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141.
Dugo P Herrero M Kumm T Giuffrida D Dugo G Mondello L 《Journal of chromatography. A》2008,1189(1-2):196-206
In the present work, a novel strategy including the use of two different comprehensive HPLC methods has been employed to study the whole carotenoid composition of mandarin essential oil. Thus, two different fully orthogonal two-dimensional HPLC methods have been used. A silica microbore column was coupled to a C(18) monolithic column to study the mandarin saponified extract, while the coupling of a cyano microbore column to a C(18) monolithic column was employed to study the intact mandarin essential oil sample in order to characterize the native carotenoid esters composition. Detection was performed by connecting a photodiode array detection (DAD) system in parallel with a MS detection system operated with an atmospheric pressure chemical ionization (APCI) interface. Thus, the carotenoid identification was carried out by combining the information provided by the DAD and MS systems and the peaks relative position in the two-dimensional chromatograms. 相似文献
142.
P. Rodríguez E. Herrero J. Solla-Gullón J. M. Feliu A. Aldaz 《Journal of Solid State Electrochemistry》2008,12(5):575-581
The reduction of acetaldehyde oxime (AO) in acid medium on platinum surfaces is a structure sensitive reaction that takes
place almost exclusively on (111) sites of Pt electrodes, and it is strongly inhibited on Pt(100) and Pt(110) surfaces. A
study using stepped electrodes with (111) terraces and monoatomic steps either with (100) and (110) orientation shows that
the activity of the electrode is also dependent on the terrace width, i.e., the wider the terrace is, the higher current density
is recorded and the more positive the peak potential for AO reduction appears. Moreover, in the electrodes with (100) step
sites, the reduction process appears at more negative potential than the electrodes with (111) step sites. Nanoparticles with
some preferential orientations were also tested for the AO reduction reaction to check the presence of (111) ordered domains
on the nanoparticles surface.
Dedicated to Teresa Iwasita on the occasion of her retirement and for her contributions to Electrochemistry. 相似文献
143.
Juan José Baeza‐Baeza Virginia Bernabé‐Zafón José Manuel Herrero‐Martínez Ernesto F. Simó‐Alfonso 《Electrophoresis》2010,31(6):1003-1010
A theoretical study on the retention behaviour and chromatographic performance of neutral solutes using a lauryl methacrylate‐based monolithic column under voltage gradient mode in CEC was carried out. Through a flexible mathematical function based on a modified Gaussian model, the peak shape of compounds was firstly fitted under constant and gradient voltage. Using the peak shape parameters and retention time, the estimation of global chromatographic performance, efficiency and peak capacity under several voltage conditions was performed. The influence of voltage gradient on the separation efficiency is discussed and simple equations are presented to calculate retention and peak widths under voltage gradient conditions. A comparison in terms of chromatographic performance of a test mixture of neutral solutes under constant and gradient voltage modes was also carried out. The experiments carried out under gradient voltage showed better efficiencies (172 000 plates/m) and lower peak widths than those obtained under constant voltage (52 000 plates/m). 相似文献
144.
Mohammad‐Reza Azani Dr. Alejandro Pérez Paz Cristina Hermosa Dr. Gonzalo Givaja Prof. Dr. Julio Gómez‐Herrero Dr. Rubén Mas‐Ballesté Dr. Felix Zamora Prof. Angel Rubio 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(46):15518-15529
Herein, we provide a systematic theoretical and experimental study of the structural and optical properties of MMX (M=metal, X=halide) chains. The influence of solvent, temperature, and concentration has been analyzed to find suitable parameters for initial building‐block associations in solution. By using density functional calculations, we have computed the dissociation energy of different MMX oligomers (up to the tetramer) in the gas phase. On the basis of these findings, we discuss the most likely disassembly scenario and propose a new interpretation of these compounds. We also calculated the charge redistribution that occurs upon MM+XMMX binding in vacuum. Time‐dependent density functional theory (TDDFT) is used to calculate the UV/visible spectra of different MMX chains up to the tetramer in the gas phase. The implications of these theoretical findings in the analysis of our experiments are discussed in the text. The overall body of data presented suggests a new way of looking at such linear structures. By taking into account these new data, we have been able to isolate single/few MMX chains on mica. 相似文献
145.
Exploring Excited‐State Tunability in Luminescent Tris‐cyclometalated Platinum(IV) Complexes: Synthesis of Heteroleptic Derivatives and Computational Calculations 下载免费PDF全文
Fabio Juliá Dr. Gabriel Aullón Dr. Delia Bautista Dr. Pablo González‐Herrero 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(52):17346-17359
The synthesis, structure, electrochemistry, and photophysical properties of a series of heteroleptic tris‐ cyclometalated PtIV complexes are reported. The complexes mer‐[Pt(C^N)2(C′^N′)]OTf, with C^N=C‐deprotonated 2‐(2,4‐difluorophenyl)pyridine (dfppy) or 2‐phenylpyridine (ppy), and C′^N′=C‐deprotonated 2‐(2‐thienyl)pyridine (thpy) or 1‐phenylisoquinoline (piq), were obtained by reacting bis‐ cyclometalated precursors [Pt(C^N)2Cl2] with AgOTf (2 equiv) and an excess of the N′^C′H pro‐ligand. The complex mer‐[Pt(dfppy)2(ppy)]OTf was obtained analogously and photoisomerized to its fac counterpart. The new complexes display long‐lived luminescence at room temperature in the blue to orange color range. The emitting states involve electronic transitions almost exclusively localized on the ligand with the lowest π–π* energy gap and have very little metal character. DFT and time‐dependent DFT (TD‐DFT) calculations on mer‐[Pt(ppy)2(C′^N′)]+ (C′^N′=thpy, piq) and mer/fac‐[Pt(ppy)3]+ support this assignment and provide a basis for the understanding of the luminescence of tris‐cyclometalated PtIV complexes. Excited states of LMCT character may become thermally accessible from the emitting state in the mer isomers containing dfppy or ppy as chromophoric ligands, leading to strong nonradiative deactivation. This effect does not operate in the fac isomers or the mer complexes containing thpy or piq, for which nonradiative deactivation originates mainly from vibrational coupling to the ground state. 相似文献
146.
