference between this value and the previously determined quantum yield with Λexc = 640 nm, π= (3.5 ± 0.4)10−3 is attributed to a blue-absorbing emitter responsible for the "anomalous" or "blue" emission of the chromoprotein in the region from ca. 400 to 550 nm. The absorption of Pr at 380 nm is consequently somewhat lower than that measured directly from the spectrum. Processes from upper excited states of the Pr phytochromobilin-derived chromophore other than rapid relaxation to the emitting state are not important. A quantum yield of Φ ' 1.2 times 10−3 is estimated for the blue fluorescence. The proportion of the blue emitters relative to Pr appears to be relatively high. 相似文献
996.
Naomi Masuda Yatsuhisa Nagano T. Kimura 《Journal of Thermal Analysis and Calorimetry》2005,81(3):533-535
Summary The standard molar enthalpy of formation of methyl methylthiomethyl sulfoxide, CH3(CH3SCH2)SO, at T=298.15 K in the liquid state was determined to be -199.4±1.5 kJ mol-1 by means of oxygen rotating-bomb combustion calorimetry. 相似文献
997.
Pettinari C Pettinari R Fianchini M Marchetti F Skelton BW White AH 《Inorganic chemistry》2005,44(22):7933-7942
New [CpM(Q)Cl] complexes (M = Rh or Ir, Cp = pentamethylcyclopentadienyl, HQ = 1-phenyl-3-methyl-4R(C=O)-pyrazol-5-one in general, in detail HQ(Me), R = CH(3); HQ(Et), R = CH(2)CH(3); HQ(Piv), R = CH(2)-C(CH(3))(3); HQ(Bn), R = CH(2)-(C(6)H(5)); HQ(S), R = CH-(C(6)H(5))(2)) have been synthesized from the reaction of [CpMCl(2)](2) with the sodium salt, NaQ, of the appropriate HQ proligand. Crystal structure determinations for a representative selection of these [CpM(Q)Cl] compounds show a pseudo-octahedral metal environment with the Q ligand bonded in the O,O'-chelating form. In each case, two enantiomers (S(M)) and (R(M)) arise, differing only in the metal chirality. The reaction of [CpRh(Q(Bn))Cl] with MgCH(3)Br produces only halide exchange with the formation of [CpRh(Q(Bn))Br]. The [CpRh(Q)Cl] complexes react with PPh(3) in dichloromethane yielding the adducts CpRh(Q)Cl/PPh(3) (1:1) which exist in solution in two different isomeric forms. The interaction of [CpRh(Q(Me))Cl] with AgNO(3) in MeCN allows generation of [CpRh(Q(Me))(MeCN)]NO(3).3H(2)O, whereas the reaction of [CpRh(Q(Me))Cl] with AgClO(4) in the same solvent yields both [CpRh(Q(Me))(H(2)O)]ClO(4) and [CpRh(Cl)(H(2)O)(2)]ClO(4); the H(2)O molecules derive from the not-rigorously anhydrous solvents or silver salts. 相似文献
998.
The enthalpy change of formation of the reaction of hydrous dysprosium chloride with ammonium pyrrolidinedithiocarbamate (APDC) and 1,10-phenanthroline (o-phen?H2O) in absolute ethanol at 298.15 K has been determined as (-16.12 ± 0.05) kJ?mol-1 by a microcalormeter. Thermodynamic parameters (the activation enthalpy, the activation entropy and the activation free energy), rate constant and kinetics parameters (the apparent activation energy, the pre-exponential constant and the reaction order) of the reaction have also been calculated. The enthalpy change of the solid-phase reaction at 298.15 K has been obtained as (53.59 ± 0.29) kJ?molt-1 by a thermochemistry cycle. The values of the enthalpy change of formation both in liquid-phase and solid-phase reaction indicated that the complex could only be synthesized in liquid-phase reaction. 相似文献
999.
Zong ChunYan Gao QingYu Wang YuMei Feng JiaMin Mao ShanCheng Zhang Lu 《中国科学B辑(英文版)》2007,50(2):205-211
The ferroin-catalyzed Belousov-Zhabotinsky(BZ) reaction,the oxidation of malonic acid by acidic bromate,is the most commonly investigated chemical system for understanding spatial pattern forma-tion. Various oscillatory behaviors were found from such as mixed-mode and simple period-doubling oscillations and chaos on both Pt electrode and Br-ISE at high flow rates to mixed-mode oscillations on Br-ISE only at low flow rates. The complex dynamic behaviors were qualitatively reproduced with a two-cycle coupling model proposed initially by Gy?rgyi and Field. This investigation offered a proper medium for studying pattern formation under complex temporal dynamics. In addition,it also shows that complex oscillations and chaos in the BZ reaction can be extended to other bromate-driven nonlinear reaction systems with different metal catalysts. 相似文献
1000.
Virginie Gueu Hongpeng You Tomokatsu Hayakawa Masayuki Nogami 《Journal of Sol-Gel Science and Technology》2007,41(3):231-236
Fluorescence and spectral hole burning properties of Eu3+ ions were studied in nanocrystals-precipitated SnO2-SiO2 glasses. The glasses were prepared to contain various amount of Eu2O3 using the sol-gel method, in which SnO2 nanocrystals were precipitated by heating in air. In the glasses containing Eu2O3 less than 1%, the Eu3+ ions were preferentially doped in the SnO2 nanocrystals and their fluorescence intensities were enhanced by the energy transfer due to the recombination of electrons
and holes excited in SnO2 crystals. The SnO2 nanocrystals-precipitated glasses exhibited the persistent spectral holes with the depth of ∼25% of the total fluorescence
intensities of the Eu3+ ions. With the increasing Eu2O3 concentration, the amount of SnO2 nanocrystals decreased and the Sn4+ ions formed the random glass structure together with the silica network. This structure change induced the fluorescence intensities
and the hole depth to decrease. 相似文献