全文获取类型
收费全文 | 204898篇 |
免费 | 3041篇 |
国内免费 | 639篇 |
专业分类
化学 | 106307篇 |
晶体学 | 3188篇 |
力学 | 8113篇 |
综合类 | 8篇 |
数学 | 25635篇 |
物理学 | 65327篇 |
出版年
2021年 | 1490篇 |
2020年 | 1838篇 |
2019年 | 1876篇 |
2018年 | 2453篇 |
2017年 | 2524篇 |
2016年 | 4124篇 |
2015年 | 2619篇 |
2014年 | 3932篇 |
2013年 | 9374篇 |
2012年 | 7331篇 |
2011年 | 8551篇 |
2010年 | 6146篇 |
2009年 | 5929篇 |
2008年 | 8070篇 |
2007年 | 7879篇 |
2006年 | 7461篇 |
2005年 | 6730篇 |
2004年 | 6171篇 |
2003年 | 5458篇 |
2002年 | 5215篇 |
2001年 | 5871篇 |
2000年 | 4408篇 |
1999年 | 3386篇 |
1998年 | 2832篇 |
1997年 | 2727篇 |
1996年 | 2674篇 |
1995年 | 2509篇 |
1994年 | 2529篇 |
1993年 | 2442篇 |
1992年 | 2779篇 |
1991年 | 2564篇 |
1990年 | 2519篇 |
1989年 | 2416篇 |
1988年 | 2390篇 |
1987年 | 2410篇 |
1986年 | 2278篇 |
1985年 | 3063篇 |
1984年 | 3104篇 |
1983年 | 2715篇 |
1982年 | 2855篇 |
1981年 | 2652篇 |
1980年 | 2647篇 |
1979年 | 2775篇 |
1978年 | 2801篇 |
1977年 | 2739篇 |
1976年 | 2746篇 |
1975年 | 2644篇 |
1974年 | 2623篇 |
1973年 | 2742篇 |
1972年 | 1763篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
基于深度学习的方法,在HL-2A装置上开发出了一套边缘局域模(ELM)实时识别算法。算法使用5200次放电数据(约24.19万数据切片)进行学习,得到一个深度为22层的卷积神经网络。为衡量算法的识别能力,识别了HL-2A装置自2009年实现稳定ELMy H模放电以来所有历史数据(约26000次放电数据),共识别出1665次H模放电,其中误识别35次,误报率为2.10%。在实际的1634次H模放电中,漏识别4次,漏识别率为0.24%。该误报率和漏报率可以满足ELM实时识别的精度要求。识别算法在实时控制环境下,对单个时间点的平均计算时间为0.46ms,可以满足实时控制的计算速度要求。 相似文献
82.
Immobilized Catalysts for Iridium‐Catalyzed Allylic Amination: Rate Enhancement by Immobilization
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Chandi C. Malakar Prof. Dr. Günter Helmchen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(19):7127-7134
The first immobilized catalyst for Ir‐catalyzed asymmetric allylic aminations is described. The catalyst is a cationic (π‐allyl)Ir complex bound by cation exchange to an anionic silica gel support. Preparation of the catalyst is facile, and the supported catalyst displayed considerably enhanced activity compared with the parent homogeneous catalyst. Up to 43 consecutive amination runs were possible in recycling experiments. 相似文献
83.
84.
85.
Susana Estopiñá-Durán Liam J. Donnelly Euan B. Mclean Bryony M. Hockin Prof. Alexandra M. Z. Slawin Dr. James E. Taylor 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(15):3950-3956
A combination of pentafluorophenylboronic acid and oxalic acid catalyses the dehydrative substitution of benzylic alcohols with a second alcohol to form new C−O bonds. This method has been applied to the intermolecular substitution of benzylic alcohols to form symmetrical ethers, intramolecular cyclisations of diols to form aryl-substituted tetrahydrofuran and tetrahydropyran derivatives, and intermolecular crossed-etherification reactions between two different alcohols. Mechanistic control experiments have identified a potential catalytic intermediate formed between the aryl boronic acid and oxalic acid. 相似文献
86.
Plasma Chemistry and Plasma Processing - The hydrocarbons present in diesel exhaust, although treated as minor pollutants, are equivalent to some of the major pollutants in terms of toxicity,... 相似文献
87.
88.
89.
Markus Bödenler Ludovic de Rochefort P. James Ross Nicolas Chanet Geneviève Guillot Gareth R. Davies 《Molecular physics》2019,117(7-8):832-848
ABSTRACTFast field-cycling (FFC) nuclear magnetic resonance relaxometry is a well-established method to determine the relaxation rates as a function of magnetic field strength. This so-called nuclear magnetic relaxation dispersion gives insight into the underlying molecular dynamics of a wide range of complex systems and has gained interest especially in the characterisation of biological tissues and diseases. The combination of FFC techniques with magnetic resonance imaging (MRI) offers a high potential for new types of image contrast more specific to pathological molecular dynamics. This article reviews the progress in FFC-MRI over the last decade and gives an overview of the hardware systems currently in operation. We discuss limitations and error correction strategies specific to FFC-MRI such as field stability and homogeneity, signal-to-noise ratio, eddy currents and acquisition time. We also report potential applications with impact in biology and medicine. Finally, we discuss the challenges and future applications in transferring the underlying molecular dynamics into novel types of image contrast by exploiting the dispersive properties of biological tissue or MRI contrast agents. 相似文献
90.
Dr. Felipe L. Coelho Eduarda S. Gil Dr. Paulo F. B. Gonçalves Dr. Leandra F. Campo Dr. Paulo H. Schneider 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(34):8157-8162
In this work, a series of 2-chalcogenylindoles was synthesized by an efficient methodology, starting from chalcogenoalkynes, including a previously unreported tellurium indole derivative. For the first time, these 2-substituted chalcogenylindoles were obtained in the absence of metal catalyst or base, under thermal conditions only. In addition, the results described herein represent a methodology with inverse regioselectivity for the chalcogen functionalization of indoles. 相似文献