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排序方式: 共有152条查询结果,搜索用时 93 毫秒
61.
62.
Manzoor Ahmed Muhammed Asghar Mohammed Yaqoob Samar Ali Nusrat Bibi Abdul Nabi 《Journal of Analytical Chemistry》2018,73(11):1098-1104
63.
Wlodzimierz Szwarc Samar K. Mukhopadhyay 《The Journal of the Operational Research Society》1995,46(6):753-761
This paper deals with scheduling n jobs on a single machine in order to minimize the weighted sum of squared waiting times of the jobs. We present a powerful decomposition mechanism, based on a precedence relation concept, that easily handles problems of the size n = 50 and 100 where the processing times and penalties are independently drawn from a uniform distribution. This mechanism is incorporated along with new branching rules in a branch-and-bound scheme that efficiently handles tough problems of the size 20 and 50. 相似文献
64.
Analytical data obtained on deoxynivalenol (DON) concentration in naturally contaminated wheat during processing in an industrial mill were statistically analyzed, and the distribution functions of DON concentration in lots of wheat, bran, wheat flour, and gluten were estimated. The analytical method had acceptable precision (HORRAT 0.25-0.32) for each test sample. The total variance combined sampling, sample preparation, and analytical variances were 0.188, 0.033, 0.42, and 0.0014 ppm2 for wheat, 1.93; flour, 0.99; bran, 4.68; and gluten, 0.29, respectively. The distribution function of DON contamination presented an asymmetric tail for high values of concentration in wheat grains and wheat flour; in bran it seemed to be bimodal with 2 separated peaks of different concentrations; in gluten the normal distribution function gave a reasonably good fit to empirical data. The function eta(c) = -In(-Inp), where p (c) is the cumulative distribution function was linear with c in the so-called extreme-value type I distribution and could be fitted by a cubic polynomial in c in the distributions determined for all the products. This variability and distributional information contributes to the design of better sampling plans in order to reduce the total variability and to estimate errors in the evaluation of DON concentration in lots of wheat and wheat products. 相似文献
65.
Tremblay-Morin JP Faure S Samar D Stern C Guilard R Harvey PD 《Inorganic chemistry》2005,44(8):2836-2842
The bismacrocycle 5,17-bis[5-(2,8,13,17-tetraethyl-3,7,12,18-tetramethylporphyrinyl)]-25,26,27,28-tetrapropoxycalix[4]arene (4) was synthesized in three steps from the corresponding bisaldehyde 5,17-diformyl-25,26,27,28-tetrapropoxycalix[4]arene. The biszinc(II) complex (5) was prepared as well, and the photophysical properties were measured using 2-MeTHF as solvent at 298 and 77 K. While computer modeling for 5 predicts that both pinched cone conformers, closed (porphyrins near each other) and open (porphyrins away from each other), may exist in the "gas phase", the experimental data indicate clearly that no zinc porphyrin...zinc porphyrin interactions are present in solution at 298 K, favoring the open conformer, where the two macrocycles are placed away from each other. On the other hand, clear evidence for a closed conformer is observed at 77 K. Variable-temperature (1)H NMR experiments show that 5 is fluxional between 298 and 183 K, while 4 keeps the open conformation for the whole temperature range. This behavior is unprecedented for calix[4]areneporphyrin compounds, and the relative porphyrin ring rigidity is postulated to explain this difference. 相似文献
66.
