全文获取类型
收费全文 | 613篇 |
免费 | 73篇 |
国内免费 | 83篇 |
专业分类
化学 | 679篇 |
晶体学 | 1篇 |
力学 | 9篇 |
综合类 | 7篇 |
数学 | 13篇 |
物理学 | 60篇 |
出版年
2024年 | 3篇 |
2023年 | 14篇 |
2022年 | 38篇 |
2021年 | 52篇 |
2020年 | 42篇 |
2019年 | 38篇 |
2018年 | 27篇 |
2017年 | 30篇 |
2016年 | 49篇 |
2015年 | 38篇 |
2014年 | 40篇 |
2013年 | 60篇 |
2012年 | 36篇 |
2011年 | 37篇 |
2010年 | 32篇 |
2009年 | 26篇 |
2008年 | 19篇 |
2007年 | 35篇 |
2006年 | 25篇 |
2005年 | 24篇 |
2004年 | 15篇 |
2003年 | 15篇 |
2002年 | 12篇 |
2001年 | 16篇 |
2000年 | 8篇 |
1999年 | 2篇 |
1998年 | 4篇 |
1997年 | 5篇 |
1996年 | 4篇 |
1995年 | 4篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1989年 | 3篇 |
1988年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1981年 | 1篇 |
排序方式: 共有769条查询结果,搜索用时 31 毫秒
631.
《化学:亚洲杂志》2017,12(24):3178-3186
Carbon‐based solid acid catalysts were successfully obtained via one‐step hydrothermal carbonization (HTC) of water hyacinth (WH) in the presence of p ‐toluenesulfonic acid (PTSA). Increasing the HTC temperature from 180 to 240 °C resulted in carbonaceous materials with increased sulfur content and less adsorbed water. The material obtained at 220 °C (WH‐PTSA‐220) contains the highest amount of acid sites and promotes the highest initial rate of two transformations, that is, methanolysis of oleic acid and dehydration of xylose to furfural. While all PSTA‐treated WH catalysts gave comparable fatty acid conversions (≈97 %) and furfural yields (≈60 %) after prolonged reaction times, the WH‐PTSA‐240 system bearing a relatively low acid density maintains the most favorable reusability profile. Higher HTC temperatures (220–240 °C) improved the catalyst reusability profiles due to graphitization and hydrophobicity of the carbon surface. The catalyst systems derived herein from biomass may have potential applications in biorefining platforms, utilizing the conversion of waste biomass to chemicals. 相似文献
632.
Yongpan Hu Dr. Wei Huang Hongshuai Wang Qing He Yuan Zhou Ping Yang Prof. Dr. Youyong Li Prof. Dr. Yanguang Li 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(34):14484-14488
Photocatalytic hydrogenation of biomass-derived organic molecules transforms solar energy into high-energy-density chemical bonds. Reported herein is the preparation of a thiophene-containing covalent triazine polymer as a photocatalyst, with unique donor-acceptor units, for the metal-free photocatalytic hydrogenation of unsaturated organic molecules. Under visible-light illumination, the polymeric photocatalyst enables the transformation of maleic acid into succinic acid with a production rate of about 2 mmol g−1 h−1, and furfural into furfuryl alcohol with a production rate of about 0.5 mmol g−1 h−1. Great catalyst stability and recyclability are also measured. Given the structural diversity of polymeric photocatalysts and their readily tunable optical and electronic properties, metal-free photocatalytic hydrogenation represents a highly promising approach for solar energy conversion. 相似文献
633.
