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排序方式: 共有196条查询结果,搜索用时 15 毫秒
21.
Katrina A. Jolliffe Mercedes Crego Calama Roel Fokkens Nico M. M. Nibbering Peter Timmerman David N. Reinhoudt 《Angewandte Chemie (International ed. in English)》1998,37(9):1247-1251
The high affinity of Ag + ions for aromatic π donors and cyano groups is exploited in a novel MALDI-TOF mass spectrometric method for the identification of hydrogen-bonded assemblies. The interaction with the Ag+ ions—which, for example, can be complexed by two phenyl groups in a sandwich-type manner (see drawing on the right)—provides positively charged assemblies in a nondestructive way. 相似文献
22.
Roel De Mondt Luc Van Vaeck Andreas Heile Heinrich F. Arlinghaus Frank Vangaever Jens Lenaerts 《Analytical and bioanalytical chemistry》2009,393(8):1917-1921
Recent publications on static secondary ion mass spectrometry (S-SIMS) focus on molecular depth profiling by using polyatomic
or ultra-low energy monoatomic projectiles. Since their applicability depends on the relationship between the ion yield and
the depth, which is hard to obtain without extensive studies, a combination of a wear test method with S-SIMS surface analysis
was performed in the current study. Using this non-sputtering procedure, the relation between the signal intensity and the
local concentration remains in principle the same as that at the surface (which is easy to determine). Mechanical erosion
was successfully applied to expose sub-surface material from organic multilayers. Through surface analysis with S-SIMS on
the gradually exposed deeper planes, molecular depth profiles could be obtained. The study was conducted on a model system
relevant to offset printing, consisting of two polymer layers, containing dyes and a surfactant, cast on an Al substrate.
Figure Concept of mechanical erosion followed by S-SIMS surface analysis to obtain molecular depth profiles 相似文献
23.
24.
Dr. Khurram Saleem Joya Dr. Yasir F. Joya Prof. Kasim Ocakoglu Prof. Roel van de Krol 《Angewandte Chemie (International ed. in English)》2013,52(40):10426-10437
The development of new energy materials that can be utilized to make renewable and clean fuels from abundant and easily accessible resources is among the most challenging and demanding tasks in science today. Solar‐powered catalytic water‐splitting processes can be exploited as a source of electrons and protons to make clean renewable fuels, such as hydrogen, and in the sequestration of CO2 and its conversion into low‐carbon energy carriers. Recently, there have been tremendous efforts to build up a stand‐alone solar‐to‐fuel conversion device, the “artificial leaf”, using light and water as raw materials. An overview of the recent progress in electrochemical and photo‐electrocatalytic water splitting devices is presented, using both molecular water oxidation complexes (WOCs) and nano‐structured assemblies to develop an artificial photosynthetic system. 相似文献
25.
Wijdeven MA Botman PN Wijtmans R Schoemaker HE Rutjes FP Blaauw RH 《Organic letters》2005,7(18):4005-4007
The stereoselective total synthesis of the novel quinolizidine alkaloid (+)-epiquinamide is presented, starting from the amino acid l-allysine ethylene acetal. Key steps in the synthesis involved a highly diastereoselective N-acyliminium ion allylation and a ring-closing metathesis reaction to provide the bicyclic skeleton. [reaction: see text] 相似文献
26.
27.
Herman Zagppey Roel H. Fokkens Steen Ingemann Nico M. M. Nibbering Helena Florencio 《Journal of mass spectrometry : JMS》1991,26(6):587-594
The regioselectivity of methyl cation transfer from (CH3)2F+, (CH3)2Cl+ and (CH3)3O+ to 1-phenyl-2-aminopropane was studied by Fourier transform ion cyclotron resonance in combination with collision-induced dissociation and neutralization-reionization mass spectrometry of the stable [M + CH3]+ ions formed in a chemical ionization source. The (CH3)2F+ ion transfers a methyl cation to the NH2 group and the phenyl ring with almost equal probability. Predominant CH3+ transfer to the NH2 group is observed for the (CH3)2Cl+ ion whereas the (CH3)3O+ ion reacts almost exclusively at the amino group. The preference for methylation at NH2 is discussed in terms of a lower methyl cation affinity of the phenyl ring than of the amino group and the existence of an energy barrier for methylation of the phenyl moiety. 相似文献
28.
