全文获取类型
收费全文 | 1286篇 |
免费 | 28篇 |
国内免费 | 5篇 |
专业分类
化学 | 687篇 |
晶体学 | 31篇 |
力学 | 35篇 |
数学 | 278篇 |
物理学 | 288篇 |
出版年
2023年 | 6篇 |
2022年 | 51篇 |
2021年 | 59篇 |
2020年 | 30篇 |
2019年 | 33篇 |
2018年 | 28篇 |
2017年 | 16篇 |
2016年 | 42篇 |
2015年 | 39篇 |
2014年 | 39篇 |
2013年 | 73篇 |
2012年 | 65篇 |
2011年 | 57篇 |
2010年 | 53篇 |
2009年 | 47篇 |
2008年 | 66篇 |
2007年 | 71篇 |
2006年 | 58篇 |
2005年 | 40篇 |
2004年 | 31篇 |
2003年 | 30篇 |
2002年 | 38篇 |
2001年 | 18篇 |
2000年 | 28篇 |
1999年 | 23篇 |
1998年 | 18篇 |
1997年 | 11篇 |
1996年 | 16篇 |
1995年 | 11篇 |
1994年 | 10篇 |
1993年 | 11篇 |
1992年 | 11篇 |
1991年 | 10篇 |
1990年 | 8篇 |
1989年 | 11篇 |
1988年 | 14篇 |
1987年 | 12篇 |
1986年 | 16篇 |
1985年 | 10篇 |
1984年 | 15篇 |
1983年 | 8篇 |
1982年 | 8篇 |
1981年 | 9篇 |
1980年 | 11篇 |
1978年 | 7篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1974年 | 4篇 |
1937年 | 3篇 |
1873年 | 6篇 |
排序方式: 共有1319条查询结果,搜索用时 15 毫秒
51.
Monika Szufla Aleksandra Choroś Dr. Wojciech Nitek Prof. Dariusz Matoga 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(37):e202200835
By using the strategy of pre-assembly chlorosulfonation applied to a linker precursor, the first sulfonated zirconium metal–organic framework ( JUK-14 ) with two-dimensional (2D) structure, was synthesized. Single-crystal X-ray diffraction reveals that the material is built of Zr6O4(OH)4(COO)8 oxoclusters, doubly 4-connected by angular dicarboxylates, and stacked in layers spaced 1.5 nm apart by the presence of sulfonic groups. JUK-14 exhibits excellent hydrothermal stability, permanent porosity confirmed by gas adsorption studies, and shows high (>10−4 S/cm) and low (<10−8 S/cm) proton conductivity under humidified and anhydrous conditions, respectively. Post-synthesis inclusion of imidazole improves the overall conductivity increasing it to 1.7×10−3 S/cm at 60 °C and 90 % relative humidity, and by 3 orders of magnitude at 160 °C. The combination of 2D porous nature with robustness of zirconium MOFs offers new opportunities for exploration of the material towards energy and environmental applications. 相似文献
52.
53.
In the paper methods of the terahertz photomixer operational frequency estimation are considered. Three methods are investigated — estimation of the frequency via direct measurements of the laser heterodyne compounds, via calculations from datasheets, and via calculations from raw collected data obtained from the photomixer system. 相似文献
54.
Regioselective formation of β‐(E)‐ and α‐alkenylsilane moiety attached to silsesquioxane core via Pt‐ and Ru‐based hydrosilylation
下载免费PDF全文
![点击此处可从《应用有机金属化学》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The first attempts to use ethynylsiloxysilsesquioxanes as reagents for hydrosilylation in the presence of Pt‐ and Ru‐based catalysts are reported. The results obtained strongly depend on the catalytic system used. The catalysts are proved to promote regioselective introduction of β‐(E)‐ and α‐fragments of the alkenylsilane group to the silsesquioxane core. The favourable features of these catalytic systems are their high selectivity and the requirement for relatively mild conditions. This methodology was also successfully applied to dihydro‐substituted organosilicon compounds to obtain a new class of silsesquioxane‐based compounds. 相似文献
55.
Dariusz Cal 《Phosphorus, sulfur, and silicon and the related elements》2013,188(4):816-824
ω-[(Arylphosphonomethyl)amino]alkylphosphonic and carboxylic acids are prepared in an easy work-up procedure, by addition of diethyl phosphite to in situ–generated arylideneaminoalkylphosphonic or carboxylic acids followed by hydrolysis with hydrochloric acid 相似文献
56.
57.
Dichloroacetylene (C2Cl2) reacts with carbazole and primary amines under phase-transfer catalytic (PTC) conditions to give 1-N-alkylimino-1,2-di(9-carbazolyl)ethanes (I) and 9-((E)-1,2-dichlorovinyl)carbazole (II) in one-step synthesis. Compounds I are formed from the addition of amines to the triple bond of C2Cl2 followed by reactions with carbazole. 相似文献
58.
59.
60.
Elwira Chrobak Ewa Michalik Joachim Kusz Maria Nowak Stanisaw Boryczka 《Acta Crystallographica. Section C, Structural Chemistry》2014,70(9):847-851
The lupane triterpenoid betulonic aldehyde [also known as betulonal; systematic name: lup‐20(29)‐en‐28‐al‐3‐one, C30H46O2] is a product of betulin oxidation. Crystals were obtained from hexane [form (I)] and dimethyl sulfoxide [form (II)] solutions. Forms (I) and (II) are both orthorhombic. The molecular geometric parameters in the two forms are similar, but the structures are different with respect to the crystal packing. Polymorph (I) contains two independent molecules in the asymmetric unit, while polymorph (II) contains only one molecule, which has a disordered aldehyde group [the disorder ratio is 0.769 (4):0.231 (4)]. In each molecule, the six‐membered rings have chair conformations, whereas the cyclopentane ring in each molecule adopts an envelope conformation. All the rings in the lupane nucleus are trans‐fused. The extended structures of both polymorphs are stabilized by weak intermolecular C—H...O and van der Waals interactions. Weak intramolecular C—H...O interactions are also observed. 相似文献