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71.
Terrado M Kuster M Raldúa D Lopez de Alda M Barceló D Tauler R 《Analytical and bioanalytical chemistry》2007,387(4):1479-1488
Data sets obtained from quantitative analysis of seventeen pesticides in water samples from a network of irrigation and drainage
channels in the Ebro river delta (Catalonia, NE Spain) have been analysed by chemometric and geostatistical methods. Samples
were taken at fourteen locations during the main rice-growing season, from May to August 2005. Principal-component analysis
enabled investigation of the spatial and temporal distribution of the main pollution patterns caused by application of pesticides
in the region under study. A first pesticide-contamination pattern from the Ebro river was differentiated from a second more
specific pattern from the water-drainage channels of the delta, collected from the rice fields. The seasonal peak in this
more specific rice pesticide source was observed in July. Coupling the results from chemometric data analysis with use of
geostatistical methods was shown to be a useful procedure for discovery of the most significant spatial and monthly variations
of the main pesticide-contamination patterns, taking into account the particular geographical structure of the area under
study. 相似文献
72.
Reversible Switching of Redox‐Active Molecular Orbitals and Electron Transfer Pathways in CuA Sites of Cytochrome c Oxidase
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Ulises Zitare Dr. Damián Alvarez‐Paggi Marcos N. Morgada Dr. Luciano A. Abriata Prof. Alejandro J. Vila Prof. Daniel H. Murgida 《Angewandte Chemie (International ed. in English)》2015,54(33):9555-9559
The CuA site of cytochrome c oxidase is a redox hub that participates in rapid electron transfer at low driving forces with two redox cofactors in nearly perpendicular orientations. Spectroscopic and electrochemical characterizations performed on first and second‐sphere mutants have allowed us to experimentally detect the reversible switching between two alternative electronic states that confer different directionalities to the redox reaction. Specifically, the M160H variant of a native CuA shows a reversible pH transition that allows to functionally probe both states in the same protein species. Alternation between states exerts a dramatic impact on the kinetic redox parameters, thereby suggesting this effect as the mechanism underlying the efficiency and directionality of CuA electron transfer in vivo. These findings may also prove useful for the development of molecular electronics. 相似文献
73.
Carlos Henrique Marchi Leandro Alberto Novak Cosmo Damião Santiago Ana Paula da Silveira Vargas 《Applied Mathematical Modelling》2013,37(12-13):7386-7397
A theoretical basis is presented for the repeated Richardson extrapolation (RRE) to reduce and estimate the discretization error of numerical solutions for heat conduction. An example application is described for the 2D Laplace equation using the finite difference method, a domain discretized with uniform grids, second-order accurate approximations, several variables of interest, Dirichlet boundary conditions, grids with up to 8,193 × 8,193 nodes, a multigrid method, single, double and quadruple precisions and up to twelve Richardson extrapolations. It was found that: (1) RRE significantly reduces the discretization error (for example, from 2.25E-07 to 3.19E-32 with nine extrapolations and a 1,025 × 1,025 grid, yielding an order of accuracy of 19.1); (2) the Richardson error estimator works for numerical results obtained with RRE; (3) a higher reduction of the discretization error with RRE is achieved by using higher calculation precision, a larger number of extrapolations, a larger number of grids and correct error orders; and (4) to obtain a given value error, much less CPU time and RAM memory are required for the solution with RRE than without it. 相似文献
74.
We define a probability measure on the space of polynomials over ? n in order to address questions regarding the attainment of the norm at given points and the validity of polynomial inequalities.Using this measure, we prove that for all degrees k ≥ 3, the probability that a k-homogeneous polynomial attains a local extremum at a vertex of the unit ball of ? 1 n tends to one as the dimension n increases. We also give bounds for the probability of some general polynomial inequalities. 相似文献
75.
