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991.
Stir bar sorptive extraction for the analysis of wine cork taint 总被引:1,自引:0,他引:1
Zalacain A Alonso GL Lorenzo C Iñiguez M Salinas MR 《Journal of chromatography. A》2004,1033(1):173-178
A magnetic stir bar with a polydimethylsiloxane coating was used to absorb 2,4,6-trichloroanisole, 2,3,4,5-tetrachloroanisole, pentachloroanisole and their respective phenols from synthetic and real wine samples. The stir bar sorptive extraction method was optimised to obtain the best extraction conditions in terms of temperature, time, pH and NaCl addition. The stir bar was desorbed in a thermal desorption system coupled to a gas chromatograph-mass spectrometer. The method proposed showed good linearity over the concentration range tested and correlation coefficients ranged from 0.96 to 0.99 for all the analytes. The reproducibility and repeatability of the method was estimated between 1.29 and 4.02%. With no a pre-concentration step and with a much reduced analysis time, all the analyzed compounds showed detection and quantification limits that were lower than those observed with other methods found in the bibliography. Except for pentachlorophenol due to its poor absorptivity in polydimethysiloxane, in red wines, LOD ranged between 7.56 and 61.56 pg/l, and LOQ ranged between 17.21 and 205.11 pg/l; while in white wines, the LOD ranged between 5.82 and 30.50 pg/l and LOQ ranged between 19.41 and 101.61 pg/l. These concentrations were always lower than their respective olfactory thresholds values. 相似文献
992.
Luca Vergnani Dr. Anne‐Laure Barra Dr. Petr Neugebauer Dr. Maria Jesus Rodriguez‐Douton Prof. Dr. Roberta Sessoli Dr. Lorenzo Sorace Prof. Dr. Wolfgang Wernsdorfer Prof. Dr. Andrea Cornia 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(11):3390-3398
Polynuclear single‐molecule magnets (SMMs) were diluted in a diamagnetic crystal lattice to afford arrays of independent and iso‐oriented magnetic units. Crystalline solid solutions of an Fe4 SMM and its Ga4 analogue were prepared with no metal scrambling for Fe4 molar fractions x down to 0.01. According to high‐frequency EPR and magnetic measurements, the guest SMM species have the same total spin (S=5), anisotropy, and high‐temperature spin dynamics found in the pure Fe4 phase. However, suppression of intermolecular magnetic interactions affects magnetic relaxation at low temperature (40 mK), where quantum tunneling (QT) of the magnetization dominates. When a magnetic field is applied along the easy magnetic axis, both pure and diluted (x=0.01) phases display pronounced steps at evenly spaced field values in their hysteresis loops due to resonant QT. The pure Fe4 phase exhibits additional steps which are firmly ascribed to two‐molecule QT transitions. Studies on the field‐dependent relaxation rate showed that the zero‐field resonance sharpens by a factor of five and shifts from about 8 mT to exactly zero field on dilution, in agreement with the calculated variation of dipolar interactions. The tunneling efficiency also changes significantly as a function of Fe4 concentration: the zero‐field resonance is significantly enhanced on dilution, while tunneling at ±0.45 T becomes less efficient. These changes were rationalized on the basis of a dipolar shuffling mechanism and transverse dipolar fields, whose effect was analyzed by using a multispin model. Our findings directly prove the impact of intermolecular magnetic couplings on SMM behavior and disclose the magnetic response of truly isolated giant spins in a diamagnetic crystalline environment. 相似文献
993.
María de la Gala Morales Mª Rosario Palomo Marín Lorenzo Calvo Blázquez Eduardo Pinilla Gil 《Electroanalysis》2012,24(5):1170-1177
The bismuth bulk electrode is proposed here for the first time in the rotating configuration (BiB‐RDE) as the electrode of choice for voltammetric analysis of selected heavy metal ions. Optimization of chemical and instrumental parameters was carried out to develop a reliable and convenient method for the determination of Zn(II), Cd(II) and Pb(II) by SWASV. Appropriate detection limits were found for environmental monitoring applications in the medium – low µg/L range. The method was validated for Pb(II) determination by certified reference materials. Successful application to the determination of Pb(II) in samples of fortified rainwater and sewage sludge from a steel industry is described. 相似文献
994.
Emma Chiavaro Lorenzo Cerretani Maria Paciulli Stefano Vecchio 《Journal of Thermal Analysis and Calorimetry》2012,108(2):799-806
In this study, accelerated storage tests were carried out at 60 °C up to 20 weeks on three extra virgin olive oils (Evoos)
with different total phenol contents and fatty acid compositions (named as EvooA, EvooB, and EvooC). Their oxidative statuses,
evaluated by means of primary oxidation value and total phenolic content, were related to both the shapes of differential
scanning calorimetry (DSC) cooling curves and thermal properties. DSC cooling curves were all deconvoluted as crystallization
occurs in a quite narrow range, and the single steps are not well separated. The first deconvoluted DSC peak for the three
samples tested, which occurs in the temperature interval between −45 °C and −30 °C, can probably be ascribable to the crystallization
of tri-unsaturated triacylglycerols. A non-isothermal crystallization kinetic procedure, derived by the well-known isothermal
Avrami equation, combined with the method of Ozawa, was applied to the first deconvoluted DSC peak only by processing the
data related to this DSC peak. Results of the modified Avrami method were found in agreement with those of the Ozawa method.
