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71.
Abdellatif El Kihel Abdelfattah Lagnaoui Tania Harjane Yasser Kattir Salaheddine Guesmi Patrick Bauchat 《Arabian Journal of Chemistry》2013,6(2):173-176
The condensation of 7-nitroindole-2-carbohydrazide derivatives with acetylacetone lead to (pyrazol-1-yl)(7-nitroindol-2-yl)ketones. 相似文献
72.
Yasser Saleh Mustafa Alajerami Suhairul Hashim Wan Muhamad Saridan Wan Hassan Ahmad Termizi Ramli 《Physica B: Condensed Matter》2012,407(13):2390-2397
Previous study proved the efficiency of copper as one of the most luminescent activators. In this work, Li2CO3–K2CO3–H3BO3 (LKB) glasses co-doped with copper oxide (CuO) and magnesium oxide (MgO) have been prepared by chemical quenching technique. Two techniques have been applied to investigate the effect of co-dopants on the physical and optical properties of the new glass network. The X-ray Diffraction (XRD) results showed the amorphous nature of the sample. Fourier transform infrared (FTIR) spectra, energy band gap, density, ion concentration, molar volume, Polaron radius and inter-nuclear distance have been analyzed in the light of the different oxidation states of co-doped ions in the glass matrix. The exchange in the concentration of magnesium and copper ions illustrated the great effect of magnesium as a co-dopant on the Photoluminescence (PL) emission of LKB doped with copper oxide. Due to the change in the copper concentration, a broad green emission with intensity of around 300 (a.u) has been observed. Enhancement of about three times has been shown with the increment of 0.1 mol% of CuO and MgO as a co-dopant technique. It is well known that magnesium oxide alone does not show strong-luminescence, but during this increment, MgO acted as activator (co-dopant) for Cu ions. This enhancement may contribute to the energy transfer from Mg2+ ions to monovalent Cu+ ion. The current results are discussed and compared with other related studies. 相似文献
73.
74.
Yasser S. Sokeirik Dr. Akiko Hoshina Masaaki Omote Dr. Kazuyuki Sato Dr. Atsushi Tarui Itsumaro Kumadaki Prof. Akira Ando Prof. 《化学:亚洲杂志》2008,3(10):1850-1856
The asymmetric addition of Me2Zn to aldehydes is very slow and mostly gives low ee values. Previously, we reported the synthesis of a fluorous chiral ligand, (4R,5S,α′R)‐2,2‐dimethyl‐α,α,α′‐tris(perfluorooctyl)‐2,3‐dioxolane‐4,5‐dimethanol ( 1 a ), derived from tartarate as a chiral pool. Ligand 1 a showed high activity toward the addition of Me2Zn to aldehydes with high enantiomeric excess. However, the very high content of fluorine makes 1 a difficult to dissolve in common solvents; hence, much solvent is required, which limits its use. This report describes the modification of 1 a by replacing either the perfluorooctyl groups with shorter perfluoroalkyl ones or the acetone ketal part with cyclohexanone ketal. The perfluorobutyl analogue 1 c is much more soluble than 1 a and shows comparable asymmetric induction toward the addition of Me2Zn to aldehydes. Furthermore, 1 c has a much lower molecular weight than 1 a . This means that 1 c is used in smaller amounts (weight) than 1 a . The cyclohexanone ketal analogue 1 d is more soluble than 1 a and more easily synthesized owing to its high solubility and ease of crystallization. Ligand 1 d showed much higher asymmetric induction toward cyclohexanecarbaldehyde, a branched aldehyde, than 1 a . Thus, 1 a was modified into ligands with higher performance. 相似文献
75.
Barbara Grzeszczyk Kamila Poławska Yasser M. Shaker Sebastian Stecko Adam Mames Magdalena Woźnica Marek Chmielewski Bartłomiej Furman 《Tetrahedron》2012,68(52):10633-10639
Kinugasa reactions between terminal acetylenes and six-membered ring nitrones when one or both components are chiral, proceed in a low to moderate yield and with a high diastereoselectivity affording mostly one, dominant β-lactam product. The first step of the reaction is controlled by the configuration of the nitrone, whereas the protonation of the C-7 center of the carbacepham skeleton in the second step depends on: a) the configuration of the bridgehead carbon atom formed in the first step, b) epimerization process in the presence of a base, and c) on the configuration of the stereogenic center in the acetylenic partner. In the case of the nitrone derived from dihydroisoquinoline, the reaction proceeds in a more complex way affording not only β-lactams, but also products derived from the alternative regio-1,3-cycloaddition, or nucleophilic addition of the acetylene to the double bond of the nitrone. 相似文献
76.
