全文获取类型
收费全文 | 320篇 |
免费 | 24篇 |
专业分类
化学 | 264篇 |
晶体学 | 4篇 |
力学 | 4篇 |
数学 | 14篇 |
物理学 | 58篇 |
出版年
2024年 | 1篇 |
2023年 | 5篇 |
2022年 | 21篇 |
2021年 | 60篇 |
2020年 | 22篇 |
2019年 | 25篇 |
2018年 | 8篇 |
2017年 | 11篇 |
2016年 | 29篇 |
2015年 | 15篇 |
2014年 | 15篇 |
2013年 | 28篇 |
2012年 | 21篇 |
2011年 | 19篇 |
2010年 | 11篇 |
2009年 | 7篇 |
2008年 | 10篇 |
2007年 | 8篇 |
2006年 | 3篇 |
2005年 | 4篇 |
2004年 | 4篇 |
2003年 | 6篇 |
2001年 | 3篇 |
2000年 | 1篇 |
1999年 | 1篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1988年 | 1篇 |
1917年 | 2篇 |
排序方式: 共有344条查询结果,搜索用时 31 毫秒
31.
Gökhan Alpaslan Mustafa Macit Ahmet Erdönmez Orhan Büyükgüngör 《Structural chemistry》2011,22(3):681-690
The Schiff base compound (Z)-1-((4-phenylamino)phenylamino)methylene)naphthalen-2(1H)-one has been synthesized and characterized by IR, UV–Vis, and X-ray single-crystal determination. Molecular geometry from
X-ray experiment of the title compound in the ground state have been compared using the Hartree–Fock (HF) and density functional
method (B3LYP) with 6−31G(d,p) basis set. Calculated results show that density functional theory DFT and HF can well reproduce
the structure of the title compound. Using the time-dependent density functional theory (TD-DFT) and Hartree–Fock (TD-HF)
methods, electronic absorption spectra of the title compound have been predicted and a good agreement with the TD-DFT method
and experimental ones is determined. The energetic behavior of the title compound in solvent media has been examined using
B3LYP method with the 6−31G(d,p) basis set by applying the polarizable continuum model (PCM). The total energy of the title
compound decreases with increasing polarity of the solvent. In addition, DFT calculations of the title compound, molecular
electrostatic potential (MEP), natural bond orbital analysis (NBO), and non-linear optical (NLO) properties were performed
at B3LYP/6−31G(d,p) level of theory. 相似文献
32.
Didik Prasetyoko Zainab Ramli Salasiah Endud Hadi Nur 《Reaction Kinetics and Catalysis Letters》2005,86(1):83-89
Summary Titanosilicalite-1 (TS-1) in combination with sulfated zirconia efficiently catalyzes the epoxidation of 1-octene with aqueous hydrogen peroxide. The presence of both octahedral zirconium and sulfate species in the catalysts enhances the epoxidation rates. 相似文献
33.
Nutrients are essential for microbial growth and metabolism in mixed-culture acid fermentations. Understanding the influence
of nutrient feeding strategies on fermentation performance is necessary for optimization. For a four-bottle fermentation train,
five nutrient contacting patterns (single-point nutrient addition to fermentors F1, F2, F3, and F4 and multi-point parallel
addition) were investigated. Compared to the traditional nutrient contacting method (all nutrients fed to F1), the near-optimal
feeding strategies improved exit yield, culture yield, process yield, exit acetate-equivalent yield, conversion, and total
acid productivity by approximately 31%, 39%, 46%, 31%, 100%, and 19%, respectively. There was no statistical improvement in
total acid concentration. The traditional nutrient feeding strategy had the highest selectivity and acetate-equivalent selectivity.
Total acid productivity depends on carbon–nitrogen ratio. 相似文献
34.
Herma Dina Setiabudi Sugeng Triwahyono Aishah Abdul Jalil Nur Hidayatul Nazirah Kamarudin Muhammad Arif Ab Aziz 《天然气化学杂志》2011,20(5):477-482
The effect of iridium loading on the properties and catalytic isomerization of n-heptane over Ir-HZSM-5 is studied. Ir-HZSM-5 was prepared by impregnation method and subjected to isomerization process in the presence of flowing hydrogen gas. XRD and BET studies show that the presence of iridium stabilizes the crystalline structure of HZSM-5, leading to more ordered framework structure and larger surface area. TGA and FTIR results substantiate that iridium species interacts with OH group on the surface of HZSM-5. Pyridine FT-IR study verifies the interaction between iridium and surface OH group slightly increased the Bro¨nsted and Lewis acid sites without changing the lattice structure of HZSM-5. The presence of iridium and the increase of strong Lewis acid sites on HZSM-5 were found to bring an increase about 4.1%, 33.2% and 11.8% in conversion, selectivity and yield of n-heptane isomerization, respectively. 相似文献
35.
