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991.
Summary The kinetics of chromic acid oxidation of phenylphosphinic acid to phenylphosphonic acid has indicated the formation of an anhydride between HCrO
4
–
and phenylphosphinic acid in its active PhP(OH)2 and inactive PhPH(O)OH forms. The ambiguity about the reactive form of phenylphosphinic acid arises from the fact that protonation of the anhydride leads to the same transition state which disproportionates in the rate-determining step to phosphonium ion and chromium(IV). These, through different reactions in the fast step, yield phenylphosphonic acid and chromium(III) as the final products. That HCrO
4
–
is the reactive species of chromium(VI) is confirmed by the fact that k0 is independent of the inital [CrVI] where k0 is defined by the Equation k0=kobs[CrVI]/[HCrO
4
–
]; kobs is the pseudo first-order rate constant with respect to chromium(VI) ([Phenyl-phosphinic acid][CrVI]).The plot between k0 and [H+] passes through the origin indicating that the reaction does not occur in the absence of H+-ions. Furthermore, the plot between log k0 and –H0, the Hammett acidity function, is linear with a slope value of 1.02±0.02 confirming the protonation of the anhydride prior to its rate-limiting disproportionation.The equilibrium constant for the anhydride formation and the composite rate constant kK, K is the protonation constant of anhydride, are reported. The equilibrium constant is almost independent of temperature.Sen Gupta and Chakaladar(3) reported values of 8.5, 9.2, 11, 12 and 13, respectively, at 26°, 30.4°, 36°, 39.4° and 46° C. The uncertainty limits were not reported. Nevertheless it is apparent from the data that the values are not greatly influenced by temperature. The statistical mean is 11±2 dm3 mol–1, in fair agreement with our values. 相似文献
992.
Ovanesyan NS Makhaev VD Aldoshin SM Gredin P Boubekeur K Train C Gruselle M 《Dalton transactions (Cambridge, England : 2003)》2005,(18):3101-3107
A series of two-dimensional (2D) oxalate-based compounds, namely [N(n-C4H9)4][M(II)Cr(III)(ox)3] (M(II) = Mn, Fe; ox = C2O4(2-)) and [N(C2H5)(n-C3H7)(n-C4H9)(n-C5H11)][M(II)M(III)(ox)(3)] ((M(II), M(III)) =(Mn, Cr), (Fe, Cr), (Mn, Fe)) were synthesised starting from racemic tris(oxalato)metalate: rac-[M(III)(ox)3]3- (M(III) = Cr, Fe). For Cr(III), the synthesis has been undertaken starting from resolved (Delta)- or (Lambda)-[Cr(III)(ox)3]3-. The natural circular dichroism measurements assess the enantioselectivity of the synthesis. X-Ray powder diffraction analysis has revealed that, when racemic reagents are used to synthesise Mn(II) containing compounds, a R3c achiral space group is found. In contrast a P6(3) chiral space group is found when starting from (Delta)- or (Lambda)-[Cr(III)(ox)3]3-. Surprisingly, whatever the optical purity of the starting building block, all Fe(II) containing compounds crystallise in the P6(3) chiral space group. The magnetic properties of the synthesised compounds confirm that these compounds are ferromagnets for M(III)= Cr. For M(II)= Mn, Theta ranges between 9 and 11 K and T(c) equals 6 K. For M(II)= Fe, Theta ranges between 14 and 16 K and Tc between 11 and 12 K. [N(C2H5)(n-C3H7)(n-C4H9)(n-C5H11)][Mn(II)Fe(III)(ox)3] is an antiferromagnet with Theta = - 107 K and T(N) = 29 K. 相似文献
993.
