全文获取类型
收费全文 | 566篇 |
免费 | 12篇 |
国内免费 | 7篇 |
专业分类
化学 | 333篇 |
力学 | 30篇 |
数学 | 101篇 |
物理学 | 121篇 |
出版年
2024年 | 1篇 |
2023年 | 4篇 |
2022年 | 36篇 |
2021年 | 29篇 |
2020年 | 19篇 |
2019年 | 13篇 |
2018年 | 17篇 |
2017年 | 12篇 |
2016年 | 18篇 |
2015年 | 14篇 |
2014年 | 15篇 |
2013年 | 45篇 |
2012年 | 31篇 |
2011年 | 46篇 |
2010年 | 26篇 |
2009年 | 22篇 |
2008年 | 31篇 |
2007年 | 14篇 |
2006年 | 24篇 |
2005年 | 21篇 |
2004年 | 22篇 |
2003年 | 18篇 |
2002年 | 18篇 |
2001年 | 12篇 |
2000年 | 9篇 |
1999年 | 2篇 |
1998年 | 5篇 |
1997年 | 7篇 |
1996年 | 2篇 |
1995年 | 4篇 |
1994年 | 5篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 4篇 |
1989年 | 1篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1985年 | 8篇 |
1984年 | 3篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1973年 | 2篇 |
1897年 | 1篇 |
排序方式: 共有585条查询结果,搜索用时 31 毫秒
41.
T. A. El-Brolossy S. Abdallah T. Abdallah M. B. Mohamed S. Negm H. Talaat 《The European physical journal. Special topics》2008,153(1):365-368
We report on the optical absorption properties of as
prepared CdSe quantum dots (QDs) measured by the photoacoustic (PA) method.
CdSe QDs were fabricated by the chemical solution deposition (CD) technique.
With increasing growing time, the redshift of the PA spectra can be clearly
observed and optical absorption in the visible region due to CdSe Q-dots is
demonstrated. The average diameters of the CdSe QDs for each growth time
interval is estimated using the effective mass approximation giving
diameters ranging from 2.6 nm to 3.4 nm. These values are comparable to
those obtained by scanning tunnelling microscope (STM). Thus, PA
spectroscopy is useful to obtain the QDs sizes as grown and with no further
preparation. In addition, PA measurements provide also the thermal
diffusivity of samples of different sizes which in this case show an
increase by at least an order of magnitude than the bulk value. 相似文献
42.
43.
Abdallah A. Badr 《Journal of Applied Mathematics and Computing》2000,7(2):455-463
In this work, we solve the Fredholm-Volterra integral equation (FVIE) when the kernel takes a potential function form under given conditions. We represent this kernel in the Weber-Sonin integral form. 相似文献
44.
John P. Shockcor Ronald C. Crouch Gary E. Martin Abdallah Cherif Jiann-Kuan Luo Raymond N. Castle 《Journal of heterocyclic chemistry》1990,27(2):455-458
One-dimensional ( 1D ) variants of two-dimensional ( 2D ) nmr techniques can frequently provide the required information in a much shorter period of time than the 2D experiment from which they were derived. Application of the 1D homonuclear Hartmann-Hahn (1D-HOHAHA) experiment to establish proton-proton connectivity networks in highly overlapped four-spin systems in the proton nmr spectra of polynuclear aromatics is described. Selective subspectra are contrasted to the data obtained in a COSY experiment on the same molecule, benzo[f][l]benzothieno [2,3 -c]quinoline. Results from the 1D-HOHAHA technique are especially useful when component resonances from several spin systems are heavily overlapped. Relayed 1D-HOHAHA provides the means of exploiting small, long range coupling pathways of polynuclear aromatics. 相似文献
45.
An in vitro investigation of the kinetics of the complex system of acid‐catalyzed conversions and subsequent reactions of proton pump inhibitors (PPIs; omeprazole, lansoprazole and pantoprazole) was carried out using differential pulse polarography at the static mercury drop electrode. Reactions were investigated in the presence of 2‐mercaptoethanol, in solutions buffered to pH values ranging from 2.0 to 5.0. The first‐order reaction network was proposed for all conversions. The rate of degradation of PPIs and subsequent reactions with 2‐mercaptoethanol were found to follow the following general order: lansoprazole > omeprazole > pantoprazole. The rate of conversion of PPIs into sulfenic acid was found to be directly dependent on the basicity of benzimidazole nitrogen of PPIs, which determines the electrophilic reactivity of the adjacent carbon (C2). The rate of conversion of the sulfenic acid of PPIs into the disulfide (the inhibition reaction) was found to be dependent on the electrophilicity of the sulfur atom of the sulfenic acid. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 498–506, 2009 相似文献
46.
