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排序方式: 共有164条查询结果,搜索用时 31 毫秒
141.
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
142.
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
143.
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
144.
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
145.
The compound NH4Mn(HSeO3)3 has been prepared and its IR spectrum and thermal behaviour have been investigated. It crystallizes in the monoc 相似文献
146.
147.
Minna GünesÛ Kalle Nttinen Jussi Valkonen 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(1):i21-i22
The title compound, CaCs2[Ag2(SCN)6]·2H2O, forms a continuous structure where the Ag atoms form chains with S atoms in the c‐axis direction. The chains are bonded together through Cs and Ca atoms. The crystal water of the structure is bonded to the Ca atoms, which lie on centers of symmetry. 相似文献
148.
149.
150.
Investigation of ZnS thin films on Si(100) by phase detection imaging and Young’s modulus microscopy
R. Resch G. Friedbacher M. Grasserbauer S. Lindroos T. Kanniainen M. P. Valkonen M. Leskelä 《Analytical and bioanalytical chemistry》1998,361(6-7):613-617
In this study phase detection imaging (PDI) and Young’s modulus microscopy (YMM) have been used for investigation of ZnS thin films deposited on Si(100) substrates with successive ionic layer adsorption and reaction (SILAR). The additional information obtained by these techniques allows a better interpretation of the topographic images in the case of the determination of the number of grains, their distribution and surface coverage. Moreover, the comparison between PDI and YMM is discussed in order to shed more light on the contrast mechanism in phase detection imaging. 相似文献