Radhey?M.?NaikEmail author Raj?K.?Tewari Pradeep?K.?Singh Anjani?Tewari Surendra?Prasad 《Transition Metal Chemistry》2005,30(8):968-977
The kinetic and mechanistic studies of HgII catalyzed exchange of coordinated cyanide in hexacyanoferrate(II) by pyrazine (Pz) were monitored by following the appearance
of the yellow complex [Fe(CN)5Pz]3− at 440 nm corresponding to metal ligand charge transfer (MLCT) transitions at temp=25.0±0.1 °C, pH=2.5±0.02 and ionic strength,
I=0.1 m (KNO3). The effect of pH, ionic strength and the concentrations of [Fe(CN)6]4− and Pz on the rate of reaction were also studied and explained. To investigate the dependency of catalytic activity of HgII, the initial rates were determined at several concentrations of HgII, keeping the concentration of other reactants constant. The kinetic observations suggest that the substitution follows an
interchange dissociative (Id) mechanism and proceeds via formation of a solvent-bound intermediate. The repetitive spectral scan is also provided as evidence for the exchange of
cyanide ions by pyrazine in [Fe(CN)6]4−. Activation parameters have also been evaluated and provided support for the proposed mechanistic scheme. 相似文献
994.
The kinetics of the solvolysis of [Co(CN)5Cl]3– have been investigated in water +2-methoxyethanol and water + diethylene glycol mixtures. Although the addition of these linear hydrophilic cosolvent molecules to water produces curvature in the variation of log(rate constant) with the reciprocal of the dielectric constant, their effect on the enthalpy and entropy of activation is minimal, unlike the effect of hydrophobic cosolvents. The application of a Gibbs energy cycle to the solvolysis in water and in the mixtures using either solvent-sorting or TATB values for the Gibbs energy of transfer of the chloride ion between water and the mixture shows that the relative stability of the emergent solvated Co(III) ion in the transition state compared to that of Co(CN)5Cl3– in the initial state increases with increasing content of cosolvent in the mixture. By comparing the effects of other cosolvents on the solvolysis, this differential increase in the relative stabilities of the two species increases with the degree of hydrophobicity of the cosolvent.List of Symbols v2
partial molar volume of the cosolvent in water + cosolvent mixtures
-
V
2
o
molar volume of the pure cosolvent
- H
mix
E
excess enthalpy of mixing water and cosolvent
- S
mix
E
excess entropy of mixing water and cosolvent
- G
t
o
(i)n
the Gibbs energy of transfer of speciesi from water into the water + cosolvent mixture excluding electrostatic contributions
-
k
s
first order rate constant for the solvolysis in water + cosolvent mixtures
-
D
s
dielectric constant of the water + cosolvent mixture
- H
*
the enthalpy of activation for the solvolysis
- S
*
the entropy of activation for the solvolysis
- G
*
the Gibbs energy of activation for the solvolysis
- V
*
the volume of activation for the solvolysis
-
i
*
speciesi in the transition state for the solvolysis
-
H
o
Hammett Acidity Function
- TATB
method for estimating the Gibbs energy of transfer for single ions assuming those for Ph4As+ and BPh
4
–
are equal 相似文献
995.
Reactions of N,N;-disubstituted hydrazinecarbothioamides 8a-c and substituted thioureidoethylthioureas 9a-c with 2,3,5,6-tetrachloro-1,4-benzoquinone (chloranil, 10a) and 2,3,5,6-tetrabromo-1,4-benzoquinone (bromanil, 10b) to form N,N;-disubstituted [1,3,4]thiadiazole-2,5-diamines 11a-c, 6,7-dichloro-3-substituted amino-1H-benzo[1,3,4]- thiadiazine-5,8-diones 12a-c, 2,3,7,8-tetrahalothianthrene-1,4,6,9-tetraones 13a,b, 5,6,8- trihalo-7-oxo-3,7-dihydro-2H-quinoxaline-1-carbothioic acid substituted amides 14a-c, 15a-c and 7-substituted imino-[1,3,6]thiadiazepane-3-thiones 16a-c are reported. Rationales for the observed conversions are presented. 相似文献
996.
997.
