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11.
Using higher levels of wave-function-based electronic structure theory than previously applied, as well as density functional theory (B-LYP and B3-LYP functionals), all theoretical models conclude that three ONOOH conformers are stationary point minima, in disagreement with some of the previous studies that we survey. In order of increasing energy, these are the cis-cis, cis-perp, and trans-perp conformers. Basis sets including diffuse functions seem to be needed to obtain a qualitatively correct representation of the internal rotation potential energy surface at higher levels of theory. Internal rotation about the peroxide bond involving the cis-cis, cis-gauche transition structure (TS), cis-perp, and cis-trans TS conformers is studied in detail. To help ascertain the relative stability of the cis-perp conformer, multireference configuration interaction energy calculations are carried out, and rule of thumb estimates of multireference character in the ground-state wave functions of the ONOOH conformers are considered. CCSD(T)/aug-cc-pVTZ physical properties (geometries, rotational constants, electric dipole moments, harmonic vibrational frequencies, and infrared intensities) are compared with the analogous experimental data wherever possible, and also with density functional theory. Where such experimental data are nonexistent, the CCSD(T) and B3-LYP results are useful representations. For example, the electric dipole moment |mu(e)| of the cis-cis conformer is predicted to be 0.97+/-0.03 D. CCSD(T) energies, extrapolated to the aug-cc-pVNZ limit, are employed in isodesmic reaction schemes to derive zero Kelvin heats of formation and bond dissociation energies of the ONOOH stationary point minima. In agreement with recent gas-phase experiments, the peroxide bond dissociation energies of the cis-cis and trans-perp conformers are calculated as 19.3+/-0.4 and 16.0+/-0.4 kcalmol, respectively. The lowest energy cis-cis conformer is less stable than nitric acid by 28.1+/-0.4 kcalmol at 0 K. 相似文献
12.
The use of reversed-phase liquid chromatography (LC) with pre-column derivatization for the analysis of amino acid mixtures is becoming established as a possible cheaper alternative to commercial amino acid analysers. The available derivatization procedures all have disadvantages when applied to clinical samples, partly due to the interferences found with body fluids when ultraviolet or fluorescence detection is used. An LC method is described for the separation of amino acids in blood or urine, using pre-column derivatization with phenylisothiocyanate (PITC), gradient elution and electrochemical detection. The use of electrochemical detection of PITC derivatives virtually eliminates interferences and enables the secondary amino acids to be measured. Examples are shown of normal urine and plasma and samples from patients with cystinuria and maple syrup urine disease. 相似文献
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J. D. Sherwood 《Transport in Porous Media》2010,81(3):479-503
Drilling fluid filtrate invades the pores of rock surrounding a well bore during drilling of the well, and contaminates the
pore fluid originally within the rock pores. Models for the flow of contaminated pore fluid towards a sampling tool within
the well bore are investigated, assuming that the filtrate has the same viscosity as the original pore fluid and that the
wellbore radius is small compared to the depth of filtrate invasion. If the filtrate contamination in the fluid withdrawn
from the rock is monitored as a function of the volume withdrawn, then it is shown that results can be inverted to give the
radial distribution of filtrate around the well bore. A new generation of guarded sampling probes is then considered, and
it is shown that the radial distribution of filtrate can be obtained by means of such a probe if the fraction of flow entering
the central sampling region of the probe is small compared to that entering the concentric annular guard probe. The effects
of dispersion, non-zero wellbore radius and anisotropic hydraulic permeability of the rock are also studied, and numerical
simulations are used to give some indication of the effect of the ratio of the filtrate viscosity to that of the original
pore fluid. 相似文献
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French SA Sokol AA Bromley ST Catlow CR Rogers SC King F Sherwood P 《Angewandte Chemie (International ed. in English)》2001,40(23):4437-4440
19.
Marla D. Swain George P. Anderson Dan Zabetakis Rachael D. Bernstein Jinny L. Liu Laura J. Sherwood Andrew Hayhurst Ellen R. Goldman 《Analytical and bioanalytical chemistry》2010,398(1):339-348
Single-domain antibodies (sdAb) specific for botulinum neurotoxin serotype A (BoNT A) were selected from an immune llama phage
display library derived from a llama that was immunized with BoNT A toxoid. The constructed phage library was panned using
two methods: panning on plates coated with BoNT A toxoid (BoNT A Td) and BoNT A complex toxoid (BoNT Ac Td) and panning on
microspheres coupled to BoNT A Td and BoNT A toxin (BoNT A Tx). Both panning methods selected for binders that had identical
sequences, suggesting that panning on toxoided material may be as effective as panning on bead-immobilized toxin for isolating
specific binders. All of the isolated binders tested were observed to recognize bead-immobilized BoNT A Tx in direct binding
assays, and showed very little cross-reactivity towards other BoNT serotypes and unrelated protein. Sandwich assays that incorporated
selected sdAb as capture and tracer elements demonstrated that all of the sdAb were able to recognize soluble (“live”) BoNT
A Tx and BoNT Ac Tx with virtually no cross-reactivity with other BoNT serotypes. The isolated sdAb did not exhibit the high
degree of thermal stability often associated with these reagents; after the first heating cycle most of the binding activity
was lost, but the portion of the protein that did refold and recover antigen-binding activity showed only minimal loss on
subsequent heating and cooling cycles. The binding kinetics of selected binders, assessed by both an equilibrium fluid array
assay as well as surface plasmon resonance (SPR) using toxoided material, gave dissociation constants (K
D ) in the range 2.2 × 10−11 to 1.6 × 10−10 M. These high-affinity binders may prove beneficial to the development of recombinant reagents for the rapid detection of
BoNT A, particularly in field screening and monitoring applications. 相似文献
20.
Gizelle Cristina Bedendo Isabel Cristina Sales Fontes Jardim Eduardo Carasek 《Journal of chromatography. A》2010,1217(42):6449-6454
A sensitive and precise analysis using hollow fiber renewal liquid membrane (HFRLM) extraction followed by high performance liquid chromatography–tandem mass spectrometry (LC–MS/MS) is described for determination of five sulfonamides in honey samples. In this procedure, the organic solvent introduced directly into the sample matrix extracts the sulfonamides and carries them over the polypropylene porous membrane. An organic solvent is immobilized inside the polypropylene porous membrane, leading to a homogeneous phase. The stripping phase at higher pH in the lumen of the membrane promotes the ionization of the target compounds releasing them to this phase. The most important parameters affecting the extraction efficiency were optimized by multivariable designs (pH and sample mass, pH and buffer for stripping phase, extraction temperature and time, type and volume of extractor solvent and use of salt to saturate the sample). Detection limits in the range of 5.1–27.4 μg kg−1 and linearity coefficient of correlation higher than 0.987 were obtained for the target analytes. The results obtained for the proposed method show that HFRLM–LC–MS/MS can be used for determination of the five sulfonamides studied in honey samples with excellent precision, accuracy, practicality and short analysis time. 相似文献