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排序方式: 共有173条查询结果,搜索用时 15 毫秒
101.
X Fang KW Ledingham P Graham DJ Smith T McCanny RP Singhal AJ Langley PF Taday 《Rapid communications in mass spectrometry : RCM》1999,13(14):1390-1397
The potential of femtosecond laser time-of-flight mass spectrometry (FLMS) for uniform quantitative analysis of molecules has been investigated. Various samples of molecular gases and vapours have been studied, using ultra-fast ( approximately 50 fs) laser pulses with very high intensity (up to 1.6 x 10(16) Wcm(-2)) for non-resonant multiphoton ionisation/tunnel ionisation. Some of these molecules have high ionisation potentials, requiring up to ten photons for non-resonant ionisation. The relative sensitivity factors (RSF) have been determined as a function of the laser intensity and it has been demonstrated that for molecules with very different masses and ionisation potentials, uniform ionisation has been achieved at the highest laser intensities. Quantitative laser mass spectrometry of molecules is therefore a distinct possibility. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
102.
Annals of Operations Research - The notion of Pareto optimality is commonly employed to formulate decisions that reconcile the conflicting interests of multiple agents with possibly different risk... 相似文献
103.
Ambrose Rajkumar Maridass S. Stanly John Xavier L. Priya S. Anbarasu P. K. Bajbai Shiva Poojan Patel 《Molecular Crystals and Liquid Crystals》2018,664(1):195-217
2-amino-5-nitropyridinium hydrogen oxalate (2A5NPHO) was grown using slow evaporation and bulk crystal of 2A5NPHO was harvested from Assembled Temperature Reduction (ATR) method. Cut and polished crystal was irradiated using Au3+ ion with various fluences. Electronic loss, nuclear energy loss and penetration depth were calculated using SRIM software. It was observed in X- ray pattern that intensity of peak was reduced. Intensity of peak decreased with increase of ion fluencies from 1013 ions/cm2 to 1014 ions/cm2. Optical properties were measured using UV-Vis spectrometer. The increase of absorption was due to excited electrons which were formed by vacancies and formation of additional defects centres. Energy band gap of irradiated crystals increased with increase of ion fluence. Energy band gap of irradiated crystals were 3.39 eV, 3.42 eV, and 3.4 eV for 1013 ions/cm2, 5 × 1013 ions/cm2 and 1014 ions/cm2 respectively and increase of band gap was due to the increase of forbidden gap. Microhardness was calculated using Vicker's Hardness tester. Increase of microhardness in irradiation crystal was due to increase of high density lattice defects produced by Au3+ of 10.8 MeV. Electrical property was calculated using dielectric constant. Increase of dielectric constant was due to large polarization which caused by disorderness and rich defects in the crystalline surface. Decrease of intensity peak in fluorescence was due to transition of excited electron to intermediated energy levels from excited state which converted into vibrational energy of lattice atoms (phonon). Morphology of irradiated crystal was seen using scanning electron microscope (SEM). It was observed from the SEM image that surface of crystal was heavily damaged. It was also noticed that the thermal stability of the irradiated single crystal increased with increase of ion fluences. Impedance of irradiated crystal was measured. The bulk resistance and grain boundary resistance also were calculated. 相似文献
104.