Michael J. Evans Douglas B. Proud Paul R. Medwell Heinz Pitsch Bassam B. Dally 《Proceedings of the Combustion Institute》2021,38(1):1099-1106
Adapting hydrogen as a carbon-free fuel for industrial applications requires new, innovative approaches, especially when radiant heat transfer is required. One possible option is to dope hydrogen with bio-oils, containing aromatics that help produce highly sooting flames. This study investigates the potential doping effects of toluene on a hydrogen-nitrogen (1:1 vol) flames. Flames with 1–5% toluene, based on the mole concentration of hydrogen, are measured using a combination of techniques including: still photographs and laser-based techniques. Toluene was mixed with hydrogen-nitrogen fuel mixture as either a vapour carried by nitrogen, or as a dilute spray. Spray flames are found to produce substantially more polycylic aromatic hydrocarbons, with significantly more soot near the nozzle exit plane, than the prevaporised flames. Increasing the dopant concentration from 1 to 3% of the hydrogen has a marked effect on soot loading in the flame, although the further increasing the dopant concentration to 5% has a far smaller effect on the soot produced in the flame. Simulations of laminar flames using detailed chemical kinetics support the above findings and reveal details of the competition between soot precursor formation and hydrocarbon oxidation. Correlations of formation rates are non-linear with toluene concentration in cases where toluene represents less than 10% of the fuel, although expected linear relationships are noted beyond this regime up to 1:1 toluene/hydrogen blends. The study provides insight and explanation into effects of toluene as a dopant, comparison between flame doping in gaseous or liquid phases and suggests that flame doping and blending should be treated as different regimes for their global effect on flame sooting characteristics. 相似文献
47.
Turky Abdallah Bayoumi Ashraf H. Sherbiny Farag F. El-Adl Khaled Abulkhair Hamada S. 《Molecular diversity》2021,25(1):403-420
Molecular Diversity - The discovery of potent STAT3 inhibitors has gained noteworthy impetus in the last decade. In line with this trend, considering the proven biological importance of... 相似文献
48.
Mansur B. Ibrahim Rami Suleiman Mohammed Fettouhi Bassam El Ali 《Transition Metal Chemistry》2017,42(1):1-8
A palladium(II)-bis(oxazoline) complex supported on silica (Pd-BOX-Si) was prepared, characterized and applied as a catalyst in Mizoroki–Heck cross-coupling reactions. The bis(oxazoline) (BOX) ligand has a hydroxyl group that can be anchored to 4-benzyl chloride-functionalized silica gel, followed by the coordination of palladium(II) chloride. The catalytic activity and the recyclability of Pd-BOX-Si have been investigated in the production of cinnamic acid derivatives via Mizoroki–Heck coupling reactions of acrylates with aryl halides; The Pd-BOX-Si catalyst demonstrated excellent catalytic activity. Characterization of the recycled Pd-BOX-Si catalyst revealed its good stability under the reaction conditions employed. 相似文献
49.
Abstract
The effect of Ni2+ cation, imidazole, and mixtures of them on the corrosion behavior of carbon steel in 0.5 M H2SO4 solution was studied by using galvanostatic polarization, potentiodynamic anodic polarization, and weight-loss techniques. Ni2+ cation, imidazole, and mixtures of them provide a good protection to carbon steel against pitting corrosion in chloride-containing solutions. The inhibiting solutions were analyzed by using UV–Vis spectrophotometry. The inhibition was explained on the basis of formation of a complex between the two components. The inhibition mechanism was discussed in terms of the results derived from corrosion and UV–Vis spectrophotometric measurements as well as conductometric investigations. 相似文献50.
Theoretical methods have been employed to investigate the structural, spectroscopic and energetic properties of difluoro(germylthio)phosphine in the Cs symmetry in the gas phase. The levels of theory used are MP2 and DFT/B3LYP and the basis set used for all atoms is 6-311G(d,p). The computed structural parameters, namely, bond lengths and bond angles and spectroscopic parameters, namely, infrared frequencies, Raman activities and NMR chemical shifts have been compared with experimental data reported in literature. The structure of this compound has been analysed using natural bond orbital approach. Both the ab initio methods perform satisfactorily when the predicted and experimental parameters are compared. We have extended this study, using the same methods and basis set, to the selenium analogue, namely, difluoro(germylseleno)phosphine for which literature is elusive. The MP2/6-311G(d,p) geometrical parameters for difluoro(germylseleno)phosphine are: r(P–Se) = 2.270, r(Ge-Se) = 2.386, r(P–F) = 1.604, r(Ge–H) = 1.530 Å, ∠(Ge–Se–P) = 91.4, ∠(F–P–F) = 96.7, ∠(Se–P–F) = 99.9 and ∠(Se–Ge–H) = 109.5°. Apart from these, we have also studied the energetic parameters for their synthesis. The results indicate that formation of the sulphur-containing compound is favoured thermodynamically. 相似文献