《Arabian Journal of Chemistry》2020,13(12):8734-8749
The current investigation highlights the synthesis of adsorption device MHa-g-poly(AN)-AE by graft copolymerization of acrylonitrile (AN) onto Holarrhena antidysenterica fiber in the presence of air along with Ferrous ammonium sulfate (FAS) and Potassium persulfate (KPS) initiators followed by quaternization process. Synthesized samples and backbone were studied using different techniques such as Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction spectroscopic (XRD) and TGA/DTA/DTG studies. High efficiency of dye adsorption (99% of malachite green dye) was achieved using an initial dye concentration of 10.0 mg L−1 with an adsorbent dose of 500 mg 50 ml−1 within the time duration of 165 min at neutral pH and 25 °C. Adsorption data best fit with Langmuir Isotherm, pseudo second-order kinetics model and follow both macro & micro-pore intra-particle diffusion. 相似文献
634.
Impact of Nonthermal Atmospheric Plasma on the Structure of Cellulose: Access to Soluble Branched Glucans
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Joakim Delaux Prof. Carmen Ortiz Mellet Christine Canaff Dr. Elodie Fourré Dr. Cédric Gaillard Dr. Abdellatif Barakat Prof. José M. García Fernández Dr. Jean‐Michel Tatibouët Dr. François Jérôme 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(46):16522-16530
We have investigated the effect of non‐thermal atmospheric plasma (NTAP) on the structure of microcrystalline cellulose. In particular, by means of different characterization methods, we demonstrate that NTAP promotes the partial cleavage of the β‐1,4 glycosidic bond of cellulose leading to the release of short‐chain cellodextrins that are reassembled in situ, preferentially at the C6 position, to form branched glucans with either a glucosyl or anhydroglucosyl terminal residue. The ramification of cellulosic chain induced by NTAP yields branched glucans that are soluble in DMSO or in water, thus opening a straightforward access to processable glucans from cellulose. Importantly, the absence of solvent and catalyst considerably facilitates downstream processing as compared to (bio)catalytic processes which typically occur in diluted conditions. 相似文献
635.
Yongpan Hu Wei Huang Hongshuai Wang Qing He Yuan Zhou Ping Yang Youyong Li Yanguang Li 《Angewandte Chemie (International ed. in English)》2020,59(34):14378-14382
Photocatalytic hydrogenation of biomass‐derived organic molecules transforms solar energy into high‐energy‐density chemical bonds. Reported herein is the preparation of a thiophene‐containing covalent triazine polymer as a photocatalyst, with unique donor‐acceptor units, for the metal‐free photocatalytic hydrogenation of unsaturated organic molecules. Under visible‐light illumination, the polymeric photocatalyst enables the transformation of maleic acid into succinic acid with a production rate of about 2 mmol g?1 h?1, and furfural into furfuryl alcohol with a production rate of about 0.5 mmol g?1 h?1. Great catalyst stability and recyclability are also measured. Given the structural diversity of polymeric photocatalysts and their readily tunable optical and electronic properties, metal‐free photocatalytic hydrogenation represents a highly promising approach for solar energy conversion. 相似文献
636.
637.
A Durable Nickel Single‐Atom Catalyst for Hydrogenation Reactions and Cellulose Valorization under Harsh Conditions
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Wengang Liu Yinjuan Chen Haifeng Qi Leilei Zhang Wensheng Yan Xiaoyan Liu Xiaofeng Yang Shu Miao Wentao Wang Chenguang Liu Prof. Dr. Aiqin Wang Prof. Dr. Jun Li Prof. Dr. Tao Zhang 《Angewandte Chemie (International ed. in English)》2018,57(24):7071-7075
Hydrothermally stable, acid‐resistant nickel catalysts are highly desired in hydrogenation reactions, but such a catalyst remains absent owing to the inherent vulnerability of nickel under acidic conditions. An ultra‐durable Ni‐N‐C single‐atom catalyst (SAC) has now been developed that possesses a remarkable Ni content (7.5 wt %) required for practical usage. This SAC shows not only high activities for hydrogenation of various unsaturated substrates but also unprecedented durability for the one‐pot conversion of cellulose under very harsh conditions (245 °C, 60 bar H2, presence of tungstic acid in hot water). Using integrated spectroscopy characterization and computational modeling, the active site structure is identified as (Ni‐N4)???N, where significantly distorted octahedral coordination and pyridinic N constitute a frustrated Lewis pair for the heterolytic dissociation of dihydrogen, and the robust covalent chemical bonding between Ni and N atoms accounts for its ultrastability. 相似文献
638.
