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231.
Enrico Borgarello Jean Desilvestro Michael Grtzel Ezio Pelizzetti 《Helvetica chimica acta》1983,66(6):1827-1834
Conduction band electrons produced by band gap excitation of TiO2-particles reduce efficiently thiosulfate to sulfide and sulfite. \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm 2e}_{{\rm cb}}^ - ({\rm TiO}_{\rm 2}) + {\rm S}_{\rm 2} {\rm O}_3^{2 - } \longrightarrow {\rm S}^{2 - } + {\rm SO}_3^{2 - } $\end{document} This reaction is confirmed by electrochemical investigations with polycrystalline TiO2-electrodes. The valence band process in alkaline TiO2-dispersions involves oxidation of S2O to tetrathionate which quantitatively dismutates into sulfite and thiosulfate, the net reaction being: \documentclass{article}\pagestyle{empty}\begin{document}$ 2{\rm h}^{\rm + } ({\rm TiO}_{\rm 2}) + 0.5{\rm S}_{\rm 2} {\rm O}_{\rm 3}^{{\rm 2} - } + 1.5{\rm H}_{\rm 2} {\rm O} \longrightarrow {\rm SO}_3^{2 - } + 3{\rm H}^{\rm + } $\end{document} This photodriven disproportionation of thiosulfate into sulfide and sulfite: \documentclass{article}\pagestyle{empty}\begin{document}$ 1.5{\rm H}_{\rm 2} {\rm O } + 1.5{\rm S}_{\rm 2} {\rm O}_{\rm 3}^{{\rm 2} - } \mathop \to \limits^{h\nu} 2{\rm SO}_3^{2 - } + {\rm S}^{{\rm 2} - } + 3{\rm H}^{\rm + } $\end{document} should be of great interest for systems that photochemically split hydrogen sulfide into hydrogen and sulfur. 相似文献
232.
Turbiez M Frère P Allain M Videlot C Ackermann J Roncali J 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(12):3742-3752
Hybrid oligothiophenes based on a various combinations of thiophene and 3,4-ethylenedioxythiophene (EDOT) groups have been synthesized. UV/Vis absorption spectra show that the number and relative positions of the EDOT groups considerably affect the width of the HOMO-LUMO gap and the rigidity of the conjugated system. Analysis of the crystallographic structure of two hybrid quaterthiophenes confirms that insertion of two adjacent EDOT units in the middle of the molecule leads to a self-rigidification of the conjugated systems by intramolecular SO interactions. Cyclic voltammetry data shows that the first oxidation potential of the oligomers decreases with increasing chain length and increasing number of EDOT groups for a given chain length. Electrochemical studies and theoretical calculations show that the positions of the EDOT units in the conjugated chain control the potential difference (DeltaE(p)) between the first and second oxidation steps. Moving the EDOT groups from the outer to the inner positions of the conjugated system increases DeltaE(p). Theoretical calculations confirm that this phenomenon reflects an increase of the intramolecular coulombic repulsion between positive charges in the dication. A thin-film field-effect transistor was fabricated by vacuum sublimation of a pentamer with alternating thiophene-EDOT structure, and the hole mobility was determined. 相似文献
233.
