全文获取类型
收费全文 | 3330篇 |
免费 | 140篇 |
国内免费 | 42篇 |
专业分类
化学 | 2903篇 |
晶体学 | 8篇 |
力学 | 57篇 |
综合类 | 10篇 |
数学 | 170篇 |
物理学 | 364篇 |
出版年
2024年 | 9篇 |
2023年 | 55篇 |
2022年 | 80篇 |
2021年 | 76篇 |
2020年 | 78篇 |
2019年 | 75篇 |
2018年 | 77篇 |
2017年 | 106篇 |
2016年 | 121篇 |
2015年 | 110篇 |
2014年 | 104篇 |
2013年 | 250篇 |
2012年 | 201篇 |
2011年 | 232篇 |
2010年 | 142篇 |
2009年 | 195篇 |
2008年 | 158篇 |
2007年 | 202篇 |
2006年 | 177篇 |
2005年 | 145篇 |
2004年 | 140篇 |
2003年 | 105篇 |
2002年 | 89篇 |
2001年 | 54篇 |
2000年 | 68篇 |
1999年 | 42篇 |
1998年 | 45篇 |
1997年 | 60篇 |
1996年 | 57篇 |
1995年 | 33篇 |
1994年 | 19篇 |
1993年 | 27篇 |
1992年 | 18篇 |
1991年 | 23篇 |
1990年 | 25篇 |
1989年 | 9篇 |
1988年 | 15篇 |
1987年 | 14篇 |
1986年 | 6篇 |
1985年 | 7篇 |
1984年 | 10篇 |
1983年 | 5篇 |
1982年 | 7篇 |
1981年 | 5篇 |
1980年 | 6篇 |
1979年 | 10篇 |
1978年 | 2篇 |
1977年 | 4篇 |
1976年 | 9篇 |
1975年 | 3篇 |
排序方式: 共有3512条查询结果,搜索用时 15 毫秒
51.
Determination of linuron in soil by stripping voltammetry with a carbon fiber microelectrode 总被引:1,自引:0,他引:1
A carbon fiber microelectrode was used for the electroanalytical determination of Linuron (LIN) in soil extracts. The microelectrode was subjected to an electrochemical pretreatment in order to improve the herbicide adsorption on the electrode surface. With this preconcentration step, detection limits of 80 ng ml−1 and determination limits of 260 ng ml−1 were reached. Optimal conditions with respect to accumulation time and potential, scan rate and pH were established. The LIN was determined in a soil sample with the method proposed and the results found were comparable to those obtained by HPLC. 相似文献
52.
Selected aspects of the chemistry of photochemical air pollution is discussed and some important, unresolved problems dilineated. The reactive species considered include NO2, O3, O(3P), O(1D), O2(1Δg), OH and HO2. Both the kinetics and mechanicsms of the reactions constituting the major tropospheric sources and sinks of these species are treated where available. The application of this information in both computer and smog chamber simulations of photochemical smog is discussed. 相似文献
53.
Summary The photodegradation behaviour of 12 nitrogen-containing herbicides (atrazine, cyanazine, terbuthylazine, terbutryn, EPTC,
buthylate, molinate, cycloate, vernolate, fenuron, chloroxuron, and methabenzthiazuron) has been examined. The compounds were
degraded completely when exposed to a mercury-vapour lamp; the degradation process was followed by consecutive GC measurements.
All the compounds studied had measurable photochemical activity, although actual and average degradation rates varied significantly.
All the compounds except terbutryn furnished more than one major degradation product, in different ratios.
Presented at Balaton Symposium '01 on High-Performance Separation Methods, Siófok, Hungary, September 2–4, 2001 相似文献
54.
Summary Ten pesticides have been completely separated by two-dimensional (2D) development on TLC plates coated with coupled layers
of octadecyl silica (reversed-phase, RP) and plain silica (normal-phase, NP). The binary mobile phases, aqueous-organic for
RP chromatography and nonaqueous for NP chromatography, were chosen from plots ofR
F against mobile-phase composition and graphicalR
F(RP)-R
F(NP) correlations. The different selectivity of the RP and NP systems enabled dispersion of spots over the plate area and good
separation. 相似文献
55.
3-Amino-1,2,4-triazole (amitrole) is a widely used pesticide, with many difficulties to be analyzed at the regulatory level in drinking water, because its high solubility in water. This paper describes a simple and fast method for the simultaneous determination of amitrole and atrazin-2-hydroxy, principal degradation product of s-triazines, by capillary zone electrophoresis. Separation and determination of these herbicides in water samples was performed in 0.02 mol l−1 phosphate buffer at pH 3.2. The method allows determination of the amitrole and atrazin-2-hydroxy in water samples in concentration lower than 100 μg l−1. The detection limits using a previous preconcentration step of amitrole in Alberche River (Comunidad Autónoma de Madrid, Spain) and drinking water spiked samples was of 4 μg l−1. 相似文献
56.
