全文获取类型
收费全文 | 41447篇 |
免费 | 1674篇 |
国内免费 | 966篇 |
学科分类
数理化 | 44087篇 |
出版年
2023年 | 278篇 |
2022年 | 379篇 |
2021年 | 1099篇 |
2020年 | 907篇 |
2019年 | 831篇 |
2018年 | 841篇 |
2017年 | 766篇 |
2016年 | 1383篇 |
2015年 | 1149篇 |
2014年 | 1385篇 |
2013年 | 2123篇 |
2012年 | 2630篇 |
2011年 | 2899篇 |
2010年 | 1849篇 |
2009年 | 1620篇 |
2008年 | 2379篇 |
2007年 | 2308篇 |
2006年 | 2095篇 |
2005年 | 2305篇 |
2004年 | 2239篇 |
2003年 | 1548篇 |
2002年 | 1128篇 |
2001年 | 819篇 |
2000年 | 719篇 |
1999年 | 497篇 |
1998年 | 405篇 |
1997年 | 393篇 |
1996年 | 475篇 |
1995年 | 400篇 |
1994年 | 379篇 |
1993年 | 404篇 |
1992年 | 385篇 |
1991年 | 322篇 |
1990年 | 270篇 |
1989年 | 255篇 |
1988年 | 215篇 |
1987年 | 216篇 |
1986年 | 215篇 |
1985年 | 292篇 |
1984年 | 252篇 |
1983年 | 210篇 |
1982年 | 220篇 |
1981年 | 208篇 |
1980年 | 200篇 |
1979年 | 171篇 |
1978年 | 187篇 |
1977年 | 151篇 |
1976年 | 145篇 |
1974年 | 141篇 |
1973年 | 128篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
2.
Dr. Yulia Y. Enakieva Dr. Anna A. Sinelshchikova Prof. Mikhail S. Grigoriev Prof. Vladimir V. Chernyshev Dr. Konstantin A. Kovalenko Prof. Irina A. Stenina Prof. Andrey B. Yaroslavtsev Prof. Yulia G. Gorbunova Prof. Aslan Y. Tsivadze 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(45):10552-10556
The design of new solid-state proton-conducting materials is a great challenge for chemistry and materials science. Herein, a new anionic porphyrinylphosphonate-based MOF ( IPCE-1Ni ), which involves dimethylammonium (DMA) cations for charge compensation, is reported. As a result of its unique structure, IPCE-1Ni exhibits one of the highest value of the proton conductivity among reported proton-conducting MOF materials based on porphyrins (1.55×10−3 S cm−1 at 75 °C and 80 % relative humidity). 相似文献
3.
氧化铝晶体是一种优良的光学透明窗口材料,更是地球内部的重要组成物质.利用气炮加载结合冲击光谱测量,不仅能够获得其发光特征,并且根据光谱分布特征得到高压结构相变信息.在自主搭建的冲击光谱动态测试平台上,结合多通道辐射高温计以及ICCD瞬态光谱测试技术在40~120 GPa的压力区间,研究了c切向氧化铝晶体的辐射发光效应.在可见光波段400~700 nm区间获得了氧化铝晶体的发光光谱和辐射温度结果,证实了光谱的结构特征和表观温度值与该压力下氧化铝的结构相变存在明显的关联性. 相似文献
4.
Dr. Antonio M. Rodríguez Dr. Pilar Prieto Prof. Antonio de la Hoz Prof. Ángel Díaz-Ortiz D. Raúl Martín Prof. José I. García 《ChemistryOpen》2015,4(3):308-317
The aim of this work was to determine the parameters that have decisive roles in microwave-assisted reactions and to develop a model, using computational chemistry, to predict a priori the type of reactions that can be improved under microwaves. For this purpose, a computational study was carried out on a variety of reactions, which have been reported to be improved under microwave irradiation. This comprises six types of reactions. The outcomes obtained in this study indicate that the most influential parameters are activation energy, enthalpy, and the polarity of all the species that participate. In addition to this, in most cases, slower reacting systems observe a much greater improvement under microwave irradiation. Furthermore, for these reactions, the presence of a polar component in the reaction (solvent, reagent, susceptor, etc.) is necessary for strong coupling with the electromagnetic radiation. We also quantified that an activation energy of 20–30 kcal mol−1 and a polarity (μ) between 7–20 D of the species involved in the process is required to obtain significant improvements under microwave irradiation. 相似文献
5.
6.
7.
8.
Iodine(III)‐Catalyzed Rearrangements of Imides: A Versatile Route to α,α‐Dialkylated α‐Hydroxy Carboxylamides 下载免费PDF全文
Anna Ulmer Dr. Maciej Stodulski Stefanie V. Kohlhepp Christoph Patzelt Dr. Alexander Pöthig Dr. Wolfgang Bettray Dr. Tanja Gulder 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(4):1444-1448
A tertiary hydroxy group α to a carboxyl moiety comprises a key structural motif in many bioactive substances. With the herein presented metal‐free rearrangement of imides triggered by hypervalent λ3‐iodane, an easy and selective way to gain access to such a compound class, namely α,α‐disubstituted‐α‐hydroxy carboxylamides, was established. Their additional methylene bromide side chain constitutes a useful handle for rapid diversification, as demonstrated by a series of further functionalizations. Moreover, the in situ formation of an iodine(III) species under the reaction conditions was proven. Our findings clearly corroborate that hypervalent λ3‐benziodoxolones are involved in these organocatalytic reactions. 相似文献
9.
Guizellini Filipe Corrêa Franzin Bruno Trevizan da Silva Matheus Antonio Abra Luciana Mazotti Hojo Ossamu Pastre Iêda Aparecida Ribeiro Clóvis Augusto Paiva-Santos Carlos de Oliveira Fertonani Fernando Luis 《Journal of Thermal Analysis and Calorimetry》2021,143(1):47-60
Journal of Thermal Analysis and Calorimetry - The aim of this work is to synthesize and characterize a new structured silver–clay dried, calcined or sintered at different temperatures... 相似文献
10.