全文获取类型
收费全文 | 4244篇 |
免费 | 983篇 |
国内免费 | 510篇 |
专业分类
化学 | 3760篇 |
晶体学 | 63篇 |
力学 | 76篇 |
综合类 | 24篇 |
数学 | 549篇 |
物理学 | 690篇 |
无线电 | 575篇 |
出版年
2024年 | 5篇 |
2023年 | 63篇 |
2022年 | 82篇 |
2021年 | 80篇 |
2020年 | 106篇 |
2019年 | 110篇 |
2018年 | 85篇 |
2017年 | 121篇 |
2016年 | 146篇 |
2015年 | 447篇 |
2014年 | 486篇 |
2013年 | 221篇 |
2012年 | 232篇 |
2011年 | 313篇 |
2010年 | 227篇 |
2009年 | 351篇 |
2008年 | 352篇 |
2007年 | 294篇 |
2006年 | 270篇 |
2005年 | 212篇 |
2004年 | 233篇 |
2003年 | 213篇 |
2002年 | 170篇 |
2001年 | 118篇 |
2000年 | 103篇 |
1999年 | 76篇 |
1998年 | 71篇 |
1997年 | 72篇 |
1996年 | 58篇 |
1995年 | 63篇 |
1994年 | 63篇 |
1993年 | 42篇 |
1992年 | 40篇 |
1991年 | 33篇 |
1990年 | 32篇 |
1989年 | 23篇 |
1988年 | 12篇 |
1987年 | 11篇 |
1986年 | 15篇 |
1985年 | 9篇 |
1984年 | 9篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1981年 | 6篇 |
1980年 | 15篇 |
1979年 | 10篇 |
1978年 | 10篇 |
1977年 | 9篇 |
1975年 | 3篇 |
1974年 | 3篇 |
排序方式: 共有5737条查询结果,搜索用时 125 毫秒
121.
The enhanced lanthanide white-emission in solid by cucurbituril-based supramolecular assembly may provide a new strategy for smart light-emitting materials. 相似文献
122.
Interactions between divalent alkali earth metal (DAEM) ions M (M?Be, Mg, Ca, Sr, Ba) and the second stable glycine conformer in the gas phase, which can transfer into the ground‐state glycine‐M2+ (except the glycine–Be2+) among each corresponding isomers when these divalent metal ions are bound, are studied at the hybrid three‐parameter B3LYP level with three different basis sets. Proton transfers from the hydroxyl to the amino nitrogen of the glycine without energy barriers have been first observed in the gas phase in these glycine–M2+ systems. The interaction between the glycine and these DAEM ions except beryllium and magnesium ion only create an amino hydrogen pointing to the original hydroxyl due to their weaker interaction relative to those divalent transition metal (DTM) ion‐bound glycine derivatives, being obviously different from that between the glycine and DTM ions, in which two amino hydrogens point to the original hydroxyl oxygen when these metal‐chelated glycine derivatives are produced. The interaction energy between the glycine and divalent magnesium would be the boundary of one or two amino hydrogens pointing to the hydrogyl oxygen, i.e., the ?170.3 kcal/mol of binding energy is a critical point. Similar intramolecular proton transfer has also been predicted for those DTM ion‐chelated glycine systems; however, that in the gas state has not been observed in the monovalent metal ion‐coordinated glycine systems. The binding energy between some monovalent TM ion and the glycine is similar to that of the glycine–Ba2+, which has the lowest binding strength among these DAEM–ion chelated glycine complexes. The difference among them only lies in the larger electrostatic and polarized effects in the latter, which favor the stability of the zwitterionic glycine form in the gas phase. According to these observations, we predict that the zwitterionic glycine would exist in the field of two positive charges in the gas phase. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 94: 205–214, 2003 相似文献
123.
124.
Summary Procedures were developed for the preparation of the 2-, 3-, 4-, and 6-monosubstituted chloro and bromo 8-quinolinols which afforded greater yields and/or reduced the number of steps in the preparation. 100 MHz1H-NMR spectra for the 12 possible monochloro and monobromo analogues are given.
Verbesserte Synthese von Monochlor- und Monobrom-8-chinolinolen
Zusammenfassung Es wurden Verfahren entwickelt, um 2-, 3-, 4- und 6-Chlor bzw. -Brom-8-chinolinole in besseren Ausbeuten und/oder bei reduzierter Anzahl von Synthesestufen herzustellen. Die1H-NMR-Spektren der 12 möglichen Monochlor- und Monobromverbindungen werden angegeben.相似文献
125.
通过对双环戊二烯的选择性羰基化加成,高产率地合成了三环[5、2、1、02,6]癸-3烯-8,9-二羧酸二甲酯。得到了无色透明的片状晶体,产率为90%。 相似文献
126.
127.
一种基于形成杂多核配合物的荧光增敏效应的研究(Ⅱ)──钴(Ⅱ)-7-(8-羟基-3,6-二磺基萘偶氮)-8-羟基喹啉-5-磺酸-硼(Ⅲ)三元体系的荧光性质及其分析应用熊国华,刘虹,俞英,黄坚锋(九江师范专科学校化学系,九江,332000)(江西大学实... 相似文献
128.
The isolation and structure elucidation of xyloccensin L from the stem bark of Xylocarpus granatum is described. Xyloccensin L is a highly oxidized heptacyclic A, B, D-seco limonoid with an α-8, 30-epoxy ring and a rare 1, 29 oxygen bridge. 相似文献
129.
D.?Mitra S.?Francis L.?VarshneyEmail author 《Journal of Thermal Analysis and Calorimetry》2004,78(3):821-829
DSC and TG studies were carried out on -radiation processed Indian natural products of medicinal importance, namely Ashwagandha (Withania Somnifera), Amla (Emblica Officinalis) and Hartiki (Terminalia chebula). DSC thermoanalytical curves were recorded from 35 to 400°C in air and nitrogen atmosphere. Similarly, TG thermoanalytical curves were taken from 35 to 700°C in air and nitrogen atmosphere. Irradiated products gave significantly different thermoanalytical profiles in comparison to non-irradiated samples. The differences were observed above decomposition temperature of 200°C and were non-linear with respect to radiation dose. Partial oxidation of the products during irradiation in air could be responsible for the observed differences. 相似文献
130.
Youheng Shi Zhihui Zhang 《Journal of inclusion phenomena and macrocyclic chemistry》1994,18(2):137-147
The interactions ofp-tert.-butylcalix[4]arene bearing polyoxyethylene chains (C3) with pyrene (Py), 1-anilino-8-naphthalenesulfonate (ANS) andN-phenyl-naphthylamine (NPN) in aqueous solution were studied by absorption and fluorescence measurements. Absorption spectral changes and fluorescence enhancements reveal that C3, which has a hydrophobic cavity, can include organic molecules and ions in aqueous solution and form 11 host-guest complexes with ANS and NPN. C3 forms inclusion complexes with Py at different stoichiometries depending on the host: guest molar ratio. Binding constants of 2.2×104, 2.0×104 and 3.6×105 dm3 mol–1 were calculated for the C3Py, C3ANS and C3NPN complexes (11), respectively, based on the Benesi-Hildebrand equation.Author for correspondence. 相似文献