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排序方式: 共有125条查询结果,搜索用时 15 毫秒
1.
Journal of Thermal Analysis and Calorimetry - This article considers viscoelastic effects on the enhancement of transportation of heat in thin-film flow when the relaxation time phenomenon is... 相似文献
2.
The growth of ordered domains in lattice gas models, which occurs after the system is quenched from infinite temperature to a state below the critical temperatureT
c, is studied by Monte Carlo simulation. For a square lattice with repulsion between nearest and next-nearest neighbors, which in equilibrium exhibits fourfold degenerate (2×1) superstructures, the time-dependent energy E(t), domain size L(t), and structure functionS(q, t) are obtained, both for Glauber dynamics (no conservation law) and the case with conserved density (Kawasaki dynamics). At late times the energy excess and halfwidth of the structure factor decrease proportional tot
–x, whileL(t) t
x, where the exponent x=1/2 for Glauber dynamics and x1/3 for Kawasaki dynamics. In addition, the structure factor satisfies a scaling lawS(k,t)=t
2xS(ktx). The smaller exponent for the conserved density case is traced back to the excess density contained in the walls between ordered domains which must be redistributed during growth. Quenches toT>T
c, T=Tc (where we estimate dynamic critical exponents) andT=0 are also considered. In the latter case, the system becomes frozen in a glasslike domain pattern far from equilibrium when using Kawasaki dynamics. The generalization of our results to other lattices and structures also is briefly discussed. 相似文献
3.
The sorptive potential of sunflower stem (180-300 μm) for Cr(III) ions has been investigated in detail. The maximum sorption (≥85%) of Cr(III) ions (70.2 μM) has been accomplished using 30 mg of high density sunflower stem in 10 min from 0.001 M nitric and 0.0001 M hydrochloric acid solutions. The accumulation of Cr(III) ions on the sorbent follows Dubinin-Radushkevich (D-R), Freundlich and Langmuir isotherms. The isotherm yields D-R saturation capacity Xm = 1.60 ± 0.23 mmol g−1, β = −0.00654 ± 0.00017 kJ2 mol−2, mean free energy E = 8.74 ± 0.12 kJ mol−1, Freundlich sorption capacity KF = 0.24 ± 0.11 mol g−1, 1/n = 0.90 ± 0.04 and of Langmuir constant KL = 6800 ± 600 dm3 mol−1 and Cm = 120 ± 18 μmol g−1. The variation of sorption with temperature (283-323 K) gives ΔH = −23.3 ± 0.8 kJ mol−1, ΔS = −64.0 ± 2.7 J mol−1 K−1 and ΔG298k = −4.04 ± 0.09 kJ mol−1. The negative enthalpy and free energy envisage exothermic and spontaneous nature of sorption, respectively. Bisulphate, Fe(III), molybdate, citrate, Fe(II), Y(III) suppress the sorption significantly. The selectivity studies indicate that Cr(III), Eu(III) and Tb(III) ions can be separated from Tc(VII) and I(I). Sunflower stem can be used for the preconcentration and removal of Cr(III) ions from aqueous medium. This cheaper and novel sorbent has potential applications in analytical and environmental chemistry, in water decontamination, industrial waste treatment and in pollution abatement. A possible mechanism of biosorption of Cr(III) ions onto the sunflower stem has been proposed. 相似文献
4.
Nargis Jamila Melati Khairuddean Sadiq Noor Khan Naeem Khan 《Magnetic resonance in chemistry : MRC》2014,52(7):345-352
The genus Garcinia is reported to possess antimicrobial, anti‐inflammatory, anticancer, hepatoprotective and anti‐HIV activities. Garcinia hombroniana in Malaysia is used to treat itching and as a protective medicine after child birth. This study was aimed to isolate the chemical constituents from the bark of G. hombroniana and explore their possible pharmacological potential. Ethyl acetate extract afforded one new (1) and six (2–7) known 3 → 8 rotameric biflavonoids. Their structures were elucidated by UV, IR and NMR (1D and 2D) spectroscopy together with electron ionization/ESI mass spectrometric techniques and were identified as (2R, 3S) volkensiflavone‐7‐O‐rhamnopyranoside (1), volkensiflavone (2), 4″‐O‐methyl‐volkensiflavone (3), volkensiflavone‐7‐O‐glucopyranoside (4), morelloflavone (5), 3″‐O‐methyl‐morelloflavone (6) and morelloflavone‐7‐O‐glucopyranoside (7). The absolute configuration of compound 1 was assigned by circular dichroism spectroscopy as 2R, 3S. The coexistence of conformers of isolated biflavonoids in solution at 25 °C in different solvents was confirmed by variable temperature NMR studies. At room temperature (25 °C), compounds 1–7 exhibited duplicate NMR signals, while at elevated temperature (90 °C), a single set of signals was obtained. Compound 5 showed significant in vitro antioxidant activities against 1,1‐diphenyl‐2‐picrylhydrazyl and 2,2′‐azino‐bis‐3‐ethyl benzthiazoline‐6‐sulfonic acid radicals. The antibacterial studies showed that compounds 5 and 6 are the most active against Staphylococcus aureus, Bacillus subtilis and Escherichia coli. Compounds 3 and 6 also showed moderate antituberculosis activity against H38Rv. Based on the research findings, G. hombroniana could be concluded as a rich source of flavanone–flavone (3 → 8) biflavonoids that exhibit rotameric behaviour at room temperature and display significant antioxidant and antibacterial activities. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
5.
