全文获取类型
收费全文 | 303篇 |
免费 | 6篇 |
国内免费 | 5篇 |
专业分类
化学 | 187篇 |
晶体学 | 1篇 |
力学 | 7篇 |
数学 | 44篇 |
物理学 | 75篇 |
出版年
2023年 | 1篇 |
2022年 | 5篇 |
2021年 | 8篇 |
2020年 | 3篇 |
2019年 | 6篇 |
2018年 | 5篇 |
2017年 | 6篇 |
2016年 | 5篇 |
2015年 | 4篇 |
2014年 | 9篇 |
2013年 | 17篇 |
2012年 | 12篇 |
2011年 | 19篇 |
2010年 | 13篇 |
2009年 | 10篇 |
2008年 | 18篇 |
2007年 | 26篇 |
2006年 | 17篇 |
2005年 | 17篇 |
2004年 | 12篇 |
2003年 | 9篇 |
2002年 | 13篇 |
2001年 | 13篇 |
2000年 | 12篇 |
1999年 | 6篇 |
1998年 | 1篇 |
1997年 | 5篇 |
1996年 | 7篇 |
1995年 | 4篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1989年 | 1篇 |
1988年 | 4篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1980年 | 4篇 |
1977年 | 2篇 |
1966年 | 1篇 |
1965年 | 1篇 |
排序方式: 共有314条查询结果,搜索用时 453 毫秒
51.
52.
53.
S. K. Perera 《Journal of Radioanalytical and Nuclear Chemistry》2005,264(2):357-363
Summary The standard procedure for analyzing gross alpha and gross beta in water is evaporation of the sample and radioactivity determination of the resultant solids by proportional counting. This technique lacks precision, and lacks sensitivity for samples with high total dissolved solids. Additionally, the analytical results are dependent on the choice of radionuclide calibration standard and the sample matrix. Direct analysis by liquid scintillation counting has the advantages of high counting efficiencies and minimal sample preparation time. However, due to the small sample aliquants used for analysis, long count times are necessary to reach required detection limits. The procedure proposed consists of evaporating a sample aliquant to dryness, dissolving the resultant solids in a small volume of dilute acid, followed by liquid scintillation counting to determine radioactivity. This procedure can handle sample aliquants containing up to 500 mg of dissolved solids. Various acids, scintillation cocktail mixtures, instrument discriminator settings, and regions of interest (ROI) were evaluated to determine optimum counting conditions. Precision is improved and matrix effects are reduced as compared to proportional counting. Tests indicate that this is a viable alternative to proportional counting for gross alpha and gross beta analyses of water samples. 相似文献
54.
Nachimuthu P Thevuthasan S Adams EM Weber WJ Begg BD Mun BS Shuh DK Lindle DW Gullikson EM Perera RC 《The journal of physical chemistry. B》2005,109(4):1337-1339
Disorder in Gd2(Ti(1-y)Zry)2O7 pyrochlores, for y = 0.0-1.0, is investigated by Ti 2p and O 1s near-edge X-ray absorption fine structure spectroscopy. Ti(4+) ions are found to occupy octahedral sites in Gd2Ti2O7 with a tetragonal distortion induced by vacant oxygen sites. As Zr substitutes for Ti, the tetragonal distortion decreases, and Zr coordination increases from 6 to 8. The migration of oxygen ions from 48f or 8b sites to vacant 8a sites compensate for the increased Zr coordination, thereby reducing the number of vacant 8a sites, which further reduces the tetragonal distortion and introduces more disorder around Ti. This is evidence for simultaneous cation disorder with anion migration. 相似文献
55.
56.
Integration of multiple objectives to evaluate the alternative operating rules for urban water supply reservoir systems can be effectively accomplished by multi-criteria decision aid techniques, where preference elicitation and modelling plays an important role. This paper describes a preference elicitation and modelling procedure involving the multi-criteria outranking method PROMETHEE in evaluating these alternative operating rules. The Melbourne water supply system was considered as the case study. Eight performance measures (PMs) were identified under four main objectives to evaluate the system performance under alternative operating rules. Three major hypothetical stakeholder groups namely, resource managers, water users, and environmental interest groups were considered in decision-making. An interviewer-assisted questionnaire survey was used to derive the preference functions and weights of the PMs. The evaluation of alternative operating rules is not covered in this paper, rather an approach to elicit and model stakeholder preferences in decision-making is described. 相似文献
57.
Spencer Jolly Dominic Perera Johann Pu Shengda D. Melvin Dominic L. R. Adamson Paul Bruce Peter G. 《Journal of Solid State Electrochemistry》2022,26(9):1961-1968
Journal of Solid State Electrochemistry - Potassium metal anode solid-state cells with a K-beta”-alumina ceramic electrolyte are found to have relatively high critical currents for dendrite... 相似文献
58.
Man-Yung Tong Tharanga PayagalaSirantha Perera Frederick M. MacDonnellDaniel W. Armstrong 《Journal of chromatography. A》2010,1217(7):1139-1148
Sodium arsenyl-(l)-(+) tartrate (Na2[As2(+)-tart2]·3H2O) was examined and evaluated as a chiral selector using capillary electrophoresis. This chiral selector showed enantioselective associations with many cationic analytes, including primary, secondary, and tertiary amines. Also, baseline separations of ruthenium(II) polypyridyl complexes were achieved within 10 min. The effect of buffer type, chiral selector concentration, voltage applied, buffer concentration, buffer pH and organic modifier concentration were examined and optimized. 相似文献
59.
Eranda Wanigasekara Sirantha Perera Jeffrey A. Crank Leonard Sidisky Robert Shirey Alain Berthod Daniel W. Armstrong 《Analytical and bioanalytical chemistry》2010,396(1):511-524
Four new ionic liquids (IL) were prepared and bonded onto 5-μm silica particles for use as adsorbent in solid-phase microextraction
(SPME). Two ILs contained styrene units that allowed for polymerization and higher carbon content of the bonded silica particles.
Two polymeric ILs differing by their anion were used to prepare two SPME fibers that were used in both headspace and immersion
extractions and compared to commercial fibers. In both sets of experiments, ethyl acetate was used as an internal standard
to take into account adsorbent volume differences between the fibers. The polymeric IL fibers are very efficient in headspace
SPME for short-chain alcohols. Immersion SPME also can be used with the IL fibers for short-chain alcohols as well as for
polar and basic amines that can be extracted at pH 11 without damage to the IL-bonded silica particles. The sensitivities
of the two IL fibers differing by the anion were similar. Their efficacy compares favorably to that of commercial fibers for
polar analytes. The mechanical strength and durability of the polymeric IL fibers were excellent.
相似文献
60.
Kim SH Perera R Hager LP Dawson JH Hoffman BM 《Journal of the American Chemical Society》2006,128(17):5598-5599
The classical heme-monooxygenase active intermediate, compound I (Cpd-I), incorporates a heme which is oxidized by two equivalents above the resting ferric state, one equivalent associated with a ferryl center, [Fe=O]2+ (FeS = 1), and the other with an active-site radical (RS = 1/2). Theoretical calculations on models of a Cpd-I with a thiolato axial ligand have presented divergent views about its electronic structure. In one picture, the radical is on the porphyrin; in the other, it is on the sulfur. In this report, ENDOR spectroscopy answers the question, does Cpd-I of the enzyme chloroperoxidase contain a porphyrin pi-cation radical or an iron-bound cysteinyl radical: the radical is predominantly on the porphyrin, with spin density on sulfur having an upper bound, rhoS = rhoSmax approximately 0.23. We further suggest that the same answer applies to Cpd-I of cytochromes P450. 相似文献