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621.
n-Butyl methyl-phenylphosphinate and methyl-phenylphosphinic n-butylamide were synthesized by different methods: the reaction of methyl-phenylphosphinic chloride with nBuOH or nBuNH2, respectively, the T3P®-promoted derivatization of methyl-phenylphosphinic acid with nBuOH or nBuNH2, the microwave-assisted direct esterification of the model phosphinic acid, and finally the alkylating esterification with n-butyl bromide under phase-transfer-catalytic and microwave-assisted conditions. The different methods, mostly elaborated by us, were compared from practical and environmentally friendly points of view. 相似文献
622.
János Raskó ákos Koós Kornélia Baán János Kiss 《Reaction Kinetics and Catalysis Letters》2007,90(1):187-195
On X-ray photoelectron spectra of the Au-Rh/TiO2 catalysts the position of Au4f peak was practically unaffected by the presence of rhodium, the peak position of Rh3d, however,
shifted to lower binding energy with the increase of gold content of the catalysts. Rh enrichment in the outer layers of the
bimetallic crystallites was experienced. The bands due to Au0-CO, Rh0-CO and (Rh0)2-CO were observed on the IR spectra of bimetallic samples, no signs for Rh+-(CO)2 were detected on these catalysts. The results were interpreted by electron donation from titania through gold to rhodium
and by the higher particle size of bimetallic crystallites. 相似文献
623.
624.
The interaction of oxygen with a carburized Mo(100) surface was investigated at different temperatures (300-1000 K). The different information depths of low-energy ion-scattering (LEIS) spectroscopy, with topmost layer sensitivity, Auger electron spectroscopy (AES), and angle-resolved X-ray photoelectron spectroscopy (ARXPS) allowed us to discriminate between reactions on the topmost layer and subsurface transformations. According to ARXPS measurements, a carbide overlayer was prepared by the high-temperature decomposition of C(2)H(4) on Mo(100), and the carbon distribution proved to be homogeneous with a Mo(2)C stoichiometry down to the information depth of XPS. O(2) adsorbs dissociatively on the carbide layer at room temperature. One part of the chemisorbed oxygen is bound to both C and Mo sites, indicated by LEIS. Another fraction of oxygen atoms probably resides in the hollow sites not occupied by C. The removal of C from the outermost layer by O(2), in the form of CO, detected by mass spectroscopy (MS), was observed at 500-600 K. The carbon-depleted first layer is able to adsorb more oxygen compared to the Mo(2)C/Mo(100) surface. Applying higher doses of O(2) at 800 K results in the inward diffusion of O and the partial oxidation of Mo atoms. This process, however, is not accompanied by the removal of C from subsurface sites. The depletion of C from the bulk starts only at 900 K (as shown by MS, AES, and XPS), very probably by the diffusion of C to the surface followed by its reaction with oxygen. At T(ads) = 1000 K, the carbon content of the sample, down to the information depth of XPS, decreased further, accompanied by the attenuation of the C concentration gradient and a substantially decreased amount of oxygen. 相似文献
625.
Yin Li Zsolt Csók Péter Szuroczki László Kollár László Kiss Sándor Kunsági-Máté 《Analytica chimica acta》2013
A novel ‘three-level’ deepened cavitand featuring a significantly sizable portal has been synthesized and its interaction with some transition metal ions has been investigated in THF/H2O binary solvent using fluorescence quenching technique. The results suggest that among the used transition metal ions including Ag+, Cd2+, Cu2+, Fe3+, Cr3+, Hg2+, La3+, Mn2+, Ni2+, Zn2+ and Co2+, only Fe3+ and Cu2+ show good quenching ability. In order to interpret the quenching mechanism, the Stern–Volmer kinetics, and the presence of both the dynamic and static quenching have been discussed. It was found that the simultaneous presence of the sphere-of-action static quenching and dynamic quenching model agrees very well with the experimental results. The limits of detection for Fe3+ and Cu2+ were found to be 2.1 × 10−6 mol L−1 (3σ) and 3.6 × 10−6 mol L−1 (3σ), respectively. Cations with potential interference, such as K+, Na+, Mg2+, Ca2+, Co2+, La3+ and Mn2+ do not have significant effects on the determinations of Fe3+ and Cu2+. This cavitand can be potentially applied as optical sensor for the detection of Fe3+ and Cu2+. 相似文献
626.
