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101.
Agnello M Belli G Bendiscioli G Bertin A Botta E Bressani T Bruschi M Bussa MP Busso L Calvo D Cereda B Cerello PG Cicalò C Corradini M Costa S De Castro S Donzella A Feliciello A Ferrero L Filippi A Filippini V Fontana A Galli D Garfagnini R Giacobbe B Gianotti P Grasso A Guaraldo C Iazzi F Lanaro A Lodi Rizzini E Lucherini V Marcello S Marconi U Masoni A Minetti B Montagna P Morando M Nichitiu F Panzieri D Pauli G Piccinini M Puddu G Rossetto E Rotondi A Rozhdestvensky AM Saino A Salvini P 《Physical review letters》1995,74(3):371-374
102.
Iengo E Zangrando E Minatel R Alessio E 《Journal of the American Chemical Society》2002,124(6):1003-1013
Treatment of the octahedral Ru(II)-dimethyl sulfoxide complexes trans-RuCl(2)(dmso-S)(4) (1), trans-RuCl(2)(dmso-O)(2)(CO)(2) (2), and trans-RuCl(2)(dmso)(3)(CO) (3) with a stoichiometric amount of 5,10-bis(4'-pyridyl)-15,20-diphenylporphyrin (4'-cis-DPyP) yields, after chromatographic purification, the novel 2+2 molecular squares of formula [trans,cis,cis-RuCl(2)(dmso-S)(2)(4'-cis-DPyP)](2) (4), [trans,cis,cis-RuCl(2)(CO)(2)(4'-cis-DPyP)](2) (5), and [trans,cis,cis-RuCl(2)(dmso-S)(CO)(4'-cis-DPyP)](2) (6), respectively. Compound 6 exists as an equimolar mixture of the isomeric metallacycles 6a and 6b, depending on whether the 4'-N(py) rings of 4'-cis-DPyP's are trans to CO or to dmso-S. Compounds 4-6 were fully characterized by NMR and IR spectroscopy and by FAB mass spectrometry. Treatment of 5 with excess zinc acetate in chloroform/methanol mixtures led to the isolation of the corresponding zinc adduct [trans,cis,cis-RuCl(2)(CO)(2)(Zn x 4'-cis-DPyP)](2) (5Zn). Treatment of 5Zn with 1 equiv of a trans ditopic N-donor ligand L (L = 4,4'-bipy, 5,15-bis(4'-pyridyl)-2,8,12,18-tetra-n-propyl-3,7,13,17-tetramethylporphyrin (4'-trans-DPyP-npm), or 5,15-bis(4'-pyridyl)-10,20-diphenylporphyrin (4'-trans-DPyP)) leads readily and selectively, according to (1)H NMR spectroscopy, to the quantitative assembling of 2:2 supramolecular adducts of stacked metallacycles of formula [(5Zn)(2)(mu-L)(2)] (7-9), which were thoroughly characterized in solution by NMR spectroscopy. NMR features indicate that, at ambient temperature, the equilibrium between 5Zn and L to yield [(5Zn)(2)(mu-L)(2)] has an intermediate to slow rate on the NMR time scale (relatively broad signals for L) and is totally shifted toward the 2:2 product (all or nothing process). Single-crystal X-ray investigations showed that, depending on the nature of the bridging ligand, in the solid state these sandwich structures can either be maintained or originate polymeric chains formulated as [(5Zn)(mu-L)](infinity). When L = 4'-trans-DPyP, both solution- and solid-state data indicate that [(5Zn)(2)(mu-4'-trans-DPyP)(2)] (9) is a discrete supramolecular assembly of two molecular squares of metalloporphyrins axially connected through other porphyrins. In this molecular box, the two bridging porphyrins are coplanar at a distance of about 11.4 A. When L = 4,4'-bipy, the corresponding adduct 7 has the anticipated sandwich-like discrete architecture [(5Zn)(2)(mu-4,4'-bipy)(2)] in solution, but it assumes a stair-like polymeric wire structure in the solid state. The polymer [(5Zn)(mu-4,4'-bipy)](infinity) is made by 5Zn squares bridged by 4,4'-bipy ligands which are axially coordinated alternatively on the two opposite sides of each square. Our work clearly established that relatively simple supramolecular adducts of porphyrins, such as molecular squares, are suitable building blocks for the construction of more elaborate assemblies of higher order by axial coordination of bridging ligands. 相似文献
103.
