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排序方式: 共有114条查询结果,搜索用时 15 毫秒
91.
Letizia Amato Lars Schulte Arto Heiskanen Stephan S. Keller Sokol Ndoni Jenny Emnéus 《Electroanalysis》2015,27(7):1544-1549
In this work, we compare pyrolyzed carbon derived from the photoresist SU‐8 alone or in combination with polystyrene and poly(styrene)‐block‐poly(dimethylsiloxane) copolymer (PS‐b‐PDMS), to be used as novel materials for micro‐ and nanoelectrodes. The pyrolyzed carbon films are evaluated with scanning electron microscopy, thermal gravimetric analysis, X‐ray photoelectron spectroscopy, contact angle analysis, and Raman spectroscopy. Furthermore, the standard rate constant for electron transfer is determined from cyclic voltammograms and found to be lower for PS‐b‐PDMS compared to PS and SU‐8 films. This may be related to the lower carbon content of PS‐b‐PDMS, as well as to its higher microstructural disorder. 相似文献
92.
Paula Irmeli Oja Timo Tapani Kouri Arto Juhani Pakarinen 《Accreditation and quality assurance》2009,14(4):193-197
The article describes the customer feedback system at a university hospital laboratory and the analysis of the feedback data
from clinical customers in 2001–2006. The most common subject matters of the feedback were suspicion of the validity of laboratory
results, delay in service and lacking test results, covering 82% of the 115 reports. The investigations of the cases revealed
errors or defects in laboratory services in 81 cases. The most common errors or defects were erroneous test results (35 cases;
43%), delayed test results (24 cases; 30%) and lacking test results (15 cases; 18%). The most common underlying causes for
a laboratory error or defect were unintended errors and non-compliance with operating instructions. Seventy-six percent of
the feedback reports led to corrective actions. It is important to react to every instance of customer feedback and to find
out possible errors or defects in the laboratory process. Uncovering the underlying causes makes adequate corrective and preventive
actions possible. 相似文献
93.
Valkonen A Kolehmainen E Lahtinen M Sievänen E Noponen V Tolonen M Kauppinen R 《Molecules (Basel, Switzerland)》2007,12(9):2161-2178
The synthetic method for preparing N-(3-hydroxypropyl) 3 alpha,12 alpha-dihydroxy-5 beta-cholan-24-amide can lead to formation of at least three different crystal forms - an anhydrous compound and two monohydrates. The structural and thermal properties of these forms have been characterized by 13C-CP/MAS-NMR and IR spectroscopy, thermo- gravimetry, differential scanning calorimetry and by powder and single crystal x-ray crystallography. In addition, theoretical 13C-NMR chemical shift calculations were also performed for the anhydrous compound and for the first monohydrate, starting from single crystal structures and the structures of these species have now been verified. The first monohydrate, C27H47NO4 x H2O, crystallizes in orthorhombic space group P2(1)2(1)2(1) with cell parameters: a = 7.1148(2), b = 18.1775(5), c = 20.1813(6), Z = 4. 相似文献
94.
Kari Ahonen Babita Behera Elina Siev?nen Arto Valkonen Manu Lahtinen Minna Tolonen Reijo Kauppinen Erkki Kolehmainen 《Structural chemistry》2010,21(1):185-190
The synthetic procedure of lithocholyl-N-(2-aminoethyl)amide yielded a mixture of several forms detected by solid state 13C CP/MAS NMR although the solution state NMR unambiguously ascertained that the compound was pure. By recrystallization from
various solvents one pure polymorph alongside with four solvates were isolated. The structures of the pure polymorph and the
solvates were characterized by 13C and 15N CP/MAS NMR and powder X-ray diffraction (PXRD) methods. Variable contact time and dipolar dephasing experiments were employed
to obtain optimized CP parameters and to distinguish various CH
n
(n = 0–3) resonances. CSA analyses of spinning side bands at different spinning rates showed small variations in the shielding
tensor values of the carbonyl group between the pure polymorph (recrystallized from acetonitrile, tetrahydrofuran and 1,4-dioxane)
and p-xylene solvate. 相似文献
95.
Ośmiałowski Borys Kolehmainen Erkki Gawinecki Ryszard Kauppinen Reijo Koivukorpi Juha Valkonen Arto 《Structural chemistry》2010,21(5):1061-1067
Abstract
Association constants of 2,6-bis(alkylcarbonylamino)pyridines (alkyl = methyl or ethyl) and their perfluoroalkyl analogues with succin- and maleimide as well as with 2,2′-dipyridylamine (complementary DAD and ADA hydrogen bonding motifs are responsible for formation of the associates) have been determined by NMR titrations and quantum chemical calculations. Interactions of 2,6-bis(alkylcarbonylamino)pyridines with imides differ by character from these of perfluoroalkyl analogues. Such large difference was not observed for the 2,2′-dipyridylamine associates. Since fluorine atoms cause carbonylamino groups to be stronger hydrogen bond donors, perfluorinated species of this type were found to be more stable. Single crystal X-ray structures of 2,6-bis(trifluoromethylcarbonylamino)pyridine and 2,6-bis(pentafluoroethylcarbonylamino)pyridine have been also determined. 相似文献96.
