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81.
Carlos Guido Bollini Mario Giambiagi Myriam Segre de Giambiagi Aloysio Paiva de Figueiredo 《Journal of mathematical chemistry》2000,28(1-3):71-81
The multicenter bond index proposed within the MO framework depends on the order of the centers for which it is calculated, outside from the 3-c case. For the 6-c case, the eventually different values are 60. A graphical approach links the MO values to VB structures. Benzene, chosen as our paradigm for the 6-c case, illustrates our proposition. 相似文献
82.
Myriam Eveno Adrian Duran Jacques Castaing 《Applied Physics A: Materials Science & Processing》2010,100(3):577-584
It is rare that the analyses of materials in paintings can be carried out by taking micro-samples. Valuable works of art are
best studied in situ by non-invasive techniques. For that purpose, a portable X-ray diffraction and fluorescence apparatus
has been designed and constructed at the C2RMF. This apparatus has been used for paintings of Rembrandt, Leonardo da Vinci,
Van Gogh, Mantegna, etc. Results are given to illustrate the performance of X-ray diffraction, especially when X-ray fluorescence
does not bring sufficient information to conclude. 相似文献
83.
Joachim Mohn Christina Biasi Samuel Bodé Pascal Boeckx Paul J. Brewer Sarah Eggleston Heike Geilmann Myriam Guillevic Jan Kaiser Kristýna Kantnerová Heiko Moossen Joanna Müller Mayuko Nakagawa Ruth Pearce Isabell von Rein David Steger Sakae Toyoda Wolfgang Wanek Sarah K. Wexler Naohiro Yoshida Longfei Yu 《Rapid communications in mass spectrometry : RCM》2022,36(13):e9296
84.
Myriam Díaz-Álvarez Antonio Martín-Esteban Esther Turiel 《Journal of separation science》2022,45(13):2356-2365
In this work, the preparation and evaluation of water-compatible molecularly imprinted polymers for triazines using 2-hydroxyethyl methacrylate and methacrylic acid as comonomers is described. Four sets of molecularly imprinted and non-imprinted polymers for propazine were prepared at varying monomer molar ratios (from 4:0 to 1:3), and evaluated for the recognition of several triazines directly in aqueous media. The evaluation was performed by loading 1 mL of an aqueous solution containing 500 ng of each selected triazine, washing with 500 μL of acetonitrile, and eluting with 500 μL of methanol followed by 2 × 500 μL of a solution of methanol containing 10% of acetic acid. Final determinations were performed by high-performance liquid chromatography-ultraviolet detection. Improvement in molecular recognition of triazines in water was obtained on those molecularly imprinted polymers incorporating 2-hydroxyethyl methacrylate in 3:1 or 2:2 molar ratios, being the former selected as optimum providing recoveries for propazine up to 80%. A molecularly imprinted solid-phase extraction protocol was developed to ensure that triazines-selective recognition takes place inside selective binding sites in pure water media. Finally, the developed method was successfully applied to the determination of the selected triazines in environmental waters providing limits of detection from 0.16 and the 0.5 μg/L concentration range. 相似文献
85.
Minerva Gamboa Myriam Campos Luis Alfonso Torres 《The Journal of chemical thermodynamics》2010,42(5):666-674
In this work, the stability of 5,10,15,20-tetraphenylporphine (TPP) and its metallic derivatives, NiTPP, CoTPP, CuTPP, and ZnTPP has been studied through differential scanning calorimetry and thermogravimetry. The decomposition temperatures are (712, 710, 708, 702, and 671) K for NiTPP, CoTPP, CuTPP, ZnTPP, and TPP, respectively. These values are in correspondence with the N–M bond length dM–N, of the metalloporphyrins. The corresponding molar enthalpies of melting ΔfusHm, were determined as (58, 57, 55, 52, and 44) kJ · mol?1 for the same series. These values are discussed in terms of the crystallographic features in the solid state. 相似文献
86.
We report on the investigation of thermal effects in high-repetition-rate pulsed optical parametric oscillators emitting in the mid-IR. We find that the thermal load induced by the nonresonant idler absorption plays a critical role in the emergence of thermally induced bistability. We then demonstrate a significant improvement of the conversion efficiency (more than 30%) when a proper axial temperature gradient is applied to the nonlinear crystal by use of a two-zone temperature-controlled oven. 相似文献
87.
