全文获取类型
收费全文 | 2331篇 |
免费 | 128篇 |
国内免费 | 6篇 |
专业分类
化学 | 1406篇 |
晶体学 | 24篇 |
力学 | 41篇 |
数学 | 423篇 |
物理学 | 571篇 |
出版年
2023年 | 20篇 |
2022年 | 20篇 |
2021年 | 39篇 |
2020年 | 53篇 |
2019年 | 43篇 |
2018年 | 50篇 |
2017年 | 76篇 |
2016年 | 138篇 |
2015年 | 95篇 |
2014年 | 85篇 |
2013年 | 154篇 |
2012年 | 154篇 |
2011年 | 202篇 |
2010年 | 118篇 |
2009年 | 98篇 |
2008年 | 99篇 |
2007年 | 80篇 |
2006年 | 67篇 |
2005年 | 50篇 |
2004年 | 48篇 |
2003年 | 49篇 |
2002年 | 26篇 |
2001年 | 21篇 |
2000年 | 36篇 |
1999年 | 21篇 |
1998年 | 26篇 |
1997年 | 16篇 |
1996年 | 18篇 |
1995年 | 12篇 |
1994年 | 18篇 |
1993年 | 14篇 |
1988年 | 11篇 |
1985年 | 19篇 |
1984年 | 24篇 |
1983年 | 17篇 |
1982年 | 14篇 |
1981年 | 20篇 |
1980年 | 22篇 |
1979年 | 14篇 |
1978年 | 15篇 |
1976年 | 13篇 |
1975年 | 11篇 |
1973年 | 12篇 |
1968年 | 11篇 |
1959年 | 23篇 |
1958年 | 33篇 |
1957年 | 34篇 |
1956年 | 16篇 |
1955年 | 12篇 |
1954年 | 22篇 |
排序方式: 共有2465条查询结果,搜索用时 15 毫秒
71.
Photochemically initiated reactions of aliphatic aldehydes, namely acetaldehyde, propionaldehyde and butyraldehyde, with methyl trifluoroacrylate afforded γ-ketoesters of the type R-CO-CF2CHF-COOCH3 in the liquid phase. In the gas phase reaction further products were formed by addition of the aldehyde fragments to the olefinic bond of the methyl trifluoroacrylate. 相似文献
72.
73.
74.
75.
New Experimental Insight into the Nature of Metal−Metal Bonds in Digallium Compounds: J Coupling between Quadrupolar Nuclei 下载免费PDF全文
Dr. Libor Kobera Scott A. Southern Dr. Gyandshwar Kumar Rao Prof. Dr. Darrin S. Richeson Prof. Dr. David L. Bryce 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(28):9565-9573
Multiple bonding between atoms is of ongoing fundamental and applied interest. Here, we report a multinuclear (1H, 13C, and 71Ga) solid‐state magnetic resonance spectroscopic study of digallium compounds which have been proposed, albeit somewhat controversially, to contain single, double, and triple Ga?Ga bonds. Of particular relevance to the nature of these bonds, we have carried out two‐dimensional 71Ga J/D‐resolved NMR experiments which provide a direct measurement of J(71Ga,71Ga) spin–spin coupling constants across the gallium?gallium bonds. When placed in the context of clear‐cut experimental data for analogous singly, doubly, and triply bonded carbon spin pairs or boron spin pairs, the 71Ga NMR data clearly support the notion of a different bonding paradigm in the gallium systems. Our findings are consistent with an increasing role across the purported gallane–gallene–gallyne series for classical and/or slipped π‐type bonding orbitals. 相似文献
76.
77.
Tomáš Hartman Vladimír Herzig Miloš Buděšínský Jindřich Jindřich Radek Cibulka Tomáš Kraus 《Tetrahedron: Asymmetry》2012,23(22-23):1571-1583
A series of flavin–cyclodextrin conjugates has been prepared and tested in the enantioselective oxidations of prochiral aromatic and aliphatic sulfides with hydrogen peroxide. The newly prepared conjugates contain isoalloxazinium or alloxazinium moieties attached to the primary rim of α- and β-cyclodextrins at the C-6 positions. In addition, flavinium units were attached to the secondary rim of the β-cyclodextrin macrocycle. The relationship between the structural features and the catalytic performance of the conjugates, including those recently reported by us, was analyzed. The rate and enantioselectivity of the sulfoxidations catalyzed by flavin–cyclodextrin conjugates are influenced mainly by the size of the cyclodextrin cavity, the type of flavin unit (alloxazine or isoalloxazine), and by the relative orientation of the flavin and cyclodextrin moieties. 相似文献
78.
79.
Vít Kremláček Erik Kertész Prof. Zoltán Benkő Milan Erben Robert Jirásko Prof. Aleš Růžička Prof. Roman Jambor Prof. Libor Dostál 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(52):13096-13097
Invited for the cover of this issue are Zoltán Benkő, Libor Dostál and co-workers at the University of Pardubice and the Budapest University of Technology and Economics. The image depicts signs for the two different pathways representing the two differing reaction types which were clearly observed for 2,1-benzazaphosphole. Read the full text of the article at 10.1002/chem.202101686 . 相似文献
80.
Mesoporous molecular sieve SBA‐15 and conventional silica gel were grafted with 3‐[2‐(diethylamino)ethylamino]propyl groups and used as supports for the preparation of deposited palladium catalysts, which were subsequently evaluated in Stille cross‐coupling reaction of aryl bromides. The highest conversions were achieved with the metal‐saturated catalyst resulting from the modified SBA‐15. Influence of various reaction parameters (solvent, additive, temperature, etc.) on the overall yield and selectivity was studied. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献