Isa Ruppen Canás Keith O’Callaghan Cian Moroney Brett Hamilton Kevin J. James Ambrose Furey 《Analytical and bioanalytical chemistry》2010,398(3):1477-1491
The azaspiracids are a family of lipophilic polyether marine biotoxins that have caused a number of human intoxication incidents
in Europe since 1995 after consumption of contaminated shellfish (Mytilus edulis). Levels of azaspiracids in shellfish for human consumption are monitored in accordance with EU guidelines: only shellfish
with less than 160 μg kg−1 are deemed safe. The limited availability of commercially available standards for azaspiracids is a serious problem, because
validated LC–MS methods are required for routine analysis of these toxins in shellfish tissues. The procedure described herein
has been used for the separation and the isolation of four azaspiracid (AZA) toxins from shellfish, for use as LC–MS–MS reference
materials. Five separation steps have been used to isolate azaspiracids 1, 2, 3, and 6. The purity of the toxins obtained
has been confirmed by multiple mass spectrometric methods using authentic azaspiracid standards. The same techniques have
been used for quantification of the toxins extracted. The isolation procedure involves several chromatographic purification
techniques: solid-phase extraction (diol sorbent, 90% mass reduction, and 95 ± 1% toxin recovery); Sephadex size-exclusion
chromatography (87% mass reduction and up to 95 ± 2% toxin recovery), Toyopearl HW size-exclusion chromatography (90% mass
reduction and up to 92.5 ± 2.5% toxin recovery), and semi-preparative LC (78 ± 3% toxin recovery). The procedure effectively
separates the toxins from the sample matrix and furnishes azaspiracid toxins (AZA1, AZA2, AZA3 and AZA6) of sufficient purity
with an average yield of 65% (n = 5). Triple-quadrupole mass spectrometry was used for qualitative and quantitative monitoring of the isolation efficiency
after each stage of the process. High-resolution mass spectrometric evaluation of the toxic isolated material in both positive
and negative modes suggests high purity. 相似文献
105.
A dual validation approach to detect anthelmintic residues in bovine liver over an extended concentration range 总被引:1,自引:0,他引:1
This paper describes a method for the detection and quantification of 38 residues of the most widely used anthelmintics (including 26 veterinary drugs belonging to the benzimidazole, macrocyclic lactone and flukicide classes) in bovine liver using two different protocols for MRL and non-MRL levels. A dual validation approach was adopted to reliably quantify anthelmintic residues over an extended concentration range (1-3000 μg kg−1). Sample extraction and purification was carried out using a modified QuEChERS method. A concentration step was included when analysing in the low μg kg−1 range. Rapid analysis was carried out by ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS), which was capable of detecting residues to <2 μg kg−1. The method has been single-laboratory validated according to the 2002/657/EC guidelines and met acceptability criteria in all but a few cases. The inclusion of 19 internal standards, including 14 isotopically labelled internal standards, improved accuracy, precision, decision limit (CCα) and detection capability (CCβ). 相似文献
106.
Abulencia A Acosta D Adelman J Affolder T Akimoto T Albrow MG Ambrose D Amerio S Amidei D Anastassov A Anikeev K Annovi A Antos J Aoki M Apollinari G Arguin JF Arisawa T Artikov A Ashmanskas W Attal A Azfar F Azzi-Bacchetta P Azzurri P Bacchetta N Bachacou H Badgett W Barbaro-Galtieri A Barnes VE Barnett BA Baroiant S Bartsch V Bauer G Bedeschi F Behari S Belforte S Bellettini G Bellinger J Belloni A Ben-Haim E Benjamin D Beretvas A Beringer J Berry T Bhatti A Binkley M Bisello D Bishai M 《Physical review letters》2006,96(15):152002
We report a measurement of the top-quark mass using events collected by the CDF II detector from pp collisions at square root of s = 1.96 TeV at the Fermilab Tevatron. We calculate a likelihood function for the top-quark mass in events that are consistent with tt --> bl(-)nu(l)bl'+ nu'(l) decays. The likelihood is formed as the convolution of the leading-order matrix element and detector resolution functions. The joint likelihood is the product of likelihoods for each of 33 events collected in 340 pb(-1) of integrated luminosity, yielding a top-quark mass M(t) = 165.2 +/- 6.1(stat) +/- 3.4(syst) GeV/c2. This first application of a matrix-element technique to tt --> bl+ nu(l)bl'- nu(l') decays gives the most precise single measurement of M(t) in dilepton events. Combined with other CDF run II measurements using dilepton events, we measure M(t) = 167.9 +/- 5.2(stat) +/- 3.7(syst) GeV/c2. 相似文献
107.
