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901.
Fahad Jaber Al-Shammary Neelofur Abdul Aziz Mian Mohammad Saleem Mian 《Journal of separation science》1991,14(4):230-234
The biologically active pricipals in nature are frequently present as only a few parts per million of complex mixtures of non-volatile components and often have limited stability. Their isolation often requires the application of all available techniques, such as adsorption chromatography, ion exchange procedures, size exclusion techniques, and solvent partition methods consistent with their physical properties and stability. The process of countercurret chromatography is essentially liquid-liquid chromatography in which the stationary liquid bed is retained in the column by a force field rather than by a solid supporting matrix. Adsorption effects are thereby eliminated. The technique is particularly advantageous in the preparative separation of milligram to gram quantities of polar and labile organic compounds and bio-particulate materials such as cells and cell fragments. Virtually any twophase solvent system, either aqueous or non-aqueous may be employed. Countercurrent chromatography (CCC) provides a convenlent alternative to adsorption chromatography for fractionation of natural products or other complex mixtures. In some cases, this high resolution method offers advantages with regard to the avoidance of contamination from solid adsorbents, versatility, and relatively inexpensive operation. The article covers some of the applications, selection of solvents, and advantages of CCC. 相似文献
902.
Flow-injection spectrophotometric procedures are described for the determination of chloride and bromide using on-line solid mercury(II) thiocyanate and silver thiocyanate minicolumns, respectively. The linear response ranges for chloride and bromide are 0.28 × 10?4?8.5 × 10?4 M and 0.38 × 10?4?2.4 × 10?4 M, respectively. The sample throughput for both systems is 100 h?1. The lifetime of the minicolumns is 50 and 200 injections, respectively. 相似文献
903.
Constant-potential amperometric detection of carbohydrates, amino acids, and other aliphatic organic compounds is possible by means of their oxidation in alkaline solution at a variety of metal/metal oxide electrodes including Pt, Au, Cu, Ni, Ag and Co. The experimental conditions required for optimum detection and the analytical performance obtainable vary widely for different electrode materials and analytes. In this work, the cyclic voltammetric behavior exhibited by selected analytes (glucose, glycine, lactic acid, ethylamine and ethanol) at each of these electrodes was used to determine the optimum potentials suitable for flow detection so that the capabilities of the different metal electrodes could be evaluated and systematically compared. In general, the Cu electrode was found to provide superior detection capabilities in terms of its range of response, detection limits and especially stability. Despite the fact that Pt and Au are typically used only with a pulsed applied potential, both can provide long-lived constant-potential detection of carbohydrates and other analytes at low concentrations if the potentials ere carefully chosen and the electrodes are allowed to undergo an initial stabilization period. 相似文献
904.
Ascorbic acid may be determined spectrophotometrically at 360 nm based on reduction of vanadotungstophosphoric acid using flow-injection analysis. The carrier stream was distilled water and the reagent streams were buffer solution (pH 3.0), 1.735 × 10?3 M dodecatungstophosphoric acid and 1.735 × 10?3 M sodium vanadate. The injection rate was 80 h?1. The calibration graph was linear up to 80 μg ml?1 ascorbic acid and the relative standard deviation for the determination of 20 μg ml?1 ascorbic acid was 1.5% (n=10). The detection limit was 1.0 μg ml?1 ascorbic acid, based on an injection volume of 250 μl. The system was applied to the determination of ascorbic acid in vitamin C tablets. 相似文献
905.
催化动力学流动注射荧光光度法测定微量亚硝酸根 总被引:6,自引:0,他引:6
基于亚硝酸根离子在硫酸介质中催化溴酸钾氧化罗央明6G使其荧光强度降低的反应,建立了快速,灵敏,简便的催化动力学流动注射荧光光度法测定亚硝酸根的新方法。 相似文献
906.
907.
用DDTC-Zn作载体流动注射在线共沉淀预富集火焰原子吸收法测定人发和水样中的痕量铅 总被引:2,自引:1,他引:2
提出了在高酸度下流动注射在线共沉淀预富集-火焰原子吸收法测定痕量铅的新体系。在0.5mol/LHCl介质中痕量铅与DDTC-Zn螯合物产生共沉淀。在线生成的沉淀物收集在编结反应器中,用甲基异丁酮溶解沉淀并直接引入火焰原子化器中进行测定。经40s富集,检测限为2.7μg/L。测定含量为200μg/L的铅时,相对标准偏差为1.3%。建立的方法已成功地应用于人发标准参考物中和水样中痕量铅的测定 相似文献
908.
Bin Lu Malcolm R. Smyth Richard O'Kennedy John Moulds Tom Frame 《Analytica chimica acta》1997,340(1-3):175-180
An amperometric immunosensor, based on a non-competitive sandwich assay and flow injection analysis (FIA), was developed for the detection of human red blood cells (RBCs). A dual working electrode, on which specific IgM and nonspecific IgM were chemically immobilised to form sensing and blank electrodes, respectively, was employed to determine the binding of specific blood cells and non-specific adsorption in one determination. Horseradish peroxidase (HRP)-labelled antiblood group A IgM was used in the assay. Sensor preparation involved chemical immobilisation of the IgMs on glassy carbon electrodes using l-ethyl-3(3-dimethyl aminopropyl)carbodiimide (EDC) as a coupling reagent in the presence of N-hydroxysuccinimide (NHS). The interference contributions, such as the non-specific adsorption of the enzyme conjugate and the blood cells, were determined and removed. A quantitative relationship between the cell binding response and its concentration was obtained in the region 1 − 30 × 108 cells ml−1. 相似文献
909.
Ali Allahverdi C.T. Ng T.C.E. Cheng Mikhail Y. Kovalyov 《European Journal of Operational Research》2008
The first comprehensive survey paper on scheduling problems with separate setup times or costs was conducted by [Allahverdi, A., Gupta, J.N.D., Aldowaisan, T., 1999. A review of scheduling research involving setup considerations. OMEGA The International Journal of Management Sciences 27, 219–239], who reviewed the literature since the mid-1960s. Since the appearance of that survey paper, there has been an increasing interest in scheduling problems with setup times (costs) with an average of more than 40 papers per year being added to the literature. The objective of this paper is to provide an extensive review of the scheduling literature on models with setup times (costs) from then to date covering more than 300 papers. Given that so many papers have appeared in a short time, there are cases where different researchers addressed the same problem independently, and sometimes by using even the same technique, e.g., genetic algorithm. Throughout the paper we identify such areas where independently developed techniques need to be compared. The paper classifies scheduling problems into those with batching and non-batching considerations, and with sequence-independent and sequence-dependent setup times. It further categorizes the literature according to shop environments, including single-machine, parallel machines, flow shop, no-wait flow shop, flexible flow shop, job shop, open shop, and others. 相似文献
910.
The present paper describes approaches utilizing the powerful flow manipulation capabilities of sequential injection analysis (SIA) to substantially improve the efficiency of gas-diffusion separation compared to its traditional implementation in flow injection analysis (FIA). Ammonia, ethylamine, diethylamine and triethylamine were used as model analytes in this study. Eleven flow manipulation approaches involving continuous flow, stop-flow, oscillating flow, and the introduction of air bubbles to separate the sample zone from the donor solution were tested. Improvement in sensitivity compared to traditional gas-diffusion FIA exceeding one order of magnitude was achieved. It was observed that this improvement increased with the molecular size of the analyte. 相似文献