全文获取类型
收费全文 | 3806篇 |
免费 | 511篇 |
国内免费 | 477篇 |
专业分类
化学 | 3222篇 |
晶体学 | 50篇 |
力学 | 12篇 |
综合类 | 16篇 |
数学 | 9篇 |
物理学 | 1485篇 |
出版年
2024年 | 6篇 |
2023年 | 30篇 |
2022年 | 111篇 |
2021年 | 91篇 |
2020年 | 147篇 |
2019年 | 122篇 |
2018年 | 82篇 |
2017年 | 109篇 |
2016年 | 146篇 |
2015年 | 141篇 |
2014年 | 157篇 |
2013年 | 345篇 |
2012年 | 222篇 |
2011年 | 222篇 |
2010年 | 175篇 |
2009年 | 217篇 |
2008年 | 243篇 |
2007年 | 269篇 |
2006年 | 242篇 |
2005年 | 197篇 |
2004年 | 183篇 |
2003年 | 170篇 |
2002年 | 133篇 |
2001年 | 156篇 |
2000年 | 104篇 |
1999年 | 119篇 |
1998年 | 100篇 |
1997年 | 77篇 |
1996年 | 67篇 |
1995年 | 69篇 |
1994年 | 49篇 |
1993年 | 45篇 |
1992年 | 31篇 |
1991年 | 30篇 |
1990年 | 21篇 |
1989年 | 29篇 |
1988年 | 16篇 |
1987年 | 20篇 |
1986年 | 12篇 |
1985年 | 6篇 |
1984年 | 9篇 |
1983年 | 9篇 |
1982年 | 9篇 |
1981年 | 9篇 |
1980年 | 11篇 |
1979年 | 7篇 |
1978年 | 6篇 |
1976年 | 5篇 |
1974年 | 3篇 |
1973年 | 5篇 |
排序方式: 共有4794条查询结果,搜索用时 15 毫秒
991.
Reversing Conventional Reactivity of Mixed Oxo/Alkyl Rare‐Earth Complexes: Non‐Redox Oxygen Atom Transfer
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)
Dr. Jianquan Hong Haiwen Tian Prof. Lixin Zhang Prof. Xigeng Zhou Dr. Iker del Rosal Prof. Linhong Weng Prof. Laurent Maron 《Angewandte Chemie (International ed. in English)》2018,57(4):1062-1067
The preferential substitution of oxo ligands over alkyl ones of rare‐earth complexes is commonly considered as “impossible” due to the high oxophilicity of metal centers. Now, it has been shown that simply assembling mixed methyl/oxo rare‐earth complexes to a rigid trinuclear cluster framework cannot only enhance the activity of the Ln‐oxo bond, but also protect the highly reactive Ln‐alkyl bond, thus providing a previously unrecognized opportunity to selectively manipulate the oxo ligand in the presence of numerous reactive functionalities. Such trimetallic cluster has proved to be a suitable platform for developing the unprecedented non‐redox rare‐earth‐mediated oxygen atom transfer from ketones to CS2 and PhNCS. Controlled experiments and computational studies shed light on the driving force for these reactions, emphasizing the importance of the sterical accessibility and multimetallic effect of the cluster framework in promoting reversal of reactivity of rare‐earth oxo complexes. 相似文献
992.
In this study, the ion-imprinting method has been integrated to develop a novel composite material for the selective separation of Pb2+ ions. Also, Pb2+ ion binding ability of the organosmectite based inorganic-organic composite incorporation of bicyclic C18 organic compound into smectite layers was conducted to draw a projection its potential use as a solid phase exchanger which is quite selective toward Pb2+ ions. The ion-imprinted nanocomposites were characterized by Fourier transform infrared (FTIR), X-ray diffraction (XRD), swelling tests, and elemental analyses. After that, maximum binding capacity, pH, and equilibrium binding time were also been optimized. In order to show the selectivity of the composite synthesized, non-imprinted composites were also synthesized in absence of Pb2+ ions during polymerization. In this step, Ni2+, Co2+, Al3+, Zn2+, and Cu2+ ions were used as competitors under batch adsorption conditions. The relative selectivity coefficients of imprinted composite were calculated as 28.5, 156.5, 69.3, 24.8 and 131.6 for Pb2+/Co2+, Pb2+/Cu2+, Pb2+/Al3+, Pb2+/Zn2+, Pb2+/Ni2+ binary solutions, respectively. Finally, reusability of the composites was evaluated to show its cost-efficiency by repeating adsorption-desorption experiments ten-times. The adsorption capacity of the imprinted composites did not change significantly whereas that of non-imprinted version reduced dramatically. 相似文献
993.
