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991.
Francesco Paolo Colonna Giuseppe Distefano Maurizio Guerra Derek Jones 《Journal of Electron Spectroscopy and Related Phenomena》1980,18(3):309-328
The photoelectron He(I) and He(II) spectra of 4H-pyran-4-one (1), 4H-thiopyran-4-one (2), 4H-pyran-4-thione (3) and 4H-thiopyran-4-thione (4) are reported. The assignments are based on experimental evidence, taking into account the results of theoretical calculations. The outermost orbital sequences proposed (X = O, S) are nX (σ), 3b1 (π), 1a2(π) for 1, 2 and 4; and 3b1(π), nX(σ) and 1a2(π) for 3. The shifts of the core-ionization energy values for 1–4 are ascribed to a drift of π-charge from the intracyclic heteroatom towards the carbonyl or thiocarbonyl group. Low-energy shake-up satellites (up to 25% with respect to the main line) are observed in the various energy regions of the XPS spectra. They are qualitatively reproduced by CNDO/2 calculations. The most important satellites derive from the transition in the ion corresponding to the 3b1 (π) → 4b1(π*) transition in the UV-visible spectra of the neutral molecules. Charge rearrangements accompanying this transition lead to charge depletion of the core-ionized atom. 相似文献
992.
Ienco A Calhorda MJ Reinhold J Reineri F Bianchini C Peruzzini M Vizza F Mealli C 《Journal of the American Chemical Society》2004,126(38):11954-11965
The dicationic complex [(triphos)Rh(mu-S)(2)Rh(triphos)](2+), 1 (modeled as 1c) [triphos = CH(3)C(CH(2)PPh(2))(3)], is known to activate two dihydrogen molecules and produce the bis(mu-hydrosulfido) product [(triphos)(H)Rh(mu-SH)(2)Rh(H)(triphos)](2+), 2 (modeled as 2b), from which 1 is reversibly obtained. The possible steps of the process have been investigated with DFT calculations. It has been found that each d(6) metal ion in 1c, with local square pyramidal geometry, is able to anchor one H(2) molecule in the side-on coordination. The step is followed by heterolytic splitting of the H-H bond over one adjacent and polarized Rh-S linkage. The process may be completed before the second H(2) molecule is added. Alternatively, both H(2) molecules are trapped by the Rh(2)S(2) core before being split in two distinct steps. Since the ambiguity could not be solved by calculations, (31)P and (1)H NMR experiments, including para-hydrogen techniques, have been performed to identify the actual pathway. In no case is there experimental evidence for any Rh-(eta(2)-H(2)) adduct, probably due to its very short lifetime. Conversely, (1)H NMR analysis of the hydride region indicates only one reaction intermediate which corresponds to the monohydride-mu-hydrosulfide complex [(triphos)Rh(H)(mu-SH)(mu-S)Rh(triphos)](2+) (3) (model 5a). This excludes the second hypothesized pathway. From an energetic viewpoint the computational results support the feasibility of the whole process. In fact, the highest energy for H(2) activation is 8.6 kcal mol(-1), while a larger but still surmountable barrier of 34.6 kcal mol(-1) is in line with the reversibility of the process. 相似文献
993.
Guldi DM Holzinger M Hirsch A Georgakilas V Prato M 《Chemical communications (Cambridge, England)》2003,(10):1130-1131
A variety of single-wall carbon nanotube samples were tested in steady-state and time-resolved emission experiments, where it was found that chemical functionalization and different degrees of oxidation affect the emission behavior. 相似文献
994.
C. Maurizio F. d'Acapito M. Benfatto S. Mobilio E. Cattaruzza F. Gonella 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(2):211-216
We present an X-ray absorption near edge structure (XANES) study on Cu+ and Cu2+ ions in silicate glasses at the Cu K-edge, aimed to determine the geometry of the local structure around the metal. This
study is based on the comparison between experimental data and theoretical calculations made in the framework of multiple
scattering theory. The XANES signals relative to several clusters are simulated on the basis of known crystalline structures
involving Cu+ and Cu2+ ions in silicate matrices. Concerning the Cu2+ in glass, the simulations suggest the presence of a square coordination of oxygen atoms around the absorber, with a possible
presence of metal ions in the second shell. As for the Cu+ ions, the metal clustering is excluded and a linear O-Cu-O coordination is evidenced.
Received 30 April 1999 相似文献
995.
Dr. Carlo Ciarrocchi Prof. Luigi Fabbrizzi Prof. Maurizio Licchelli Prof. Angelo Taglietti 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(26):e202200462
A radical anion −NO2.− is formed upon an electrochemically reversible one-electron reduction of the square-planar NiII complex of N-nitrobenzylcyclam. The −NO2.− group goes to occupy an axial position of the metal ion, thus establishing a significant electronic interaction with the metal center. In particular, the ESR spectrum supports the occurrence of an electron transfer from −NO2.− to the metal, which therefore presents a significant NiI character. On re-oxidation, the nitrobenzyl side chain detaches and the NiII complex is restored, providing an example of a fully reversible redox driven intramolecular motion. 相似文献
996.
