全文获取类型
收费全文 | 249篇 |
免费 | 3篇 |
国内免费 | 41篇 |
专业分类
化学 | 251篇 |
力学 | 2篇 |
物理学 | 40篇 |
出版年
2023年 | 4篇 |
2022年 | 2篇 |
2021年 | 2篇 |
2020年 | 3篇 |
2019年 | 5篇 |
2018年 | 5篇 |
2017年 | 5篇 |
2016年 | 1篇 |
2015年 | 4篇 |
2014年 | 7篇 |
2013年 | 14篇 |
2012年 | 8篇 |
2011年 | 14篇 |
2010年 | 15篇 |
2009年 | 19篇 |
2008年 | 21篇 |
2007年 | 21篇 |
2006年 | 15篇 |
2005年 | 10篇 |
2004年 | 7篇 |
2003年 | 7篇 |
2002年 | 13篇 |
2001年 | 5篇 |
2000年 | 12篇 |
1999年 | 4篇 |
1998年 | 7篇 |
1997年 | 4篇 |
1996年 | 7篇 |
1995年 | 3篇 |
1994年 | 9篇 |
1993年 | 7篇 |
1992年 | 7篇 |
1991年 | 6篇 |
1990年 | 2篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1987年 | 4篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1982年 | 2篇 |
1979年 | 1篇 |
排序方式: 共有293条查询结果,搜索用时 31 毫秒
1.
George W. C. Hung 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(2):211-235
The measurement of sorption and diffusion behavior of liquid ethanol and water solvent mixtures in polyurethane membrane were made simultaneously by thermogravimetry. The individual amounts of sorbed water and ethanol in the polymer membrane were estimated by thermogravimetry and differentiated by mass spectrometry. In addition, from a single dynamic thermogravimetric experiment the activation energy for solvent molecules desorbing from the polymer membrane was also determined. The thermodynamic activity of ethanol vapor in equilibrium with the ethanol-water-polyurethane system was determined by gas-liquid chromatography. The clustering functions, the mean numbers of solvent molecules in the clusters, and those associating with polymer sites were evaluated by applying simplified mathematical derivatives using the experimentally determined values of activity and volume fraction of solvent molecules. It was found that at lower ethanol concentration the tendency for ethanol molecules to cluster together is high. At higher ethanol activity, ethanol-polymer site interactions predominantly occurred. Similar results were observed for ethanol-water molecules. However, water molecules in this particular system did not exhibit a self-associating tendency nor interact with the polymer sites. It was concluded that the Zimm-Lundberg clustering theory can be adequately applied to the interpretation of sorption and diffusion behavior of liquid ethanol-water mixtures in the polymer membrane. 相似文献
2.
M. Qasim H. Fredrickson P. Honea J. Furey J. Leszczynski S. Okovytyy 《SAR and QSAR in environmental research》2013,24(5):495-515
Highest occupied and lowest unoccupied molecular orbital energies, formation energies, bond lengths and FTIR spectra all suggest competing CL-20 degradation mechanisms. This second of two studies investigates recalcitrant, toxic, aromatic CL-20 intermediates that absorb from 370 to 430?nm. Our earlier study (Struct. Chem., 15, 2004) revealed that these intermediates were formed at high OH? concentrations via the chemically preferred pathway of breaking the C–C bond between the two cyclopentanes, thereby eliminating nitro groups, forming conjugated π bonds, and resulting in a pyrazine three-ring aromatic intermediate. In attempting to find and make dominant a more benign CL-20 transformation pathway, this current research validates hydroxylation results from both studies and examines CL-20 transformations via photo-induced free radical reactions. This article discusses CL-20 competing modes of degradation revealed through: computational calculation; UV/VIS and SF spectroscopy following alkaline hydrolysis; and photochemical irradiation to degrade CL-20 and its byproducts at their respective wavelengths of maximum absorption. 相似文献
3.
《Physics and Chemistry of Liquids》2012,50(3):297-303
Kinetic studies on the photochemical oxidation of 1,3-diphenylisobenzofuran have been carried out in binary liquid mixtures of N,N-dimethylformamide (DMF) with 1-propanol (PrOH). The strongest influence of solvating effects upon the course of this reaction was observed for compositions of the studied mixture corresponding respectively to ca. 50?mol% of PrOH. Additionally, we have carried out analogous studies of photooxidation of cis-cyclooctene. Similarly as previously, the noticeable influence of solvating effects upon the course of this reaction corresponded to ca. 50?mol% of DMF. We suspect that the mechanism of this effect is associated with the formation of the polar intermediate during the ene reaction being easier. 相似文献
4.
《中国化学快报》2020,31(7):1970-1973
The biogeochemical transformation of gold (Au), i.e. its dissolution and re-precipitation, is critical in supergene transport of Au and formation of Au granules. Besides biogenic reduction, the formation Au granules can also be driven by chemical processes. Previous studies have showed the formation of Au nanoparticles (AuNPs) from ionic Au(III) can be mediated by dissolved organic matter under sunlight. In this letter, we further demonstrated that these AuNPs can further slowly (in years) grow into visible Au granules. Different sized nano-flower and fractal dendrite-like branched gold structures (from tens of nanometres to over 100 μm) were observed in the Au granule sample. This growth of AuNPs into visible Au granules may play a critical role in the supergene mineralization and enrichment of secondary Au and drive the biogeochemical cycle of Au. 相似文献
5.
