全文获取类型
收费全文 | 1455篇 |
免费 | 29篇 |
国内免费 | 238篇 |
专业分类
化学 | 1135篇 |
晶体学 | 10篇 |
力学 | 30篇 |
综合类 | 4篇 |
数学 | 2篇 |
物理学 | 541篇 |
出版年
2023年 | 20篇 |
2022年 | 15篇 |
2021年 | 17篇 |
2020年 | 31篇 |
2019年 | 22篇 |
2018年 | 16篇 |
2017年 | 41篇 |
2016年 | 34篇 |
2015年 | 43篇 |
2014年 | 46篇 |
2013年 | 61篇 |
2012年 | 70篇 |
2011年 | 132篇 |
2010年 | 85篇 |
2009年 | 132篇 |
2008年 | 104篇 |
2007年 | 148篇 |
2006年 | 146篇 |
2005年 | 86篇 |
2004年 | 88篇 |
2003年 | 64篇 |
2002年 | 38篇 |
2001年 | 47篇 |
2000年 | 30篇 |
1999年 | 27篇 |
1998年 | 23篇 |
1997年 | 30篇 |
1996年 | 22篇 |
1995年 | 22篇 |
1994年 | 15篇 |
1993年 | 13篇 |
1992年 | 11篇 |
1991年 | 9篇 |
1990年 | 10篇 |
1989年 | 6篇 |
1988年 | 7篇 |
1987年 | 4篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1982年 | 2篇 |
1977年 | 1篇 |
排序方式: 共有1722条查询结果,搜索用时 15 毫秒
1.
The sonocatalytic degradation of EDTA (C0 = 5 10−3 M) in aqueous solutions was studied under 345 kHz (Pac = 0.25 W mL−1) ultrasound at 22–51 °C, Ar/20%O2, Ar or air, and in the presence of metallic titanium (Ti0) or core-shell Ti@TiO2 nanoparticles (NPs). Ti@TiO2 NPs have been obtained using simultaneous action of hydrothermal conditions (100–214 °C, autogenic pressure P = 1.0–19.0 bar) and 20 kHz ultrasound, called sonohydrothermal (SHT) treatment, on Ti0 NPs in pure water. Ti0 is composed of quasi-spherical particles (30–150 nm) of metallic titanium coated with a metastable titanium suboxide Ti3O. SHT treatment at 150–214 °C leads to the oxidation of Ti3O and partial oxidation of Ti0 and formation of nanocrystalline shell (10–20 nm) composed of TiO2 anatase. It was found that Ti0 NPs do not exhibit catalytic activity in the absence of ultrasound. Moreover, Ti0 NPs remain inactive under ultrasound in the absence of oxygen. However, significant acceleration of EDTA degradation was achieved during sonication in the presence of Ti0 NPs and Ar/20%O2 gas mixture. Coating of Ti0 with TiO2 nanocrystalline shell reduces sonocatalytic activity. Pristine TiO2 anatase nanoparticles do not show a sonocatalytic activity in studied system. Suggested mechanism of EDTA sonocatalytic degradation involves two reaction pathways: (i) sonochemical oxidation of EDTA by OH/HO2 radicals in solution and (ii) EDTA oxidation at the surface of Ti0 NPs in the presence of oxygen activated by cavitation event. Ultrasonic activation most probably occurs due to the local heating of Ti0/O2 species at cavitation bubble/solution interface. 相似文献
2.
TiO2-based photocatalysis has become a viable technology in various application fields such as (waste)water purification, photovoltaics/artificial photosynthesis, environmentally friendly organic synthesis and remediation of air pollution. Because of the increasing impact of bad air quality worldwide, this review focuses on the use and optimization of TiO2-based photocatalysts for gas phase applications. Over the past years various specific aspects of TiO2 photocatalysis have been reviewed individually. The intent of this review is to offer a broad tutorial on (recent) trends in TiO2 photocatalyst modification for the intensification of photocatalytic air treatment. After briefly introducing the fundamentals of photocatalysis, TiO2 photocatalyst modification is discussed both on a morphological and an electronic level from the perspective of gas phase applications. The main focus is laid on recent developments, but also possible opportunities to the field. This review is intended as a solid introduction for researchers new to the field, as well as a summarizing update for established investigators. 相似文献
3.