Donaire A Jiménez B Fernández CO Pierattelli R Niizeki T Moratal JM Hall JF Kohzuma T Hasnain SS Vila AJ 《Journal of the American Chemical Society》2002,124(46):13698-13708
The blue copper proteins (BCPs), pseudoazurin from Achromobacter cycloclastes and rusticyanin from Thiobacillus ferrooxidans, have been investigated by (1)H NMR at a magnetic field of 18.8 T. Hyperfine shifts of the protons belonging to the coordinated ligands have been identified by exchange spectroscopy, including the indirect detection for those resonances that cannot be directly observed (the beta-CH(2) of the Cys ligand, and the NH amide hydrogen bonded to the S(gamma)(Cys) atom). These data reveal that the Cu(II)-Cys interaction in pseudoazurin and rusticyanin is weakened compared to that in classic blue sites (plastocyanin and azurin). This weakening is not induced by a stronger interaction with the axial ligand, as found in stellacyanin, but might be determined by the protein folding around the metal site. The average chemical shift of the beta-CH(2) Cys ligand in all BCPs can be correlated to geometric factors of the metal site (the Cu-S(gamma)(Cys) distance and the angle between the CuN(His)N(His) plane and the Cu-S(gamma)(Cys) vector). It is concluded that the degree of tetragonal distortion is not necessarily related to the strength of the Cu(II)-S(gamma)(Cys) bond. The copper-His interaction is similar in all BCPs, even for the solvent-exposed His ligand. It is proposed that the copper xy magnetic axes in blue sites are determined by subtle geometrical differences, particularly the orientation of the His ligands. Finally, the observed chemical shifts for beta-CH(2) Cys and Ser NH protons in rusticyanin suggest that a less negative charge at the sulfur atom could contribute to the high redox potential (680 mV) of this protein. 相似文献
67.
Muhammad Yousaf Yaqoob Mohammad Asghar Muhammad Ali Samar Waseem Amir 《Journal of Analytical Chemistry》2022,77(3):318-327
Journal of Analytical Chemistry - A simple and sensitive flow injection chemiluminescence method was developed for the determination of cefixime trihydrate (CFX) based on its enhancing effect on... 相似文献
68.
Fayed Eman A. Nosseir Eman S. Atef Ahmed El‑Kalyoubi Samar A. 《Molecular diversity》2022,26(1):341-363
Molecular Diversity - Several coumarin-containing substitute nitrogen heterocycles have recently received considerable importance due to their diverse pharmacological properties. One-pot and rapid... 相似文献
69.
Samar Eid 《Journal of organometallic chemistry》2008,693(16):2755-2760
Cp2Ti(dithiolene) and Cp2Ti(diselenolene) complexes containing the N-methyl-1,3-thiazoline-2-thione-4,5-dithiolate ligand (Me-thiazdt), the N-phenyl-1,3-thiazoline-2-thione-4,5-dithiolate ligand (Ph-thiazdt) and the N-methyl-1,3-thiazoline-2-thione-4,5-diselenolate ligand (Me-thiazds) have been synthesized. Three approaches have been developed in order to generate the dithiolene or the diselenolene ligands which were reacted with Cp2TiCl2 to form the corresponding heteroleptic complexes. Their X-ray crystal structures, UV-Vis absorption spectra as well as their redox properties, determined by cyclic voltammetry have been investigated and discussed. Variable-temperature 1H NMR experiments have been performed in order to determine the activation energies of the chelate ring inversion. 相似文献
70.
Gareth S. A. Wright Hyun Chul Lee Clemens Schulze‐Briese J. Günter Grossmann Richard W. Strange S. Samar Hasnain 《Journal of synchrotron radiation》2013,20(2):383-385
This study analyses the potential for laboratory‐based size‐exclusion chromatography (SEC) integrated small‐angle X‐ray scattering (SAXS) instrumentation to characterize protein complexes. Using a high‐brilliance home source in conjunction with a hybrid pixel X‐ray detector, the efficacy of SAXS data collection at pertinent protein concentrations and exposure times has been assessed. Scattering data from SOD1 and from the complex of SOD1 with its copper chaperone, using 10 min exposures, provided data quality in the range 0.03 < q < 0.25 Å?1 that was sufficient to accurately assign radius of gyration, maximum dimension and molecular mass. These data demonstrate that a home source with integrated SEC–SAXS technology is feasible and would enable structural biologists studying systems containing transient protein complexes, or proteins prone to aggregation, to make advanced preparations in‐house for more effective use of limited synchrotron beam time. 相似文献