《中国化学会会志》2018,65(5):591-596
We demonstrate that silica microspheres can act as a sensitive fluorescent sensor and adsorbent of Ag+ in aqueous media. These thiol‐functionalized silica microspheres are doped with quantum dots (QDs) using organosilane chemistry in a one‐step preparation. Ligand exchange takes place between the thiolated organosilane and acid‐capped QDs, making the doping easy. Ag+ adsorption by the silica microspheres causes the decrease of fluorescence intensity of the QDs. The detection limit for Ag+ is found to be 10 μmol/L. The abundance of thiol groups on the surface of the microspheres could effectively remove Ag+ through strong interaction. When microspheres with a diameter of 1.1 μm are used as the adsorbents, the adsorption capacity for Ag+ reached 102 mg/g. This excellent adsorption ability is due to the abundance of thiol groups that act as the active sites, facilitating the adsorption of the massive metal ions on the surface of the microspheres. Furthermore, the adsorption isotherm data follows the Freundlich model. The structure and content of the silica microspheres were investigated by scanning and high‐resolution transmission electron microscopy, energy dispersive X‐ray spectroscopy, and Raman analysis, and the fluorescence properties were characterized by fluorescence microscopy. 相似文献
994.
995.
Daniele Falcomer Carla Cannas Barbara Lasio Adolfo Speghini Marco Bettinelli 《Journal of solid state chemistry》2006,179(8):2452-2457
A one-step solvothermal synthesis is proposed for the preparation of nanocrystalline single-phase TiO2 in the anatase form doped with lanthanide ions Eu3+, Er3+ and Sm3+. The structural properties of these products have been investigated by using X-ray powder diffraction, electron microscopy and Raman spectroscopy. Furthermore, the laser-excited luminescence spectra of the samples have been measured and analyzed. Following this route, the doping process turns out to be highly favorite and the resulting materials show an efficient luminescence in the visible region. 相似文献
996.
997.
The surface modification of polyethylene (PE) by neutral nitrogen species (ground and excited state N2 as well as atomic N; modified nitrogen plasma treatment) has been compared to the effect of nitrogen ion bombardment using X-ray Photoelectron Spectroscopy (XPS) and contact angle measurements. XPS results indicate that a greater nitrogen concentration was grafted during the modified nitrogen plasma treatment of PE, an effect that was attributed to surface sputtering during ion beam modification. The distribution of nitrogen-containing functionalities was strongly dependent upon the treatment strategy; the modified nitrogen plasma treatment lead predominantly to imine groups being formed at the PE surface, while amine groups were the dominant species produced during ion beam modification. The presence of electron irradiation during the modified nitrogen plasma treatment of PE did not modify the rate of nitrogen incorporation or change the nature of N-containing functional groups produced but did lead to a systematic decrease in contact angle. 相似文献
998.