《印度化学会志》2023,100(3):100919
For years, the human race has awaited a more convenient, greener, and largely efficient material for energy conversion and electronic applications. Cu2O thin films produced by spray pyrolysis meet the economic viability and cost requirements, and it is widely assumed that they will lead to the production of functionally viable technologies. The spray pyrolysis method was used to added titanium into copper (I) oxide thin films with a deposition temperature of 200 °C and annealing for 2 h at 200 °C in this study. The Ti-doped Cu2O's optical, surface morphology, and photovoltaic characteristics have all been thoroughly explored. The best characteristics were obtained at 3% Ti doped Cu2O. The near-band emission of Ti-doped Cu2O was moved from 385 nm to 400 nm. The bandgap was reduced from 2.35 to 1.98Ev at 3% Ti doped Cu2O. As a result, Cu2O (Ti)-based solar cells' short circuit current density and open circuit voltage were greatly improved. It has been demonstrated that adding Ti to p-CuO/n-Si solar cells enhances their photovoltaic performance. 相似文献
4.
Christina Wartmann Dr. Shiny Nandi Dr. Jörg-Martin Neudörfl Prof. Dr. Albrecht Berkessel 《Angewandte Chemie (International ed. in English)》2023,62(35):e202306584
The titanium complex of the cis-1,2-diaminocyclohexane (cis-DACH) derived Berkessel-salalen ligand is a highly efficient and enantioselective catalyst for the asymmetric epoxidation of terminal olefins with hydrogen peroxide (“Berkessel-Katsuki catalyst”). We herein report that this epoxidation catalyst also effects the highly enantioselective hydroxylation of benzylic C−H bonds with hydrogen peroxide. Mechanism-based ligand optimization identified a novel nitro-salalen Ti-catalyst of the highest efficiency ever reported for asymmetric catalytic benzylic hydroxylation, with enantioselectivities of up to 98 % ee, while overoxidation to ketone is marginal. The novel nitro-salalen Ti-catalyst also shows enhanced epoxidation efficiency, as evidenced by e.g. the conversion of 1-decene to its epoxide in 90 % yield with 94 % ee, at a catalyst loading of 0.1 mol-% only. 相似文献
5.
Dr. Yusuke Imamura Kyohei Takaoka Yuma Komori Dr. Masanori Nagatomo Prof. Dr. Masayuki Inoue 《Angewandte Chemie (International ed. in English)》2023,62(10):e202219114
Taxol is a clinically used drug for the treatment of various types of cancers. Its 6/8/6/4-membered ring (ABCD-ring) system is substituted by eight oxygen functional groups and flanked by four acyl groups, including a β-amino acid side chain. Here we report a 34-step total synthesis of this unusually oxygenated and intricately fused structure. Inter- and intramolecular radical coupling reactions connected the A- and C-ring fragments and cyclized the B-ring, respectively. Functional groups of the A- and C-rings were then efficiently decorated by employing newly developed chemo-, regio-, and stereoselective reactions. Finally, construction of the D-ring and conjugation with the β-amino acid delivered taxol. The powerful coupling reactions and functional group manipulations implemented in the present synthesis provide new valuable information for designing multistep target-oriented syntheses of diverse bioactive natural products. 相似文献
6.
Bize Gao Dr. Quanren Zhu Prof. Dr. Yanhui Yi Yue Li Guoxing Wu Yitong Guo Prof. Dr. Zhaochi Feng Prof. Dr. Hongchen Guo 《欧洲无机化学杂志》2023,26(22):e202200661
The epoxidation of propylene with dilute H2O2 aqueous solution over titanium silicalite-1 (TS-1) zeolite catalyst is a green chemical reaction for propylene oxide (PO) production. Carrying out the reaction in gas-phase can get rid of problems caused by using methanol solvent. This paper reports an attempt of using non-zeolite catalyst for the gas-phase epoxidation. Amorphous Ti/SiO2, obtained by grafting amorphous SiO2 with TCl4 in ethanol solvent in a chemical liquid-phase deposition (CLD) process, has been used as the catalyst. Results show that the CLD Ti/SiO2 with appropriate Si/Ti molar ratio is an active catalyst for gas-phase epoxidation, achieving 9.8 % propylene conversion and 66.9 % PO selectivity with 40.3 % H2O2 utilization, which indicates that this amorphous Ti/SiO2 catalyst deserves extensive studies in the future. 相似文献
7.
