全文获取类型
收费全文 | 108篇 |
免费 | 2篇 |
国内免费 | 7篇 |
专业分类
化学 | 53篇 |
综合类 | 2篇 |
数学 | 20篇 |
物理学 | 42篇 |
出版年
2022年 | 2篇 |
2020年 | 1篇 |
2019年 | 1篇 |
2017年 | 2篇 |
2016年 | 1篇 |
2015年 | 2篇 |
2014年 | 6篇 |
2013年 | 10篇 |
2012年 | 6篇 |
2011年 | 13篇 |
2010年 | 5篇 |
2009年 | 4篇 |
2008年 | 6篇 |
2007年 | 11篇 |
2006年 | 8篇 |
2005年 | 7篇 |
2004年 | 4篇 |
2003年 | 2篇 |
2002年 | 3篇 |
2000年 | 1篇 |
1998年 | 2篇 |
1997年 | 3篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1992年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1980年 | 1篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1966年 | 1篇 |
1959年 | 1篇 |
1933年 | 2篇 |
1932年 | 1篇 |
排序方式: 共有117条查询结果,搜索用时 15 毫秒
31.
Ablajan K 《Journal of mass spectrometry : JMS》2011,46(1):77-84
Isoflavone mono‐O‐glycosides were investigated by electrospray ionization tandem mass spectrometry with a quadrupole linear ion trap mass spectrometer in negative ion mode. Isoflavonoids having different positions of glycosylation or methylation were differentiated according to the relative abundances of Y0? and [Y0? H]?? ions generated from the [M ? H]? ion. It is found that the site of glycosyl or methyl group significantly affects relative abundances of the Y0? and [Y0? H]?? ions. In addition, the characteristic ion [Y0? 2H]? was observed in the product ion spectrum of genistein 7‐O‐β‐D ‐glucoside and was also detected, together with the [Y0? CH3]?? and [Y0? H ? CH3]? ions in the product ion spectra of glycitin and 6‐methoxy genistein 7‐O‐β‐D ‐glucoside. The structures of isoflavonoids can be characterized and identified according to the formation of these diagnostic ions. The results obtained from this investigation can promote the rapid identification of isoflavonoids in crude plant extracts. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
32.
Silvia Kováčová Lucia Kováčiková Margita Lácová Andrej Boháč Marta Sališová 《Chemical Papers》2010,64(6):806-811
Perkin condensation with subsequent intramolecular lactonisation as one pot syntheses of 2-(2-oxo-2H-chromen-3-yl)acetic acids VIIa-Xa has been studied. The required acids VIIa-Xa were prepared as precursors of recently discovered compounds possessing antineoplastic activities. Syntheses of VIIa-Xa were carried out using para substituted 2-hydroxybenzaldehydes II-VI, succinic acid anhydride, sodium succinate under thermal or microwave conditions. Significant shortening of the reaction
time under microwave irradiation was observed (18–50 min instead of 1.5–5 h of heating). Microwave assisted reactions proceeded
more smoothly to give higher yield of the required products VIIa-Xa (31–61 %) compared to those under classical thermal conditions e.g. 21.8 % for IXa (Hurenkamp et al., 2007). Seven reaction by-products were isolated and determined as 2H,2′H-3,3′-bichromene-2,2′-diones VIIb-Xb and (E)-3-(2-hydroxystyryl)-2H-chromen-2-ones VIIc-IXc. 相似文献
33.
We present experimental results of enhanced second- and third-harmonic generation efficiency from Fresnel-lensing effects. We obtained enhancement by a factor of 6 in the third-harmonic yield by simply limiting the laser beam with an iris. Higher enhancement factors (up to 16) were obtained with a Fresnel zone plate. The experimental findings are in good agreement with the results of a simple theoretical analysis. 相似文献
34.
We report the first direct measurements of the atomic dipole phase in the process of high-order harmonic generation. Differently from previously reported studies based on frequency chirp measurements, we use extreme ultraviolet interferometry as the most natural and direct way to measure phase shifts. Our approach has the important advantage of allowing us to investigate the effects associated to both the main quantum paths involved in the emission of a particular harmonic, thus offering a particularly clear and simple picture of the underlying electronic dynamics. 相似文献
35.
We are presenting in this volume the collection of extended abstracts that were selected for presentation at EUROCOMB?11 in Budapest. EUROCOMB conferences are organized biannually, the series was started in Barcelona 2001, and continued with Prague 2003, Berlin 2005, Seville 2007 and Bordeaux 2009. Since Prague EUROCOMB?03 the European Prize is awarded at the meeting. The prize is established to recognize excellent contributions in Combinatorics, Discrete Mathematics and their Applications by young European researchers (eligibility of EU) not older than 35. It is supported by DIMATIA and by private sources.The role of combinatorics is growing in the contemporary research in mathematics, computer science, engineering, also in physics, life and social sciences. This is reflected in the growing interest in EUROCOMB conferences, which became an established forum of the frontier research in these fields. This year a total of 188 contributions were submitted and the Program Committee selected 135 extended abstracts to be presented at the conference. As a comparison, there were 142 contributions for EUROCOMB?07 in Seville and 92 of those were selected for presentation.We thank all members of the Program Committee for their work. We also thank to allmembers of the Organizing Committee of EUROCOMB?11 for all their work in preparing the meeting in lovely Budapest. 相似文献
36.
We demonstrate efficient generation of high-order anti-Stokes Raman sidebands in a highly transient regime, using a pair of approximately 100-fs laser pulses tuned to Raman resonance with vibrational transitions in methane or hydrogen. The use of this technique looks promising for efficient subfemtosecond pulse generation. 相似文献
37.
38.
Kovacev M Fomichev SV Priori E Mairesse Y Merdji H Monchicourt P Breger P Norin J Persson A L'Huillier A Wahlström CG Carré B Salières P 《Physical review letters》2005,95(22):223903
We demonstrate a new scheme for extreme ultraviolet (xuv) Fourier-transform spectroscopy based on the generation of two phase-locked high-harmonic beams. It allows us to measure for the first time interferograms at wavelengths as short as 90 nm, and open the perspective of performing high-resolution Fourier-transform absorption spectroscopy in the xuv. Our measurements also demonstrate that a precise control of the relative phase of harmonic pulses can be obtained with an accuracy on an attosecond time scale, of importance for future xuv pump-xuv probe attosecond spectroscopy. 相似文献
39.
Molecular Diversity - An efficient and simple procedure for the synthesis of 6-amino-5-cyano-4-phenyl-pyrano[2,3-c]pyrazole-4-carboxylic acid esters was developed via a one-pot reaction of... 相似文献
40.
The donor impurity-related electron states in GaAs cone-like quantum dots under the influence of an externally applied static electric field are theoretically investigated. Calculations are performed within the effective mass and parabolic band approximations, using the variational procedure to include the electron–impurity correlation effects. The uncorrelated Schrödinger-like electron states are obtained in quasi-analytical form and the entire electron–impurity correlated states are used to calculate the photoionisation cross section. Results for the electron state energies and the photoionisation cross section are reported as functions of the main geometrical parameters of the cone-like structures as well as of the electric field strength. 相似文献