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111.
Adriana DoyleAlvaro Saavedra Maria Luiza B. TristãoMárcio Nele Ricardo Q. Aucélio 《Spectrochimica Acta Part B: Atomic Spectroscopy》2011,66(5):368-372
Official guidelines to perform chlorine determination in crude oil are (i) American Society for Testing and Materials (ASTM) D6470, which is based on the extraction of water from the oil and subsequent determination of the chloride by potentiometry, (ii) ASTM D3230, that measures the conductivity of a solution of crude oil in a mixture of organic solvents and (iii) US Environmental Protection Agency (EPA) 9075 that uses energy dispersive X-ray fluorescence spectrometry to quantify chlorine and it is applicable for the range from 200 μg g− 1 to percent levels of the analyte. The goal of this work is to propose method to quantify lower amounts of chlorine in crude oil using energy dispersive X-ray fluorescence spectrometry using a simple calibration strategy. Sample homogenization procedure was carefully studied in order to enable accurate results. The calibration curve was made with standards prepared by diluting aqueous NaCl standard in glycerin. The method presented a linear response that covers the range from 8 to at least 100 μg g− 1 of chlorine. Chlorine in crude oil samples from Campos Basin - Brazil were quantified by the proposed method and by potentiometry after extraction of chlorine from the oil. Results achieved using both methods were statistically the same at 95% confidence level. 相似文献
112.
Ferranti P Nasi A Bruno M Basile A Serpe L Gallo P 《Rapid communications in mass spectrometry : RCM》2011,25(9):1173-1183
In recent years, the occurrence of cyanobacterial blooms in eutrophic freshwaters has been described all over the world, including most European countries. Blooms of cyanobacteria may produce mixtures of toxic secondary metabolites, called cyanotoxins. Among these, the most studied are microcystins, a group of cyclic heptapeptides, because of their potent hepatotoxicity and activity as tumour promoters. Other peptide cyanotoxins have been described whose structure and toxicity have not been thoroughly studied. Herein we present a peptidomic approach aimed to characterise and quantify the peptide cyanotoxins produced in two Italian lakes, Averno and Albano. The procedure was based on matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry mass spectrometry (MALDI-TOF-MS) analysis for rapid detection and profiling of the peptide mixture complexity, combined with liquid chromatography/electrospray ionisation quadrupole time-of- flight tandem mass spectrometry (LC/ESI-Q-TOF-MS/MS) which provided unambiguous structural identification of the main compounds, as well as accurate quantitative analysis of microcystins. In the case of Lake Averno, a novel variant of microcystin-RR and two novel anabaenopeptin variants (Anabaenopeptins B(1) and Anabaenopeptin F(1)), presenting homoarginine in place of the commonly found arginine, were detected and characterised. In Lake Albano, the peculiar peptide patterns in different years were compared, as an example of the potentiality of the peptidomic approach for fast screening analysis, prior to fine structural analysis and determination of cyanotoxins, which included six novel aeruginosin variants. This approach allows for wide range monitoring of cyanobacteria blooms, and to collect data for evaluating possible health risks to consumers, through the panel of the compounds produced along different years. 相似文献
113.
Copper is trafficked to cellular destinations by homeostatic proteins that also prevent adverse reactivity of the metal. The copper metallochaperone HAH1 (human Atx1) binds Cu(I) via a CXXC motif on loop1/α1 of a βαββαβ ferredoxin-like structure. A similar fold constitutes each of the six metal-binding domains (MBDs) of the two P-type ATPases (Menkes and Wilson disease proteins), the destination for copper bound to HAH1. In this work we have investigated the influence of pH on copper trafficking between HAH1 and the first MBD of the Menkes protein (MNK1). Cu(I) affinities of 5.6 × 10(17) and 3.6 × 10(17) M(-1) have been determined at pH 7.0 for HAH1 and MNK1, respectively, from competition titrations with the chromophoric Cu(I) ligand bathocuproine disulfonate. The mutation of Lys60 on loop5 of HAH1 to Ala (the corresponding residue is Phe67 in MNK1) results in a 3-fold lowering of the affinity for Cu(I) at pH 7.0. The Cu(I) affinity of WT HAH1 exhibits a different pH-dependence compared to MNK1 and Lys60Ala HAH1. This arises because the pK(a) of the second Cys ligand in the CXXC motif of HAH1 is 1.5 pH units lower due to stabilization of the thiolate via a hydrogen-bonding interaction with the side chain of Lys60. The thermodynamic gradient for Cu(I) transfer between HAH1 and MNK1 depends on pH. The decrease in the pK(a) of the Cys ligand in HAH1 can also influence the kinetics of Cu(I) transfer. 相似文献
114.