Yuying Huang Fengqiang Sun Tianxing Wu Zhong Huang Zihe Zhang 《Journal of solid state chemistry》2011,184(3):644-58
CdS hollow microspheres have been successfully prepared by a photochemical preparation technology at room temperature, using polystyrene latex particles as templates, CdSO4 as cadmium source and Na2S2O3 as both sulphur source and photo-initiator. The process involved the deposition of CdS nanoparticles on the surface of polystyrene latex particles under the irradiation of an 8 W UV lamp and the subsequent removal of the latex particles by dispersing in dichloromethane. Photochemical reactions at the sphere/solution interface should be responsible for the formation of hollow spheres. The as-prepared products were characterized by X-ray diffraction, transmission electron microscopy and scanning electron microscopy. Such hollow spheres could be used in photocatalysis and showed high photocatalytic activities in photodegradation of methyl blue (MB) in the presence of H2O2. The method is green, simple, universal and can be extended to prepare other sulphide and oxide hollow spheres. 相似文献
6.
Stéphanie Delbaere Gaston Vermeersch Jean-Claude MicheauAuthor vitae 《Journal of Photochemistry and Photobiology, C: Photochemistry Reviews》2011,12(2):74-105
The good understanding of a photochromic reaction mechanism requires the establishment of the list of all the transient species and the definition of their connecting processes. The purpose of kinetic studies is the determination of the main photochromic parameters, such as the quantum yields of photoisomerization, rate constants of thermal relaxation and spectra of transient species. These data allow the establishment of structure properties relationships in order to select the best substituents to improve photochromic performances within a given series. In this review, we describe the dynamic behaviour of various photochromic systems during thermal relaxation after irradiation, from the simplest mono-exponential decay to the more complicated multi-exponential dynamics. Then, we analyse the evolution of the long-lived isomers under continuous irradiation. Several pedagogical examples and tricks to perform easy kinetic analysis are given in the appendices. 相似文献
7.
Matthieu Manceau 《Polymer Degradation and Stability》2010,95(12):2666-2669
Photochemical stability of three thermo-cleavable polymers was investigated as thin films under atmospheric conditions. A significant increase in lifetime was observed once the side-chain was cleaved emphasizing the detrimental effect of solubilizing groups on the photochemical stability of conjugated polymers. In addition to their ease of processing, thermo-cleavable polymers thus also offer a greater intrinsic stability under illumination. 相似文献
8.
This article surveys the intercalation characteristics of a number of clay minerals which can be utilized as host materials for photofunctional organic–inorganic hybrid systems as well as photochemical anisotropic reaction fields. The introduction of this review describes the chemical compositions and the structural features of various kinds of artificial as well as naturally produced clays. The chemical structures of these clays are often considered to be complicated due to their unfamiliar names which are sometimes taken from the areas where they originate although, structurally, only slight differences actually exist. The second chapter summarizes the adsorption and aggregation properties of typical organic dyes in clays. The aggregation behavior is sensitive to the kind and amount of metallic ions present in the lattice of the clays, the amount of adsorbed water as well as the structure of the organic guests to be intercalated. All of these factors are discussed in relation to the adsorption and aggregation behavior. In the third chapter, the photochemical reactions of excited metal complexes adsorbed in clays are discussed. Electron transfers for [Ru(bpy)3]2+ in clays are described, showing that the clay layers provide reaction fields which stabilize the resulting charge separated species. This article aims to provide important insights into the fundamental mechanisms and properties of anisotropic reaction fields for the applications in design of promising, new photochemical and photobiological systems and processes. 相似文献
9.
本文用自旋捕捉技术与ESR方法研究了五种硝基芴酮与五种不同的伯、仲、叔脂肪胺的光化夺氢反应中的活泼自由基。结果表明,当胺中有N上氢和α—C上氢时,优先形成N—中心自由基:仅当无N上氢时,才形成C—中心自由基。 相似文献
10.
N-取代酰胺-二苯酮体系光化夺氢反应活泼自由基的ESR研究 总被引:3,自引:2,他引:1
本文用自由基捕捉剂2,3,5,6-四甲基亚硝基苯(ND)及苯亚甲基叔丁基氮氧化物(PBN)与ESR相结合的方法研究了十二种取代酰胺RC6H4NHC(0)CH3(R-CH3、Cl、Br、H、NO2)、C6H5N(R)C(0)CH3(R=CH3、C2H5)及HC(0)NR2(R-CH3、C2H5)与二苯酮光化夺氢反应中的活泼自由基。结果表明:
1.对于RC6H4NHC(0)CH3,二苯酮夺取氮上H形成R-C6H4NC(0)CH3自由基。
2.对C6H5N(R)C(0)CH3及HC(O)NR2,二苯酮夺取与羰基相连的甲基氢、羰基上氢及与N相连碳上的氢分别形成
C6H5N(R)C(0)CH2、C(0)NR2、C6H5N(CHR')C(0)CH3及。 相似文献