Andrés Guerrero Rebeca Herrero Esther Quintanilla Dr. Juan Z. Dávalos Dr. José‐Luis M. Abboud Prof. Dr. Pedro B. Coto Dr. Dieter Lenoir Prof. Dr. 《Chemphyschem》2010,11(3):713-721
We show that the radical cations of adamantane (C10H16.+, 1 H.+) and perdeuteroadamantane (C10D16.+, 1 D.+) are stable species in the gas phase. The radical cation of adamantylideneadamantane (C20H28.+, 2 H.+) is also stable (as in solution). By using the natural 13C abundances of the ions, we determine the rate constants for the reversible isergonic single‐electron transfer (SET) processes involving the dyads 1 H.+/ 1 H, 1 D.+/ 1 D and 2 H.+/ 2 H. Rate constants for the reaction 1 H.++ 1 D? 1 H+ 1 D.+ are also determined and Marcus’ cross‐term equation is shown to hold in this case. The rate constants for the isergonic processes are extremely high, practically collision‐controlled. Ab initio computations of the electronic coupling (HDA) and the reorganization energy (λ) allow rationalization of the mechanism of the process and give insights into the possible role of intermediate complexes in the reaction mechanism. 相似文献
147.
148.
A new approach to the multivariate sensitivity concept based on the determination of the capability of discrimination of a method of analysis is shown. Thus the analytical sensitivity is defined in this work by the analyte concentration that a analytical method is able to discriminate, which implies the estimation of the ‘false noncompliance’ and ‘false compliance’. In this approach the estimation of the multivariate analytical sensitivity is independent of scale factors and calibration models, and allows one to study the behavior of a analytical method for several concentrations and matrix. The estimation of this parameter in the simultaneous determination of selenium, copper, lead and cadmium by stripping voltammetry when using soft calibration is carried out, showing that different multivariate analytical sensitivities are obtained for each metal. 相似文献
149.
Fernandez-Torre D Escribano R Herrero VJ Maté B Moreno MA Ortega IK 《The journal of physical chemistry. B》2005,109(38):18010-18017
The theoretical infrared refractive indices of two systems related to atmospheric research, nitric acid (NA) and nitric acid monohydrate (NAM) crystals, have been computed using a methodology based on first-principles. The effects of lack of coherence in the infrared beam in RAIR and transmission spectra have also been treated using a model based on classical optics. The optical constants of NA crystals are presented for the first time; the results on NAM are compared to empirical values previously published with good general agreement. With the optical constants of NA, polarized reflection-absorption infrared spectra are predicted and compared to experimental spectra recorded also for the first time, for a set of varying film thickness. The global agreement is satisfactory. The effects of a number of experimental factors in transmission spectra of NAM are assessed, in an attempt to explain observed differences among experimental spectra. It is concluded that the spectral disparities are probably due to differences in the nature of the samples. 相似文献
150.
Simó C Herrero M Neusüss C Pelzing M Kenndler E Barbas C Ibáñez E Cifuentes A 《Electrophoresis》2005,26(13):2674-2683
In this work, a new capillary electrophoresis-mass spectrometry (CE-MS) procedure is developed to analyze proteins in Spirulina platensis microalgae. It is demonstrated that a fine optimization of several separation parameters is essential in order to achieve suitable CE-MS analysis of these proteins in natural extracts from microalgae. Namely, optimization of the composition of the separation buffer, electrospray conditions, and washing routine between runs are required in order to obtain reliable and reproducible CE-MS analyses of the main proteins found in this microalga (namely, allophycocyanin-alpha chain, allophycocyanin-beta, c-phycocyanin-alpha, and c-phycocyanin-beta). The relative molecular mass of these biopolymers is determined using two different MS instruments coupled to CE, i.e., CE-ion trap-MS and CE-time of flight-MS (CE-TOF-MS). A comparison between the results obtained with both instruments is carried out. The high resolution of the TOF-MS enables the distinction of small modifications in proteins and, thus, a more accurate mass determination. Interestingly, molecular mass values obtained by both CE-MS procedures agree very well while these experimental values are only in partial agreement with those theoretically expected (i.e., genetically derived masses). Some protein modifications due to amino acids exchange induced by nucleotide codon mutations are proposed to explain this difference. 相似文献