全文获取类型
收费全文 | 408篇 |
免费 | 29篇 |
国内免费 | 2篇 |
专业分类
化学 | 232篇 |
晶体学 | 1篇 |
力学 | 13篇 |
数学 | 68篇 |
物理学 | 125篇 |
出版年
2023年 | 10篇 |
2021年 | 19篇 |
2020年 | 11篇 |
2019年 | 9篇 |
2018年 | 17篇 |
2017年 | 11篇 |
2016年 | 35篇 |
2015年 | 13篇 |
2014年 | 16篇 |
2013年 | 24篇 |
2012年 | 25篇 |
2011年 | 28篇 |
2010年 | 17篇 |
2009年 | 7篇 |
2008年 | 12篇 |
2007年 | 15篇 |
2006年 | 11篇 |
2005年 | 13篇 |
2004年 | 14篇 |
2003年 | 13篇 |
2002年 | 9篇 |
2001年 | 6篇 |
2000年 | 5篇 |
1999年 | 3篇 |
1998年 | 3篇 |
1996年 | 5篇 |
1994年 | 7篇 |
1993年 | 4篇 |
1992年 | 4篇 |
1989年 | 4篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1983年 | 2篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1980年 | 5篇 |
1979年 | 4篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1973年 | 3篇 |
1972年 | 3篇 |
1971年 | 2篇 |
1967年 | 2篇 |
1935年 | 2篇 |
1928年 | 2篇 |
1927年 | 2篇 |
1884年 | 2篇 |
1875年 | 2篇 |
排序方式: 共有439条查询结果,搜索用时 31 毫秒
101.
MISTRAL: a transmission soft X‐ray microscopy beamline for cryo nano‐tomography of biological samples and magnetic domains imaging
下载免费PDF全文
![点击此处可从《Journal of synchrotron radiation》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Andrea Sorrentino Josep Nicolás Ricardo Valcárcel Francisco Javier Chichón Marc Rosanes Jose Avila Andrei Tkachuk Jeff Irwin Salvador Ferrer Eva Pereiro 《Journal of synchrotron radiation》2015,22(4):1112-1117
The performance of MISTRAL is reported, the soft X‐ray transmission microscopy beamline at the ALBA light source (Barcelona, Spain) which is primarily dedicated to cryo soft X‐ray tomography (cryo‐SXT) for three‐dimensional visualization of whole unstained cells at spatial resolutions down to 30 nm (half pitch). Short acquisition times allowing for high‐throughput and correlative microscopy studies have promoted cryo‐SXT as an emerging cellular imaging tool for structural cell biologists bridging the gap between optical and electron microscopy. In addition, the beamline offers the possibility of imaging magnetic domains in thin magnetic films that are illustrated here with an example. 相似文献
102.
Nicolás Ríos‐Lombardía Eduardo Busto Dr. Vicente Gotor‐Fernández Dr. Vicente Gotor Prof. Raúl Porcar Eduardo García‐Verdugo Dr. Santiago V. Luis Prof. Ignacio Alfonso Dr. Santiago García‐Granda Prof. Amador Menéndez‐Velázquez Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(3):836-847
This paper reports a simple and robust modular synthetic strategy that leads to a large variety of configurationally and structurally diverse imidazole‐based chiral ionic liquids (CILs) by lipase‐catalyzed resolution. The intimate microscopic interactions of the supramolecular ionic network of these imidazolium chiral salts at the molecular level are investigated both spectroscopically (NMR, FT‐IR‐ATR) and theoretically, and a topological analysis of the experimental electron densities obtained by X‐ray dif fr action of single crystals is performed. Our results support the key role played by the relative configuration of the ‐OR group on the hydrogen‐bonding pattern and its strong influence on the final physical properties of the imidazolium salt. We also obtained a reasonable correlation between the observed melting point and the non‐covalent interactions. The spectroscopic data and the topological analysis reflect the key role played by hydrogen bonds between the OH and imidazolium C2H groups in both cation–anion and cation–cation interactions, with the presence of an OH group leading to an additional inter‐cation interaction. This interaction significantly affects the properties of stereoisomeric salts. Even more interestingly, we also studied the effect of the chirality by comparing enantiopure CILs with their racemic mixtures and found that, with the exception of trans‐Cy6‐OH‐Im‐Bn‐Br, the melting points of the racemic mixtures are higher than those of the corresponding enantiomerically pure forms. For stereoisomeric examples, we have successfully explained the differences in melting temperatures in light of the corresponding structural data. Chirality should therefore be taken into account as a highly attractive design vector in the preparation of ILs with specifically desired properties. 相似文献
103.
104.
Núñez C Bastida R Macías A Valencia L Neuman NI Rizzi AC Brondino CD González PJ Capelo JL Lodeiro C 《Dalton transactions (Cambridge, England : 2003)》2010,39(48):11654-11663
The Py(2)N(4)S(2) octadentate coordinating ligand afforded dinuclear cobalt, copper and zinc complexes and the corresponding mixed metal compounds. The overall geometry and bonding modes have been deduced on the basis of elemental analysis data, MALDI-TOF-MS, IR, UV-vis and EPR spectroscopies, single-crystal X-Ray diffraction, conductivity and magnetic susceptibility measurements. In the copper and zinc complexes, a μ-hydroxo bridge links the two metal ions. In both cases, the coordination geometry is distorted octahedral. Magnetic and EPR data reveal weakly antiferromagnetic high spin Co(II) ions, compatible with a dinuclear structure. The magnetic characterization of the dinuclear Cu(II) compound indicates a ferromagnetically coupled dimer with weak antiferromagnetic intermolecular interactions. The intra-dimer ferromagnetic behaviour was unexpected for a Cu(II) dimer with such μ-hydroxo bridging topology. We discuss the influence on the magnetic properties of non-covalent interactions between the bridging moiety and the lattice free water molecules. 相似文献
105.