In particular, Avrami and Ozawa's exponents lie from 2 to 4 (being those of fresh samples always lower than those subjected
to the accelerated oxidation test). Crystallization is relatively slow for fresh samples whereas after the first 4 weeks;
it occurs faster in EvooB and EvooC. 相似文献
995.
Aragoni MC Arca M Demartin F Devillanova FA Isaia F Garau A Lippolis V Jalali F Papke U Shamsipur M Tei L Yari A Verani G 《Inorganic chemistry》2002,41(25):6623-6632
The macrocycles L(1)-L(3) incorporating N(2)S(3)-, N(2)S(2)O-, and N(2)S(2)-donor sets, respectively, and containing the 1,10-phenanthroline unit interact in acetonitrile solution with heavy metal ions such as Pb(II), Cd(II), and Hg(II) to give 1:1 ML, 1:2 ML(2), and 2:1 M(2)L complex species, which specifically modulate the photochemical properties of the ligands. The stoichiometry of the complex species formed during spectrofluorometric titrations and their formation constants in MeCN at 25 degrees C were determined from fluorescence vs M(II)/L molar ratio data. The complexes [Pb(L(1))][ClO(4)](2).(1)/(2)H(2)O (1), [Pb(L(2))][ClO(4)](2).MeNO(2) (1a), [Pb(L(3))(2)][ClO(4)](2).2MeCN (1b), and [Cd(L(3))][NO(3)](2) (2b) were also characterized by X-ray diffraction studies. The conformation adopted by L(1)-L(3) in these species reveals the aliphatic portion of the rings folded over the plane containing the heteroaromatic moiety with the ligands trying to encapsulate the metal center within their cavity. In 1, 1a, and 2b the metal ion completes the coordination sphere by interacting with counteranion units and solvent molecules. On the contrary, the 1:2 complex 1b shows Pb(II) sandwiched between two symmetry-related molecules of L(3) reaching an overall [4N + 4S] eight-coordination. 相似文献
996.
Manfredo Hrner Lorenzo do C. Visentin Marisa Dahmer Jairo Bordinhao 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(5):m286-m287
In the title complex, [Pd(C12H8FN4O2)2(C5H5N)2] or trans‐[Pd(FC6H4N=N—NC6H4NO2)(C5H5N)2], the Pd atom lies on a centre of inversion in space group P. The coordination geometry about the Pd2+ ion is square planar, with two deprotonated 3‐(2‐fluorophenyl)‐1‐(4‐nitrophenyl)triazenide ions, FC6H4N=N—NC6H4NO2?, acting as monodentate ligands (two‐electron donors), while two neutral pyridine molecules complete the metal coordination sphere. The whole triazenide ligand is not planar, with the largest interplanar angle being 16.8 (5)° between the phenyl ring of the 2‐fluorophenyl group and the plane defined by the N=N—N moiety. The Pd—N(triazenide) and Pd—N(pyridine) distances are 2.021 (3) and 2.039 (3) Å, respectively. 相似文献
997.
Carmona D Ferrer J Lorenzo M Santander M Ponz S Lahoz FJ López JA Oro LA 《Chemical communications (Cambridge, England)》2002,(8):870-871
The iridium complex [Ir(mu-Cl)(PN)(PPh3)]2 (1) reacts with H2 affording only the kinetic isomer OC-6-55-C of the dihydride [IrClH2(PN)(PPh3)] (2) and with methanol yielding, also exclusively, the thermodynamic isomer OC-6-53-C (2b) of the same dihydride; complex 2b has been characterised by X-ray diffractometric methods. 相似文献
998.
999.
Dr. Matthieu Autillo Laetitia Guerin Dr. Thomas Dumas Dr. Mikhail S. Grigoriev Dr. Alexandre M. Fedoseev Sebastiano Cammelli Pier Lorenzo Solari Dr. Dominique Guillaumont Dr. Philippe Guilbaud Dr. Philippe Moisy Dr. Hélène Bolvin Dr. Claude Berthon 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(17):4435-4451
The magnetic properties of LnIII and AnIII complexes formed with dipicolinate ligands have been studied by NMR spectroscopy. To know precisely the geometries of these complexes, a crystallographic study by single-crystal X-ray diffraction (XRD) and extended X-ray absorption fine structure (EXAFS) in solution was performed. Several methods to separate the paramagnetic shifts observed in the NMR spectra were applied to these complexes. Methods using a number of nuclei of the dipicolinate ligands revealed an abrupt change in the geometries of the complexes and a metal–ligand interaction in the middle of the lanthanide series. A study of the variation of the paramagnetic shifts with temperature demonstrated that higher-order terms of the dipolar and contact contributions are required, especially for the lightest LnIII and almost all the studied AnIII. Bleaney's parameters <Sz>a and relating to the contact and dipolar terms, respectively, were deduced from experimental data and compared with the results of ab initio calculations. Quite a good agreement was found for the temperature dependencies of <Sz>a and . However, the values obtained from cation magnetic anisotropy calculations showed some discrepancies with the values derived from Bleaney's equation defined for LnIII. Other parameters, such as the crystal field parameter and the hyperfine constants Fi obtained from the experimental data of the [An(ethyl-dpa)3]3− complexes (ethyl-dpa=4-ethyl-2,6-dipicolinic acid), are at odds with the assumptions underlying Bleaney's theory. 相似文献
1000.