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141.
Kimel" B. G. Tumanov V. V. Faustov V. I. Promyslov V. M. Egorov M. P. Nefedov O. M. 《Russian Chemical Bulletin》2002,51(8):1568-1574
Reactions of a number of germylenes and dimethylsilylene with a phosphaalkene, 2,2-bis(trimethylsilyl)-1-phenyl-1-phosphaethene (1), were studied. The reaction of short-lived dimethylgermylene with 1 produced a phosphagermirane 3 (the first representative of a new class of heterocyclic compounds). Compound 3 was characterized in solution by 1H, 13C, 31P, and 29Si NMR spectroscopy. Subsequent reaction of 3 with dimethylgermylene results in 2,2,3,3-tetramethyl-4,4-bis(trimethylsilyl)-1-phenyl-2,3-digerma-1-phosphacyclobutane 4, which has not been reported so far. In order to rationalize different reactivities of germylenes towards alkenes and phosphaalkenes, the addition products of GeH2 to ethylene and phosphaethene (HP=CH2) were studied using the G2 computational scheme and DFT PBE technique. The adducts of GeMe2 (GeCl2) with HP=CH2 and of GeMe2 with PhP=C(SiH3)2 were also calculated by the DFT PBE method. According to calculations, the exothermicity, DE, of cycloaddition of GeH2 and GeMe2 to the phosphaalkenes HP=CH2 and PhP=C(SiH3)2 (43.5—39.7 kcal mol–1) is nearly twice as high as the exothermicity of cycloaddition of these germylenes to ethylene. In addition to the minimum corresponding to the three-membered cycle, a number of minima corresponding to quite stable donor-acceptor complexes in which the Ge atom is coordinated by the lone electron pair of the P atom in the phosphaalkene molecule were located on the potential energy surface of the germylene—phosphaalkene system. The complexation energy of the complex of GeH2 (GeMe2) with phosphaethene is 25.0 (16.9) kcal mol–1. For GeCl2, the exothermicity of cycloaddition to HP=CH2 decreases to 7.6 kcal mol–1 and the complexation energy decreases to 8.2 kcal mol–1. 相似文献
142.
Xifra R Ribas X Llobet A Poater A Duran M Solà M Stack TD Benet-Buchholz J Donnadieu B Mahía J Parella T 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(17):5146-5156
A family of highly stable organometallic Cu(III) complexes with monoanionic triazamacrocyclic ligands (L(i)) with general formula [CuL(i)]+ have been prepared and isolated, and their structural, spectroscopic, and redox properties thoroughly investigated. The HL(i) ligands have been designed in order to understand and quantify the electronic effects exerted by electron donor and electron-withdrawing groups on either the aromatic ring or the central secondary amine or on both. In the solid state the Cu(III) complexes were mainly characterized by single-crystal X-ray diffraction analysis, whereas in solution their structural characterization was mainly based on 1H NMR spectroscopy given the diamagnetic nature of the d(8) square-planar Cu(III) complexes. Cyclic voltammetry together with 1H NMR and UV/Vis spectroscopy have allowed us to quantify the electronic effects exerted by the ligands on the Cu(III) metal center. A theoretical analysis of this family of Cu(III) complexes has also been undertaken by DFT calculations to gain a deeper insight into the electronic structure of these complexes, which has in turn allowed a greater understanding of the nature of the UV/Vis transitions as well as the molecular orbitals involved. 相似文献
143.
Understanding the Reactivity of Planar Polycyclic Aromatic Hydrocarbons: Towards the Graphene Limit
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Yago García‐Rodeja Prof. Dr. Miquel Solà Dr. Israel Fernández 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(30):10572-10580
The Diels–Alder reactivity of maleic anhydride towards the bay regions of planar polycyclic aromatic hydrocarbons was explored computationally in the DFT framework. The process becomes more and more exothermic and the associated activation barriers become lower and lower when the size of the system increases. This enhanced reactivity follows an exponential behavior that reaches its maximum for systems having 18–20 benzenoid rings in their structures. This peculiar behavior was analyzed in detail by using the activation strain model of reactivity in combination with energy decomposition analysis. The influence of the change in the aromaticity of the polycyclic compound during the process on the respective activation barriers was also studied. 相似文献
144.