When α,β-unsaturated γ-dimethoxymethyl cyclohexenones are excited to the S2(π,π*) state, certain unimolecular reactions can be observed to compete with S2 → S1 internal conversion. These reactions do not occur from the S1(n,π*) or the lowest T(π,π* and n,π*) states. They comprise the radical elimination of the formylacetal substituent (cf. 8 , 9 → 32 + 33 ), γ → α formylacetal migration (cf. 6 → 27 , 8 → 30 , 9 → 34 , 12 → 37 ), and a cyclization process involving the transfer of a methoxyl hydrogen to the α carbon and ring closure at the β position (cf. 6 → 28 , 8 → 31 , 12 → 38 , 20 → 40 + 41 ). The quantum yield of the ring closure 20a → 40a + 41a is 0.016 at ≤ 0.05M concentration. It is independent of the excitation wavelength within the π→π* absorption band (238–254 nm), but Φ ( 40a + 41a ) decreases at higher concentrations. According to the experimental data the reactive species of these specifically π→π*-induced transformations is placed energetically higher than the S1(n,π*) state, and it is either identical with the thermally equilibrated S2(n,π*) state, or reached via this latter state. The linear dienone 14 undergoes a similar π→π*-induced cyclization (→ 42 ) whereas the benzohomologue 26 proved unreactive, and the dienone 22 at both n → π and π→π* excitation only gives rise to rearrangements generally characteristic of cross-conjugated cyclohexadienones. 相似文献
234.
Jean -François Labarre Marcel Graffeuil Jean -Paul Faucher Maurice Pasdeloup Jean -Pierre Laurent 《Theoretical chemistry accounts》1968,11(5):423-433
Résumé Une utilisation conjointe des méthodes L.C.A.O.-C.U.V. et d'itération tournante permet d'atteindre des structures électroniques ( + ) cohérentes avec l'U.V.(et donc le gradient de population électronique de liaison qui conditionne l'aromaticité) de huit borazines et boroxines, substitués ou non, de symètrie D
3h
. L'échelle d'aromaticité obtenue permet de rendre compte des propriétés magnétiques (RMN, RQ, effet Faraday, diamagnétisme) de ce type de molécules. On parvient en particulier aux deux conclusions essentielles suivantes: les borazines sont nettement plus aromatiques que les boroxines isologues et la greffe de groupements méthyles ou d'atomes de chlore, qu'elle se fasse sur le bore ou sur l'azote, confère toujours au dérivé substitué une aromaticité au moins égale à celle du borazine lui-même.
Recherche effectuée dans le cadre de la R.C.P. n du C.N.R.S. 相似文献
A simple method to calculate the - and -electron structure of borazines and of substituted boroxines of symmetry D3h: A theoretical estimation of the relative aromaticity of those molecules
( + ) electronic structures calculations are performed for eight D 3h borazines and boroxines, using in concert previously published U.V.-consistent H.M.O.-L.C.A.O. and bond by bond iteration methods. An estimation of bond electronic populations gradients is so obtained, allowing to set up a new aromaticity scale for such molecules. The main results are the following: Borazines are much more aromatic than isologous boroxines and B-or N-graft of alkyl groups or chlorine atoms never decreases (and generally increases) aromaticity.
Zusammenfassung Es wird für acht Borazol- und Boroxolverbindungen mit D 3h -Symmetrie unter Verwendung einer am UV-Spektrum geeichten iterativen HMO-LCAO-Theorie die - und -Elektronenstruktur bestimmt. Hiermit kann eine Abschätzung des Gradienten der Bindungselektronendichten gewonnen werden, aus der eine Einteilung der Moleküle nach ihrem aromatischen Charakter hervorgeht. Es ergibt sich, daß die Borazole aromatischer sind als die isoelektronischen Boroxole und daß eine Substitution der H-Atome am Bor oder Stickstoff durch Chlor oder Methylgruppen die Aromatizität fast immer erhöht, jedenfalls aber nie erniedrigt.
Recherche effectuée dans le cadre de la R.C.P. n du C.N.R.S. 相似文献
235.
