全文获取类型
收费全文 | 375篇 |
免费 | 23篇 |
国内免费 | 5篇 |
专业分类
化学 | 273篇 |
晶体学 | 1篇 |
力学 | 23篇 |
数学 | 41篇 |
物理学 | 65篇 |
出版年
2023年 | 2篇 |
2022年 | 12篇 |
2021年 | 24篇 |
2020年 | 25篇 |
2019年 | 17篇 |
2018年 | 24篇 |
2017年 | 26篇 |
2016年 | 42篇 |
2015年 | 7篇 |
2014年 | 28篇 |
2013年 | 47篇 |
2012年 | 22篇 |
2011年 | 18篇 |
2010年 | 23篇 |
2009年 | 20篇 |
2008年 | 14篇 |
2007年 | 10篇 |
2006年 | 6篇 |
2005年 | 9篇 |
2004年 | 4篇 |
2003年 | 2篇 |
2001年 | 3篇 |
2000年 | 1篇 |
1998年 | 1篇 |
1996年 | 2篇 |
1994年 | 1篇 |
1991年 | 2篇 |
1986年 | 1篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1976年 | 5篇 |
1969年 | 1篇 |
排序方式: 共有403条查询结果,搜索用时 15 毫秒
81.
An important goal of spray cooling research is the ability to predict local heat transfer from the spray hydrodynamics. It is postulated that the local normal pressure exerted by the spray onto the heated surface can be used to obtain the local heat transfer coefficient. This hypothesis was tested using data obtained from hollow cone, full cone, and linear sprays at four nozzle pressures and three stand-off distances. A correlation between the pressure and heat transfer coefficient was determined from the data, then used to “predict” the heat transfer coefficient to verify the accuracy of the correlation. The area averaged heat transfer coefficient could be predicted within 25%, indicating that pressure can be used to predict the local heat transfer coefficient in the single-phase regime. 相似文献
82.
83.
Keshvar Rahimpour Ali Shafagh-Azar Hassan Abbasi Amir Mohammad-Gholizadeh Zeinab Hezarkhani Reza Teimuri-Mofrad 《应用有机金属化学》2020,34(6):e5633
A ferrocenyl-based, chromophore-containing 1-indanone derivative was synthesized through crotonic condensation between 4-chlorobutylferrocenecarboxaldehyde and 5,6-dimethoxy-1-indanone followed by the nucleophilic substitution of chlorine atom of the obtained dyad with different aromatic and aliphatic amines. The electrochemical and optical properties of the synthesized compounds were investigated to explore the relationship between their structures and optical and electrochemical properties. The bandgaps determined from optical absorption spectra ranged from 2.05 to 2.15 eV. The important electrochemical parameters, including the peak potential separation, peak current ratios, and the dependence of peak currents on the scan rate, were studied. Results showed an electrochemically reversible redox system with diffusion-controlled redox process for the synthesized compounds. The study of quantum chemistry was performed on the synthesized compounds using the density functional theory approach. The B3LYP method and 6-311 G(d) basis set were used for optimizing the structures in the gas phase. The theoretical and experimental results show that these compounds can be considered as candidates to be used in optical applications. 相似文献
84.
A new supramolecular zinc(II) complex containing 4‐biphenylcarbaldehyde isonicotinoylhydrazone ligand: Nanostructure synthesis,catalytic activities and Hirshfeld surface analysis 下载免费PDF全文
Yunes Abbasi Tyula Abedien Zabardasti Hamid Goudarziafshar Monika Kucerakova Michal Dusek 《应用有机金属化学》2018,32(3)
A new potentially tridentate hydrazone ligand, 4‐biphenylcarbaldehyde isonicotinoylhydrazone (4‐bpinh), was prepared by the condensation of biphenyl‐4‐carboxaldehyde with isonicotinic acid hydrazide. Then, its nano‐sized and single crystal of zinc complex were synthesized using sonochemical and heat gradient methods, respectively. The structure of complex, [Zn(4‐bpinh)2 Br2] (1), was determined by single‐crystal X‐ray diffraction, FT‐IR, and elemental analysis, and the nano‐structure of complex was characterized by FT‐IR, XRD, and SEM. The single crystal X‐ray structure of complex showed that the metal center has a distorted tetrahedral geometry and the hydrazone ligand acts as monodentate trough the pyridyl N atom. Moreover, the analysis of crystal structures indicates the existence of intermolecular interactions such as N/C–H?Br/O, N/C–H?π, and π?π stacking in the stabilization of complex structure which finally led to the formation of the three‐dimensional supramolecular structure. Also, the impact of this interactions was more studied using Hirshfeld surface analysis and corresponding 2D fingerprint plots. Furthermore, the catalytic activity of 1 was studied in the selective oxidation of various sulfides to corresponding sulfoxides using hydrogen peroxide as the oxidative agent. 相似文献
85.
