全文获取类型
收费全文 | 112篇 |
免费 | 11篇 |
专业分类
化学 | 85篇 |
力学 | 3篇 |
数学 | 22篇 |
物理学 | 13篇 |
出版年
2023年 | 1篇 |
2022年 | 2篇 |
2021年 | 4篇 |
2020年 | 7篇 |
2019年 | 7篇 |
2018年 | 2篇 |
2017年 | 2篇 |
2016年 | 9篇 |
2015年 | 10篇 |
2014年 | 3篇 |
2013年 | 12篇 |
2012年 | 5篇 |
2011年 | 10篇 |
2010年 | 3篇 |
2009年 | 5篇 |
2008年 | 7篇 |
2007年 | 3篇 |
2006年 | 2篇 |
2005年 | 8篇 |
2004年 | 2篇 |
2003年 | 5篇 |
2002年 | 3篇 |
2001年 | 2篇 |
2000年 | 1篇 |
1998年 | 1篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1981年 | 2篇 |
1975年 | 1篇 |
排序方式: 共有123条查询结果,搜索用时 62 毫秒
31.
开放式基金防范由于证券市场信息的非对称性导致的系统性风险,是开放式基金投资决策中的一个重要问题。本文基于分形市场理论及对中国股市的实证研究,提出了开放式基金防范信息性风险的有效策略。 相似文献
32.
Spanel P Diskin AM Abbott SM Wang T Smith D 《Rapid communications in mass spectrometry : RCM》2002,16(22):2148-2153
We describe a method by which the concentrations of volatile compounds in the headspace of their dilute aqueous solutions in sealed containers can be determined using on-line selected ion flow tube mass spectrometry (SIFT-MS). Thus, the changing number density of the molecules of the volatile compound in the carrier gas of the SIFT-MS instrument is described in terms of its changing flow rate as the pressure in the sealed container decreases during the sampling procedure. It is shown that the best analytical procedure is to determine the mean concentration of the trace gas in the liquid headspace over a given sampling time and relate this to the required concentration, which is the initial equilibrium concentration established before the pressure in the sealed container reduces significantly. To test the validity of this analytical approach, the headspace concentrations of acetaldehyde, ethanol and acetone above aqueous solutions of known concentrations have been determined. Hence, the Henry's Law constants for these compounds have been determined and found to agree with the published values. The confirmation of the quality of this sampling methodology combined with SIFT-MS for the analysis of volatile compounds in liquid headspace paves the way for the rapid analyses of biological liquids such as urine and serum for clinical diagnosis and physiological monitoring. 相似文献
33.
34.
The unimolecular decomposition of CF3CH2O (2,2,2-trifluoroethoxy) radical generated from 355 nm pulsed nanosecond laser photolysis of CF3CH2ONO (2,2,2-trifluoroethylnitrite) in the gas phase has been studied using Fourier transform infrared absorption spectroscopy. The radical preferentially dissociates via its C–H bond cleavage to yield CF3CHO (trifluoroacetaldehyde) as the major product. The infrared spectrum of formaldehyde, one of the products of C–C bond dissociation of CF3CH2O was not observed under a range of nitrite and argon buffer gas pressures. Similar results were obtained when thermal heating and broadband xenon lamp irradiation of the nitrite were carried out. The addition of high pressures of NO further decreased the production of CF3CHO since recombination of NO with the trifluoroethoxy radical competes with the unimolecular dissociation process. Surprisingly, CF3CDO was also the only product observed when the deuterated species CF3CD2ONO was photolysed by the 355 nm laser. These observations contradicted MP2/aug-cc-pVTZ calculations which were found to favour the C–C bond dissociation channel. However, 355 nm photolysis of CF3CH2ONO in the presence of O2 yielded trifluoroethylnitrate, CF3CH2ONO2 as the main product while CF3CHO and CF2O were also observable at much lower yields. 相似文献
35.
36.
Weihui Ou Binbin Zhou Junda Shen Tsz Wing Lo Dangyuan Lei Shengliang Li Jing Zhong Yang Yang Li Jian Lu 《Angewandte Chemie (International ed. in English)》2020,59(17):6790-6793
Hot carriers (HCs) and thermal effects, stemming from plasmon decays, are crucial for most plasmonic applications. However, quantifying these two effects remains extremely challenging due to the experimental difficulty in accurately measuring the temperature at reaction sites. Herein, we provide a novel strategy to disentangle HCs from photothermal effects based on the different traits of heat dissipation (long range) and HCs transport (short range), and quantitatively uncover the dominant and potential‐dependent role of photothermal effect by investigating the rapid‐ and slow‐response currents in plasmon‐mediated electrochemistry at nanostructured Ag electrode. Furthermore, the plasmoelectric surface potential is found to contribute to the rapid‐response currents, which is absent in the previous studies. 相似文献
37.
38.
Tsz Kin Tam Marcos Pita Mikhail Motornov Ihor Tokarev Sergiy Minko Evgeny Katz 《Electroanalysis》2010,22(1):35-40
The modified electrode functionalized with a mixed‐polymer brush composed of poly(2‐vinylpyridine) and polyacrylic acid tethered to the surface demonstrated switchable interfacial properties discriminating negatively and positively charged redox species. The switchable electrochemical process was characterized by differential pulse voltammetry and Faradaic impedance spectroscopy. The electrochemical system was discussed as a model of an electrochemical multiplexer with two chemical redox inputs, the pH input operating as the selecting signal and one electronic output signal readable by the impedance spectroscopy in the form of the interfacial resistance. The modified electrode represents a novel component for integration with biocatalytic and biocomputing systems aiming at biochemically and electronically controlled actuators. 相似文献
39.
Tsz Ho Chan 《Journal of Number Theory》2009,129(2):316-324
We consider the question of approximating any real number α by sums of n rational numbers with denominators 1?q1,q2,…,qn?N. This leads to inquiries on approximating a real number by rational numbers with a prescribed number of prime factors in the denominator as well as by rational numbers with smooth denominator. 相似文献
40.
Let be an increasing nonconstant sequence of positive real numbers. Under certain conditions on this sequence we prove the following
inequality
where n,m ∈ ℕ and r is a positive number, a
n
! denotes . The upper bound is the best possible. This inequality generalizes the Martins’ inequality. A special case of the above inequality
solves an open problem by F. Qi in Generalization of H. Alzer’s Inequality, J. Math. Anal. Appl. 240 (1999), 294–297. 相似文献