Dandan Chen Dr. Dariusz W. Szczepanik Prof. Jun Zhu Prof. Miquel Solà 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(57):12964-12971
Species with adaptive aromaticity are aromatic in the ground and lowest-lying triplet excited states and they have normally intermediate singlet-triplet gaps. Few examples of compounds with adaptive aromaticity are known to date, including 16-valence-electron (16e) metallapentalenes. A sweeping search could be conducted to discover new members of this group, but efficient designs with an explicit strategy would facilitate the quest for new members of this elusive family. Density functional theory calculations and aromaticity evaluations have been performed to reveal the nature of triplet-state aromaticity in 16e metallapentalenes. Our results show that coordination of strong σ- or π-donor ligands helps achieving adaptive aromaticity of 16e metallapentalenes by means of a spin delocalization mechanism. These results have important implications for understanding the unusual properties of the organometallic adaptive aromatics, leading the way to efficient design of new compounds with tunable singlet-triplet gaps. 相似文献
145.
Pau Besalú-Sala Dr. Josep M. Luis Prof. Dr. Miquel Solà 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(63):14481-14487
In the last 30 years, fullerene-based materials have become popular building blocks for devices with a broad range of applications. Among fullerene derivatives, endohedral metallofullerenes (EMFs, M@Cx) have been widely studied owing to their unique properties and reactivity. For real applications, fullerenes and EMFs must be exohedrally functionalized. It has been shown that encapsulated metal cations facilitate the Diels–Alder reaction in fullerenes. Herein, the Bingel–Hirsch (BH) addition of ethyl bromomalonate over a series of ion-encapsulated M@C60 (M=Ø, Li+, Na+, K+, Mg2+, Ca2+, and Cl−; Ø@C60 stands for C60 without any endohedral metal) is quantum mechanically explored to analyze the effect of these ions on the BH addition. The results show that the incarcerated ion has a very important effect on the kinetics and thermodynamics of this reaction. Among the systems studied, K+@C60 is the one that leads to the fastest BH reaction, whereas the slowest reaction is given by Cl−@C60. 相似文献
146.
147.
On the lightning hazard warning using electrostatic field: Analysis of summer thunderstorms in Spain
Daniel Aranguren Joan Montanya Gloria Solá Victor March David Romero Horacio Torres 《Journal of Electrostatics》2009,67(2-3):507-512
This work presents an analysis of lightning warnings based on atmospheric electrostatic field measurements achieved in the city of Terrassa (northeastern Spain). Seven summer thunderstorms were analyzed. Lightning location data were obtained from two lightning detection networks that provide cloud-to-ground (CG) and intra-cloud (IC) flash information. Warning behaviour was studied on the basis of the “two area method” using both electrostatic field (EF) thresholds and polarity reversal detection. The study of the total lightning locations (CG + IC) with respect to the electric field mill (EFM) site lets investigate the possible EF threshold and EF polarity inversion values useful for warning. The probability of detection (POD) and the false alarm ratio (FAR) were evaluated in both cases obtaining slightly better results by using polarity change criteria. The paper also includes a discussion about the lead times (LTs) obtained between the trigger of a warning and a CG located in the area of concern (AOC). 相似文献
148.
149.
We present a QM and QM/MM study of steric and electronic effects in the main steps of Rh-catalyzed carbonylation reactions. All the considered systems adopt a square-planar geometry prior to CH(3)I oxidative addition. As regards the octahedral complexes after CH(3)I oxidative addition, a comparison between the various models indicates that the energy gain due to the CH(3)I oxidative addition is reduced by the steric pressure of the substituents on the ligand. The substantially similar results obtained with the QM/MM and QM models indicate that electronic effects are not particularly relevant in determining the energetic of oxidative addition. As regards the P,P-Ph octahedral complex, the geometries in which the CO group is trans to the added CH(3) group, or trans to one of the P atoms, are of similar energy. A comparison between the various models indicates that the energy barrier of the CO insertion reaction is lowered by the presence of substituents on the chelating ligands. This effect is related to a relief of the steric pressure on the complex as the systems move from a six-coordinated octahedral geometry toward a five-coordinated square-pyramidal geometry. The energy barrier calculated for the P,S-Ph system is in rather good agreement with the experimental value, whereas that of the P,P-Ph system is somewhat underestimated. Inclusion of solvent effects with a continuum model leads to a slightly better agreement. The thermodynamic products adopt a square-pyramidal geometry with the COCH(3) group in the apical position. 相似文献
150.
Nondegenerate plane congruences in the four-dimensional complex projective space with degenerate general focal conic are classified by using the focal method due to Corrado Segre. 相似文献