全文获取类型
收费全文 | 205篇 |
免费 | 6篇 |
专业分类
化学 | 108篇 |
晶体学 | 1篇 |
力学 | 6篇 |
数学 | 26篇 |
物理学 | 70篇 |
出版年
2022年 | 4篇 |
2021年 | 3篇 |
2020年 | 3篇 |
2019年 | 2篇 |
2018年 | 4篇 |
2016年 | 10篇 |
2015年 | 11篇 |
2014年 | 6篇 |
2013年 | 8篇 |
2012年 | 8篇 |
2011年 | 5篇 |
2010年 | 6篇 |
2009年 | 7篇 |
2008年 | 10篇 |
2007年 | 11篇 |
2006年 | 10篇 |
2005年 | 11篇 |
2004年 | 8篇 |
2003年 | 7篇 |
2002年 | 11篇 |
2001年 | 5篇 |
2000年 | 7篇 |
1999年 | 3篇 |
1998年 | 3篇 |
1997年 | 2篇 |
1996年 | 5篇 |
1995年 | 4篇 |
1994年 | 2篇 |
1993年 | 4篇 |
1992年 | 3篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1989年 | 4篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 4篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1966年 | 2篇 |
1965年 | 1篇 |
排序方式: 共有211条查询结果,搜索用时 15 毫秒
111.
We demonstrate the possibility to control the spatial mode of a narrow-linewidth, continuous-wave, infrared radiation beam generated by difference frequency in a periodically poled crystal. This can be achieved by acting directly on a few experimental parameters. We show that hollow beams can be generated. A numerical routine has been developed and results agree with experimental observations, without requiring any free parameters. The relevance of these results for high-resolution spectroscopy and atom manipulation is discussed. 相似文献
112.
Pacetti D Malavolta M Bocci F Boselli E Frega NG 《Rapid communications in mass spectrometry : RCM》2004,18(20):2395-2400
Since phosphatidylcholine (PC) is the most abundant phospholipid (PL) class in human serum, its concentration represents an important marker for the evaluation of lipid absorption and metabolism. High-performance liquid chromatography coupled on-line with electrospray ionization ion-trap tandem mass spectrometry (HPLC/ESI-MS/MS) was successfully applied to the quantitative analysis of PC molecular species from serum of cystic fibrosis (CF) subjects before and after supplementation with docosahexaenoic acid (DHA). Seven molecular species of PC (containing C16:0/C20:4, C16:0/C22:6, C18:0/C20:4, C18:0/C22:6, C16:0/C18:1, C16:0/C18:2 and C18:0/C18:2, respectively) were quantified using MS in the negative scan mode with 1,2-diundecanoyl-sn-glycero-phosphocholine as the internal standard. The molecular species containing DHA, C16:0/C22:6 and C18:0/C22:6, increased from 41.3 +/- 31.7 and 33.1 +/- 18.2 to 85.4 +/- 20.4 and 52.1 +/- 20.7 microg/mL serum, respectively, after a 3-month supplementation. Interestingly, the species containing arachidonic acid (C18:0/C20:4 and C16:0/C20:4) decreased from 115 +/- 55 and 139 +/- 57 to 58.1 +/- 22.5 and 70.5 +/- 28.1, respectively. HPLC/ESI-MS/MS allowed the direct analysis of the lipid extract without previous purification of PLs, thus it is a useful analytical support in CF research in order to understand the extent of lipid dysfunctions typical of CF or other diseases. The present method might also be used for quantitative analysis of each serum phospholipid class molecular species. However, the instrument response was found to be very dependent on the phospholipid class considered, and thus the use of appropriate standards for each class of PLs is recommended. 相似文献
113.
We show that in pure gauge QCD (or any pure non-Abelian gauge theory) the condition for the existence of a global minimum of energy with a gluon (gauge boson) mass scale also implies the existence of a fixed point of the beta function. We argue that the frozen value of the coupling constant found in some solutions of the Schwinger-Dyson equations of QCD can be related to this fixed point. We also discuss how the inclusion of fermions modifies this property. 相似文献
114.
Absolute frequency measurements of the 2(3)S1-->2(3)P 0,1,2 atomic helium transitions around 1083 nm
Pastor PC Giusfredi G De Natale P Hagel G De Mauro C Inguscio M 《Physical review letters》2004,92(2):023001
We measure the frequency of the 2(3)S1-->2(3)P(0,1,2) transitions of helium in a metastable beam using an optical frequency comb synthesizer. The relative uncertainty of these measurements ranging from 5x10(-11) to 7x10(-12) is, to our knowledge, the most precise result for any optical helium transition. Considering existing accurate values of the 2(3)P fine structure, we measure a centroid value of the 2(3)S-2(3)P frequency of 276 736 495 624.6(2.4) kHz, improving the previous interferometric measurement by 30 times. New accurate values of the 2(3)S-2(3)P and 2(3)P Lamb-shift energies are obtained. 相似文献
115.