Ali Abbasi Ali Karimi Hamidreza Aghabozorg Sepehr Sadighi Maryam Alizadeh Aval 《国际化学动力学杂志》2020,52(3):159-166
MoS2 has been commonly used as a catalyst in hydrodesulfurization (HDS) of petroleum cuts in crude oil refineries. In this study, the synthesis of unsupported MoS2 and Co-promoted MoS2 nanosheets produced from molybdenum oxide and thiourea is reported. The synthesized samples were characterized by using x-ray fluorescence, x-ray diffraction, Brunauer–Emmett–Teller (BET), temperature-programmed reduction, thermal gravimetric analysis, and transmission electron microscopy methods, and then they were utilized for HDS of diesel through a fixed-bed catalytic reactor. Results indicated that a cobalt promoter affected both the number and the performance of active sites of the molybdenum sulfides, and the activity of the promoted MoS2 catalyst was consistently higher than that of the MoS2 catalyst. More significantly, the activity of the promoted catalyst was slightly declined during 48 h continuous HDS reaction, which indicated the stability of this catalyst. Additionally, during 12 h of test run, the HDS activity of the promoted catalyst was about 60% higher than MoS2 one. 相似文献
86.
HERAVI Majid M. BEHBAHANI Farahnaz K. OSKOOIE Hossien A. BAMOHARRAM Fatemeh F. 《中国化学》2008,26(12):2150-2154
A simple and efficient method has been developed for the synthesis of β-amino alcohols by ring opening of epoxides in the presence of a catalytic amount of H14[NaP5W29MoO110] at room temperature under solvent-free conditions. The reaction works well for both aromatic and aliphatic amines. 相似文献
87.
88.
In this study, combined technique of solid-phase extraction based on multi-walled carbon nanotubes with bio-coacervation extraction (SPE-MWCNT-BCAE) has been developed as a new sample preparation method for the determination of atrazine from water samples. The proposed method involves two steps: analyte enrichment on the solid sorbent and subsequently elution of the analyte by an appropriate solvent. Multi-walled carbon nanotubes (MWCNTs) were used as the sorbent. They have high specific surface area, nano-scale structure and high diffusion rate. The second step is based on the use of bioaggregates for analyte re-enrichment, which consists of biosurfactants and ionic liquid. This method follows the principles of green chemistry. Parameters affecting the extraction efficiency were optimized. Under optimum conditions, the enrichment factor was 176. The linear dynamic range (LDR) and limit of detection (LOD) were 2–100 µg L?1 and 0.66 µg L?1, respectively. The relative standard deviation (RSD) for six replicate measurements was 3.8%. The method was applied to the determination of ultratrace levels of atrazine in environmental water samples with satisfactory results. 相似文献
89.
Sajjad Abbasi Ali Sarafraz-Yazdi Amirhassan Amiri Ferial Ghaemi 《Journal of the Iranian Chemical Society》2018,15(1):153-161
We describe a magnetic nanocomposite that consists of Fe3O4/carbon nanosphere/polypyrrole (Fe3O4/CNS/PPy). The synthesized nanocomposites were characterized by scanning electron microscopy, transmission electron microscopy, and Fourier transform infrared spectroscopy. The nanocomposite was successfully applied to extract of the polycyclic aromatic hydrocarbons (PAHs) from water samples. Compared to Fe3O4/PPy, the Fe3O4/CNS/PPy nanocomposite exhibits improved properties in terms of extraction. The amount of adsorbent, salt effect, extraction time, desorption time, type, and the volume of desorption solvent were optimized. Following the desorption of the extracted analytes, the PAHs (i.e., naphthalene, 2-methylnaphthalene, 2-bromonaphthalene, fluorene, and anthracene) were quantified by gas chromatography–flame ionization detector. The PAHs can be determined in 0.05–100.00 ng mL?1 concentration range, with limits of detection (at an S/N ratio of 3) ranging from 0.01 to 0.05 ng mL?1. The repeatability of the method was investigated with relative standard deviations of lower than 9.9% (n = 5). Also, the recoveries from spiked real water samples were in the range of 88.9–99.0%. The results indicate that the novel material can be successfully applied for the extraction and analysis of PAHs from water samples. 相似文献
90.
Mohammed M. Hashemi Yusef Ahmadibeni Hossien Ghafuri 《Monatshefte für Chemie / Chemical Monthly》2003,134(1):107-110
Summary. Hydrogen peroxide readily oxidizes Hantzsch type 1,4-dihydropyridines in the presence of cobalt(II) acetate as catalyst at room temperature. No evidence of a dealkylation
process for 4-alkyl 1,4-dihydropyridines has been observed.
Corresponding author. E-mail: mhashemi@sharif.ac.ir
Received January 16, 2002; accepted (revised) April 20, 2002 相似文献