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121.
We investigate the weak leptonic decays of light and heavy pseudoscalar mesons in a relativistic quark model of independent
quarks. We perform a static calculation of the decay constantf
M purely on grounds of simplicity. In order to minimize the possible uncertainty in the static calculation, we estimate the
ratios of the decay constants which are found to be in good agreement, in the heavy flavor sector, with the predictions of
other models available in the literature and existing experimental data. However, there is a noticeable discrepancy in the
current prediction for pion decay constant which demonstrates the inherent limitations of the static approximation in the
study of non-strange light mesons. 相似文献
122.
Mass difference oft-flavored hadrons is calculated using bag model modified for considering heavy quarks inside the bag. Both electric and magnetic
contributions to mass differences are evaluated without the assumption of degenerate intermediate state. Mass differences
between up and down quarks inside the bag is taken to be a constant in the absence of a dynamical calculations for the same. 相似文献
123.
Imidazole(Im), benzimidazole(BzIm), morpholine (Morph) and their derivatives react with Co(CNS)2 and dimethylglyoxime(DH2) in ethanolic medium in presence of air to form a number of new cobalt(III) complexes of the type trans-[Co(DH)2(L)(SCN)], which are characterised on the basis of electronic and IR spectra, NMR (1H and 13C) and mass spectra as well as thermogravimetric (TG-DTA) and conductance measurements. The thiocyanate groups are S-bonded. The NMR observations suggest that in solution these compounds exist as mixtures of the neutral species [Co(DH)2(L)(SCN)] and the salt [Co(DH)2(SCN)2]? [Co(DH)2(L)2]+. The mass spectra does not show the molecular ion peak of the complex. The TG-DTA measurements show that the thermolysis of these complexes proceeds through polymeric intermediates giving CO3O4 as the end product. 相似文献
124.
The kinetics of formation, acid-catalysed aquation, ligand isomerisation (CoIIIOSO2+→CoIIISO3+), intramolecular electron-transfer,
and base-catalysed hydrolysis and isomerisation of O-bonded sulphito complexes, cis-[Co(en)2(B)(OSO2–O)]+[B=benzimidazole
(bzimH), N-methylimidazole (N-meim)] and the anation of cis-[Co(en)2(B)OH)]2+ [B=bzimH, N-meim and imH (imidazole)] by oxSO2−3
are reported. Steric acceleration is observed in the formation and acid-catalysed aquation of the O-sulphito complexes. The
ligand isomerisation leads to loss of the monodentate amine with the formation of trans-[Co(en)2(SO3–S)2]− (in an excess of
sulphite). Steric acceleration is more pronounced in the isomerisation and base hydrolysis than in the redox process. The
results indicate cis labilisation of the coordinated O-sulphite.
The [(tetraethylenepentamine)Co(OSO2–O)]+ cation undergoes base hydrolysis 103 times faster than the corresponding (en)2(B)
complexes; base-catalysed ligand isomerisation for the former is not observed unlike in the latter. The anation of cis-[Co(en)2(B)OH]2+
(B=imH, bzimH, N-meim) by SO2−3 in a mild alkali pH range (pH=7.9–9.6) and in an excess of SO2−3, yields exclusively trans-[Co(en)2(SO3–S)2]−
with no evidence for the formation of the cis-[Co(en)2(B)(SO3–S)]+ or its O-sulphito analogue. The intramolecularly generated
amido conjugate base of the sulphite ion-pair, {cis-[Co(en)2(B)OH]2+,SO32−}.41cm{cis-[Co(en)(en-H) (B)- OH2]2+,SO32−}, is
believed to generate a five-coordinate intermediate (TBP) that captures the S-end of SO2−3 selectively from a site trans-to
the amine B so that the amine is labilised by the trans effect of the sulphite. The NH-deprotonated coordinated imidazolate
or benzimidazolate species, cis-[Co(en)2(bzm/im)OH]+, do not undergo anation by SO2−3.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
125.
Prashanta K. Mishra Vivekananda Chakravortty Kailash C. Dash 《Transition Metal Chemistry》1991,16(1):73-75
Summary Zr(acac)4 undergoes ligand exchanges with various tri- and tetradentate Schiff base ligands, forming compounds of the Zr(L)2 type (H2L=tetradentate H2Sal2en, H2Sal2pn, H2Sal2
o-phen and the tridentate H2SAP) and Zr(acac)2L (H2L=H2SAN. H2SAE). Upon reaction with a combination of tri- and tetradentate ligands, Zr(acac)4 yields Zr(L)(L) complexes (H2L=H2Sal2en or H2Sal2
o-phen; H2L=H2SAN, H2SAE, or H2SAP), which have been characterised by analytical data, m.ps, electrical conductivities, i.r. and n.m.r (1H and13C) spectra, they have a coordination number of 6, 7 or 8. 相似文献
126.
