全文获取类型
收费全文 | 735篇 |
免费 | 72篇 |
国内免费 | 38篇 |
专业分类
化学 | 370篇 |
晶体学 | 2篇 |
力学 | 51篇 |
综合类 | 5篇 |
数学 | 4篇 |
物理学 | 413篇 |
出版年
2024年 | 2篇 |
2023年 | 14篇 |
2022年 | 19篇 |
2021年 | 19篇 |
2020年 | 8篇 |
2019年 | 11篇 |
2018年 | 17篇 |
2017年 | 22篇 |
2016年 | 30篇 |
2015年 | 38篇 |
2014年 | 36篇 |
2013年 | 67篇 |
2012年 | 48篇 |
2011年 | 47篇 |
2010年 | 53篇 |
2009年 | 53篇 |
2008年 | 52篇 |
2007年 | 45篇 |
2006年 | 50篇 |
2005年 | 40篇 |
2004年 | 28篇 |
2003年 | 27篇 |
2002年 | 24篇 |
2001年 | 10篇 |
2000年 | 12篇 |
1999年 | 13篇 |
1998年 | 9篇 |
1997年 | 10篇 |
1996年 | 3篇 |
1995年 | 12篇 |
1994年 | 7篇 |
1993年 | 8篇 |
1991年 | 5篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1984年 | 1篇 |
1982年 | 1篇 |
1976年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有845条查询结果,搜索用时 0 毫秒
1.
Pirjo Sainio Irma Mäkinen Jaap-Willem Hutter Theo den Ouden Mikael Krysell 《Accreditation and quality assurance》2006,11(3):116-121
The international joint project HYCREF (Contract No. G6RD-CT-2002-00854), funded by the European Commission in the 5th Framework programme, aimed to develop methods to prepare homogeneous and stable reference materials of water, soil, and waste contaminated with mineral oil hydrocarbons and to certify the mineral oil content by gas chromatographic methods. The results of a feasibility study for the preparation of three soil reference materials are discussed in this paper, and for the preparation of three waste reference materials in the second part (Koch et al., Accred Qual Assur submitted for publication). The soil materials were selected to represent different soil types and contamination levels. The project plan set three requirements for these reference materials: uncertainty in the mineral oil content resulting from the certification exercise <5%, a sample inhomogeneity of <3% and a minimum long-term stability of 5 years. For the most part, these requirements were met within this project. 相似文献
2.
Fengfu Fu Liangjun Xu Wei Ye Yiquan Chen Mingyu Jiang Xueqin Xu 《中国颗粒学报》2006,4(6):323-326
Different-sized aerosols were collected by an Andersen air sampler to observe the detailed morphology of the black carbon (BC) aerosols which were separated chemically from the other accompanying aerosols, using a Scanning Electron Microscope equipped with an Energy Dispersive X-ray Spectrometer (SEM-EDX). The results indicate that most BC aerosols are spherical particles of about 50 nm in diameter and with a homogeneous surface. Results also show that these particles aggregate with other aerosols or with themselves to form larger agglomerates in the micrometer range. The shape of these 50-nm BC spherical particles was found to be very similar to that of BC particles released from petroleum-powered vehicular internal combustion engines. These spherical BC particles were shown to be different from the previously reported fullerenes found using Matrix-Assisted Laser Desorption/Ionization Time-Of-Flight Mass Spectrometry (MALDI-TOF-MS). 相似文献
3.
4.
Backman Ulrika Jokiniemi Jorma K. Auvinen Ari Lehtinen Kari E.J. 《Journal of nanoparticle research》2002,4(4):325-335
We have prepared spherical non-agglomerated silver nanoparticles by an evaporation–condensation–dilution/cooling technique. Silver was evaporated from a crucible in a tubular flow reactor. A porous tube diluter was used to quench the carrier gas at the outlet of the reactor to enhance the formation of small particles and to suppress agglomeration and other particle growth mechanisms. The number size distribution of the prepared particles was measured with a differential mobility analyser–condensation nucleus counter combination and the size and the shape of the particles were analysed with transmission electron microscope. The system was modelled using a sectional aerosol dynamics computer code to estimate the importance of different aerosol processes. In all conditions the particles obtained were non-agglomerated and spherical. The mean particle diameter varied from 4 to 10-nm depending on boundary conditions. From the modelling studies it can be concluded that the nucleation rate is the most important parameter controlling the final particle size. 相似文献
5.
Oleg S. Ugolnikov Igor A. Maslov 《Journal of Quantitative Spectroscopy & Radiative Transfer》2006,102(3):499-512
The work is devoted to the analysis of the surface photometric observations of two total lunar eclipses in 2004. The lunar surface relative brightness distribution inside the umbra was used to retrieve the vertical distribution of aerosol extinction of the solar radiation expanding by a tangent path and its dependence on the location at the limb of the Earth. The upper altitude of troposphere aerosol layer was estimated for different latitude zones. The correlation between additional aerosol extinction in the upper troposphere and cyclones was investigated. 相似文献
6.
