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排序方式: 共有348条查询结果,搜索用时 31 毫秒
111.
Cuello-Nuñez Susana Benning Jocelyn Liu Chuan Branton Peter Hu Jin McAdam Kevin G. Coburn Steven Braybrook Julian Goenaga-Infante Heidi 《Analytical and bioanalytical chemistry》2018,410(26):6795-6806
Analytical and Bioanalytical Chemistry - Fractionation data for cadmium in tobacco products, as obtained by sequential leaching of cadmium species with ICP-MS/MS analysis, and separately by X-ray... 相似文献
112.
In this paper the effect of bias and geometric symmetry breaking on the electronic spectrum of a model molecular system is studied. Geometric symmetry breaking can either enhance the dissipative effect of the bias, where spectral peaks are disabled, or enable new excitations that are absent under zero bias conditions. The spectral analysis is performed on a simple model system by solving for the electronic response to an instantaneously impulsive perturbation in the dipole approximation. The dynamical response is extracted from the electronic equations of motion as expressed by the Keldysh formalism. This expression provides for the accurate treatment of the electronic structure of a bulk-coupled system at the chosen model Hamiltonian electronic structure level. 相似文献
113.
Wiesenmayer E Luetkens H Pascua G Khasanov R Amato A Potts H Banusch B Klauss HH Johrendt D 《Physical review letters》2011,107(23):237001
It is widely believed that, in contrast to its electron-doped counterparts, the hole-doped compound Ba(1-x)K(x)Fe(2)As(2) exhibits a mesoscopic phase separation of magnetism and superconductivity in the underdoped region of the phase diagram. Here, we report a combined high-resolution x-ray powder diffraction and volume-sensitive muon spin rotation study of Ba(1-x)K(x)Fe(2)As(2) showing that this paradigm does not hold true in the underdoped region of the phase diagram (0≤x≤0.25). Instead we find a microscopic coexistence of the two forms of order. A competition of magnetism and superconductivity is evident from a significant reduction of the magnetic moment and a concomitant decrease of the magnetoelastically coupled orthorhombic lattice distortion below the superconducting phase transition. 相似文献
114.
Charmaine Arderne Kyle Fraser Batchelor Bhawna Uprety Rahul Chandran Heidi Abrahamse 《Acta Crystallographica. Section C, Structural Chemistry》2020,76(7):663-672
The reactivity of the cobalt(III) complexes dichlorido[tris(2‐aminoethyl)amine]cobalt(III) chloride, [CoCl2(tren)]Cl, and dichlorido(triethylenetetramine)cobalt(III) chloride, [CoCl2(trien)]Cl, towards different amino acids (l ‐proline, l ‐asparagine, l ‐histidine and l ‐aspartic acid) was explored in detail. This study presents the crystal structures of three amino acidate cobalt(III) complexes, namely, (l ‐prolinato‐κ2N,O)[tris(2‐aminoethyl)amine‐κ4N,N′,N′′,N′′′]cobalt(III) diiodide monohydrate, [Co(C5H8NO2)(C6H18N4)]I2·H2O, I , (l ‐asparaginato‐κ2N,O)[tris(2‐aminoethyl)amine‐κ4N,N′,N′′,N′′′]cobalt(III) chloride perchlorate, [Co(C4H7N2O3)(C6H18N4)](Cl)(ClO4), II , and (l ‐prolinato‐κ2N,O)(triethylenetetramine‐κ4N,N′,N′′,N′′′)cobalt(III) chloride perchlorate, [Co(C4H7N2O3)(C6H18N4)](Cl)(ClO4), V . The syntheses of the complexes were followed by characterization using UV–Vis spectroscopy of the reaction mixtures and the initial rates of reaction were obtained by calculating the slopes of absorbance versus time plots. The initial rates suggest a stronger reactivity and hence greater affinity of the cobalt(III) complexes towards basic amino acids. The biocompatibility of the complexes was also assessed by evaluating the cytotoxicity of the complexes on cultured normal human fibroblast cells (WS1) in vitro. The compounds were found to be nontoxic after 24 h of incubation at concentrations up to 25 mM. 相似文献
115.
116.