Silvestro L Gheorghe M Iordachescu A Ciuca V Tudoroniu A Rizea Savu S Tarcomnicu I 《Analytical and bioanalytical chemistry》2011,401(3):1023-1034
A new sensitive and fast quantitative analytical method for the simultaneous determination of clopidogrel, its main metabolite
clopidogrel carboxylic acid, and the newly described acyl glucuronide metabolite, in human plasma samples, is presented. The
analytical procedures (plasma storage, handling, and extract storage in the autosampler) were optimized in order to avoid
back-conversion; a known drawback in measurements of clopidogrel. Clopidogrel acyl glucuronide was confirmed as a major source
of back-conversion to the parent drug in the presence of methanol, and thorough stability experiments were carried out to
find the most appropriate conditions for an accurate analysis of clopidogrel and the two metabolites. The method was validated
by assessing selectivity, sensitivity, linearity, accuracy, and precision for all three analytes, in accordance to Food and
Drug Administration guidelines. Spiked quality controls in plasma as well as incurred samples were used to verify back-conversion
in the selected conditions, with results meeting European Medicines Agency acceptance criteria (concentrations within 80–120%
of the first reading). The method was then applied to a pharmacokinetic study, and for the first time, a pharmacokinetic curve
of clopidogrel acyl glucuronide in human plasma is presented. The concentrations ranged up to 1,048.684 ng/mL, with a mean
of 470.268 ng/mL, while clopidogrel had a mean C
max of 1.348 ng/mL; these orders of magnitude show how much the back-conversion of this metabolite may influence clopidogrel
quantification if it is not properly controlled. 相似文献
115.
González-Gago A Brandsma SH Leonards PE de Boer J Marchante-Gayón JM Garcia Alonso JI 《Analytical and bioanalytical chemistry》2011,401(8):2639-2649
A gas chromatography electron capture negative ionization mass spectrometry (GC(ECNI)MS) procedure for the determination of
priority polybrominated diphenyl ethers (PBDEs; congeners 28, 47, 99, 100, 153 and 154) in water samples at regulatory EU
levels has been developed. The method is based on the use of 81Br-labelled PBDEs for isotope dilution analysis and the measurement of 79Br/81Br isotope ratios in gas chromatography peaks with the electron capture negative ionization technique. The suitability of
this ion source for the precise and accurate measurement of bromine isotope ratios has been demonstrated. The general ECNI-IDMS
procedure was evaluated by the analysis of NIST SRM 1947 (Lake Michigan fish tissue) with satisfactory results. For the analysis
of water samples, 500 mL of the samples were spiked with the labelled PBDEs and extracted with 10 mL isooctane for 30 min.
The extract was evaporated down to ca. 100 μL and injected in the GC(ECNI)MS. Detection limits ranged from 0.014 −1 to 0.089 pg mL−1 depending on the congener. Recoveries from real water samples, spiked at a level of 0.5 pg mL−1, ranged from 77% to 102%. 相似文献
116.
Aloe plants have been widely documented in artists’ treatises dating from the sixteenth to the nineteenth century as a source
of colorant to achieve lustrous golden glazes on tin- and silver-foiled objects and warm-toned finishes on musical instruments,
such as violins. Aloe extracts contain characteristic anthraquinone and phenolic components which impart a distinctive orange
tone and fluorescence to mixtures containing them. Because of the low concentration of colorant in the coatings and its probable
degradation by high temperature during manufacture, the identification of aloe in heated oil–resin mixtures represents an
analytical challenge. For this reason, the possible presence of aloe in glazes and coatings has been largely overlooked. This
paper describes various analytical approaches to the identification of aloe in historic samples, from comparison with results
obtained from reference standards and mock-up samples. Complementary analytical techniques including thermally assisted hydrolysis
and methylation–gas chromatography–mass spectrometry, high-performance liquid chromatography, laser desorption–mass spectrometry,
matrix-assisted laser desorption-ionization-mass spectrometry and surface-enhanced Raman scattering were used. Different chemical
markers were identified by the individual methods and the advantages and limitations of each technique for the identification
of aloe in oil–resin varnishes are discussed. 相似文献
117.
