全文获取类型
收费全文 | 2015篇 |
免费 | 96篇 |
国内免费 | 15篇 |
专业分类
化学 | 1874篇 |
晶体学 | 2篇 |
力学 | 15篇 |
综合类 | 6篇 |
数学 | 87篇 |
物理学 | 142篇 |
出版年
2024年 | 3篇 |
2023年 | 30篇 |
2022年 | 31篇 |
2021年 | 47篇 |
2020年 | 50篇 |
2019年 | 50篇 |
2018年 | 54篇 |
2017年 | 75篇 |
2016年 | 80篇 |
2015年 | 75篇 |
2014年 | 63篇 |
2013年 | 176篇 |
2012年 | 132篇 |
2011年 | 122篇 |
2010年 | 92篇 |
2009年 | 117篇 |
2008年 | 96篇 |
2007年 | 132篇 |
2006年 | 91篇 |
2005年 | 97篇 |
2004年 | 77篇 |
2003年 | 56篇 |
2002年 | 52篇 |
2001年 | 36篇 |
2000年 | 39篇 |
1999年 | 28篇 |
1998年 | 30篇 |
1997年 | 31篇 |
1996年 | 18篇 |
1995年 | 19篇 |
1994年 | 12篇 |
1993年 | 13篇 |
1992年 | 15篇 |
1991年 | 17篇 |
1990年 | 22篇 |
1989年 | 5篇 |
1988年 | 11篇 |
1987年 | 12篇 |
1986年 | 1篇 |
1985年 | 4篇 |
1984年 | 5篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1978年 | 2篇 |
排序方式: 共有2126条查询结果,搜索用时 93 毫秒
11.
环境样品中痕量邻苯二甲酸酯的分离与测定 总被引:11,自引:0,他引:11
本文研究了以小粒径(10-40μ)硅胶柱色谱分离富集、反相高效相色谱分析测定大气颗粒物、土主植物样品中痕量邻苯二甲酸酯的方法,方法操作简单,回收率高,空白值低,利用该方法分析了部分环境样品中邻苯二甲酯酯含量。 相似文献
12.
Diane Beauchemin 《Mikrochimica acta》1989,99(3-6):273-281
The certification of marine materials for trace metals is a process which challenges every technique involved, especially if a technique is as recent as inductively coupled plasma mass spectrometry (ICP-MS), Developmental work was required for several materials (natural waters, biological materials, marine sediments). It is reviewed here, in an attempt to show how one can take full advantage of ICP-MS. This includes a review of the digestion procedures developed for the multielement analysis of biological materials and marine sediments in order to minimize spectroscopic interferences. The multielement analysis of natural waters is also reviewed, in particular that of saline waters which requires a separation of the analytes from the alkali and alkaline earths elements and a preconcentration of the analytes on a column of silicaimmobilized 8-hydroxyquinoline. The potential of performing this separation/preconcentration procedure on-line is showed using both published and original results. Finally, the application of ICP-MS to speciation is illustrated by the determination of methylmercury in biological materials after extraction, and by the determination of arsenic species by high performance liquid chromatography coupled to ICP-MS.Presented in part at the 1989 European Winter Conference on Plasma Spectrochemistry, Reutte, AustriaThe work described was carried out while the author was a Research Associate at the Analytical Chemistry Section, Chemistry Division, National Research Council of Canada, Ottawa, K1A OR9, Canada 相似文献
13.
14.
Nicolas Le Calvez 《中国化学会会志》2002,49(4):585-592
The aim of this study was to develop an analytical method to determine the organochlorine concentrations in sediments. Combination of Microwave assisted Solvent Extraction (MASE) and capillary gas chromatography with specific detection (electron capture detector) was a viable approach for the determination of pesticides in solid matrixes. In this study, MASE development was focused on the selection of a suitable extraction solvent for all the target analytes. MASE procedure was validated by comparison with conventional methods such as Soxhlet and sonication extraction. The proposed method was then applied to determine the organochlorine insecticides concentrations in samples from Authie Bay (France). Environmental water samples were analysed and five target analytes were detected in concentrations from 0.03 to 0.56 ng/g of dry sediment. These investigations showed the accumulation and the persistency of these products in sediments in spite of the fact they were banned a few decades ago. 相似文献
15.
