全文获取类型
收费全文 | 94篇 |
免费 | 3篇 |
专业分类
化学 | 77篇 |
力学 | 2篇 |
数学 | 3篇 |
物理学 | 15篇 |
出版年
2023年 | 1篇 |
2020年 | 1篇 |
2019年 | 1篇 |
2016年 | 1篇 |
2014年 | 4篇 |
2013年 | 15篇 |
2012年 | 4篇 |
2011年 | 3篇 |
2010年 | 4篇 |
2009年 | 3篇 |
2008年 | 3篇 |
2007年 | 7篇 |
2006年 | 11篇 |
2005年 | 5篇 |
2004年 | 6篇 |
2003年 | 2篇 |
2002年 | 2篇 |
2001年 | 1篇 |
1999年 | 2篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1988年 | 3篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 2篇 |
1973年 | 1篇 |
排序方式: 共有97条查询结果,搜索用时 31 毫秒
81.
Claudio Aroca Eloísa Lopez Pedro S. Sanchez 《Journal of magnetism and magnetic materials》1981,23(2):193-199
A study about the influence of an electric current flowing through an amorphous ribbon Fe40Ni40P14B6 has been done. It has been found that the magnetization curves are strongly influenced by such a current (from 0 up to 5000 Hz). Bitter patterns under the action of the current have been observed in order to gain a better knowledge of these effects. The wall energy has been evaluated from a simple model. 相似文献
82.
In the last decades, researchers have realised that the impact of trace elements (TE) in environmental solid substrates on
ecological systems and biota cannot be ascertained appropriately by means of total metal content measurements. Assessment
of TE chemical forms, types of binding and reactivity of their associations with particulate forms has, thus, been commonly
performed via batch-wise equilibrium-based sequential extraction fractionation methods able to discern TE bound to different
soil-phase compartments.
In this paper, novel analytical strategies for monitoring the mobility, bioavailability and the eventual impact of anthropogenic
TE in environmental solids are addressed. The potential of passive dosimeters based on microdialysis sampling for on-site,
real-time monitoring of chemical contaminants in pore soil solution is thoroughly discussed and critically compared with active
microsamplers. Recent miniaturised configurations designed for following the fate of target pollutants and the on-going chemical
changes occurring at local soil sites, e.g., the rhizosphere environment, at high temporal resolution are also presented in
detail.
Kinetic information on the lability of the various TE forms associated to soil phases under simulated environmental changing
conditions – that yield improved knowledge on short-term hazards of TE for the environment – can be obtained in a fully automated
mode by means of flow-through microcolumn fractionation procedures. The use of sequential injection analysis, in terms of
the implementation of on-line dynamic fractionation, is described and illustrated via selected examples comprising the well-accepted
three-step SM&T sequential fractionation, protocol. 相似文献
83.
A fluorimetric flow-injection method for the determination of nitrogen-containing substrates, which can be enzymatically degraded to ammonium/ammonia is described. The generated ammonia is detected fluorimetrically after on-line derivatization with o-phthaldialdehyde (OPA) and sulphite. The derivatization procedure is optimized by a fractional factorial design at two levels and by a super modified simplex procedure to obtain a high sensitivity and a low detection limit for ammonia in the micromolar concentration range. Under the given flow conditions the detection limit is 1 μM, and considerable selectivity for ammonia over primary amines such as unconverted substrate and amino acids is achieved. Two enzymatic systems, incorporating immobilized creatinine iminohydrolase (CIH) and L-aspartase column reactors, respectively, are tested as model systems. The feasibility of the CIH system for the practical assay of creatinine in serum samples is demonstrated. 相似文献
84.
Díez E Fernández R Marqués-López E Martín-Zamora E Lassaletta JM 《Organic letters》2004,6(16):2749-2752
Enantiopure N,N-dialkylhydrazones 3 smoothly react with N-benzyloxycarbonyl-N-benzyl glycine as an aminoketene precursor to afford trans-3-amino-4-alkylazetidin-2-ones 4 as single diasteromers. As an exception, hydrazone 3f (R = OBn) affords cis-(3R,4R)-4f under modified conditions. N-N Bond cleavage of cycloadducts 4 afforded free azetidinones 5 in high yields. [structure: see text] 相似文献
85.
A flow injection (FI) on-line sorption preconcentration procedure utilizing a packed column reactor and combined with electrothermal atomic absorption spectrometry (ETAAS) is proposed for the determination of low levels of Cr(VI) in water samples. Polytetrafluoroethylene (PTFE) beads packed in a mini-column is used as sorbent material. The complex formed between Cr(VI) and ammonium pyrrolidine dithiocarbamate (APDC) is sorbed on the PTFE beads, and is subsequently eluted by an air-monosegmented discrete zone of absolute ethanol (35 μl), the analyte being quantified by ETAAS.The preconcentration procedure using the proposed column significantly enhances the preconcentration efficiency as compared with the preconcentration approach incorporating an open tubular PTFE knotted reactor (KR). Comparing the two procedure for equal surface sorption area, the advantages of using a packed column are observed in terms of limit of detection, enrichment factor and retention efficiency. With a preconcentration time of 60 s, and a sample flow rate of 5.0 ml l−1, the enrichment factor (30.1) and the retention efficiency (24.1%) were doubled, yielding a detection limit (3σ) as low as 8.8 ng l−1. The sample frequency was 16.7 h−1. The concentration efficiency was 8.38 and the precision was 1.05% at 0.5 μg l−1 of Cr(VI). The proposed column has been applied successfully to the analysis of natural water and synthetic seawater. Its performance was verified by the analysis of two certified Cr(VI)-reference materials and by recovery measurements on spiked samples. 相似文献
86.
Pertti Elo 《Journal of organometallic chemistry》2009,694(18):2927-9007
Synthesis of new titanium and zirconium dichloro complexes bearing malonate-based enaminoketonato (N,O) ligand is described. NMR studies of the catalyst precursors reveal that synthesized complexes have different configurational isomers in solution state and that they undergo structural change within NMR timescale. After MAO activation complexes exhibited low to moderate activities in ethylene polymerization producing bi- or multimodal polyethylenes. 相似文献
87.
88.
89.
Channel plasmon-polariton guiding by subwavelength metal grooves 总被引:1,自引:0,他引:1
We report on realization of channel plasmon-polariton (CPP) propagation along a subwavelength metal groove. Using imaging with a near-field microscope and end-fire coupling with a tapered fiber connected to a tunable laser at telecommunication wavelengths (1425-1620 nm), we demonstrate low-loss (propagation length approximately 100 microm) and well-confined (mode width approximately 1.1 microm) CPP guiding along a triangular 0.6 microm-wide and 1 microm-deep groove in gold. We develop a simple model based on the effective-index method that accounts for the main features of CPP guiding and provides a clear physical picture of this phenomenon. 相似文献
90.
A study of BaO has been made by use of thermogravimetric analysis, oxygen concentration analysis, and X-ray lattice parameter measurements in the temperature range 850°C ? T ? 1420°C and oxygen pressure range 7 × 10-6 atm ? pO2 ? 0·820 atm. Both the weight gain by the BaO samples and subsequently determined excess oxygen concentration were found to be directly proportional to . The enthalpy of incorporation oxygen in the lattice was determined to be ?0·395 ± 0·034 eV. Creation of vacancies on cation sites or of oxygen interstitials are consistent with the experimental results. As an alternative, the formation of O22? ions, (as in BaO2) as a result of incorporation of excess oxygen in the lattice, has been suggested. 相似文献