Min Lu Saad Sadiq Daniel J. Feaster Hemant Ishwaran 《Journal of computational and graphical statistics》2018,27(1):209-219
Estimation of individual treatment effect in observational data is complicated due to the challenges of confounding and selection bias. A useful inferential framework to address this is the counterfactual (potential outcomes) model, which takes the hypothetical stance of asking what if an individual had received both treatments. Making use of random forests (RF) within the counterfactual framework we estimate individual treatment effects by directly modeling the response. We find that accurate estimation of individual treatment effects is possible even in complex heterogenous settings but that the type of RF approach plays an important role in accuracy. Methods designed to be adaptive to confounding, when used in parallel with out-of-sample estimation, do best. One method found to be especially promising is counterfactual synthetic forests. We illustrate this new methodology by applying it to a large comparative effectiveness trial, Project Aware, to explore the role drug use plays in sexual risk. The analysis reveals important connections between risky behavior, drug usage, and sexual risk. Supplementary material for this article is available online. 相似文献
6.
Sadiq‐ur‐Rehman Bilal Ahmad Khan Muhammad Aziz Chaudhary Khawaja Ansar Yasin Saqib Ali 《Heteroatom Chemistry》2015,26(6):417-425
Di‐ and triorganotin(IV) carboxylates, RnSn(OCOC(R2)=CHR1)4–n (n = 2 and 3; R = Me, Et, n‐Bu, Ph; R1 = 3‐CH3O‐4‐OHC6H3, R2 = C6H5) were prepared by reacting the corresponding organotin(IV) chloride with the silver salt of the (E)‐3‐(4‐hydroxy‐3‐methoxyphenyl)‐2‐phenylpropenoic acid. The title compounds were investigated and characterized by elemental analysis, infrared (FT‐IR), multinuclear (1H, 13C, 119Sn) NMR, and mass spectrometry, and possible structures were proposed. The complexes and ligand acid ( HL ) have been evaluated in vitro against various bacteria and fungi. The results noticed during the biocidal activity screenings proved their in vitro biological potential. They were also tested for cytotoxicity. 相似文献
7.
Farhan M. Khan Muhammad A. Abbasi Aziz-ur-Rehman Sabahat Z. Siddiqui Abdul R. Sadiq Butt Hussain Raza Ayesha Zafar Syed A. Ali Shah Muhammad Shahid Sung-Yum Seo 《Journal of heterocyclic chemistry》2021,58(5):1089-1103
By using a convergent methodology, a novel series of N-arylated 4-yl-benzamides containing a bi-heterocyclic thiazole–triazole core was synthesized, and the structures of these hybrid molecules, 9a–k , were corroborated through spectral analyses. The in vitro studies of these multifunctional molecules demonstrated their potent carbonic anhydrase inhibition relative to the standard used. The kinetics mechanism was exposed by Lineweaver–Burk plots, which revealed that 9j inhibited carbonic anhydrase non-competitively by forming an enzyme-inhibitor complex. The inhibition constants Ki calculated from Dixon plots for this compound was 1.2 μM. The computational study was also persuasive with the experimental results, and these molecules disclosed good results of all scoring functions and interactions, which suggested a good binding to carbonic anhydrase. So, it was predicted from the inferred results that these molecules might be considered as promising medicinal scaffolds for various diseases related to the uncontrolled production of this enzyme. 相似文献
8.
M. Sadiq M. Bensitel K. Nohair J. Leglise C. Lamonier 《Journal of Saudi Chemical Society》2012,16(4):445-449
The synthesis of vanadyl phosphate by reaction of an alcoholic solution of V2O5 and o-H3PO4 has been studied. The solids obtained were investigated by various physico-chemical techniques as in situ X-ray diffraction (XRD), thermogravimetric analysis (TGA), and differential thermal analysis (DTA) under inert atmosphere. The compounds have been further characterized by infrared and UV–Visible spectroscopies. The isopropanol conversion is carried out to evaluate the catalytic activity of the samples. The isopropanol conversion increases with the reaction temperature from 433 to 503 K for vanadyl phosphorus oxides calcined at a different temperature. However, the conversion attains 100% at 503 K, and the solid calcined at 973 K exhibits high selectivity towards propene (100% at 503 K). 相似文献
9.
In this paper, we present the parallelization of tabu search on a network of workstations using PVM. Two parallelization strategies are integrated: functional decomposition strategy and multi-search threads strategy. In addition, domain decomposition strategy is implemented probabilistically. The performance of each strategy is observed and analyzed. The goal of parallelization is to speedup the search in finding better quality solutions. Observations support that both parallelization strategies are beneficial, with functional decomposition producing slightly better results. Experiments were conducted for the VLSI cell placement, an NP-hard problem, and the objective was to achieve the best possible solution in terms of interconnection length, timing performance (circuit speed), and area. The multiobjective nature of this problem is addressed using a fuzzy goal-based cost computation. 相似文献
10.
M. Zubair Sadiq M. B. Imran S. Javaid Khurshid 《Journal of Radioanalytical and Nuclear Chemistry》1995,199(2):79-88
Domestically produced diagnostic cold kits, viz. glucoheptonate (GH), diisopropyliminodiacetic acid (DISIDA), dimercaptosuccinic acid (DMSA), diethylenetriamine-pentaacetic acid (DTPA), methylenediphosphonate (MDP) and Sn-colloid were labeled with99mTc and their in-vivo distribution in experimental animals (rats) was evaluated prior to use in humans for diagnostic scanning. The biodistribution pattern was found in accordance with the latest guidelines of the International Atomic Energy Agency (IAEA), which serve as a standard for small scale producers. 相似文献