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991.
M. V. L. Fook A. G. Souza M. F. S. Trindade M. M. Conceiçăo J. C. O. Santos S. Prasad V. J. Fernandes Jr. S. C. L Crispim 《Journal of Thermal Analysis and Calorimetry》2004,75(2):513-520
The high-density polyethylene, thermoplastic widely-used in the production of industrial domestic utilities, was collected
in two situations: virgin high-density polyethylene (JV 060) and post-consumption high-density polyethylene (with features
of low-density polyethylene). After collecting the samples, they were submitted to natural aging with the quantification of
the incident solar radiation for 180 days. The samples were characterized by melt flow index, differential scanning calorimetry,
tensile strength, rupture load, elongation at break and infrared. The results showed that after 180 days of exposure the virgin
high-density polyethylene presented physical properties similar to the post-consumption polyethylene.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
992.
A method for the determination of trace amounts of arsenic in food samples using flow injection analysis and atomic absorption spectrometry with hydride generation (FI-HG AAS) was developed. The parameters of the flow injection system and the hydride generation were optimized with respect to reagent concentrations, atomization temperature, injection volume, reaction coil length and carrier flow rate. The limits of detection and quantification were 0.34µgL–1 and 1.2µgL–:1, respectively, and the analytical curve is linear up to 30.0µgL–1 arsenic. The relative standard deviation for 12 replicates varies between 5% for 4.0µgL–1 As and 1.8% for 30.0µgL–1 As, with an injection frequency of up to 135h–1. Interferences from Ni(II), Cu(II), Fe(III), Cr(III), Mo(II), Bi(III), Se(IV), Se(VI), Sb(III) and Sb(V) could be masked with a mixture of ascorbic acid-KI in a 5.0molL–1 HCl solution. The accuracy of the proposed method was evaluated by using certified reference materials of biological samples, and the method was used to determine the content of arsenic in fish and coffee beans. 相似文献
993.
A flow injection analysis (FIA) system for the determination of histamine was developed using histamine dehydrogenase (HmDH)-based electrode. Histamine dehydrogenase was immobilized in an osmium-derivatized redox polymer, poly(1-vinylimidazole) complexed with Os(4,4′-dimethylbipyridine)2Cl2 (PVI-dmeOs), film on a glassy carbon electrode. As expected from the characteristics of this enzyme in a solution, this electrode exhibits high selectivity to histamine and is not sensitive to other primary amines including common biogenic amines, putrescine, cadaverine and tyramine. The detection limit for histamine was 100 pmol ( μl injection) at a S/N ratio of 3, and response linearity was retained up to 0.6 mM. The FIA system was successfully applied to the determination of histamine in fish samples. The performance of the FIA system is discussed and compared with a high-performance liquid chromatography (HPLC) method which is routinely used for histamine analysis. 相似文献
994.
A time-based flow injection (FI) separation pre-concentration system coupled to an electrothermal atomic absorption spectrometer (graphite furnace) has been developed for the direct ultra-trace determination of selenite and selenate in drinking water. The pre-concentration of both forms of selenium is carried out onto a micro-column packed with an anionic resin (Dowex 1X8) that is placed in the robotic arm of the autosampling device. Selenite and selenate are sequentially eluted with HCl 0.1 M and HCl 4 M, respectively. The interference of large quantities of chloride during selenium atomisation is prevented by using iridium as a “permanent” chemical modifier. The features of the pre-concentration separation system for both species are: 53% efficiency of retention and an enhancement factor of 82 for a pre-concentration time of 180 s (sample flow rate=3 ml min−1) with HCl elution volumes of 100 μl. The detection limit (3 s) is 10 ng l−1 for the two species and the relative standard deviation (n=10) at the 200 ng l−1 level is 3.5% for selenite and 5.6% for selenate. The addition of selenite and selenate stock standard solutions to tap water samples yields a 97-103% recovery of both species. 相似文献
995.
A flow-injection analysis atomic absorption spectrometric (FIA-AAS) method was developed for the determination of trace amounts of arsenic, selenium and mercury in a proposed estuarine sediment standard reference material (SRM 1646a). The samples were prepared in two manners: a) A wet digestion procedure with HNO3, H2SO4, and HClO4 using a reflux column and b) A microwave-oven digestion procedure utilizing HNO3, H2SO4, and HCl for As and Se, and HNO3 for Hg. Microwave-oven digestion provides results comparable to those found by reflux column digestion and reduces the sample preparation time by a factor of 10. The proposed method employing the microwave-oven digestion procedure coupled with FIA-AAS for As and Se, and FIA-CVAAS for Hg, has detection limits of 0.15 ng As/ml, O.17 ng Se/ml and 0.15 ng Hg/ml.On leave from the Defense Metallurgical Research Laboratory, Hyderabad, India 相似文献
996.