106.
Palumbo Piccionello A Guarcello A Buscemi S Vivona N Pace A 《The Journal of organic chemistry》2010,75(24):8724-8727
The reaction of various 1,2,4-oxadiazoles with an excess of hydrazine in DMF has been investigated. 3-Amino-1,2,4-triazoles are produced through a reductive ANRORC pathway consisting of the addition of hydrazine to the 1,2,4-oxadiazole followed by ring-opening, ring-closure, and final reduction of the 3-hydroxylamino-1,2,4-triazole intermediate. The general applicability of 1,2,4-oxadiazoles ANRORC reactivity is demonstrated also in the absence of C(5)-linked electron-withdrawing groups. 相似文献
107.
Tognalli NG Fainstein A Vericat C Vela ME Salvarezza RC 《The journal of physical chemistry. B》2006,110(1):354-360
Resonant Raman and surface-enhanced Raman scattering (SERS) spectroscopies, complemented with scanning tunnel microscopy and electrochemical techniques, have been used to obtain information about the amount and spatial distribution of methylene blue (MB) molecules immobilized on sulfur and four ultrathin molecular alkanethiolate films self-assembled on Au(111) and rough Au electrodes. The intensity of the Raman signals allow one to estimate the amount of immobilized MB at different organic films, whereas the decrease in the SERS intensity as a function of distance for the rough Au electrodes is used to locate the average position of the MB species with respect to the Au substrate. We found that significant amounts of cationic MB species are able to diffuse into methyl-terminated thiols, but they are stopped at the outer plane of the self-assembled monolayer (SAM) by negatively charged carboxylate groups. The relative shift of C-N stretching Raman modes indicates that the binding of MB to S is different from that found for MB on thiols. Most of the molecules immobilized on methyl- and carboxylate-terminated thiols are electrochemically inactive, suggesting that strong coupling between the Au electrode and the MB molecules is needed for charge transfer. Our results are consistent with a small population of electrochemically active MB species very close to the Au surface that reach this position driven by their lipophilic (hydrophobic) character through defects at SAMs. 相似文献
108.
Suppose {f
1,...,f
m
} is a set of Lipschitz maps of
d
. We form the iterated function system (IFS) by independently choosing the maps so that the map f
i
is chosen with probability p
i
(
m
i=1
p
i
=1). We assume that the IFS contracts on average. We give an upper bound for the upper Hausdorff dimension of the invariant measure induced on
d
and as a corollary show that the measure will be singular if the modulus of the entropy
i
p
i
log p
i
is less than d times the modulus of the Lyapunov exponent of the system. Using a version of Shannon's Theorem for random walks on semigroups we improve this estimate and show that it is actually attainable for certain cases of affine mappings of . 相似文献
109.
Paul Jara Nicolás Yutronic Guillermo González 《Journal of inclusion phenomena and macrocyclic chemistry》1995,22(3):203-210
The synthesis and structural aspects of urea host-guest inclusion compounds containing linear secondary alkylamines (dibutyl-,dipentyl-, dihexyl-, dioctyl-) at 25°C are reported. Elemental analysis,13C CP-MAS NMR and1H-NMR Spectroscopy, and Powder X-ray Diffraction Analysis confirm the inclusion process. The basic host structure of the products is similar to that of urea-hydrocarbon systems.13C MAS-NMR experiments show chemical shift differences for the confined guest molecule with respect to the liquid phase. Stoichiometry and |c
g| values for the inclusion compounds with dipentyl-and dihexylamine suggest a commensurate structure. 相似文献
110.
Moreno Frías M Jiménez Torres M Garrido Frenich A Martínez Vidal JL Olea-Serrano F Olea N 《Biomedical chromatography : BMC》2004,18(2):102-111
A study was undertaken to determine the extent of organochlorine pesticide (OP) and polychlorinated biphenyl (PCB) contamination in infant formula milk and in the human milk, fat and serum of women from an agricultural area in Southern Spain. A procedure is proposed that simultaneously detects trace levels of lindane, endosulfan-ether, vinclozolin, aldrin, endosulfan-lactone, endosulfan-alpha, 4,4'DDE, 2,4'DDT, endosulfan-beta, 4,4'DDT, kepone, endosulfate-sulfate, methoxychlor, mirex, 2,3,4 PCB, 2,2',4,5 PCB, 2,3,4,5 PCB and 2,2',3,3',6,6'PCB. After liquid-liquid or solid-liquid extraction, the extract of the sample was cleaned by high performance liquid chromatography (HPLC) and the fi rst eluted fraction was analysed by gas chromatography (GC) with mass spectrometry (MS) detector in tandem mode. To evaluate the validity of the method the following parameters were studied: linearity, detection limits, quantification limits, specificity, percentage recovery and precision. A study of the uncertainty associated with the analytical method was also carried out. 相似文献