Summary The kinetics and mechanism of reversible complexation of NiII with (2-imidazoleazo)benzene (IAB), 2,2-biimidazole (Biim) and 2,2-bibenzimidazole (Bibzm) have been investigated at 15–35 °C, I = 0.30 mol dm–3. The stability constants, K
M, of the [NiL]2+ species vary in the sequence: [Ni(IAB)]2+ < [Ni(Bibzm)]2+ < [Ni(Biim)]2+. The values of the spontaneous dissociation rate constant (k
r) at 25 °C decrease in the sequence: [Ni(IAB)]+ > [Ni(Biim)]2+ > [Ni(Bibzm)]2+. The aquation of [Ni(IAB)]2+ is insensitive to acid catalysis, whilst [Ni(Biim)]2+ is relatively more susceptible towards acid-catalysed aquation than [Ni(Bibzm)]2+. The chelate ring in [NiL]2+ (L = IAB, Biim or Bibzm) is sterically strained. The formation of [Ni(IAB)]2+ and [Ni(Bibzm)]2+ may be chelation controlled while the normal I
d mechanism is supported by our data for [Ni(Biim)]2+. 相似文献
127.
Summary The aquation of pentaammine (substituted salicylato) cobalt(III) complexes [(NH3)5CoO2CC6H3(X)OH]2+,X = 5-SO3, 5-Br, 5-NO2, and 3-NO2 in the presence of ferric ion was studied spectrophotometrically in the 65°–80° range. Ferric ion catalyses the aquation of the substratesvia formation of a reactive binuclear species.Reprints of this article are not available. 相似文献
128.
The solubility and solubility product of silver permanganate in water have been determined at the temperatures ranging from 15 to 35°C over 5°C intervals in the presence of an added electrolyte, sodium perchlorate. The solubility of silver permanganate ranges from 0.966 x 10?5 mol 1?1 at 15°C to 1.420x10?5 moll?1 at 35°C and the corresponding solubility product 0.933 x 10?10 mol2 1?2 at 15°C to 2.017 x 10?10 mol2 1?2 at 35°C. The standard potentials of the Ag(s)/AgMnO4(s)/ MnO?4 electrode have been calculated at these temperatures. The mean activity coefficients of silver permanganate at various rounded molarities of sodium perchlorate solutions, and the standard thermodynamic quantities for the process AgMnO4(s)→Ag+ (aq)+MnO?4(aq) have been calculated at these temperatures. 相似文献
129.
The solubility and solubility product of silver iodate in formamide in sodium perchlorate solutions have been determined at 25, 30 and 35°C. The solubilities in pure formamide are found to be 2.169 × 10?4, 2.488 × 10?4, and 2.943 × 10?4 mole I?1, respectively, at these temperatures, and the corresponding solubility products are 4.609 × 10?8, 6.053 × 10?8, and 8.448 × 10?8 mole2 1?2. The standard potential of the Ag(s)/AgIO3(s)/IO3? electrode has been calculated and found to be 0.2562 V at 25°C. The mean activity coefficients of silver iodate at various rounded molarities of sodium perchlorate solutions, and the standard thermodynamic quantities for the process AgIO3(s)åAg+ (solvated) + IO3? (solvated) have been calculated at these three temperatures. 相似文献
130.
The MnIV complex of 1,8-bis(2-hydroxybenzamido)-3,6-diazaoctane (MnIVL) with phenolate-amido-amine coordination is reduced by l-ascorbic acid and oxalic acid obeying overall 1:1 stoichiometry. The reactions are biphasic and MnIIIL− is the reactive intermediate. The product of oxidation of ascorbic acid (H2Asc) is dehydroascorbic acid and that of oxalic acid (H2OX) is CO2, while MnII is the end product from MnIV. Both MnIVL and MnIIIL− form outer sphere adducts with H2Asc and H2OX with high values of equilibrium constants of formation (Q>102 dm3 mol−1, I = 0.5 mol dm−3, 25.8 °C, 1.5% v/v MeOH+H2O). The adduct formation is diffusion controlled and is attributed to hydrogen bonding interactions between the reactants.
The rate constants for the electron transfer in (MnIV/IIIL, H2A), (MnIV/IIIL, HA−) (H2A = H2Asc, H2OX) and for (MnIVL, H2Asc)+H2Asc, (MnIIIL−, HAsc−)+HAsc− are reported. There was no evidence of direct coordination of the reductants to the MnIV/III center indicating an outer sphere (ET) mechanism. 相似文献