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991.
César Ricardo Teixeira Tarley Felipe Nascimento Andrade Fernanda Midori de Oliveira Marcela Zanetti Corazza Luiz Fernando Mendes de Azevedo Mariana Gava Segatelli 《Analytica chimica acta》2011,(2):145
A novel ion imprinted polyvinylimidazole-silica hybrid copolymer (IIHC) was synthesized and used as a selective solid sorbent for Pb2+ ions preconcentration using an on-line solid phase extraction (SPE) system coupled to TS-FF-AAS. The ionic hybrid sorbent was prepared using 1-vinylimidazole and 3-(trimethoxysilyl)propylmethacrylate as monomers, Pb2+ ions as template, tetraethoxysilane as reticulating agent and 2,2′-azobis-isobutyronitrile as initiator. The best on-line SPE conditions concerning sorption behavior, including sample pH (6.46), buffer concentration (9.0 mmol L−1), eluent (HNO3) concentration (0.5 mol L−1) and preconcentration flow rate (4.0 mL min−1), were optimized by means of full factorial design and Doehlert matrix. The analytical curve ranged from 2.5 to 65.0 μg L−1 (r = 0.999) with limit of detection of 0.75 μg L−1; the precision (repeatability) calculated as relative standard deviation (n = 10) was 5.0 and 3.6% for Pb2+ concentration of 10.0 and 60.0 μg L−1, respectively. From on-line breakthrough curve, column capacity was 3.5 mg g−1. Preconcentration factor (PF), consumptive index (CI) and concentration efficiency (CE) were 128.0, 0.16 mL and 25.6 min−1, respectively. The selective performance of the sorbent, based on relative selectivity coefficient, was compared to NIC (non imprinted copolymer) for the binary mixture Pb2+/Cd2+, Pb2+/Cu2+ and Pb2+/Zn2+. The results showed that ion imprinted polyvinylimidazole-silica hybrid polymer had higher selectivity for Pb2+ than NIC at 64.9, 16.0 and 8.8 folds. The developed method was successfully applied for highly sensitive and selective Pb2+ determination in different kinds of water samples, parenteral solutions and urine. Accuracy was also assessed by analyzing certified reference fish protein (DORM-3) and marine sediment (MESS-3 and PACS-2) with satisfactory results. 相似文献
992.
A liquid‐phase microextraction technique was developed using dispersive liquid‐liquid microextraction based on solidification of floating organic drop combined with flame atomic absorption spectrometry, for the extraction and determination of trace amounts of cobalt in water samples. Microextraction efficiency factors, such as the type and volume of extraction and dispersive solvents, pH, extraction time, the chelating agent amount, and ionic strength were investigated and optimized. Under optimum conditions, an enrichment factor of 160 was obtained from 10.0 mL of water sample. The calibration graph was linearin the range of 1.15‐110 μg L?1 with a detection limit of 0.35 μg L?1. The relative standard deviation for ten replicate measurements of 10 and 100 μg L?1 of cobalt were 3.26% and 2.57%, respectively. The proposed method was assessed through the analysis of certified reference water or recovery experiments. 相似文献
993.
We report for the first time, the synthesis of siloxane-imide co-polymers by the reaction of mixtures of 1,4-bis(aminobutyl)tetramethyldisiloxane (ABTMDS) and 1,3-bis(4-aminophenoxy)benzene (TPE-R) with bisphenol A diphthalic anhydride (BPADA) using water as the polymerization solvent. A series of co-polymers were prepared incorporating 10, 20, 40 and 100 mol% of ABTMDS with the aromatic diamine TPE-R as the co-monomer. The synthesized co-polymers showed number average molecular weights in the range of 25,000–60,000. As expected the glass transition temperatures (Tgs) and moduli of the polymers were found to decrease with increasing amounts of the siloxane monomer and the homo-polymer containing only the siloxane diamine showing the lowest Tg (60 °C). The resulting polymers could be solution cast into strong and flexible membranes which showed significant decreases in water absorption and moisture permeability compared to the control polymer without siloxane groups. The polymers were characterized by FTIR, 13C and 1H NMR, GPC, DSC and mechanical properties and structural comparisons were made with similar polymers made by standard solvent synthesis methods. Also cross-linked polymers were prepared by the reaction of ABTMDS with the aromatic homo-polymer control and their membrane properties were compared to those of the water synthesized siloxane co-polymers with a similar siloxane content. 相似文献
994.