Sreeruttun RK Ramasami P Wannere CS Paul A Schleyer PV Schaefer Iii HF 《The Journal of organic chemistry》2005,70(22):8676-8686
[reaction: see text] The adiabatic electron affinity (EA(ad)) of the CH(3)-C[triple bond]C(*) radical [experiment = 2.718 +/- 0.008 eV] and the gas-phase basicity of the CH(3)-C[triple bond]C:(-) anion [experiment = 373.4 +/- 2 kcal/mol] have been compared with those of their fluorine derivatives. The latter are studied using theoretical methods. It is found that there are large effects on the electron affinities and gas-phase basicities as the H atoms of the alpha-CH(3) group in the propynyl system are substituted by F atoms. The predicted electron affinities are 3.31 eV (FCH(2)-C[triple bond]C(*)), 3.86 eV (F(2)CH-C[triple bond]C(*)), and 4.24 eV (F(3)C-C[triple bond]C(*)), and the predicted gas-phase basicities of the fluorocarbanion derivatives are 366.4 kcal/mol (FCH(2)-C[triple bond]C:(-)), 356.6 kcal/mol (F(2)CH-C[triple bond]C:(-)), and 349.8 kcal/mol (F(3)C-C[triple bond]C:(-)). It is concluded that the electron affinities of fluoropropynyl radicals increase and the gas-phase basicities decrease as F atoms sequentially replace H atoms of the alpha-CH(3) in the propynyl system. The propargyl radicals, lower in energy than the isomeric propynyl radicals, are also examined and their electron affinities are predicted to be 0.98 eV ((*)CH(2)-C[triple bond]CH), 1.18 eV ((*)CFH-C[triple bond]CH), 1.32 eV ((*)CF(2)-C[triple bond] CH), 1.71 eV ((*)CH(2)-C[triple bond]CF), 2.05 eV ((*)CFH-C[triple bond]CF), and 2.23 eV ((*)CF(2)-C[triple bond]CF). 相似文献
998.
Neubert H Halket JM Fernandez Ocaña M Patel RK 《Journal of the American Society for Mass Spectrometry》2004,15(3):336-343
Large signals from alpha-cyano-4-hydroxycinnamic acid (CHCA) matrix complexes with sodium and potassium ions were found to interfere with sensitive matrix-assisted laser desorption/ionization (MALDI) analysis of a hydrochloric acid digest of gelatine preparations. The nature of some selected matrix clusters was investigated by conventional post-source decay and LIFT-TOF/TOF experiments. The matrix clusters fragmented readily by neutral evaporation to give smaller sized matrix cluster species without matrix disintegration. Their characterization distinguished them from peptide signals, in particular from those that had the same nominal mass and differed only in the fractional part of the mass as encountered for gelatine-derived peptides. Knowledge of the molecular composition of these cluster species allowed using them for internal calibration of the MALDI mass spectra. The hydrolytic peptides could be analyzed with increased sensitivity when using 2,5-dihydroxy benzoic acid (DHB) as the MALDI matrix. 相似文献
999.
5‐Amino‐3,4‐diphenylthieno[2,3‐c]pyridazine‐6‐carbonitrile 2a was reacted with propylene diamine to give tetrahydropyrimidinyl derivative 3 . The latter compound ( 3 ) underwent certain cyclocondensation reactions to produce pyrimidothienopyridazines 4–6 . Also, the reactions of 5‐amino‐3,4‐diphenylthieno[2,3‐c]pyridazine‐6‐carboxamide with heterocyclic aldehydes and/or cycloalkanones were carried out and their products were identified. Moreover, some novel pyridazinothienopyrimidobenzimidazoles 14–17 were synthesized. 相似文献
1000.
Room temperature ionic liquids are found to catalyze efficiently the three component-coupling reactions of aldehydes, amines and homophthalic anhydride under mild and convenient conditions to afford the corresponding cis-isoquinolonic acids in excellent yields with high cis-selectivity. 相似文献