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81.
82.
83.
Martin RE Gubler U Cornil J Balakina M Boudon C Bosshard C Gisselbrecht JP Diederich F Gunter P Gross M Bredas JL 《Chemistry (Weinheim an der Bergstrasse, Germany)》2000,6(19):3622-3635
A series of monodisperse Et3-Si-end-capped poly(triacetylene) (PTA) oligomers ranging from monomer to hexadecamer was prepared by a fast and efficient statistical deprotection-oxidative Hay oligomerization protocol. The PTA oligomers exhibit an increasingly deep-yellow color with lengthening of the pi-conjugated backbone, feature excellent solubility in aprotic solvents, and exhibit melting points up to > 22 degrees C for the hexadecameric rod. This new dramatically extended oligo(enediyne) series now enables to investigate the evolution of the physico-chemical effects in PTAs beyond the linear 1/n versus property regime into the higher oligomer region where saturation becomes apparent. We report the results of joint experimental and theoretical studies, including analysis of the 13C NMR spectra, evaluation of the linear (UV/ Vis) and nonlinear [third-harmonic generation (THG) and degenerate four-wave mixing (DFWM)] optical properties, and characterization of the redox properties with cyclic and steady-state voltammetry. Up to the hexadecameric rod, an increasingly facile one-electron reduction step is observed, showing at the stage of the dodecamer, a leveling off tendency from the linear correlation between the inverse number of monomer units and the first reduction potential. The effective conjugation length (ECL) determined by means of UV/Vis spectroscopy revealed a pi-electron-delocalization length of about n = 10 monomeric units, which corroborates well with the oligomeric length for which in the 13C NMR spectrum C(sp2) and C(sp) resonances start to overlap. Third-harmonic generation (THG) and degenerate four-wave mixing (DFWM) measurements revealed for the second-order hyperpolarizability gamma a power law increase gammma-alpha-n(a) for oligomers up to the octamer with exponential factors a= 2.46+/-0.10 and a=2.64+/-0.20, respectively, followed by a smooth saturation around n = 10 repeating units. The power law coefficient a calculated with the help of the valence effective Hamiltonian (VEH) method combined to a sum-over-states (SOS) formalism corroborates well with the values found by both THG and DFWM experiments. Up to the PTA heptamer, INDO (intermediate neglect of differential overlap)-calculated gas-phase ionization potentials and electron affinities obey a linear relationship as a function of the inverse number of monomer units displaying a strong electron-hole symmetry. The onset of saturation for the electron affinity is calculated to occur around the octamer, in accordance with experimentally obtained results from electrochemical measurements. 相似文献
84.
Henning A. Hppe Henning Trill Gunter Kotzyba Bernd D. Mosel Rainer Pttgen Wolfgang Schnick 《无机化学与普通化学杂志》2004,630(2):224-228
The isotypic nitridosilicates MYb[Si4N7] (M = Sr, Ba, Eu) were obtained by the reaction of the respective metals with Si(NH)2 in a radiofrequency furnace below 1600 °C. On the basis of powder diffraction data of MYb[Si4N7] Rietveld refinements of the lattice constants were performed; these confirmed the previously published single‐crystal data. The compounds contain a condensed network of corner‐sharing [N(SiN3)4] units. The central nitrogen thus exhibits ammonium character. Magnetic susceptibility measurements of MYb[Si4N7] (M = Sr, Ba, Eu) show paramagnetic behavior with experimental magnetic moments of 3.03(2), (Sr), 2.73(2) (Ba), and 9.17(2) (Eu) μB per formula unit. In EuYbSi4N7 the europium and ytterbium atoms are in stable divalent and trivalent states, respectively. According to the non‐magnetic character of the alkaline earth cations, ytterbium has to be in an intermediate valence state YbIII‐x in the strontium and barium compound. Consequently, either a partial exchange N3—/O2— resulting in compositions MYbIII‐x[Si4N7—xOx] or an introduction of anion defects according to MYbIII‐x[Si4N7—x/3□x/3] has to be assumed. The phase width 0 ≤ x ≤ 0.4 was estimated according to the magnetic measurements. 151Eu Mössbauer spectra of EuYb[Si4N7] at 78 K show a single signal at an isomer shift of δ = —12.83(3) mm s—1 subject to quadrupole splitting of ΔEQ = 5.7(8) mm s—1, compatible with purely divalent europium. 相似文献
85.
Jeongbin Yim Sujeong Kim Gunter Walcher Wolfgang Pfleiderer 《Helvetica chimica acta》1993,76(5):1970-1979
The nonenzymatic synthesis of aurodrosopterin ( 5 ) from 6-acetyl-2-amino-3, 7, 8, 9-tetrahydro-4H-pyrimido-[4,5-b][1,4]diazepin-4-one ( 3 ) and 7,8-dihydrolumazine ( 4 ) at pH 3 (HCl) was performed. The identity of the synthesized compound with the natural eye pigment isolated from drosophila heads was confirmed by thin-layer chromatography on cellulose and by comparisons of the 1H-NMR and UV/VIS spectra. The nonenzymatic synthesis of a neodrosopterin-like red pigment from 3 and 2,4-diamino-7,8-dihydropteridine was also carried out, but its identity could not be established. This pigment, called aminodrosopterin, has an absorption peak at 489 nm, which is very close to that of neodrosopterin. 相似文献
86.