The ground‐state equilibrium geometries, electronic structures and vertical excitation energies of methyl‐ and methoxyl‐substituted phenol radical cations and phenoxyl radicals have been investigated using time‐dependent density‐functional theory (namely TD‐B3LYP) and complete‐active‐space second‐order perturbation theory (CASPT2). The “anomalous” large redshifts of the absorption maxima of the phenol radical species observed in the ultraviolet–visible spectral region upon di‐meta‐methoxyl substitution are reproduced by the calculations. Furthermore, these “anomalous” shifts which were unexplained to date can be rationalized on the basis of a qualitative molecular orbital perturbation analysis. 相似文献
117.
Erin Hart Damini Grover Heidi Zettl Victoria Koshevarova Michael H. Abraham 《Physics and Chemistry of Liquids》2016,54(2):141-154
Experimental data have been compiled from the published chemical and engineering literature on the enthalpies of solvation for 92 different inorganic gases and organic vapours in acetic acid. The compiled data are used to derive mathematical correlations based on the Abraham solvation parameter model. The derived expressions describe the experimental solvation enthalpies in acetic acid to within a standard deviation (SD) of 2.2 kJ mol?1. Principal Component Analysis (PCA) on the five equation coefficients from a derived Abraham model correlation shows that acetic acid does not resemble hydroxylic solvents in terms of enthalpic interactions, but is more akin to moderately polar solvents such as ethyl acetate or acetone. 相似文献
118.
Linjalahti H Feng G Mareque-Rivas JC Mikkola S Williams NH 《Journal of the American Chemical Society》2008,130(13):4232-4233
The catalysis of phosphoryl transfer by metal ions has been intensively studied in both biological and artificial systems, but the status of the transient pentacoordinate phosphoryl species (as transition state or intermediate) is the subject of considerable debate. We report that dinuclear metal ion complexes that incorporate second sphere hydrogen bond donors not only promote the cleavage of RNA fragments just as efficiently as the activated analogue HPNPP but also provide the first examples of metal ion catalyzed phosphate diester isomerization close to neutral pH. This observation implies that the reaction catalyzed by these complexes involves the formation of a phosphorane intermediate that is sufficiently long-lived to pseudorotate. 相似文献
119.
Goenaga Infante H Ovejero Bendito Mdel C Cámara C Evans L Hearn R Moesgaard S 《Analytical and bioanalytical chemistry》2008,390(8):2099-2106
A method for the accurate determination of ultratrace selenium species of relevance to cancer research, such as gamma-glutamyl-Se-methylselenocysteine
(γ-glutamyl-SeMC), using species-specific double isotope dilution analysis (IDA) with HPLC–ICP–MS is reported for the first
time. The 77Se-enriched γ-glutamyl-SeMC spike was produced in-house by collecting the fraction at the retention time of the γ-glutamyl-SeMC
peak from a chromatographed aqueous extract of 77Se-enriched yeast, pooling the collected fractions and freeze-drying the homogenate. The Se content of this spike was characterised
using reverse isotope dilution mass spectrometry (IDMS) and the isotopic composition of this spike was checked prior to quantification
of the natural abundance dipeptide species in garlic using speciated IDA. The extraction of the γ-glutamyl-SeMC species in
water was performed in a sonication bath for 2 h after adding an appropriate quantity of 77Se-enriched γ-glutamyl-SeMC to 50 mg of garlic to give optimal 78Se/77Se and 82Se/77Se ratios of 1.5 and 0.6, respectively. The effect of ultrasonic nebulisation, in comparison with the loading of the ICP with
carbon (through the addition of methane gas on-line), on the detection of Se associated with γ-glutamyl-SeMC using collision/reaction
cell ICP–MS with hydrogen as collision gas was investigated. Sensitivity enhancements of approximately fourfold and twofold
were achieved using USN and methane mixed plasma, respectively, in comparison with conventional nebulisation and conventional
Ar ICP–MS. However, an approximately twofold improvement in the detection limit was achieved using both approaches (42 ng
kg−1 for 78Se using peak height measurements). The use of species-specific IDMS enabled quantification of the dipeptide species at ng
g−1 levels (603 ng g−1 Se) in the complex food matrix with a relative standard deviation (RSD, n = 4) of 4.5%, which was approximately half that obtained using standard addition as a confirmatory technique. Furthermore,
good agreement was found between the γ-glutamyl-SeMC species concentrations obtained using both calibration methods. 相似文献
120.
Heidi Haynal 《Journal of Algebra》2008,319(10):4199-4221