Emily C. Hernández Allan Witkowski Sylvia Daunert Leonidas G. Bachas 《Mikrochimica acta》1995,120(1-4):63-72
The present study explores the attractiveness of combining flow-injection (FI) with lead hydride generation atomic absorption spectrometry (AAS) to improve the selectivity and sensitivity of analysis. Lead hydride was generated in three acid-oxidant media: HNO3-(NH4)2S2O8, lactic acid-K2Cr2O7 and HNO3-H2O2. The effect of chemical parameters (acid-oxidant concentration and NaBH4 concentration) was investigated and the performance of each generation medium in terms of interferences, sensitivity and detection limits was compared with that obtained in batch mode. In all cases improved sensitivity (HNO3-H2O2, 0.8 ng Pb; lactic acid-K2Cr2O7, 0.2 ng Pb; (NH4)2S2O8-HNO3, 4ng Pb) was obtained, most notably in HNO3-H2O2, which provided 12 times higher sensitivity than in batch mode and sharper absorption peaks. Furthermore, interference by Cu and Ni was lower in the proposed FI-HG system. Compared with the batch mode, about 10 to 100 times higher concentrations of interferent are tolerated in the sample. The use of FI also allows work at a lower NaBH4 concentration. The method was applied to the determination of lead in water samples with a sampling frequency of 180 samples per hour. In terms of both sensitivity and freedom from interferences, lactic acid-K2Cr2O7 was the best of the generation media tested.On leave from the School of Environmental Studies, Jadavpur University, Calcutta 700032, India 相似文献
997.
A flow injection chemiluminescence method was described for the determination of four phenothiazine drugs, namely, chlorpromazine hydrochloride, perphenazine hydrochloride, fluphenazine hydrochloride and thioridazine hydrochloride. Strong Chemiluminescence (CL) signal was produced when above-mentioned drug was injected into the mixed stream of luminol with KMnO4. The linear ranges of the method were 0.0020-1.0 μg/mL chlorpromazine hydrochloride, 0.0040-3.0 μg/mL perphenazine hydrochloride, 0.0020-5.0 μg/mL fluphenazine hydrochloride and 0.0050-1.0 μg/mL thioridazine hydrochloride. The detection limits were 0.4 ng/mL chlorpromazine hydrochloride, 0.7 ng/mL perphenazine hydrochloride, 2 ng/mL fluphenazine hydrochloride and 0.7 ng/mL thioridazine hydrochloride. The proposed method was applied to the determination of chlorpromazine hydrochloride in injections and in mental patient's urine samples and the satisfactory results were achieved. The possible CL reaction mechanism was also discussed briefly. 相似文献
998.
Summary A new restricted access media (RAM) type of precolumn, Bio Trap 500 C18, for direct injection of plasma samples in column-switching systems was evaluated with respect to the elution of plasma proteins
in different mobile phases, the loading capacity of plasma samples, the chromatographic behavior during plasma injections
and protein contamination of the packing and sealings. More than 95% of plasma proteins could be excluded from the precolumn
within three minutes for all selected mobile phases. Quantitative analyte recoveries could be obtained by injecting plasma
samples ranging from 5 to 500 μL with the analyte mass>150 ng onto a BioTrap 500 C18 column (20×4 mm I.D.). One precolumn tolerated about 15 mL of plasma injection without out noticeable change in retention
and pressure. Clogging of the precolumn was encountered (≥45 mL of plasma) due mainly to the adsorption of proteins on the
packing. The performance of the analytical column (Kromasil C18) was also examined. The column efficiency decreased by 60% after processing 45 mL plasma in total. 相似文献
999.
A procedure is described for the quantitative determination of amino acids in hepatic and brain tissue samples from the rat. Because the presence of certain matrix components in the tissue material led to interference with chromatographic analysis they were removed by a prechromatographic “clean-up” step. Quantitative analysis of amino acids, as their N-heptafluorobutyryl iso-butyl ester derivatives, was achieved by high resolution gas chromatography on an apolar fused silica open tubular column. Reproducibility data from the complete procedure are presented; coefficients of variation for arginine and histidine in hepatic tissue varied between 7.1 and 10.1% whereas those for most other amino acids were better than 5%, with a mean recovery of 90%. 相似文献
1000.
The present work reports the first spectrofluorimetric gas-diffusion flow injection (GD-FI) assay for the determination of chlorine dioxide in water samples (tap, mineral and soda water). The method is based on the fluorescence quenching of chromotropic acid (CA) (λex. = 347 nm, λem. = 371 nm) caused by the analyte. The chemical and instrumental variables of the system were studied in terms of maximum sensitivity. The gas-diffusion cell was thermostated at 40 °C to enhance the vaporization of chlorine dioxide and thus the sensitivity of the method. The quenching effect of chlorine dioxide on CA was linear in the range 0.09-3.41 mg l− 1, while the precisions either close to the quantitation limit or near to the middle of the linear section of the calibration graph were satisfactory in both cases (sr = 2.6% and 1.5% (n = 10) at 0.17 and 1.71 mg l− 1 level, respectively). The developed method proved to be adequately selective and sensitive with 3σ limit of detection equal to cL = 0.03 mg l− 1. The application of the assay to spiked tap, mineral and soda water samples yielded accurate results with recovery values in the range 94.1-105.9%. 相似文献