Time-resolved laser-induced spectrofluorimetry was used for the determination of uranium at the ng 1?1 level in alkaline water with high chloride and sulphide contents in order to obtain a better understanding of uranium mobilization under natural reducing conditions. The optimum complexing medium, limit of detection and results obtained for several waters from different localities in the Pyrenees are presented. These data seem to confirm that even at very low uranium concentrations, thermodynamic control by a mineral phase takes place. 相似文献
16.
17.
A new in-loop solid-phase microextraction (in-loop-SPME) technique, based on an aluminum capillary tube coupled to HPLC, is described for on-line isolation, concentration, and analysis of analytes from aqueous samples. L-Dopa and L-dopamine, in aqueous solutions, were selected as model compounds. The main conditions affecting extraction of the analytes from aqueous samples, desorption, injection, and chromatographic separation were investigated. The method is simple and reproducible. Using the proposed method, reliable determination of L-dopa and L-dopamine at parts-per-billion concentrations was achieved. The calibration plots were linear in the range of 2.5–1500 ng mL−1 with correlation coefficients of 0.999 and 0.998 for L-dopa and L-dopamine, respectively. The detection limits were 0.5–1 ng mL−1 with a relative standard deviation less than 4.1%. Concentration factors more than 100-fold were obtained for these compounds. 相似文献
18.
A method has been developed for species-selective analysis of organotin compounds in solid, biological samples. The procedure is based on accelerated solvent extraction (ASE) of analytes and includes extraction of the tin species with a methanol–water (90% methanol) solution of acetic acid/sodium acetate containing tropolone (0.03% w/v), their ethylation with NaBEt4, and separation and detection by GC–FPD. The analytical procedure was optimized with an unspiked sample of harbor porpoise (Phocoena phocoena) liver. Effects of ASE operational variables (extraction temperature and pressure, solvent composition, number of static extraction steps) are discussed. Method detection limits (MDL) were in the range 6–10 ng(Sn) g–1 dry weight and 7–17 ng(Sn) g–1 dry weight for butyl- and phenyltin compounds, respectively. Recoveries were comparable with or better than those obtained by use of other procedures reported in the literature. The analytical procedure was validated by analysis of NIES No. 11 (fish tissue) certified reference material. 相似文献
19.
Chaozhang Huang 《Talanta》2007,73(2):274-281
Mesoporous titanium dioxide as a novel solid-phase extraction material for flow injection micro-column preconcentration on-line coupled with ICP-OES determination of trace metals (Co, Cd, Cr, Cu, Mn, Ni, V, Ce, Dy, Eu, La and Yb) in environmental samples was described. Possessing a high adsorption capacity towards the metal ions, mesoporous titanium dioxide has found to be of great potential as an adsorbent for the preconcentration of trace metal ions in samples with complicated matrix. The experimental parameters including pH, sample flow rate, volume, elution and interfering ions on the recovery of the target analytes were investigated, and the optimal experimental conditions were established. Under the optimized operating conditions, a preconcentration time of 90 s and elution time of 18 s with enrichment factor of 10 and sampling frequency of 20 h−1 were obtained. The detection limits of this method for the target elements were between 0.03 and 0.36 μg L−1, and the relative standard deviations (R.S.D.s) were found to be less than 6.0% (n =7, c =5 ng mL−1). The proposed method was validated using a certified reference material, and has been successfully applied for the determination of the afore mentioned trace metals in natural water samples and coal fly ash with satisfactory results. 相似文献
20.
Comparison of adsorbents for on-line solid-phase extraction of polycyclic aromatic hydrocarbons before liquid chromatography with UV detection 总被引:1,自引:0,他引:1
Summary On-line solid-phase extraction (SPE) coupled with reversed-phase liquid chromatography and UV detection at 254 nm has been
used for the determination of trace-level polycyclic aromatic hydrocarbons (PAH) in soil extracts. Five commercially available
adsorbents (C8, C18, PLRP-S, PRP-1, and Bond-Elut Env) were evaluated. Results showed that recovery of the PAH decreased with increasing molecular
weight, because of their poorer solubility. Recovery of high-molecular-weight PAH was significantly improved by addition of
10% (v/v) acetonitrile to the sample before loading of the SPE adsorbent. PAH recovery ranged from 64.0 to 108% when a 50
mL sample spiked with 1 μg L−1 was applied to these adsorbents. Determination of PAH was possible with detection limits below 0.05 μg L−1, which corresponds to 0.2 μg kg−1 soil. The method was successfully used to determine PAH in soil extracts. 相似文献