36.
Serife Nur Deveci Tuncer Acar Osman Alagoz 《Mathematical Methods in the Applied Sciences》2020,43(5):2772-2782
In this study, we introduce newly defined Gamma operators which preserve constants and e2μ·, μ>0 functions. In accordance with this purpose, we focus on their approximation properties such as uniform convergence, rate of convergence, asymptotic formula, and saturation results. Superior properties of introduced operators have been tested both theoretically and numerically in certain senses to highlight the performance of the new constructions of Gamma operators. 相似文献
37.
Phase‐type distribution closure properties are utilized to devise algorithms for generating reliability functions of systems with basic structures. These structures include series, parallel, K‐out‐of‐N, and standby structures with perfect/imperfect switch. The algorithms form a method for system reliability modeling and analysis based on the relationship between the system lifetime and component lifetimes for general structures. The proposed method is suitable for functional system reliability analysis, which can produce reliability functions of systems with independent components instead of only system reliability values. Once the system reliability function is obtained, other reliability measures such as the system's hazard function and mean time to failure can be obtained efficiently using only matrix algebra. Dimensional and numerical comparisons with computerized symbolic processing are also presented to show the superiority of the proposed method. 相似文献
38.
The difficulty of resolving the multiobjective combinatorial optimization problems with traditional methods has directed researchers to investigate new approaches which perform better. In recent years some algorithms based on ant colony optimization (ACO) metaheuristic have been suggested to solve these multiobjective problems. In this study these algorithms have been reported and programmed both to solve the biobjective quadratic assignment problem (BiQAP) instances and to evaluate the performances of these algorithms. The robust parameter sets for each 12 multiobjective ant colony optimization (MOACO) algorithms have been calculated and BiQAP instances in the literature have been solved within these parameter sets. The performances of the algorithms have been evaluated by comparing the Pareto fronts obtained from these algorithms. In the evaluation step, a multi significance test is used in a non hierarchical structure, and a performance metric (P metric) essential for this test is introduced. Through this study, decision makers will be able to put in the biobjective algorithms in an order according to the priority values calculated from the algorithms’ Pareto fronts. Moreover, this is the first time that MOACO algorithms have been compared by solving BiQAPs. 相似文献
39.
Carbon‐doped titania (C‐TiO2) nanoparticles were synthesized by the sol–gel method at different calcination temperatures (300–600°C) employing titanium tetraisopropoxide (TTIP) as the titanium source and polyoxyethylene sorbitan monooleate (Tween 80) as the carbon source. The physical properties of C‐TiO2 samples were characterized by X‐ray diffraction (XRD) and scanning electron microscopy (SEM). The photocatalytic activities were checked through the photodegradation of phenolphthalein (PHP) under ultraviolet irradiation. The UV spectrum showed that the carbon doping extends the absorption range of TiO2 to the visible region. However, the photocatalytic activity is affected by the electron–hole recombination phenomenon, as revealed by the photoluminescence (PL) study. According to the PL spectra, carbon doping reduces the edge‐to‐edge electron–hole recombination. Nevertheless, the number of defect sites is greatly influenced by the calcination temperature of C‐TiO2. C‐TiO2 that was calcined at 400°C showed the highest photodegradation percentage of PHP, which was mainly attributed to the synergic effect of the low direct edge‐to‐edge electron–hole recombination, high content of defect sites, and retention of active electrons on the surface hydroxyl group. 相似文献
40.
The Zn(II) complex, dichloro[N-hydroxy-1,1-di(2-pyridinyl)methanimine]zinc(II), was synthesized from the reaction between ZnCl2 and di-2-pyridylketone oxime. The structural and spectral characterizations were performed by using single crystal X-ray diffraction, FT-IR, Laser-Raman, NMR and UV–Vis spectroscopic techniques. To support experimental evidences, computational results were obtained with the DFT/B3LYP method using the 6-311++G(d,p)+LanL2DZ mixed basis set. Theoretical analyses of some structural and spectroscopic results of effects of intermolecular Cl···H interactions in the crystal packing of the Zn(II) complex were investigated with the mentioned computational level. The non-bonding interactions in the experimental crystal packing of the complex were examined by Hirshfeld surface analysis. The HOMO and LUMO analyses were used for investigation of electronic transitions obtained with UV–Vis spectroscopy. NBO analyses were used to investigate the hyperconjugation interactions between donor and acceptor groups, coordination environment, electronic configuration and electron numbers of the Zn(II) metal ion and the natural atomic charges of the complex. The nucleophilic and electrophilic reactive sites of the complex were studied by MEP surface analysis. The static polarizabilities (α) and static hyperpolarizabilities (β) were analyzed theoretically to characterize NLO profile of the complex. The interaction with A-DNA (PDB ID: 1ZF6) of the Zn(II) complex was investigated with a molecular docking study. 相似文献