57.
Kenjiro Hattori Tomoko Takeuchi Mika Ogata Ayumi Takanohashi Katsuhiko Mikuni Katsuyoshi Nakanishi Hideo Imata 《Journal of inclusion phenomena and macrocyclic chemistry》2007,57(1-4):339-342
We obtained the association constants Ka of estrogen (E2) and environmental chemicals by the surface plasmon resonance (SPR) assay using the immobilized mono-6-O-α-maltosyl-β-CD (G2βCD) compared with the immobilized β-CD and the immobilized estrogen receptor (ER). The association behavior of G2βCD was shown as a ER model compound. The calibration curve was determined by the initial rate of association depending on
the various concentrations, and the minimum detectable concentrations in the order of parts per billion were calculated. The
SPR assay has advantages that the pre-treatment of the sample is not necessary and the immobilized ligand is stable and useful
for the repeated measurement. 相似文献
58.
Ewa Dabek-Zlotorzynska Maria Piechowski Fang Liu Scott Kennedy Joseph F. Dlouhy 《Journal of chromatography. A》1997,770(1-2):349-359
Capillary electrophoresis (CE) with indirect UV detection utilizing a pyromellitate-based electrolyte was used for the routine analysis of major anions in atmospheric aerosols collected on filters with high-volume (Hi-Vol) samplers. The long-term reliability of the CE system was checked over an 8-month period during which over 2900 samples were analyzed. In addition, approximately 1100 samples were analyzed in parallel by ion chromatography (IC). It has been shown that acceptable analytical performance can be routinely obtained. The agreement between the CE and IC results is good, generally better than 20% at concentrations larger than 1 mg l−1. 相似文献
59.
Noppe H De Wasch K Poelmans S Van Hoof N Verslycke T Janssen CR De Brabander HF 《Analytical and bioanalytical chemistry》2005,382(1):91-98
An analytical procedure enabling routine analysis of four environmental estrogens at concentrations below 1 ng L–1 in estuarine water samples has been developed and validated. The method includes extraction of water samples using solid-phase extraction discs and detection by gas chromatography (GC) with tandem mass spectrometry (MS–MS) in electron-impact (EI) mode. The targeted estrogens included 17- and 17-estradiol (aE2, bE2), estrone (E1), and 17-ethinylestradiol (EE2), all known environmental endocrine disruptors. Method performance characteristics, for example trueness, recovery, calibration, precision, accuracy, limit of quantification (LOQ), and the stability of the compounds are presented for each of the selected estrogens. Application of the procedure to water samples from the Scheldt estuary (Belgium – The Netherlands), a polluted estuary with reported incidences of environmental endocrine disruption, revealed that E1 was detected most frequently at concentrations up to 7 ng L–1. aE2 was detected once only and concentrations of bE2 and EE2 were below the LOQ.Presented at the 9th FECS Conference on Chemistry and the Environment, Bordeaux, France, 29 August–1 September 2004 相似文献
60.
Interactive liquid chromatography (iLC) for polymer analysis is usually applied to the characterisation of distributions other than molar mass. In particular, its use for the determination of chemical-composition, functionality-type and tacticity distributions has been demonstrated. The application of iLC for the determination of molar mass distributions (MMDs), however, has not yet been fully explored. An expanded version of the reversed-phase liquid chromatography model has been developed to describe and predict how the retention behaviour of polydisperse polystyrene samples changes with molar mass. The relationship between molar mass and the parameters of the model has been investigated in some detail and non-linear correlations were found. From the model and the relationships between the model parameters and molar mass, calibration curves (retention time versus molar mass) were constructed to predict changes in chromatographic selectivity across a given molar mass range. These calibration curves were compared to experimentally obtained curves and, in most cases, excellent agreement was found. The dramatic enhancement in selectivity that can be obtained with iLC in comparison to size-exclusion chromatography (SEC) was illustrated by measuring matrix-assisted laser desorption ionisation (MALDI) MS spectra of fractions collected during a gradient-LC separation. In the low-molar mass range, essentially monodisperse fractions were obtained. Calibration curves, predicted by the model and validated experimentally using narrow-dispersity standards and MALDI-MS spectra of fractions, were used to determine the molar mass distribution of some narrowly distributed polystyrene samples. Molar mass distributions for such standards were found to be somewhat lower than the values reported by the manufacturers. The results also deviated from those obtained by MALDI-MS. 相似文献