A new element tracer technique has firstly been established to estimate the contributions of mineral aerosols from both inside and outside Beijing. The ratio of Mg/Al in aerosol is a feasible element tracer to distinguish between the sources of inside and outside Beijing. Mineral aerosol, inorganic pollution aerosol mainly as sulfate and nitrate, and organic aerosol are the major components of airborne particulates in Beijing, of which mineral aerosol accounted for 32%―67% of total suspended particles (TSP), 10%―70% of fine particles (PM2.5), and as high as 74% and 90% of TSP and PM2.5, respectively, in dust storm. The sources from outside Beijing contributed 62% (38%―86%) of the total mineral aerosols in TSP, 69% (52%―90%) in PM10, and 76% (59%―93%) in PM2.5 in spring, and 69% (52%―83%), 79% (52%―93%), and 45% (7%―79%) in TSP, PM10, and PM2.5, respectively, in winter, while only ~20% in summer and autumn. The sources from outside Beijing contributed as high as 97% during dust storm and were the dominant source of airborne particulates in Beijing. The contributions from outside Beijing in spring and winter are higher than those in summer, indicating clearly that it was related to the various meteorological factors. 相似文献
7.
Jocelyn Jalbert Roland Gilbert Pierre Tétreault Brigitte Morin Denise Lessard-Déziel 《Cellulose (London, England)》2007,14(4):295-309
In this study, headspace gas chromatography/mass spectrometry has been used to assess the volatile by-products generated by
the ageing of oil-impregnated paper insulation of power transformers. Sealed-glass ampoules were used to age under oxidative
conditions 0.5-g specimens of insulating paper in 9 mL of inhibited mineral oil in a temperature range of 60–120 °C and moisture
of 0.5, 1 and 2% (w/w). A linear relationship between one of the oil-soluble degradation by-products, i.e. methanol, and the
number of ruptured 1,4-β-glycosidic bonds of cellulose, regardless of the type of paper (ordinary Kraft or thermally-upgraded
(TU) Kraft paper), was established for the first time in this field. Ageing at 130 °C of model compounds of the Kraft paper
constituents (α-cellulose, hemicellulose and lignin) and two cellulosic breakdown by-products (D-(+)-glucose and 1,6-anhydro-β-d-glucopyranose) confirmed that the α-cellulose degradation was mostly responsible for the presence of this molecule in the
system. Furthermore, additional 130 °C-tests with six different papers and pressboard samples under a tight control of initial
moisture indicated that at least one molecule of methanol is formed for each rupture of 1,4-β-glucosidic bond of the molecular
chains. Stability tests showed that the ageing indicator is stable under the oxygen and temperature conditions of open-breathing
transformers. The presence of methanol was detected in 94% of oil samples collected from over than 900 in-service pieces of
equipment, confirming the potential for this application. Lastly, the tests have shown that oil-oxidation by-products and
TU-nitrogenous agents modify the methanol partitioning coefficients in the paper/oil/air system, which makes their study essential
over a range of field conditions encountered by power transformers. Results are presented and discussed in comparison with
2-furfuraldehyde, which is the current reference in the domain. 相似文献
8.
Summary The rapid, simultaneous, suppressed ion chromatographic determination of alkali, alkaline earth metals and ammonium in highly mineralized waters has been examined using the novel cation exchange IonPac CS12 column. General ability for the determination of lithium, sodium, ammounium, potassium, magnesium, calcium and strontium in concentrations from a few g to several mg per liter was studied. The relative standard deviations of retention times of all seven cations were below 0.7% and the relative standard deviations of the measurements of peak areas and peak heights were mostly below 5%. Six natural mineral waters of different types were selected for evaluation of the method. It was not possible to determine lithium in the one run and ammonium usually partially coelutes with sodium precluding quantitative determination. Strontium was undetectable because of the necessary dilutions. All the reltionships between peak areas and concentrations or peak height and concentrations were linear and there was also no evidence of the effect of different matrices on the slope of regression lines. 相似文献
9.
Extracting organotin compounds (OTC) from soils is difficult due to the high cation exchange and complexation capacity of soils, and little information about OTC in soils is available. In this study, a new extraction method, combining 1 M CaCl2, 0.1% tropolone, and glacial acetic acid was developed. Recoveries of mono-substituted OTC from spiked plant litter, and soil samples were improved substantially to 40% compared to classical glacial acetic acid extraction commonly used in sedimentology, yielding <10% recovery in C-rich soil samples. Simultaneously, the recovery of other OTC, trimethyllead and monomethylmercury was satisfactory. The recoveries of most species from the spiked litter, upland and wetland soils exceeded 70%. The new method extracted much more organometallics from unspiked organic soils and litter than microwave- and ultrasound-assisted extraction and accelerated solvent extraction, most likely due to exchange of organometallics from the solid phase by Ca2+. The method is simple, highly efficient and with low contamination. Together with GC-ICP-mass spectrometry, the method allows the detection of these organometallics in the pg g−1 range and it is particularly suitable for soil and plant materials with low organometallics contents. 相似文献
10.
火焰原子吸收光谱法测定南湖菱中矿质元素 总被引:5,自引:0,他引:5
用火焰原子吸收光谱法测定嘉兴南湖菱中钾、钠、钙、镁、铁、铜、锌、锰、镉、铅金属元素的含量。结果表明,南湖菱中有较高的矿物质营养价值,有害元素的含量低于国家食品允许标准。 相似文献