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排序方式: 共有191条查询结果,搜索用时 15 毫秒
1.
Tanja Brezo-Borjan Zorica Stojanovi Zvonimir Suturovi Jovana Kos Sneana Kravi Ana urovi 《Monatshefte für Chemie / Chemical Monthly》2020,151(3):285-291
A new electroanalytical method for vitamin B1 determination, based on adsorptive chronopotentiometric stripping analysis and non-specific adsorption onto mercury film electrode, was developed and validated. Stripping chronopotentiograms showed a single well-defined oxidation wave corresponding to vitamin B1 at about − 0.43 V in citrate buffer pH 6.0. The most important experimental factors affecting the monitored electroanalytical response of vitamin B1 were investigated and optimised. Under the optimal experimental conditions, linear response of vitamin B1 was obtained in the concentration range of 5–50 mg dm−3, with the achieved limit of detection of 1.64 mg dm−3, and the limit of quantitation of 4.97 mg dm−3. A mean recovery of 97.1% and relative standard deviations of 3.75% were achieved. The developed electrochemical procedure was successfully applied for the determination of vitamin B1 in pharmaceutical products. The results of the proposed method were in good agreement with those obtained by parallel HPLC analyses, confirming an accuracy of the developed method. 相似文献
2.
This paper introduces a new framework for implicit restarting of the Krylov–Schur algorithm. It is shown that restarting with arbitrary polynomial filter is possible by reassigning some of the eigenvalues of the Rayleigh quotient through a rank‐one correction, implemented using only the elementary transformations (translation and similarity) of the Krylov decomposition. This framework includes the implicitly restarted Arnoldi (IRA) algorithm and the Krylov–Schur algorithm with implicit harmonic restart as special cases. Further, it reveals that the IRA algorithm can be turned into an eigenvalue assignment method. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
3.
Gordan Horvat Josip Požar Zvonimir Dojnović Dragutin Grgec Saša Blažeka 《Journal of Thermal Analysis and Calorimetry》2014,117(2):901-907
A quasi-adiabatic calorimeter for determining the molar solution enthalpies (Δsol H) of non-volatile solids was constructed. The design of the instrument was adjusted to allow the determination of solution enthalpies of small amounts of solids. For that purpose, the novel apparatus for sample dosage with virtually negligible “blank heat” was built. The rather low heat capacity of the calorimeter was achieved by reducing the volume of the reaction cell (20 mL), the dosing unit, and electric elements (the thermistor and the heater). Good thermal isolation of the reaction cell from the surroundings was accomplished by placing the cell into an evacuated polypropylene vessel. A computer program for processing the calorimetric data according to modified Regnault–Pfaundler method was written. The performance of the calorimeter was tested by determining the heats of the reactions serving as thermochemical standards at 25 °C (the dissolution of KCl and NaCl in water and the dissolution of tris(hydroxymethyl)-aminomethane in 0.1 mol dm?3 HCl(aq)). The obtained data were in very good agreement with the literature values. 相似文献
4.
5.
Anita Pti
ek Siro
i Ana Re
ek Zvonimir Katan
i Zlata Hrnjak-Murgi 《Molecules (Basel, Switzerland)》2021,26(11)
The studied samples were prepared from polyethylene (PE) polymer which was coated with modified polycaprolactone (PCL) film in order to obtain bilayer films. Thin PCL film was modified with casein/aluminum oxide compound to enhance vapor permeability as well as mechanical and thermal properties of PE/PCL films. Casein/aluminum oxide modifiers were used in order to achieve some functional properties of polymer film that can be used in various applications, e.g., reduction of water vapor permeability (WVTR) and good mechanical and thermal properties. Significant improvement was observed in mechanical properties, especially in tensile strength as well as in water vapor values. Samples prepared with aluminum oxide particles indicated significantly lower values up to 60%, and samples that were prepared with casein and 5% Al2O3 showed the lowest WVTR value. 相似文献
6.
7.
Zvonimir Janko 《Israel Journal of Mathematics》2006,154(1):185-189
We classify minimal non-quaternion-free finite 2-groups which possess a nonmodular proper subgroup. 相似文献
8.
9.
Dörr FA Kovačevi B Maksi ZB Pinto E Volmer DA 《Journal of the American Society for Mass Spectrometry》2011,22(11):2011-2020
The aim of this study was to investigate the unusual gas-phase dissociation behavior of two epimer pairs of protonated gonyautoxins
(GTX) following electrospray ionization in comparison to their deprotonated counterparts. The chemical structures of the investigated
GTX1-4 variants vary in their substitution pattern at N-1 and the stereochemical orientation of the hydroxysulfate group at C-11
(11α for GTX1/2 versus 11β for GTX3/4). The direct comparison of mass spectra in positive and negative ion modes illustrated two distinct features: first, an intriguing
difference between protonated 11α and 11β species, where 11α conformations exhibited almost complete dissociation of [M +
H]+ ions via facile SO3 elimination, while 11β species remained mostly intact as [M + H]+; and second, the lack of such differences for the deprotonated counterparts. In this study, we propose an acid-catalyzed
elimination mechanism from density functional theory calculations, initiated by a proton transfer of a guanidinium proton
to the hydroxysulfate group with simultaneous SO3 release, which is only possible for the 11α conformation based on intramolecular distances. The same mechanism explains the
lack of a comparable SO3 loss in the negative ion mode. CID experiments supported this proposed mechanism for GTX1 and GTX2. Computational modeling of product ions seen in the CID spectra of GTX3 and GTX4 established that the lowest energy dissociation pathway for the 11β epimers is elimination of water with the possibility
for further SO3 release from the intermediate product. Experimental data for structurally analogous decarbamoyl gonyautoxins confirmed the
evidence for the GTX compounds as well as the proposed elimination mechanisms. 相似文献
10.
Bond-stretch isomerism in benzo[1,2:4,5]dicyclobutadienle (BDCB) has been investigated using the MR-AQCC/6-31G(d) method, a high-level multireference ab initio approach including size-extensivity corrections. The applied theoretical approach includes both nondynamical and dynamical electron correlation effects. Full MR-AQCC geometry optimizations of localized (1) and delocalized (3) isomers as well as the transition structure (TS) have been determined using D2h, symmetry restriction. The calculations show that both isomers are approximately of equal stability separated by a barrier with a height of about 5 kcal mol(-1). Thus, the present results strongly indicate that benzof[1,3:4,5]dicyclobutadiene is a very good candidate for an organic compound exhibiting bond-stretch isomerism, since isomers 1 and 3 correspond to true minima on the double-well potential energy surface, which are separated by a sufficiently high barrier. It is particularly important to emphasize that isomer 3 represents a realization of the highly elusive quasi-[10]annulene. 相似文献