E. V. Trofimova A. N. Fedotov R. A. Gazzaeva S. S. Mochalov Yu. S. Shabarov N. S. Zefirov 《Chemistry of Heterocyclic Compounds》2003,39(2):205-212
The N-oxide of N-(4-nitrobenzylidene)-2-cyclopropylaniline is converted by the action of strong acids into the corresponding 2,1-benzoxazinium derivative. Under identical conditions the N-oxide of N-(4-nitrobenzylidene)-2-cyclopropylmethylaniline forms the corresponding 2,1-benzoxazinium and 2,1-benzoxazepinium salts in a ratio of 1 : 2. The 2,1-benzoxazepinium ions are thermodynamically less stable and are isomerized with time into 2,1-benzoxazinium ions. Treatment of 2,1-benzoxazinium salts with hydrobromic acid solution and subsequent neutralization leads to o-(2-hydroxyalkyl)anilines and p-nitrobenzaldehyde. The effect of the nature of the ortho substituent on the direction of the conversions of the corresponding arylcyclopropanes is discussed. 相似文献
999.
Bahruddin Saad Ching Ching Chong Abdussalam Salhin Mohamad Ali Md Fazlul Bari Ismail Ab Rahman Norita Mohamad Muhammad Idiris Saleh 《Analytica chimica acta》2006,555(1):146-156
Sorbent materials based on three thiacrown ethers, 1,4,7,10-tetrathiacyclododecane (12S4), 1,4,7,10,13-pentathiacyclopentadecane (15S5) and 1,4,7,10.13,16-hexathiacyclooctadecane (18S6) were prepared either by immobilizing the ligands into sol-gel (SG) matrix or coating on commercial solid phase extraction (SPE) column. SG sorbents were characterized by FT-IR, energy dispersive X-ray microanalysis (EDX) and thermogravimetric analysis/derivative thermogravimetric analysis (TGA/DTG). A marked thermal stability of the ligands when immobilized in sol-gel matrix was noted. The competitive sorption characteristics of a mixture of eleven metal ions (Mg2+, Zn2+, Cd2+, Co2+, Mn2+, Ca2+, Cu2+, Ni2+, Ag+, V4+, Hg2+) using: (i) batch method with ligands trapped in SG matrices, and (ii) off-line SPE column containing coated ligands were studied using ICP-MS. The extraction of metals were optimized for key parameters such as pH, contact time/flow rate, particle size (for SG sorbents) and ligand concentration. Under the optimized conditions, all the immobilized thiacrown ethers exhibited highest selectivity toward Ag+, with lesser responses to Hg2+ while the extraction of other metal ions were negligible. Among the SG sorbents, 18S6-SG offer the highest capacity and the best selectivity over Hg2+. However, for practical applications such as for selective isolation and preconcentration of Ag+, the SPE type especially based on 18S6 is preferred as analysis time and recoveries are favorable. The sorbents can be repeatedly used three times as there was no significant deterioration in the metal uptake (%E > 90%) or interference from other metal ions. The optimized procedures were successfully applied for the separation and preconcentration of traces Ag+ in different water samples. 相似文献
1000.
以柠檬酸、乙二胺和乙酸锌为前体,采用一步水热法制备了一种稳定的、高荧光量子产率的水溶性锌掺杂碳量子点(Zn-CQDs)。通过透射电子显微镜(TEM)、X射线衍射(XRD)、傅立叶红外光谱(FTIR)、紫外-可见吸收光谱(UV-Vis)、荧光光谱对Zn-CQDs的结构和光学性能进行了表征。研究表明,Cu~(2+)对Zn-CQDs的荧光产生猝灭,体系的荧光信号处于"关闭"状态,还原型谷胱甘肽(GSH)的存在,使Zn-CQDs-Cu~(2+)体系的荧光得以恢复,体系的荧光信号处于"打开"状态。由此构建了"关-开"型荧光探针用于谷胱甘肽(GSH)的选择性、高灵敏检测。探究了反应p H值和反应时间对荧光恢复体系的影响,同时考察了果蔬中常见的有机小分子和离子对Zn-CQDs-Cu~(2+)体系荧光强度的影响,在最佳实验条件下,GSH浓度在0. 05~80μmol/L内与Zn-CQDs荧光恢复率呈线性关系,检出限达63 nmol/L。将该探针用于果蔬中GSH的检测,样品的加标回收率为98. 6%~101%,相对标准偏差为1. 8%~3. 1%,结果令人满意。 相似文献