Carl Henrik Grbitz Kari Rissanen Arto Valkonen smund Husab 《Acta Crystallographica. Section C, Structural Chemistry》2009,65(6):o267-o272
The amino acid l ‐phenylalanine has been cocrystallized with d ‐2‐aminobutyric acid, C9H11NO2·C4H9NO2, d ‐norvaline, C9H11NO2·C5H11NO2, and d ‐methionine, C9H11NO2·C5H11NO2S, with linear side chains, as well as with d ‐leucine, C9H11NO2·C6H13NO2, d ‐isoleucine, C9H11NO2·C6H13NO2, and d ‐allo‐isoleucine, C9H11NO2·C6H13NO2, with branched side chains. The structures of these 1:1 complexes fall into two classes based on the observed hydrogen‐bonding pattern. From a comparison with other l :d complexes involving hydrophobic amino acids and regular racemates, it is shown that the structure‐directing properties of phenylalanine closely parallel those of valine and isoleucine but not those of leucine, which shares side‐chain branching at Cγ with phenylalanine and is normally considered to be the most closely related non‐aromatic amino acid. 相似文献
97.
On the mechanism of extractive electrospray ionization (EESI) in the dual-spray configuration 总被引:1,自引:0,他引:1
Wang R Gröhn AJ Zhu L Dietiker R Wegner K Günther D Zenobi R 《Analytical and bioanalytical chemistry》2012,402(8):2633-2643
Dual-spray extractive electrospray ionization (EESI) mass spectrometry as a versatile analytical technique has attracted much interest due to its advantages over conventional electrospray ionization (ESI). The crucial difference between EESI and ESI is that in the EESI process, the analytes are introduced in nebulized form via a neutral spray and ionized by collisions with the charged droplets from an ESI source formed by spraying pure solvent. However, the mechanism of the droplet–droplet interactions in the EESI process is still not well understood. For example, it is unclear which type of droplet–droplet interaction is dominant: bounce, coalescence, disruption, or fragmentation? In this work, droplet–droplet interaction was investigated in detail based on a theoretical model. Phase Doppler anemometry (PDA) was employed to investigate the droplet behavior in the EESI plume and provide the experimental data (droplet size and velocity) necessary for theoretical analysis. Furthermore, numerical simulations were performed to clarify the influence of the sheath gas flow on the EESI process. No coalescence between the droplets in the ESI spray and the droplets in the sample spray was observed using various geometries and sample flow rates. Theoretical analysis, together with the PDA results, suggests that droplet fragmentation may be the dominant type of droplet–droplet interaction in the EESI. The interaction time between the ESI droplet and the sample droplet was estimated to be <5 μs. This work gives a clear picture of droplet–droplet interactions in the dual-spray EESI process and detailed information for the optimization of this method for future applications that require higher sensitivity. 相似文献
98.
N Probst A Madarász A Valkonen I Pápai K Rissanen A Neuvonen PM Pihko 《Angewandte Chemie (International ed. in English)》2012,51(34):8495-8499
Hold them tight: Guided by X-ray structures, bifunctional thiourea catalysts containing an activating intramolecular hydrogen bond were redesigned. The new catalysts were used to effect a highly enantioselective Mannich reaction between malonates and both aliphatic and aromatic imines (see scheme; Boc=tert-butoxycarbonyl). 相似文献
99.
Müller M Albrecht M Sackmann J Hoffmann A Dierkes F Valkonen A Rissanen K 《Dalton transactions (Cambridge, England : 2003)》2010,39(47):11329-11334
A series of phosphonium salts with pentafluorobenzyl substituents have been synthesized and were investigated in the crystal as well as in solution. The solid state structures of 1a, 1b and 2d reveal the presence of anion-π as well as CH-anion interactions. The two attractive, yet competitive forces seem to act in concert and a directing effect of the CH interaction on the relative position between anion and π-system is observed. The search for anion-π interactions in solution failed. Only CH-anion interactions proved to be important in solution. 相似文献
100.
Jaakko Niinimäki Arto Korkiakoski Outi Ojala Jaro Karppinen Jyrki Ruohonen Marianne Haapea Raija Korpelainen Antero Natri Osmo Tervonen 《Magnetic resonance imaging》2009
The value of apparent diffusion coefficient (ADC) measurements in intervertebral disc has been studied because ADC provides an estimate of free diffusion of unbound water and could be used as a quantitative tool to estimate degenerative changes. However, the challenging nature of diffusion imaging of spine and limited numbers of subjects in earlier studies has produced contradictory findings. We aimed to determine the relation between ADC and visual degenerative changes in lumbar intervertebral discs in a sufficiently large homogeneous study group. Lumbar spines of 228 volunteer middle-aged men were MR imaged at 1.5 T including anatomic and diffusion-weighted imaging. ADC values, T2 signal intensity and height, and width of the three lowest lumbar intervertebral discs were measured and disc degeneration visually graded. The calculated average ADC of 530 measured discs was 2.01×10−3 mm2/s±0.29 (±S.D.). The reduction in ADC between visually normal and moderately degenerated discs was 4%. Severely degenerated discs showed 5% larger ADC values than normal discs, presumably due to free water in cracks and fissures of those discs. T2 signal intensity of the disc was significantly correlated with the ADC values, whereas other measured parameters did not show correlation. There was no evident difference in ADC between the studied anatomic lumbar levels. Because there is considerable overlap between ADC values of normal and degenerated discs, we conclude that ADC measurements of intervertebral discs, at least with current technology, have limited clinical value. 相似文献