Jamil?A.?NasserEmail author Luc?Chassagne Suat?Top?u Jorge?Linares Yasser?Alayli 《The European Physical Journal B - Condensed Matter and Complex Systems》2014,87(3):69
In spin-conversion (SC) compounds containing molecules organized around an iron (II) ion the fundamental level of the ion is low spin (LS), S = 0, and its first excited one is high spin (HS), S = 2. This energy diagram is due to the ligands field interaction on 3d electrons and to the spin pairing energy. Heating the compound increases the magnetic susceptibility which corresponds to a change of populations of both levels and consequently a change of spin value of the molecules. This mechanism, called spin conversion (SC), can be accompagnied by thermal hysteresis observed by studying magnetic susceptibility or high spin fraction. In that case one considers that the (SC) takes place through a first-order phase transition due to intermolecular interactions. In the atom-phonon coupling model the molecules are considered as two-level systems, or two-level atoms, and it is assumed that the elastic force constant value of the spring which links two atoms first neighbours is depending on the electronic states of both atoms. In this study we calculate the partition function of a linear chain of N atoms (N ≤ 16) and we describe the role of phonons and that of the parameter Δ which corresponds to the distance in energy between both levels. The chain free-energy function is F atph . We introduce for the chain a free-energy function defined by the set (F HS , F LS , F barr ) and we show that F atph tends towards the previous set when N → ∞. The previous set allows to describe a first order phase transition between a (LS) phase and a (HS) one. At the crossing point between the function F LS and F HS , and around this point, there is an intermediate free-energy barrier which prevents the chain to change phase which can lead to thermal hysteresis. The energy gap between the free-energy function F atph and that defined by the set (F HS , F LS , F barr ) is small. So we can expect that a nanoparticule takes for free-energy function that defined by the set and then displays a thermal hysteresis. 相似文献
77.
Andreas Bertsch Andreas Leinenbach Anton Pervukhin Markus Lubeck Ralf Hartmer Carsten Baessmann Yasser Abbas Elnakady Rolf Müller Sebastian Böcker Christian G. Huber Oliver Kohlbacher 《Electrophoresis》2009,30(21):3736-3747
De novo sequencing of peptides using tandem MS is difficult due to missing fragment ions in the spectra commonly obtained after CID of peptide precursor ions. Complementing CID spectra with spectra obtained in an ion‐trap mass spectrometer upon electron transfer dissociation (ETD) significantly increases the sequence coverage with diagnostic ions. In the de novo sequencing algorithm CompNovo presented here, a divide‐and‐conquer approach was combined with an efficient mass decomposition algorithm to exploit the complementary information contained in CID and ETD spectra. After optimizing the parameters for the algorithm on a well‐defined training data set obtained for peptides from nine known proteins, the CompNovo algorithm was applied to the de novo sequencing of peptides derived from a whole protein extract of Sorangium cellulosum bacteria. To 2406 pairs of CID and ETD spectra contained in this data set, 675 fully correct sequences were assigned, which represent a success rate of 28.1%. It is shown that the CompNovo algorithm yields significantly improved sequencing accuracy as compared with published approaches using only CID spectra or combined CID and ETD spectra. 相似文献
78.
Yasser Saleh Mustafa Alajerami Suhairul Hashim Wan Muhamad Saridan Wan Hassan Ahmad Termizi Ramli Azman Kasim 《Physica B: Condensed Matter》2012,407(13):2398-2403
Several studies showed the interesting properties of trivalent lanthanide ions when doped in various types of glasses. Optical and physical properties of lithium magnesium borate glasses doped with Dy3+ then with Sm3+ ions were determined by measuring their absorption and luminescence spectra in the visible region. The absorption spectra of Dy3+ showed eight absorption bands with hypersensitive transition at 1265 nm (6H15/2→6F11/2-6H9/2) and three PL emission bands at 588 nm (4F9/2→6H15/2), 660 nm (4F9/2→6H13/2) and 775 nm (4F9/2→6H11/2). Regarding the Sm3+, nine absorption bands were observed with hypersensitive transition at 1237 nm (6H5/2–6F7/2); the PL spectrum showed four prominent peaks at 4G5/2→6H5/2 (yellow color), 4G5/2→6H7/2 (bright orange color), 4G5/2→6H9/2 (orange reddish color) and 4G5/2→6H11/2 (red color), respectively. Finally, a series of physical parameters such as the oscillator strengths, refractive index, ions concentration, Polaron radius and other parameters were calculated for each dopant. 相似文献
79.
Optical bistability for two-level atomic system in a ring cavity is investigated outside the rotating wave approximation (RWA) using non-autonomous Maxwell-Bloch equations with Fourier decomposition up to first harmonic. The first harmonic output field component exhibits reversed or closed loop bistability simultaneously with the usual (anti-clockwise) bistability in the fundamental field component. 相似文献
80.
Yasser M.Z. Ahmed Mohamed I. Riad Ahmed I. Zaky Mohammed Abdel-Aziz Mohamed M.H. Shalabi 《中国颗粒学报》2007,5(6):391-394
In line with recent attention on porous metals having low and medium porosities in the range of 20-50%, this paper studies the effect of porosity on the mechanical properties of sintered copper compacts. Experiments were designed to investigate the effect of porosity, applied stress and sliding velocity on the wear rate of copper compacts, leading to the finding that the effects of both porosity and applied stress of the wear test on the wear rate are approximately similar and higher than that of sliding velocity. The investigation concerning the effect of porosity on compressive strength indicated that the stress-strain curve of high-porosity compact exhibited identifiable ultimate strength points, though low-porosity compact showed distinct stages of elastic plastic behavior. 相似文献