Removal of sulfonamide antibiotics upon conventional activated sludge and advanced membrane bioreactor treatment 总被引:1,自引:0,他引:1
García Galán MJ Díaz-Cruz MS Barceló D 《Analytical and bioanalytical chemistry》2012,404(5):1505-1515
This work reports the removal efficiencies of nine sulfonamides (SAs) and one of their acetylated metabolites during conventional activated sludge (CAS) and membrane bioreactor (MBR) treatments. Two different types of membranes were studied, hollow-fiber membranes and flat-sheet membranes, in two separate pilot plants operating in parallel to a full-scale CAS treatment. A total of 48 water samples and 16 sewage sludge samples were analyzed by liquid chromatography-tandem mass spectrometry. We obtained 100% elimination in the MBR effluents for three SAs (sulfadiazine, sulfadimethoxine, and sulfamethoxypyridazine) and the metabolite. For the rest of the SAs, the removal efficiencies during CAS and MBR treatments were similar and usually below 55%. Sulfamethizole was the most recalcitrant SA, exhibiting negative removal efficiencies in all the treatments investigated. The concentrations of SAs in the different sewage sludge types were also calculated and ranged from 0.01 to 11 ng g(-1). Furthermore, adsorption and biodegradation of SAs in activated sludge were investigated in two sets of batch reactors, which were spiked at high and low concentration (1,000 and 50 ng mL(-1), respectively). All SAs followed a similar trend and, with the exception of sulfathiazole, were not fully eliminated after 25 days of treatment. 相似文献
76.
Biljana Nigović Miranda Damić Rade Injac Nina Kočevar Glavač Borut Štrukelj 《Chromatographia》2009,69(11-12):1299-1305
A new micellar electrokinetic capillary chromatographic (MEKC) method has been developed for simultaneous quantitation of atorvastatin (AT) and its related substances. The separation was carried out in an extended light path capillary at applied voltage of 30 kV using a background electrolyte consisting of 10 mM sodium tetraborate buffer pH 9.5, 50 mM sodium dodecyl sulphate and 20% (v/v) methanol. The addition of methanol to the running buffer resulted in a very effective choice to achieve resolution between the peaks of charged substances adjacent to AT as well as the peaks of neutral drug-related substances. Linear calibration curves were established over the concentration range 100–1,200 μg mL?1 for AT and 1.0–12.5 μg mL?1 for related substances. The proposed MEKC procedure has been validated with respect to selectivity, precision, linearity, limits of detection, and quantitation, accuracy and robustness. The method has been successfully applied to the determination of AT and purity evaluation of bulk drug and formulated products. 相似文献
77.
Sebastián Bouzat Damián H. Zanette 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,70(4):557-565
We study an SIS epidemiological model for a sexually
transmitted infection in a monogamous population where the formation
and breaking of couples is governed by individual preferences. The
mechanism of couple recombination is based on the so-called bar
dynamics for the marriage problem. We compare the results with those
of random recombination – where no individual preferences exist –
for which we calculate analytically the infection incidence and the
endemic threshold. We find that individual preferences give rise to
a large dispersion in the average duration of different couples,
causing substantial changes in the incidence of the infection and in
the endemic threshold. Our analysis yields also new results on the
bar dynamics, that may be of interest beyond the field of
epidemiological models. 相似文献
78.
Welsh onion (Allium fistulosum L.) is usually used to enhance the flavor characteristics of various foods. Volatile compounds in Welsh onions, including sulfur-containing compounds, may vary during heat process and storage. Accordingly, the changes in the volatile compounds in Welsh onions, subjected to heat and antioxidant (ascorbic acid and glutathione) treatments during storage, are investigated in the present study. The majority of sulfur-containing compounds in Welsh onions showed significant differences between the untreated Welsh onions and heated Welsh onions. During the heating of the Welsh onions, some sulfur-containing compounds, such as 2-methylthiirane, 1-(methyldisulfanyl)prop-1-ene, 1-[[(E)-prop-1-enyl]disulfanyl]propane, 1-(propyltrisulfanyl)propane, 1-[[(E)-prop-1-enyl]trisulfanyl]propane, and (methyltetrasulfanyl)methane, showed significant differences between the untreated and heated Welsh onions (p < 0.05). In addition, partial least square discriminant analysis (PLS-DA) was applied to discriminate the heated Welsh onion samples added with different antioxidants. The heated Welsh onion samples added with ascorbic acid was mainly associated with 2-phenylacetaldehyde, acetic acid, methylsulfanylmethane, prop-2-ene-1-thiol, undecan-2-one, and (2E,4E)-deca-2,4-dienal. Moreover, the key volatile compounds in the heated Welsh onion samples added with glutathione were 3-ethylthiophene, 1-(methyldisulfanyl)-1-methylsulfanylpropane, 1-methylsulfanylpentane, 2-prop-2-enylsulfanylpropane, and 1-propan-2-ylsulfanylbutane. 相似文献
79.
80.