基于热重分析仪考察了神府烟煤焦、稻草焦和神府烟煤-稻草混合焦样气化反应活性及共气化过程协同行为。并借助电感耦合等离子体发射光谱仪和扫描电子显微镜-能谱仪联用装置探讨了共气化过程活性矿物组分的迁移转化特性,以关联解释共气化协同行为演变。结果表明,与煤焦单独气化相比,稻草焦掺混有利于提高煤焦整体气化反应活性。混合焦样共气化过程协同行为随碳转化率的提高呈先逐渐减弱的抑制作用,达到某一碳转化率(记为转折碳转化率)后呈不断增强的协同促进作用,且转折碳转化率随气化温度升高而提高。神府烟煤-稻草混合焦样共气化过程协同行为演变主要归因于共气化过程活性K和Ca转化特性的共同影响。神府烟煤-稻草混合焦样共气化整体协同行为呈协同促进作用,并随气化温度的升高而减弱。 相似文献
639.
Abstract The application of high pressures to biomaterials can often result in significant structural modifications and, in some cases, also lead to changes in the rates and the equilibria of any associated biological activities. Pressure-induced changes can conveniently be monitored by molecular spectroscopy. We present here a brief overview of the effects of high pressures on the IR and Raman spectra of biomaterials that have been reported over the past 25 years. Examples of the biomaterials that have been examined are model antithyroid drugs, proteins, amino acids, dental materials, human bones, and bioorganometallic compounds. In addition, some recent investigations on the effect of pressure on microbial activity and the conversion of biomass into molecular hydrogen under supercritical water conditions are discussed. Two typical diamond-anvil cells (DACs), which are used for high-pressure vibrational spectroscopic measurements, are also described here. 相似文献
640.
Selma Zahirović Robert Scharler Pia Kilpinen Ingwald Obernberger 《Combustion Theory and Modelling》2013,17(1):61-87
While reasonably accurate in simulating gas phase combustion in biomass grate furnaces, CFD tools based on simple turbulence–chemistry interaction models and global reaction mechanisms have been shown to lack in reliability regarding the prediction of NOx formation. Coupling detailed NOx reaction kinetics with advanced turbulence–chemistry interaction models is a promising alternative, yet computationally inefficient for engineering purposes. In the present work, a model is proposed to overcome these difficulties. The model is based on the Realizable k–? model for turbulence, Eddy Dissipation Concept for turbulence–chemistry interaction and the HK97 reaction mechanism. The assessment of the sub-models in terms of accuracy and computational effort was carried out on three laboratory-scale turbulent jet flames in comparison with the experimental data. Without taking NOx formation into account, the accuracy of turbulence modelling and turbulence–chemistry interaction modelling was systematically examined on Sandia Flame D and Sandia CO/H2/N2 Flame B to support the choice of the associated models. As revealed by the Large Eddy Simulations of the former flame, the shortcomings of turbulence modelling by the Reynolds averaged Navier–Stokes (RANS) approach considerably influence the prediction of the mixing-dominated combustion process. This reduced the sensitivity of the RANS results to the variations of turbulence–chemistry interaction models and combustion kinetics. Issues related to the NOx formation with a focus on fuel bound nitrogen sources were investigated on a NH3-doped syngas flame. The experimentally observed trend in NOx yield from NH3 was correctly reproduced by HK97, whereas the replacement of its combustion subset by that of a detailed reaction scheme led to a more accurate agreement, but at increased computational costs. Moreover, based on results of simulations with HK97, the main features of the local course of the NOx formation processes were identified by a detailed analysis of the interactions between the nitrogen chemistry and the underlying flow field. 相似文献