全文获取类型
收费全文 | 877篇 |
免费 | 106篇 |
国内免费 | 4篇 |
专业分类
化学 | 778篇 |
晶体学 | 1篇 |
力学 | 16篇 |
数学 | 83篇 |
物理学 | 109篇 |
出版年
2023年 | 32篇 |
2022年 | 25篇 |
2021年 | 50篇 |
2020年 | 76篇 |
2019年 | 82篇 |
2018年 | 31篇 |
2017年 | 20篇 |
2016年 | 77篇 |
2015年 | 55篇 |
2014年 | 37篇 |
2013年 | 70篇 |
2012年 | 55篇 |
2011年 | 67篇 |
2010年 | 26篇 |
2009年 | 18篇 |
2008年 | 34篇 |
2007年 | 22篇 |
2006年 | 35篇 |
2005年 | 28篇 |
2004年 | 16篇 |
2003年 | 14篇 |
2002年 | 11篇 |
2001年 | 9篇 |
2000年 | 8篇 |
1999年 | 6篇 |
1997年 | 4篇 |
1996年 | 5篇 |
1995年 | 4篇 |
1994年 | 5篇 |
1992年 | 4篇 |
1991年 | 4篇 |
1988年 | 3篇 |
1985年 | 4篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1975年 | 3篇 |
1973年 | 2篇 |
1934年 | 2篇 |
1932年 | 2篇 |
1931年 | 2篇 |
1930年 | 2篇 |
1928年 | 2篇 |
1913年 | 1篇 |
1894年 | 1篇 |
排序方式: 共有987条查询结果,搜索用时 15 毫秒
981.
Dajana Durach Lukas Neudert Peter J. Schmidt Oliver Oeckler Wolfgang Schnick 《ChemInform》2015,46(39):no-no
Agglomerates of a few μm of the yellow phosphor La3BaSi5N9O2:Ce3+ are obtained by heating a mixture of LaF3, La(NH2)3, BaH2, Si(NH)2, and CeF3 in a radio frequency furnace under N2 (1600 °C, 10 h; cooling to 900 °C within 44 h). 相似文献
982.
Jonas F. Goebel Julian Löffler Zhongyi Zeng Jens Handelmann Albert Hermann Ilja Rodstein Dr. Tobias Gensch Prof. Dr. Viktoria H. Gessner Prof. Dr. Lukas J. Gooßen 《Angewandte Chemie (International ed. in English)》2023,62(9):e202216160
Palladium-catalyzed couplings of silicon enolates with aryl electrophiles are of great synthetic utility, but often limited to expensive bromide substrates. A comparative experimental study confirmed that none of the established ligand systems allows to couple inexpensive aryl chlorides with α-trimethylsilyl alkylnitriles. In contrast, ylide functionalized phosphines (YPhos) led to encouraging results. A statistical model was developed that correlates the reaction yields with ligand features. It was employed to predict catalyst structures with superior performance. With this cheminformatics approach, YPhos ligands were tailored specifically to the demands of Hiyama couplings. The newly synthesized ligands displayed record-setting activities, enabling the elusive coupling of aryl chlorides with α-trimethylsilyl alkyl nitriles. The preparative utility of the catalyst system was demonstrated by the synthesis of pharmaceutically meaningful α-aryl alkylnitriles, α-arylcarbonyls and biaryls. 相似文献
983.
Jonas F. Goebel Johanna Stemmer Florian Belitz Lukas J. Gooßen 《Angewandte Chemie (International ed. in English)》2023,62(24):e202301839
The 3d-metal catalyst Mn(CO)5Br was found to efficiently promote ortho C−H allylations of arenecarboxylates in the presence of neocuproine as the ligand. Despite the simplicity of directing group and catalyst system, the selectivity goes well beyond the state-of-the-art in that mono-allylated products are obtained exclusively with high selectivities for the least hindered ortho-position. The directing group can optionally be removed by in situ decarboxylation, opening up a regioselective entry to allyl arenes. The preparative utility of the process and its othogonality to other approaches was demonstrated by 44 products with otherwise hard-to-access substitution patterns, including 3-bromo-allylbenzene, 3-allylbenzofuran, or 5-allyl-2-methylnitrobenzene. 相似文献
984.
Dr. Marat Meleshin Lukas Koch Dr. Christoph Wiedemann Prof. Dr. Mike Schutkowski 《Angewandte Chemie (International ed. in English)》2023,62(25):e202301543
Herein we report a mild, efficient, and epimerization-free method for the synthesis of peptide-derived 2-thiazolines and 5,6-dihydro-4H-1,3-thiazines based on a cyclodesulfhydration of N-thioacyl-2-mercaptoethylamine or N-thioacyl-3-mercaptopropylamine derivatives. The described reaction can be easily carried out in aqueous solutions at room temperature and it is triggered by change of the pH, leading to complex thiazoline or dihydrothiazine derivatives without epimerization in excellent to quantitative yields. The new method was applied in the total synthesis of the marine metabolite mollamide F, resulting in the revision of its stereochemistry. 相似文献
985.
Lukas Scheibelberger Toda Stankovic Kaja Liepert Andreas Kienzle Eva-Maria Patronas Dr. Theresa Balber Prof. Dr. Markus Mitterhauser Prof. Dr. Arvand Haschemi Dr. Katharina Pallitsch 《European journal of organic chemistry》2023,26(31):e202300339
Fluorinated carbohydrates are valuable tools for enzymological studies due to their increased metabolic stability compared to their non-fluorinated analogues. Replacing different hydroxyl groups within the same monosaccharide by fluorine allows to influence a wide range of sugar–receptor interactions and enzymatic transformations. In the past, this principle was frequently used to study the metabolism of highly abundant carbohydrates, while the metabolic fate of rare sugars is still poorly studied. Rare sugars, however, are key intermediates of many metabolic routes, such as the pentose phosphate pathway (PPP). Here we present the design and purely chemical synthesis of a set of three deoxyfluorinated analogues of the rare sugars d -xylulose and d -ribulose: 1-deoxy-1-fluoro-d -ribulose ( 1DFRu ), 3-deoxy-3-fluoro-d -ribulose ( 3DFRu ) and 3-deoxy-3-fluoro-d -xylulose ( 3DFXu ). Together with a designed set of potential late-stage radio-fluorination precursors, they have the potential to become useful tools for studies on the complex equilibria of the non-oxidative PPP. 相似文献
986.
Dr. Qiang Liu Niklas Pfriem Dr. Guanhua Cheng Dr. Eszter Baráth Prof. Yue Liu Prof. Johannes A. Lercher 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2023,135(3):e202208693
The intracrystalline ionic environment in microporous zeolite can remarkably modify the excess chemical potential of adsorbed reactants and transition states, thereby influencing the catalytic turnover rates. However, a limit of the rate enhancement for aqueous-phase dehydration of alcohols appears to exist for zeolites with high ionic strength. The origin of such limitation has been hypothesized to be caused by the spatial constraints in the pores via, e.g., size exclusion effects. It is demonstrated here that the increase in turnover rate as well as the formation of a maximum and the rate drop are intrinsic consequences of the increasingly dense ionic environment in zeolite. The molecularly sized confines of zeolite create a unique ionic environment that monotonically favors the formation of alcohol-hydronium ion complexes in the micropores. The zeolite microporous environment determines the kinetics of catalytic steps and tailors the impact of ionic strength on catalytic rates. 相似文献