以硫脲为掺杂剂,采用溶胶-凝胶法制备了氮硫共掺杂TiO2(N,S-TiO2)。用比表面孔隙仪(BET)、X射线衍射仪(XRD)、紫外-可见漫反射(UV-Vis DRS)和X射线光电子能谱(XPS)对制备的光催化剂进行了表征,用表面光电压仪(SPS)和捕获剂研究了光催化剂的光生电荷分离效应。以甲基橙为模拟污染物,在模拟自然光照射下考察了样品的光催化性能。结果表明:硫脲/Ti的摩尔比为30%所制备氮硫共掺杂TiO2具有较高的光催化活性,光催化活性是纯TiO2的5倍。氮硫共掺杂使TiO2具有更高的比表面和光生电荷分离效应,从而有利于提高光催化活性。 相似文献
8.
Changjiu Xia Long Ju Yi Zhao Hongyi Xu Bin Zhu Feifei Gao Min Lin Zhenyu Dai Xiaodong Zou Xingtian Shu 《催化学报》2015,(6):845-854
The reaction mechanism of the oxidation of cyclohexanone catalyzed by titanium silicate zeolite TS-1 using aqueous H2O2 as the oxidant was investigated by combining density function theory (DFT) calculations with experimental studies. DFT calculations showed that H2O2 was adsorbed and activated at the tetrahedral Ti sites. By taking into account the adsorption energy, molecular size, steric hindrance and structural information, a reaction mechanism of Baeyer-Villiger oxidation catalyzed by TS-1 that involves the activation of H2O2 was proposed. Experimental studies showed that the major products of cyclohexanone oxidation by H2O2 catalyzed by a hollow TS-1 zeolite wereε-carprolactone, 6-hydroxyhexanoic acid, and adipic acid. These products were analyzed by GC-MS and were in good agreement with the proposed mechanism. Our studies showed that the reaction mechanism on TS-1 zeolite was different from that on Sn-beta zeolite. 相似文献
9.
纳米TiO2修饰的La0.6Sr0.4Co0.2Fe0.8O3-δ(LSCF)阴极被直接应用于YSZ电解质电池上. TiO2可阻止LSCF和YSZ间的化学反应,抑制SrZrO3的形成. LSCF-0.25 wt% TiO2阴极电池在0.7 V和600°C下的电流密度是LSCF阴极电池的1.6倍.电化学阻抗谱结果表明, TiO2修饰显著加快了氧离子注入电解质的过程,这可能与TiO2抑制了阴极/电解质界面处高电阻SrZrO3层的形成有关.本文为在ZrO2基电解质上使用高性能的(La,Sr)(Co,Fe)O3阴极材料提供了一种简单有效的方法. 相似文献
10.
分别采用1,4-(双乙氧基硅烷)苯(1,4-BTEB)和1,2-三乙氧基硅基乙烷(1,2-BTESE)作为有机硅源,正硅酸乙酯(TEOS)为无机硅源,钛酸四丁酯(TBOT)为钛源,以Pluronic EO20PO70EO20(P123)为模板剂在酸性环境下水热合成制备了Ti掺杂的有机-无机有序介孔有机硅材料Ti-SBA-15-ben和Ti-SBA-15-et.同时,在合成过程中加入H2O2作为配合剂调节钛源水解速度,制备得到Ti-SBA-15-ben-H和Ti-SBA-15-et-H.采用FT-IR、DR UV-Vis、N2物理吸附、XRD、TG-DSC、TEM等方法对制备的样品进行了表征.结果表明:合成过程中加入H2O2制备的苯基桥连有机硅杂化材料具有较好的疏水性能,其骨架中活性4价位钛含量高,结构有序性最好.在以叔丁基过氧化氢(TBHP)为氧源的环己烯氧化反应中对制备的催化材料进行了对比评价,结果表明:Ti-SBA-15-ben-H表现出最高的催化活性,其催化的反应以环氧化产物为主,环己烯的转化率为26.9%,环氧选择性为32.8%,T i-SBA-15-et催化的反应以烯丙位氧化产物2-环己烯-1-酮为主,环己烯的转化率为8.5%,2-环己烯-1-酮选择性为41.2%. 相似文献