Mark Schülke Gábor Kiss Hubert Paulus Martin Lammers Vaidyanath Ramachandran Kannan Sankaran Karl-Heinz Müller 《Analytical and bioanalytical chemistry》2009,393(8):1843-1856
Metal hydrides are one of the most promising technologies in the field of hydrogen storage due to their high volumetric storage
density. Important reaction steps take place at the very surface of the solid during hydrogen absorption. Since these reaction
steps are drastically influenced by the properties and potential contamination of the solid, it is very important to understand
the characteristics of the surface, and a variety of analytical methods are required to achieve this. In this work, a TiMn2-type metal hydride alloy is investigated by means of high-pressure activation measurements, X-ray photoelectron spectroscopy
(XPS), secondary neutral mass spectrometry (SNMS) and thermal desorption mass spectrometry (TDMS). In particular, TDMS is
an analytical tool that, in contrast to SIMS or SNMS, allows the hydrogen content in a metal to be quantified. Furthermore,
it allows the activation energy for desorption to be determined from TDMS profiles; the method used to achieve this is presented
here in detail. In the results section, it is shown that the oxide layer formed during manufacture and long-term storage prevents
any hydrogen from being absorbed, and so an activation process is required. XPS measurements show the oxide states of the
main alloy elements, and a layer 18 nm thick is determined via SNMS. Furthermore, defined oxide layers are produced and characterized
in UHV using XPS. The influence of these thin oxide layers on the hydrogen sorption process is examined using TDMS. Finally,
the activation energy of desorption is determined for the investigated alloy using the method presented here, and values of
46 kJ/mol for hydrogen sorbed in UHV and 103 kJ/mol for hydrogen originating from the manufacturing process are obtained. 相似文献
627.
Summary A new sensitive HPLC-FLD method has been developed and validated for the determination of cisapride in human plasma for a
bioequivalence study. A gradient method was used to remove late-eluting plasma components of no interest. The separation was
performed on a Li-ChroCART 250-4 Purospher RP-18 (5 μm particle) analytical column fitted with a LiChroCART 4-4 Purospher
RP-18 endcapped (5 μm particle) guard column. The excitation and emission wavelengths were 295 and 350 nm during fluorescence
detection. The calibration plot was linear in the range of 5–200 ng mL−1. A demethoxy analogue of cisapride was used as internal standard. 相似文献
628.
Differential scanning calorimetry and electron paramagnetic resonance experiments were performed on glycerinated skeletal
muscle fibres to study the effect of the binding of nucleotides and nucleotide analogues to myosin. The thermal unfolding
of muscle fibres in rigor showed three discrete domain regions with thermal stability of 52.2, 58.8 and 67.8°C. AMP.PNP and
ATP plus AlF3 or BeF2 affected markedly the transitions, which implies the strong interaction between AMP.PNP or nucleotide analogues and catalytic
domain of myosin, and a partial dissociation of heads from actin. ADP.BeFx and states model the transition states of the ATP
hydrolysis cycle which precede the powerstroke of the muscle fibres. Spectrum deconvolution on isothiocyanate-labelled fibres
in AMP.PNP-state resulted in two populations; 50% of labels was highly ordered with respect to fibre axis, whereas the other
50% of labels was randomly oriented. The myosin heads which showed high degree of order were in the strongly binding ADP-state.
The spectra in - and ADP.BeFx state reflected random orientation of labels with increased rotational mobility in comparison
with rigor. The results suggest that myosin in muscle fibres in ADP.BeFx state exists in two forms.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
629.
Spatially Distributed Current Oscillations with Electrochemical Reactions in Microfluidic Flow Cells 下载免费PDF全文
Prof. Dr. Adrian Bîrzu Yanxin Jia Varun Sankuratri Yifan Liu Prof. Dr. István Z. Kiss 《Chemphyschem》2015,16(3):555-566
The formation of spatiotemporal patterns is investigated by using a chemical reaction on the surface of a high‐aspect‐ratio metal electrode positioned in a flow channel. A partial differential equation model is formulated for nickel dissolution in sulfuric acid in a microfluidic flow channel. The model simulations predict oscillatory patterns that are spatially distributed on the electrode surface; the downstream portion of the metal surface exhibits large‐amplitude, nonlinear oscillations of dissolution rates, whereas the upstream portion displays small‐amplitude, harmonic oscillations with a phase delay. The features of the dynamical response can be interpreted by the dependence of local dynamics on the widely varying surface conditions and the presence of strong coupling. The patterns can be observed for both contiguous and segmented metal surfaces. The existence of spatially distributed current oscillations is confirmed in experiments with Ni electrodissolution in a microfluidic device. The results show the impact of a widely heterogeneous environment on the types of patterns of chemical reaction rates. 相似文献
630.
Endre Bartó Ibolya Prauda Ferenc Kilár Ibolya Kiss Attila Felinger 《Journal of separation science》2015,38(17):2975-2982
The understanding of the retention behavior of large molecules is an area of interest in liquid chromatography. Resorcinarene‐based cavitands are cavity‐shaped cyclic oligomers that can create host–guest interactions. We have investigated the chromatographic behavior of two types of cyclic tetramers as analytes in high‐performance liquid chromatography. The experiments were performed at four different temperatures (15, 25, 35, 45°C) on two types of reversed stationary phases (C8 and C18) from two different manufacturers. We have found a huge difference between the retention of resorcinarenes and cavitands. In some cases, the retention factor of cavitands was even a hundred times larger than the retention factor of resorcinarenes. The retention of methylated derivates was two to four times larger compared to that of demethylated compounds on every column. The opposite retention behavior of the resorcinarenes and cavitands on the two types of stationary phases showed well the difference of the selectivity of the XTerra and BDS Hypersil columns. The retention mechanism was studied by the thermodynamic parameters calculated from the van't Hoff equation. 相似文献