Mara E. F. Braibante Gunter Clar Marcos A. P. Martins 《Journal of heterocyclic chemistry》1993,30(4):1159-1160
1-Methyl-5-(trifluoromethyl)-1H-pyrazoles 2, 3 and 4,5-dihydro-1-phenyl-5-(trifluoromethyl)-1H-pyrazol-5-ol 4 were prepared by reaction of 4-alkoxy-1,1,1-trifluoro-3-alken-2-ones 1 and hydrazine, methylhydrazine, and phenylhydrazine, respectively, in good yields. Compound 1 proved to be a versatile building block for the regiospecific construction of pyrazole rings having an 5-trifluoromethyl substituent. 相似文献
87.
Flamigni L Talarico AM Serroni S Puntoriero F Gunter MJ Johnston MR Jeynes TP 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(11):2649-2659
[2]Catenanes made up of several polyether-strapped porphyrin macrocycles interlinked with the cyclic electron acceptor cyclobis(paraquat-p-phenylene) were spectroscopically, photophysically, and electrochemically characterized. The catenanes exhibit very rich redox behavior due to the presence of several different and interacting electro-active subunits. The redox patterns represent useful "fingerprints" that provide detailed information on the electronic interactions and the chemical environments that the electroactive subunits experience in the supramolecular arrays. A photoinduced electron transfer from the porphyrin excited state (charge separation CS) occurs with tau=20 ps in the catenanes with a larger strap and faster than 20 ps (instrumental resolution) in the catenanes with a shorter strap. The resulting charge-separated state recombines to the ground state (charge recombination CR) with lifetimes similar in all cases, 41+/-4 ps. Comparison of the electron transfer rates CS and CR in the host-guest complexes of the same porphyrins with the noncyclic electron acceptor paraquat, indicate slower reactions in the [2]catenanes. This behavior is assigned to the different separation between reacting partners determined by the type of bond (weak interaction or mechanical) and to a two-step consecutive electron transfer to different sites of the macrocyclic electron acceptor in the catenanes which retards charge recombination. 相似文献
88.
This work provides a theoretical analysis of multicomponent adsorption kinetics for conditions typical of protein adsorption in porous ion exchangers as well as experimental results for the adsorption of lysozyme/cytochrome c mixtures in the cation exchanger SP-Sepharose-FF. The theory predicts the formation of overshoots in the intraparticle concentration profiles and in the total amount adsorbed for the more weakly adsorbed component. An analytical solution valid for the case where the isotherms are rectangular is developed and found to be in good agreement with the limiting behavior of the general numerical solution of the model equations. The experimental results show that the two proteins are competitively adsorbed and that an overshoot of adsorbed cytochrome c occurs during simultaneous adsorption. Model predictions based on the assumption that the adsorption isotherms are rectangular and that lysozyme completely displaces cytochrome c are in qualitative and quantitative agreement with the experimental kinetics suggesting that the overshoot phenomena observed with multicomponent systems in these resins can be explained with a diffusion model without the need to account for flux coupling or electrophoretic contributions to transport. 相似文献
89.
Gunter Weiß 《Journal of Geometry》1981,17(1):46-49
LetV be a quadrilateral in aMoufang-plane , in which theFano-proposition is valid. Take the pointsP,Q,R respectively in the diagonalsp,q,r ofV and construe the pointsP
*,Q
*,R
* inp,q, r harmonic toP,Q,R with respect to pairs of edges ofV. IfP,Q,R are collinear, so areP
*,Q
*,R
*, if and only if is aPappos-plane. Is V classical, the pointsP
1
p,Qq,Rr and their harmonic conjugatesP
1
*
,Q
*,R
* (construed as above mentioned) lay in a curve of 2nd order.
R. Artzy zum 70. Geburtstag zugeeignet 相似文献
R. Artzy zum 70. Geburtstag zugeeignet 相似文献
90.
The stereoisomers 1a–8a of decalin-1,3-diol have been synthesized by LAH-reduction of cis- and trans-decalin-1, 3-dione, respectively. With the exception of trans-decalin-1a,3e- and -1e,3a-diols, 7a and 8a, the stereoisomers have been isolated by column chromatography, and their configurations have been determined by 1H-NMR, IR and chemical methods. It is shown by the aid of deuterated derivatives, that the elimination of H2O, MeOH and CH2O from the molecular ions of the stereoisomeric diols and di-O-methyl ethers, respectively, occurs predominantly by stereospecific reactions, if the ground state conformation of the molecule corresponds to the geometry of the transition state of the elimination reaction. The steric control of the fragmentations is greatly reduced, if conformational changes of the molecular ions have to occur prior to fragmentation. No clear steric effects are observed, if none of the conformations of the intact molecular ions corresponds to the transition state. These steric effects can be used to identify the various stereoisomers of decalin-1,3-diol and 1,3-dimethoxy-decalin by mass spectrometry. 相似文献