Fu R Wang X Li C Santiago-Miranda AN Pielak GJ Tian F 《Journal of the American Chemical Society》2011,133(32):12370-12373
The feasibility of using solid-state magic-angle-spinning NMR spectroscopy for in situ structural characterization of the LR11 (sorLA) transmembrane domain (TM) in native Escherichia coli membranes is presented. LR11 interacts with the human amyloid precursor protein (APP), a central player in the pathology of Alzheimer's disease. The background signals from E. coli lipids and membrane proteins had only minor effects on the LR11 TM resonances. Approximately 50% of the LR11 TM residues were assigned by using (13)C PARIS data. These assignments allowed comparisons of the secondary structure of the LR11 TM in native membrane environments and commonly used membrane mimics (e.g., micelles). In situ spectroscopy bypasses several obstacles in the preparation of membrane proteins for structural analysis and offers the opportunity to investigate how membrane heterogeneity, bilayer asymmetry, chemical gradients, and macromolecular crowding affect the protein structure. 相似文献
118.
Aubert V Ordronneau L Escadeillas M Williams JA Boucekkine A Coulaud E Dragonetti C Righetto S Roberto D Ugo R Valore A Singh A Zyss J Ledoux-Rak I Le Bozec H Guerchais V 《Inorganic chemistry》2011,50(11):5027-5038
A series of cationic Ir(III) substituted bipyridyl ()(N(∧)N (N(∧)N-bpy) complexes incorporating electron-donor and -acceptor substituents, [Ir(C(∧)N-ppy-R')(2)(N(∧)N-bpy-CH═CH-C(6)H(4)-R)][X] (X(-) = PF(6)(-) or C(12)H(25)SO(3)(-)), 2 (a, R = NEt(2) and R' = Me; b, R = O-Oct and R' = Me; c, R = NO(2) and R' = C(6)H(13); C(∧)N-ppy = cyclometalated 2-phenylpyridine, [Ir(C(∧)N-ppy-Me)(2)(N(∧)N-bpy-CH═CH-thienyl-Me)][PF(6)], 2d, and the dithienylethene (DTE)-containing complex 2e have been synthesized and characterized, and their absorption, luminescence, and quadratic nonlinear optical (NLO) properties are reported. Density functional theory (DFT) and time-dependent-DFT (TD-DFT) calculations on the complexes facilitate a detailed assignment of the excited states involved in the absorption and emission processes. All five complexes are luminescent in a rigid glass at 77 K, displaying vibronically structured spectra with long lifetimes (14-90 μs), attributed to triplet states localized on the styryl-appended bipyridines. The second-order NLO properties of 2a-d and related complexes 1a-d with 1,10-phenanthrolines have been investigated by both electric field induced second harmonic generation (EFISH) and harmonic light scattering (HLS) techniques. They are characterized by high negative EFISH μβ values which decrease when the ion pair strength between the cation and the counterion (PF(6)(-), C(12)H(25)SO(3)(-)) increases. The EFISH response is mainly controlled by metal-to-ligand charge-transfer/ligand-to-ligand charge-transfer (MLCT/L'LCT) processes. A combination of HLS and EFISH techniques is used to evaluate both the dipolar and octupolar contributions to the total quadratic hyperpolarizability, demonstrating that the major contribution is controlled by the octupolar part. The incorporation of a photochromic DTE unit into the N(∧)N-bpy ligand (complex 2e) allows the luminescence to be switched ON or OFF. The photocyclisation of the DTE unit can be triggered by using either UV (365 nm) or visible light (430 nm), leading to an efficient quenching of the ligand-based 77 K luminescence, which can be restored upon irradiation of the closed form at 715 nm. In contrast, no significant modification of the EFISH μβ value is observed upon photocyclization, suggesting that the quadratic NLO response is dominated by the MLCT/L'LCT processes, rather than by the intraligand excited states localized on the substituted bipyridine ligand. 相似文献
119.
Gomez AG de Silveira G Doan H Cheng CH 《Chemical communications (Cambridge, England)》2011,47(20):5876-5878
We demonstrate an alternative route to tune the morphology of zeolite L crystals using C(2)H(5)OH as the co-solvent in the synthesis gel. A low aspect ratio (0.2 to 0.4) of zeolite L crystals was obtained at lower synthesis temperature (150 °C) and shorter synthesis duration (3 days). 相似文献
120.
We prove that the fields of asymptotic lines of a real hyperbolic homogeneous polynomial are isotopic to the corresponding fields of its hyperbolic homogeneous part. We also show some combinatorial identities which are related to such isotopy. 相似文献