Dr. Ivana Miletto Dr. Marta Meazza Dr. Geo Paul Prof. Maurizio Cossi Prof. Enrica Gianotti Prof. Leonardo Marchese Dr. Ramon Rios Prof. Marc Pera-Titus Prof. Robert Raja 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(72):e202202771
A designed N-heterocyclic carbene (NHC) catalyst was covalently anchored on a range of mesoporous and hierarchical supports, to study the influence of pore size in the benzoin condensation of furfural. The structural and spectroscopic characteristics of the anchored catalysts were investigated, also with the help of molecular dynamics simulations, in order to rationalize the degree of stability and recyclability of the heterogenized organocatalysts. Quantitative yields (99 %) and complete recyclability were maintained after several cycles, vindicating the design rationale. 相似文献
997.
Maurizio Pandolfi 《Meccanica》1967,2(4):209-212
Summary The velocity field in an axial multistage turbomachinery is easily investigated, ignoring the fluid viscosity and compressibility, by means of the actuator disc theory. By developing this theory, general expressions of fluid velocity in such a machine are obtained, these in turn yield the approximate expressions usually given in the literature.
Sommario Lo studio del campo di moto in una turbomacchina a più stadi puramente assiale per fluido inviscido ed incomprimibile viene sviluppato in modo agevole mediante la teoria del disco attuatore. Nella presente nota vengono ricavate, sviluppando tale teoria, le espressioni generali delle velocità del fluido in una tale macchina e da queste vengono derivate successivamente le espressioni approssimate comunemente riportate nella bibliografia a proposito.相似文献
998.
Cristian Marchioli Maurizio Picciotto Alfredo Soldati 《International Journal of Multiphase Flow》2007
The present study reports detailed statistics for velocity and transfer rates of heavy particles dispersed in turbulent boundary layers. Statistics have been extracted from a homogeneous source of data covering a large target parameter space and are used here to analyze the effects of gravity and lift on particle dispersion and deposition in a systematic way. Datasets were obtained performing Direct Numerical Simulation (DNS) of particle-laden turbulent upward/downward flow in a vertical channel. Six values for the particle timescale (the particle Stokes number, St) ranging three orders of magnitude were considered to analyze the deposition process as the controlling mechanism was shifting from turbulent diffusion to inertia-moderated crossing trajectories. For the particle timescales examined, gravity and lift do not influence the qualitative behavior of particles even though velocity profiles and deposition coefficients are modified in a non-monotonic fashion, reaching an optimum for St ? 15. Physical mechanisms for the different behavior are discussed. Raw data and statistics obtained from the present DNS are made available at http://cfd.cineca.it (mirror site: http://158.110.32.35/download/database) and can be used to test simple models and closure equations for multiphase RANS and Large Eddy simulations. 相似文献
999.
Maurizio Romeo 《Meccanica》1992,27(4):275-280
The reflection of an acoustic beam onto a fluid-solid interface is studied under the assumption that the solid medium is viscoelastic. The incident beam is represented as a superposition of plane monochromatic homogeneous waves and its profile is assumed to be Gaussian shaped. The outcoming wave field at the interface, and away from it in the fluid, is numerically calculated for different values of the frequency and of the beam width.
Sommario Si studia la riflessione di un fascio di onde acustiche sulla superficie di separazione fra un liquido ed un solido nell'ipotesi che il mezzo solido sia viscoelastico. Il fascio incidente ha un profilo gaussiano e viene rappresentato mediante la sovrapposizione di onde piane monocromatiche omogenee. Si calcola numericamente il profilo del fascio riflesso sia sull'interfaccia, sia lontano da essa nel fluido, per diversi valori della frequenza e della larghezza del fascio.相似文献
1000.
Donatella Nardiello Carmen PalermoAnna Natale Maurizio QuintoDiego Centonze 《Analytica chimica acta》2015
In this work, the application of a new pulsed amperometric detection (PAD) waveform at a glassy carbon electrode, operating in typical chromatographic mobile phases, is proposed for the sensitive and reproducible determination of arylethanolaminic and phenolic moiety based compounds (e.g. beta-agonists and polyphenols). Preliminary experiments by cyclic voltammetry were carried out to investigate the electrochemical behaviour and to select the detection and cleaning electrode potentials. The proposed potential-time profile was designed to prevent the carbon electrode fouling under repeated analyses, thus ensuring a reproducible and sensitive quantitative determination, without the need of any mechanical or chemical electrode cleaning procedure. The waveform electrochemical parameters, including detection and delay times, were optimized in terms of sensitivity, limit of detection and response stability. The optimized waveform allowed the sensitive and stable detection of model compounds, such as clenbuterol and caffeic acid, that showed detection limits of 0.1 μg L−1 and 14 μg L−1, quantification limits of 0.4 μg L−1 and 46 μg L−1, and linearity up to 100 μg L−1 (r = 0.9993) and 10 mg L−1 (r = 0.9998), respectively. Similar results were obtained for other compounds of the same classes, with precision values under repeatability conditions ranging from 3.0 to 5.9%. The proposed method can be then considered as an excellent alternative to the post-column detection of beta-agonists, phenols and polyphenols. 相似文献