Roger W. Binkley Michael G. Ambrose David G. Hehemann 《Journal of carbohydrate chemistry》2013,32(2):203-219
Abstract The reactions of bromide, chloride, and iodide ions with 1,3,4, 6-tetra-O-acetyl-2-O-(trifluoromethylsulfonyl) -α-D-glucopyranose (2) and with 1, 3, 4, 6-tetra-O-acetyl-2-O-(trifluoromethylsulfonyl)-β-D-mannopyranose (3) gave good to excellent yields of the corresponding deoxyhalogeno sugars. In contrast, when the gluco triflate 2 and tetra-butylammonium fluoride were heated under reflux in benzene, only 5-(acetoxymethyl)-2-formylfuran (13) was formed. Reaction of the manno triflate 3 under similar conditions produced 1, 3,4, 6-tetra-O-acetyl-2-deoxy-2-fluoro-β-D-gluco-pyranose (17), 1. 3, 4. 6-tetra-O-acetyl-2-deoxy-β-D-erythro-hex-2-eno-pyranose (18), 4,6-di-O-acetyl-1, 5-anhydro-2-deoxy-D-erythro-hex-l-enitol-3-ulose (19), and 1, 2, 3, 4, 6-penta-O-acetyl-β-D-glucopyranose (20). The mechanisms of the reactions of The triflates 2 and 3 with fluoride ion are discussed. 相似文献
108.
Moriarty M Lee A O'Connell B Kelleher A Keeley H Furey A 《Analytical and bioanalytical chemistry》2011,401(8):2481-2493
Serotonin is a major neurotransmitter and affects various functions both in the brain and in the rest of the body. It has
been demonstrated that altered serotinergic function is implicated in various psychiatric disorders including depression and
schizophrenia. Serotonin has also been implicated along with dopamine in attention deficit–hyperkinetic disorder (AD-HKD).
This study provides a versatile validated method for the analysis of serotonin, hydroxyindole acetic acid and dopamine in
urine using LC-MS/MS. This method was then used to quantify these analytes in a test group of 17 children diagnosed with severe
AD-HKD. This group was compared to a matched control group to investigate the possibility that one of these compounds may
be a potential biomarker for this condition. The developed method provided good linear calibration curves for the multiplex
assay of analytes in urine (0.05–3.27 nmol/L; R
2 ≥ 0.9977). Acceptable inter-day repeatability was achieved for all analytes with RSD values (n = 9) ranging from 1.1% to 9.3% over a concentration range of 0.11–3.27 μmol/L in urine. Excellent limits of detection (LOD)
and limits of quantitation (LOQ) were achieved with LODs of 8.8–18.2 nmol/L and the LOQs of 29.4–55.7 nmol/L for analytes
in urine. Recoveries were in the ranges of 98–104%, 100–106% and 91–107% for serotonin, 5-HIAA and dopamine, respectively.
An appropriate sample clean-up procedure for urine was developed to ensure efficient recovery and reproducibility on analysis.
Evaluation of matrix effects was also carried out and the influence of ion suppression on analytical results reported. Confirmatory
analysis was carried out on a linear trap quadrupole-Orbitrap mass spectrometer to obtain high mass accuracy data of the target
analytes in the clinical samples. 相似文献
109.
MR Eskildsen AB Abrahamsen PL Gammel DJ Bishop NH Andersen K Mortensen PC Canfield 《Pramana》2002,58(5-6):903-905
We compare the results of small angle neutron scattering on the flux line lattice (FLL) obtained in the borocarbide superconductor
LuNi2B2C with the applied field along the c- and a-axes. For H‖c the temperature dependence of the FLL structural phase transition from square to hexagonal symmetry was investigated. Above
10 K the transition onset field. H
2(T), rises sharply, bending away from H
c2(T) in contradiction to theoretical predictions of the two merging. For H‖a a first order FLL reorientation transition is observed at H
tr=3–3.5 kOe. Below H
tr the FLL nearest neighbor direction is parallel to the b-axis, and above H
tr to the c-axis. This transition cannot be explained using nonlocal corrections to the London model. 相似文献
110.