A frequency-dependent lineshape analysis of the ESR spectra of ternary systems in solution has been carried out. The 5′-ATP—Mn(II)—Trp complex has been chosen as a model system. The analysis points out the presence of inverted spectra at both X- and Q-bands. The lineshape is described by a distribution of configurational sites, Yl(ω) = ΣkPkYk(H). The temperature dependence of the ESR linewidth has also been investigated and is discussed in terms of chemical equilibria and correlation times. 相似文献
104.
Freek Brinkmann Niels Ebbe Dam Eva Deák Francesca Durbiano Enzo Ferrara Judit Fűkő Hans D. Jensen Michal Máriássy Rubina H. Shreiner Petra Spitzer Uwe Sudmeier Michael Surdu Leoš Vyskočil 《Accreditation and quality assurance》2003,8(7-8):346-353
This paper surveys the state of the art for primary methods for the evaluation of electrolytic conductivity in aqueous solutions as they are currently carried out in several national metrological institutes (NMIs). The theoretical and practical basic knowledge of this measurement is described. Analysis of and comments on the different approaches are offered to give emphasis to technical difficulties and possible solutions. Further development is foreseeable, ensuring a common effort for the sharing of expertise that has been undertaken at the NMIs. In particular, improvements are expected towards traceable measurements of solutions with conductivity values lower than those actually standardized, down to the level of ultrapure water. 相似文献
105.
106.
107.
The formulation of a thermodynamic framework for mixtures based on absolute, excess or net adsorption is discussed and the qualitative dependence with pressure and fugacity is used to highlight a practical issue that arises when extending the formulations to mixtures and to the Ideal Adsorbed Solution Theory (IAST). Two important conclusions are derived: the correct fundamental thermodynamic variable is the absolute adsorbed amount; there is only one possible definition of the ideal adsorbed solution and whichever starting point is used the same final IAST equations are obtained, contrary to what has been reported in the literature. 相似文献
108.
109.
Bozio R Cecchetto E Fabbrini G Ferrante C Maggini M Menna E Pedron D Riccò R Signorini R Zerbetto M 《The journal of physical chemistry. A》2006,110(20):6459-6464
This paper presents the synthesis and two photon-induced absorption (TPA) properties of a functionalized distyrylbenzene (DSB) 1 containing a tetra-azacyclododecane (cyclen) receptor for Zn(II). The influence of Zn(II) on one- and two-photon absorption characteristics of 1 has been investigated in dimethyl sulfoxide. The experiments show that the TPA action spectrum of uncomplexed 1, at 750 nm employing nanosecond-long excitation pulses, is 5 times more intense than that of the complexed form. This moderate contrast between the bound and unbound species confirms, however, the potential of this design scheme for the development of molecular structures with enhanced sensitivity and contrast to be used as Zn(II) sensors through TPA-induced fluorescence microscopy. 相似文献
110.
Aime S Fedeli F Sanino A Terreno E 《Journal of the American Chemical Society》2006,128(35):11326-11327
A novel procedure for making the pH responsiveness of a Gd-based probe independent of its concentration has been developed. The method is based on a ratiometric approach and requires the measurement, at magnetic fields higher than 1 T, of the paramagnetic contribution to the longitudinal and the transverse NMR relaxation rates of water protons in the presence of a Gd-based probe with a rotational mobility in the nanosecond time scale. The method has been tested and validated in vitro by using a macromolecular adduct based on the polyornithine backbone, whose rotational mobility is pH dependent. The results reported in this communication improve substantially the diagnostic potential of MRI responsive agents. 相似文献