Wincel H Fokkens RH Nibbering NM 《Rapid communications in mass spectrometry : RCM》2000,14(3):135-140
There is a general fascination with regard to the origin of life on Earth. There is an intriguing possibility that prebiotic precursors of life occurred in the interstellar space and were then transported to the early Earth by comets, asteroids and meteorites. It is probable that some part of the prebiotic molecules may have been generated by gas-phase ion/molecule reactions. Here we show experimentally that gaseous ion/molecule reactions of the amino acids, Glu and Met, may promote the synthesis of protonated dipeptides such as (Glu-Glu)H(+) and (Glu-Met)H(+) and their chemical growth to larger protonated peptides. 相似文献
29.
Angang Song Igal Levine Roel van de Krol Thomas Dittrich Sean P. Berglund 《Chemical science》2020,11(41):11195
p-Type CuBi2O4 is considered a promising metal oxide semiconductor for large-scale, economic solar water splitting due to the optimal band structure and low-cost fabrication. The main challenge in utilizing CuBi2O4 as a photoelectrode for water splitting, is that it must be protected from photo-corrosion in aqueous solutions, an inherent problem for Cu-based metal oxide photoelectrodes. In this work, several buffer layers (CdS, BiVO4, and Ga2O3) were tested between CuBi2O4 and conformal TiO2 as the protection layer. RuOx was used as the co-catalyst for hydrogen evolution. Factors that limit the photoelectrochemical performance of the CuBi2O4/TiO2/RuOx, CuBi2O4/CdS/TiO2/RuOx, CuBi2O4/BiVO4/TiO2/RuOx and CuBi2O4/Ga2O3/TiO2/RuOx heterojunction photoelectrodes were revealed by comparing photocurrents, band offsets, and directed charge transfer measured by modulated surface photovoltage spectroscopy. For CuBi2O4/Ga2O3/TiO2/RuOx photoelectrodes, barriers for charge transfer strongly limited the performance. In CuBi2O4/CdS/TiO2/RuOx, the absence of hole traps resulted in a relatively high photocurrent density and faradaic efficiency for hydrogen evolution despite the presence of pronounced deep defect states at the CuBi2O4/CdS interface. Hole trapping limited the performance moderately in CuBi2O4/BiVO4/TiO2/RuOx and strongly in CuBi2O4/TiO2/RuOx photoelectrodes. For the first time, our results show that hole trapping is a key factor that must be addressed to optimize the performance of CuBi2O4-based heterojunction photoelectrodes.CdS, BiVO4, and Ga2O3 buffer layers were tested between CuBi2O4 and TiO2 in heterojunction photoelectrodes. Photoelectrochemical analysis and modulated surface photovoltage spectroscopy revealed that interface hole traps impacted device performance. 相似文献
30.
Steen Ingemann Steen Hammerum Peter J. Derrick Roel H. Fokkens Nico M. M. Nibbering 《Journal of mass spectrometry : JMS》1989,24(10):885-888
Deuterium substitution at remote sites gives rise to inverse secondary kinetic isotope effects on the α-cleavage of a number of tertiary amines in the ion source, but to normal isotope effects on reactions occurring in the field-free regions. The change from normal to inverse secondary isotope effects when the internal energy of the reacting ions increases is consistent with transition-state models that involve slight lowering of vibrational frequencies also for bonds well removed from the site of cleavage. The isotope effect on the reactions of ions of high internal energy is caused by the influence that even small changes of isotope-dependent frequencies have on the state sums (a statistical weight effect favouring loss of the labelled radical), whereas the behaviour of low-energy ions is determined by the zero-point energy changes which favour loss of the unlabelled fragment. 相似文献