Geometry optimization of the cis and the trans isomers of several octahedral dioxo complexes of d(2) electronic configuration are performed using the gradient-corrected density functional theory (B3LYP and, for some key structures, BP86). With only monodentate sigma donor ligands (ReO(2)(NH(3))(4)(+), 7), the usual energy order is found (i.e., the trans isomer is the most stable). Complexes with a chelating bidentate ligand, OsO(2)(OCH(2)CH(2)O)(NH(3))(2) (10) and ReO(2)(HN=CHCH=NH)(NH(3))(2)(+) (11), are used as models for the experimental complexes 5 and 2 in which the arrangement of the O=M=O unit is trans and cis, respectively. Our calculations actually show an inversion of the relative energy of the two isomers in going from 10 to 11: while the trans isomer is found to be the most stable in 10, the unusual cis diamagnetic isomer is favored by about 29 kcal mol(-)(1) in 11. This result is traced to the geometric and electronic properties of the bidentate ligand, in particular an acute bite angle and good pi acceptor character. In complex 14 with a bipyridine chelating ligand (weaker pi acceptor than diaza-1,4-butadiene in 11), this energy difference is, however, reduced to 7.5 kcal mol(-)(1) (partial geometry optimization). 相似文献
236.
Roncali J 《Chemical Society reviews》2005,34(6):483-495
This tutorial review covers recent contributions in the area of linear pi-conjugated systems bound to fullerenes in view of their application as active materials in photovoltaic devices. The first part discusses the concepts of double-cable polymer and molecular hetero-junction and presents several examples of chemically or electrochemically synthesized C60-derivatized conjugated polymers. The second and main part of the article concerns the various classes of C60-derivatized pi-conjugated oligomers designed in view of their utilization in single-component photovoltaic devices. Thus, C60-containing pi-conjugated systems such as oligoarylenevinylenes, oligoaryleneethynylenes and oligothiophenes are discussed on the basis of the relationships between molecular structure, photophysical properties and performances of the derived photovoltaic devices. A brief last section presents some recent examples of surface-attached molecular hetero-junctions based on self-assembled monolayers and discusses possible routes for future research. 相似文献
237.
Christian Coulombeau Claude Beguin Christiane Coulombeau 《Journal of fluorine chemistry》1977,9(6):483-491
Equilibrium constants for the fluorinated species HF, F-, HF-2 and H2F2 in formic acid and in a 1M potassium formate solution in formic acid have been studied by 19F NMR. The chemical shifts of these species have been determined from measurements of the shifts for various initial mixtures of differing concentrations of dissolved HF, F- and HF-2. From these values, relative concentrations of HF, F-, and HF-2 and H2F2 in each solution have been calculated through a numerical method. The following constants were obtained: K1 = [H+][F-]/[HF] = 1.1 x 10-5M; KD = [HF][F-]/[HF-2] = 0.5 M; K′1 = [H+][HF-2]/[H2F2]= 1.1 x 10-5 M; K′D = [HF]2/[H2F2]=0.5 M. 相似文献
238.
We have synthesized 5H-imidazo[2,1-c]pyrrolo[1,2-a][1,4]benzodiazepine 1 in five steps from 1-(2-amino-methylphenyl) pyrrole 4 . Amidino derivatives 11-12 have also been prepared. 相似文献
239.
Claude Didierjean Guy Boussard Andr Aubry 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(7):o394-o396
The title dipeptide, 1‐(tert‐butoxycarbonyl‐d ‐alanyl)‐N‐isopropyl‐l ‐pipecolamide or Boc‐d ‐Ala‐l ‐Pip‐NHiPr (H‐Pip‐OH is pipecolic acid or piperidine‐2‐carboxylic acid), C17H31N3O4, with a d –l heterochiral sequence, adopts a type II′β‐turn conformation, with all‐trans amide functions, where the C‐terminal amide NH group interacts with the Boc carbonyl O atom to form a classical i+3 i intramolecular hydrogen bond. The Cα substituent takes an axial position [Hα (Pip) equatorial] and the trans pipecolamide function is nearly planar. 相似文献
240.
We report the synthesis of 1,4,8-triazaspiro[4.5]decan-2-one derivatives from N-benzyl-4-piperidone and N-protected amino acid amides on solid support. We have translated the chemistry from solution to solid phase using a backbone amide linker (BAL) mimic. Using a parallel combinatorial approach, we performed the optimization of the synthesis on SynPhase™ Lanterns. 相似文献