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121.
Carter MD Calcutt MW Malow BA Rose KL Hachey DL 《Journal of mass spectrometry : JMS》2012,47(3):277-285
Melatonin (MEL) and its chemical precursor N-acetylserotonin (NAS) are believed to be potential biomarkers for sleep-related disorders. Measurement of these compounds, however, has proven to be difficult due to their low circulating levels, especially that of NAS. Few methods offer the sensitivity, specificity and dynamic range needed to monitor MEL and its precursors and metabolites in small blood samples, such as those obtained from pediatric patients. In support of our ongoing study to determine the safety, tolerability and PK dosing strategies for MEL in treating insomnia in children with autism spectrum disorder, two highly sensitive LC-MS/MS assays were developed for the quantitation of MEL and precursor NAS at pg/mL levels in small volumes of human plasma. A validated electrospray ionization (ESI) method was used to quantitate high levels of MEL in PK studies, and a validated nanospray (nESI) method was developed for quantitation of MEL and NAS at endogenous levels. In both assays, plasma samples were processed by centrifugal membrane dialysis after addition of stable isotopic internal standards, and the components were separated by either conventional LC using a Waters SymmetryShield RP18 column (2.1?×?100 mm, 3.5?μm) or on a polyimide-coated, fused-silica capillary self-packed with 17?cm AquaC18 (3?μm, 125??). Quantitation was done using the SRM transitions m/z 233?→?174 and m/z 219?→?160 for MEL and NAS, respectively. The analytical response ratio versus concentration curves were linear for MEL (nanoflow LC: 11.7-1165 pg/mL, LC: 1165-116,500 pg/mL) and for NAS (nanoflow LC: 11.0-1095 pg/mL). 相似文献
122.
James W. Favell Kerry L. Wilkinson Ieva Zigg Sarah M. Lyons Renata Ristic Carolyn J. Puglisi Eric Wilkes Randell Taylor Duane Kelly Greg Howell Marianne McKay Lucky Mokwena Tim Plozza Pei Zhang AnhDuyen Bui Ian Porter Orrin Frederick Jasha Karasek Colleen Szeto Bruce S. Pan Steve Tallman Beth Anne McClure Hui Feng Eric Herv Anita Oberholster Wesley F. Zandberg Matthew Noestheden 《Molecules (Basel, Switzerland)》2022,27(15)
Vineyard exposure to wildfire smoke can taint grapes and wine. To understand the impact of this taint, it is imperative that the analytical methods used are accurate and precise. This study compared the variance across nine commercial and research laboratories following quantitative analysis of the same set of smoke-tainted wines. In parallel, correlations between the interlaboratory consensus values for smoke-taint markers and sensory analyses of the same smoke-tainted wines were evaluated. For free guaiacol, the mean accuracy was 94 ± 11% in model wine, while the free cresols and 4-methylguaiacol showed a negative bias and/or decreased precision relative to guaiacol. Similar trends were observed in smoke-tainted wines, with the cresols and glycosidically bound markers demonstrating high variance. Collectively, the interlaboratory results show that data from a single laboratory can be used quantitatively to understand smoke-taint. Results from different laboratories, however, should not be directly compared due to the high variance between study participants. Correlations between consensus compositional data and sensory evaluations suggest the risk of perceivable smoke-taint can be predicted from free cresol concentrations, overcoming limitations associated with the occurrence of some volatile phenols, guaiacol in particular, as natural constituents of some grape cultivars and of the oak used for barrel maturation. 相似文献
123.
Robert A. Huggins 《Ionics》1995,1(4):292-297
The driving force for phase transformations in solids can be modified by the presence of magnetic fields. The basic principles
involved in this effect are presented. It is shown how changes in the magnetic contribution to the total Gibbs free energy
are related to other parameters, such as the activities of mobile species, the potentials of solids in electrochemical systems,
and the temperature dependence of phase equilibria. The application of this effect in solid state ionic systems containing
mixed ionic-electronic conductors with high rates of chemical diffusion, such as metal hydrides, is discussed.
Paper presented at the 2nd Euroconference on Solid State Ionics, Funchal, Madeira, Portugal, Sept. 10–16, 1995 相似文献
124.