Liquid phase microextraction applications in food analysis 总被引:2,自引:0,他引:2
Asensio-Ramos M Ravelo-Pérez LM González-Curbelo MÁ Hernández-Borges J 《Journal of chromatography. A》2011,1218(42):7415-7437
Over the last years, liquid-phase microextraction (LPME) in its different application modes (single drop microextraction, dispersive liquid-liquid microextraction and hollow fiber-LPME) has been increasingly applied for the extraction of both inorganic and organic analytes from different matrices. Its advantages over conventional extraction procedures (simplicity, effectiveness, rapidity and low consumption of organic solvents) has also attracted its application in the complex food analysis field, in which it has clearly provided good and challenging results. A comprehensive review dealing with those articles published since its introduction till the end of March 2011 is presented, offering also a critical vision of the analytical potential of LPME for the analysis of foods. 相似文献
995.
On the basis of optimized structures of two kinds thiophene oligomers, we investigated the configuration and conformation dependent optical and electronic properties of α or β substituted oligothiophene (PT) and oligo(thienylenevinylene) (PTV) isomers, respectively, at the TD‐DFT/6‐31+G(d,p)//PBE0/6‐31G(d) level. The corresponding properties of polymers were predicted by extrapolation method. The broad absorption regions for polythiophene and/or poly(thienylenevinylene) can be ascribed to the coexistence of various conformational and/or configurational isomers with similar energies and each corresponding excited state possessing different absorption spectrum and overlapping each other. Furthermore, the reorganization energies for electron (λe) and hole (λh) of α or β substituted PTV and PT indicate them to be potential ambipolar charge transport materials under the proper operating conditions. Therefore, these results are important because they can provide a rational way for the design of multifunctional materials with broad absorption and ambipolar charge transport properties for solar cells devices. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011 相似文献
996.
Denis Jacquemin Julien Preat Eric A. Perpète Daniel P. Vercauteren Jean‐Marie André Ilaria Ciofini Carlo Adamo 《International journal of quantum chemistry》2011,111(15):4224-4240
Using time‐dependent density functional theory and the polarizable continuum model, we have simulated the absorption spectra of an extended series of azobenzene dyes. First, we have determined a theoretical level optimal for this important class of dyes, and it turned out that a C‐PCM‐CAM‐B3LYP/6‐311+G(d,p)//C‐PCM‐B3LYP/6‐311G(d,p) approach represents an effective compromise between chemical accuracy and computational cost. In a second stage, we have compared the theoretical and experimental transition energies for 46 n → π☆ and 141 π → π☆ excitations. For the full set, that spans over a 302–565 nm domain, we obtained a mean absolute deviation of 13 nm (0.10 eV) and a linear correlation coefficient of 0.95, illustrating the accuracy of our approach, though some significant outliers pertained. In a last step, the impact of several modifications, that is, trans/cis isomerization, variation of the acidity of the medium and azo/hydrazo tautomerism have been modeled with two functionals. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 相似文献
997.
Mahadevappa Naganathappa Ajay Chaudhari 《International journal of quantum chemistry》2011,111(9):2064-2071
We present theoretical vibrational and absorption spectra of aminoacetonitrile, its cation, anion, cyanoprotonated, and aminoprotonated aminoacetonitrile. We used second‐order Moller–Plesset perturbation method (MP2) with TZVP basis set to obtain ground state geometries and vibrational spectra. Time dependent density functional theory method was used to obtain absorption spectra. Shifts in vibrational modes for aminoacetonitrile upon ionization and protonation are determined. The C≡N stretching mode which is the most important mode in detection of nitriles in space is more intense in aminoacetonitrile ions and its two protonated form and is less IR active for neutral aminoacetonitrile. The nature of electronic transition for these molecules is identified. All the electronic transitions for neutral aminoacetonitrile and its cation are the σ → σ* electronic transitions, whereas its anion and protonated aminoacetonitrile display the σ → σ* as well as π → π* transitions. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011 相似文献
998.
The title compound, 1′,3′-dihydrospiro[fluorene-9,2′-perimidine] has been synthesized and characterized by NMR, ESI-MS, IR, elemental analysis, UV–vis and fluorescence spectroscopy. The crystal structures of the title compound and its co-crsytal with 9-fluorenone have also been determined by X-ray single crystal diffraction. Density functional theory (DFT) calculations and vibrational frequencies have been performed at B3LYP/6-31G* level. The comparisons between the experimental vibrational frequencies and the predicted data show that B3LYP/6-31G* method can simulate the IR of the title compound on the whole. The theoretical electronic absorption spectra have been calculated by using TD-DFT method and compared with the experimental result. The solid-fluorescence determination of the title compound reveals two emission bans at 430 and 590 nm while its co-crystal reveals only one emission band at 590 nm. 相似文献
999.
1000.