Donatella Nardiello Carmen PalermoAnna Natale Maurizio QuintoDiego Centonze 《Analytica chimica acta》2015
In this work, the application of a new pulsed amperometric detection (PAD) waveform at a glassy carbon electrode, operating in typical chromatographic mobile phases, is proposed for the sensitive and reproducible determination of arylethanolaminic and phenolic moiety based compounds (e.g. beta-agonists and polyphenols). Preliminary experiments by cyclic voltammetry were carried out to investigate the electrochemical behaviour and to select the detection and cleaning electrode potentials. The proposed potential-time profile was designed to prevent the carbon electrode fouling under repeated analyses, thus ensuring a reproducible and sensitive quantitative determination, without the need of any mechanical or chemical electrode cleaning procedure. The waveform electrochemical parameters, including detection and delay times, were optimized in terms of sensitivity, limit of detection and response stability. The optimized waveform allowed the sensitive and stable detection of model compounds, such as clenbuterol and caffeic acid, that showed detection limits of 0.1 μg L−1 and 14 μg L−1, quantification limits of 0.4 μg L−1 and 46 μg L−1, and linearity up to 100 μg L−1 (r = 0.9993) and 10 mg L−1 (r = 0.9998), respectively. Similar results were obtained for other compounds of the same classes, with precision values under repeatability conditions ranging from 3.0 to 5.9%. The proposed method can be then considered as an excellent alternative to the post-column detection of beta-agonists, phenols and polyphenols. 相似文献
116.
117.
Bartalini S Cancio P Giusfredi G Mazzotti D De Natale P Borri S Galli I Leveque T Gianfrani L 《Optics letters》2007,32(8):988-990
We report what we believe to be the first absolute frequency measurement performed using a quantum-cascade laser (QCL) referenced to an optical frequency comb synthesizer (OFCS). A QCL at 4.43 microm has been used for producing near-infrared radiation at 858 nm by means of sum-frequency generation with a Nd:YAG source in a periodically poled lithium niobate nonlinear crystal. The absolute frequency of the QCL source has been measured by detecting the beat note between the sum frequency and a diode laser at the same wavelength, while both the Nd:YAG and the diode laser were referenced to the OFCS. Doppler-broadened line profiles of (13)CO(2) molecular transitions have been recorded with such an absolute frequency reference. 相似文献
118.
119.
Nastasi F Puntoriero F Palmeri N Cavallaro S Campagna S Lanza S 《Chemical communications (Cambridge, England)》2007,(45):4740-4742
In the solid state, a non-luminescent platinum(ii) dithiooxamide species adsorbs gaseous HCl, yielding a tight ion pair species which exhibits photoluminescence; the process is quantitatively reversed on heating or by exposing the sample to ammonia vapors. 相似文献
120.
Osz K Nagy Z Pappalardo G Di Natale G Sanna D Micera G Rizzarelli E Sóvágó I 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(25):7129-7143
A 31-mer polypeptide, which encompasses residues 84-114 of human prion protein HuPrP(84-114) and contains three histidyl residues, namely one from the octarepeat (His85) and two histidyl residues from outside the octarepeat region (His96 and His111), and its mutants with two histidyl residues HuPrP(84-114)His85Ala, HuPrP(84-114) His96Ala, HuPrP(84-114)His111Ala and HuPrP(91-115) have been synthesised and their Cu2+ complexes studied by potentiometric and spectroscopic (UV/Vis, CD, EPR, ESI-MS) techniques. The results revealed a high Cu2+-binding affinity of all peptides, and the spectroscopic studies made it possible to clarify the coordination mode of the peptides in the different complex species. The imidazole nitrogen donor atoms of histidyl residues are the exclusive metal-binding sites below pH 5.5, and they have a preference for macrochelate structure formation. The deprotonation and metal-ion coordination of amide functions take place by increasing the pH; all of the histidines can be considered to be independent metal-binding sites in these species. As a consequence, di- and trinuclear complexes can be present even in equimolar samples of the metal ion and peptides, but the ratios of polynuclear species do not exceed the statistically expected ones; this excludes the possibility of cooperative Cu2+ binding. The species with a (N(im),N,N)-binding mode are favoured around pH 7, and their stability is enhanced by the macrochelation from another histidyl residue in the mononuclear complexes. The independence of the histidyl sites results in the existence of coordination isomers and the preference for metal binding follows the order of: His111>His96>His85. Deprotonation and metal-ion coordination of the third amide functions were detected in slightly alkaline solutions at each of the metal-binding sites; all had a (N(im),N,N,N)-coordination mode. Spectroscopic measurements also made it clear that the four lysyl amino groups of the peptides are not metal-binding sites in any cases. 相似文献