Pure LiMn2O4 and lithium manganese oxide spinels with partial replacement of manganese by cobalt up to 20 mole%, LiCoxMn2−xO4, were prepared. The effect of extended cycling on the crystal structure was investigated. A capacity decrease with increasing
cobalt content was observed in the potential range about 4100 mV vs. Li/Li+. Cycling behavior is significantly improved, compared to LiMn2O4. LiCoxMn2−xO4 is discharged in a single phase reaction in the upper potential range around 4100 mV vs. Li/Li+, whereas pure LiMn2O4 shows a two phase behavior. LiMn2O4 shows a significant broadening of peaks in plots of differential capacity and change in shape of the voltage profile upon
extended cycling. LiCoxMn2−xO4 shows neither broadening nor change. Voltage profiles and plots of the differential capacity differ significantly compared
to spinels with lithium substitution, Li1+xMn2−xO4. In contrast to Li1+xMn2-xO4, LiCoxMn2-xO4 is discharged in a two step process in the range of 0 ≤ × ≤ 0,5.
Paper presented at the 3rd Euroconference on Solid State Ionics, Teulada, Sardinia, Italy, Sept. 15–22, 1996 相似文献
125.
Sindhaghatta D. Venkataramu Donald E. Pearson Albert H. Beth Charles R. Park Jane H. Park 《Tetrahedron letters》1985,26(11):1403-1406
Stearic acid spin label substituted with deuterium in all positions and15N in the paramagnetic group has been synthesized and was found to display a 5.5 fold gain in sensitivity in the EPR spectrum and a 60% decrease in linewidth compared to the unmodified analog. 相似文献
126.
K. R. P. M. Rao Frank E. Huggins Bhaswati Ganguly Vikram Mahajan Gerald P. Huffman Burton Davis Robert J. O'Brien Liguang Xu V. U. S. Rao 《Hyperfine Interactions》1994,93(1):1755-1758
Mössbauer spectroscopy was used to investigate the effect of heating the Fischer-Tropsch catalyst 100 Fe/5 Cu/4.2 K/24 SiO2 in two different atmospheres while ramping the temperature of the catalyst from room temperature to 280 °C in 5.5 h prior to pretreatment of the catalyst. Preheating in H2/CO=0.7 gave rise to an iron (Fe2+) silicate, while preheating in helium resulted in the formation of -carbide Fe2.2C. Iron oxides and -carbide Fe5C2 were also formed in both preheat treatments. 相似文献
127.
128.
Schubert BA Wagner NJ Kaler EW Raghavan SR 《Langmuir : the ACS journal of surfaces and colloids》2004,20(9):3564-3573
Polymer solutions in the vicinity of the theta-point are known to undergo shear-induced turbidity or phase separation. The present study shows that a similar phenomenon also occurs for certain wormlike micellar solutions. Wormlike micelles are the self-assembled counterparts of polymers and are characterized by their ability to reversibly break and recombine. In the system of interest, the micelles are formed by the cationic surfactant erucyl bis(hydroxyethyl)methylammonium chloride (EHAC), in conjunction with a salt such as sodium chloride (NaCl) or sodium salicylate (NaSal). Micellar samples that become turbid under shear show evidence of critical concentration fluctuations and may contain predominantly branched micelles. The shear-induced turbidity in these samples correlates with the appearance of flow-dichroism in rheooptic experiments and with an increase in low-q scattering in small-angle light scattering under flow (flow-SALS) experiments. The characteristic "butterfly" pattern, with enhanced scattering in the flow direction and a dark streak perpendicular to the flow direction, is typically observed in flow-SALS. The results suggest that the turbidity is due to a shear-induced growth of concentration fluctuations, which in turn manifests as large anisotropic domains, typically oriented along the vorticity axis. 相似文献
129.
130.
Beth ApselJohn A Bender Maya EscobarDavid E Kaelin Jr. Omar D LopezStephen F Martin 《Tetrahedron letters》2003,44(5):1075-1077
Utilizing a general entry we had developed for the synthesis of C-aryl glycosides, we have prepared the juglone derivatives 18-20 as well as the juglone precursor 13. Because 19 had been previously converted in two steps by Suzuki into galtamycinone (1), its preparation constitutes a total synthesis of 1. 相似文献