M. Milagros Delgado‐Zamarreño Myriam Bustamante‐Rangel Sergio Sierra‐Manzano Marcela Verdugo‐Jara Rita Carabias‐Martínez 《Journal of separation science》2009,32(9):1430-1436
Tocopherols and tocotrienols have been simultaneously determined in food samples using a rapid and simple analytical method including pressurized liquid extraction (PLE) and LC with electrochemical detection. Separation was carried out on a Phenomenex Synergi 4 μm Hydro‐RP 80A column, using a solution of 2.5 mM acetic acid/sodium acetate in methanol/water (99:1, v/v) as mobile phase at a flow rate of 1.0 mL/min. Column temperature was maintained at 30°C. Detection was performed by coulometric detection at 500 mV except for (β+γ)‐tocotrienol, in wheat and rye samples, which was at +350 mV. A palm oil containing a relatively large amount of γ‐tocotrienol and lower concentrations of α‐ and δ‐tocotrienols and α‐ and γ‐tocopherols was used to provide reference retention times for the tocotrienols. Analyte quantification was performed using the external standard method. The calibration equations of tocopherols were used to quantify both tocopherols and their corresponding tocotrienols. The extraction recoveries obtained using the optimized PLE conditions were in the 80–114% range, with RSDs lower than 15%. The method was successfully applied to the determination of tocotrienols and tocopherols in cereal (wheat, rye, barley, maize and oat) and palm oil samples. 相似文献
88.
Different models have been described in the literature to evaluate the total porosity of CEC columns: gravimetric, flow as well as conductivity-based methods. In this study, these models have been compared for two kinds of CEC columns: two mixed-mode silica particle stationary phases and different monolithic columns (acrylate or polystyrene divinylbenzene-based). The total porosities measured from the conductivity-based methods were lower than the total column porosities obtained by gravimetric or flow methods for all the investigated columns while the wide distribution of observed values shows that conductivity-based methods discriminate columns more efficiently with very different properties. We propose a conductivity-based method taking into account the actual length proposed by Horvath, to evaluate what we call an "actual electrokinetic" porosity (AEP). This parameter, based on electrokinetic theory only, affords the most consistent evaluation of porosity under experimental CEC conditions for the packed- and acrylate-based monolithic columns. To illustrate the potential of AEP and actual EOF for the estimation of the performances of a CEC system (stationary and mobile phases) we studied the influence of the mobile-phase composition on these parameters for CEC separations with an ammonium embedded packed stationary phase. The AEP and the actual electroosmotic mobility should allow a better understanding of the perfusive EOF and stationary-phase wettability. For neutral compounds (substituted phenols), AEP evaluation allowed us to predict the mobile-phase conditions able to enhance the efficiency while both AEP and actual EOF had to be considered in the case of peptide analysis. 相似文献
89.
90.
Zhang H Le Potier I Smadja C Zhang J Taverna M 《Analytical and bioanalytical chemistry》2006,386(5):1387-1394
An in-capillary derivatization of amino acids and peptides with 4-fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F) was developed
for their subsequent capillary electrophoretic analysis with laser-induced fluorescence detection (λ
ex=488 nm). The in-capillary derivatization was achieved in zone-passing mode by introducing successive plugs of sample and
NBD-F into a fused silica capillary previously equilibrated with an alkaline borate buffer. To prevent NBD-F hydrolysis and
to achieve a reliable derivatization, NBD-F was prepared daily in absolute ethanol and a plug of absolute ethanol was introduced
between the sample and NBD-F reagent plugs. Various parameters influencing the derivatization efficiency were investigated
and the optimum conditions were as follows: background electrolyte (BGE), 20 mM borate buffer (pH 8.8); introduction time,
4 s for sample and 2 s for NBD-F; molar ratio of NBD-F/sample, above 215; temperature, 45 °C for amino acids and 35 °C for
peptides; applied voltage, +15 kV. The validation of the in-capillary derivatization method under optimal conditions showed
a good linearity between the heights of the derivative peaks and the concentrations of the amino acids. The intra-day relative
standard deviations of the migration times and the peak heights were less than 1.3% and 4.6%, respectively. The efficient
derivatization and separation of a mixture of valine, alanine, glutamic acid and aspartic acid were achieved using this technique.
Peptides such as buccaline and β-protein fragment 1–42 could also be derivatized using the developed in-capillary derivatization
procedure.
In‑capillary derivatization and separation of amino acids with different concentrations.
From the top to bottom the concentrations are 1.11×10−5 M, 5.55×10−6 M, 2.78×10−6 M, 6.95×10−7 M. for valine; 1.26×10−5 M, 6.30×10−6 M, 3.15×10−6 M, 7.88×10−7 M for alanine; 3.78×10−5 M, 1.89×10−5 M, 9.45×10−6 M, 2.36×10−6 M for glutamic acid;, 4.27×10−5 M, 2.14×10−5 M, 1.07×10−5 M, 2.68×10−6 M for aspartic acid.
Experiment conditions: injection order: 4s for sample, 1s for absolute ethanol, and then 2s for 5.24×10−2 M NBD‑F; BGE: 20 mM borate pH 8.77; Applied voltage: 15 kV. 相似文献