全文获取类型
收费全文 | 171251篇 |
免费 | 1804篇 |
国内免费 | 508篇 |
专业分类
化学 | 88337篇 |
晶体学 | 3040篇 |
力学 | 7171篇 |
综合类 | 3篇 |
数学 | 19522篇 |
物理学 | 55490篇 |
出版年
2020年 | 1401篇 |
2019年 | 1552篇 |
2018年 | 1981篇 |
2017年 | 2066篇 |
2016年 | 3185篇 |
2015年 | 1894篇 |
2014年 | 3116篇 |
2013年 | 7663篇 |
2012年 | 5753篇 |
2011年 | 6891篇 |
2010年 | 5027篇 |
2009年 | 5005篇 |
2008年 | 6538篇 |
2007年 | 6433篇 |
2006年 | 6080篇 |
2005年 | 5508篇 |
2004年 | 5105篇 |
2003年 | 4595篇 |
2002年 | 4456篇 |
2001年 | 5220篇 |
2000年 | 3869篇 |
1999年 | 2970篇 |
1998年 | 2481篇 |
1997年 | 2389篇 |
1996年 | 2242篇 |
1995年 | 2116篇 |
1994年 | 2095篇 |
1993年 | 2004篇 |
1992年 | 2305篇 |
1991年 | 2249篇 |
1990年 | 2196篇 |
1989年 | 2122篇 |
1988年 | 2119篇 |
1987年 | 2124篇 |
1986年 | 2021篇 |
1985年 | 2635篇 |
1984年 | 2687篇 |
1983年 | 2386篇 |
1982年 | 2497篇 |
1981年 | 2310篇 |
1980年 | 2288篇 |
1979年 | 2436篇 |
1978年 | 2464篇 |
1977年 | 2390篇 |
1976年 | 2439篇 |
1975年 | 2362篇 |
1974年 | 2328篇 |
1973年 | 2505篇 |
1972年 | 1623篇 |
1971年 | 1337篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
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
62.
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
63.
64.
65.
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
66.
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
67.
Probing the Catalytic Activity of Reduced Graphene Oxide Decorated with Au Nanoparticles Triggered by Visible Light
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. Jiale Wang Dr. Fabiane J. Trindade Caroline B. de Aquino Joana C. Pieretti Prof. Dr. Sergio H. Domingues Prof. Dr. Romulo A. Ando Prof. Dr. Pedro H. C. Camargo 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(27):9889-9894
Hybrid materials in which reduced graphene oxide (rGO) is decorated with Au nanoparticles (rGO–Au NPs) were obtained by the in situ reduction of GO and AuCl4?(aq) by ascorbic acid. On laser excitation, rGO could be oxidized as a result of the surface plasmon resonance (SPR) excitation in the Au NPs, which generates activated O2 through the transfer of SPR‐excited hot electrons to O2 molecules adsorbed from air. The SPR‐mediated catalytic oxidation of p‐aminothiophenol (PATP) to p,p′‐dimercaptoazobenzene (DMAB) was then employed as a model reaction to probe the effect of rGO as a support for Au NPs on their SPR‐mediated catalytic activities. The increased conversion of PATP to DMAB relative to individual Au NPs indicated that charge‐transfer processes from rGO to Au took place and contributed to improved SPR‐mediated activity. Since the transfer of electrons from Au to adsorbed O2 molecules is the crucial step for PATP oxidation, in addition to the SPR‐excited hot electrons of Au NPs, the transfer of electrons from rGO to Au contributed to increasing the electron density of Au above the Fermi level and thus the Au‐to‐O2 charge‐transfer process. 相似文献
68.
Dr. Man-Bo Li Daniels Posevins Dr. Karl P. J. Gustafson Dr. Cheuk-Wai Tai Dr. Andrey Shchukarev Dr. Youai Qiu Dr. Jan-E. Bäckvall 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(1):210-215
A highly selective and efficient oxidative carbocyclization/borylation of enallenols catalyzed by palladium immobilized on amino-functionalized siliceous mesocellular foam (Pd-AmP-MCF) was developed for diastereoselective cyclobutenol synthesis. The heterogeneous palladium catalyst can be recovered and recycled without any observed loss of activity or selectivity. The high diastereoselectivity of the reaction is proposed to originate from a directing effect of the enallenol hydroxyl group. Optically pure cyclobutenol synthesis was achieved by the heterogeneous strategy by using chiral enallenol obtained from kinetic resolution. 相似文献
69.
Journal of Structural Chemistry - An analysis is presented for the results obtained in the studies initiated by A. E. Shvelashivili, Corresponding Member, Academy of Sciences of Georgia, and... 相似文献
70.
Radiophysics and Quantum Electronics - We consider whether it is possible in principle to retrieve the key parameters of the mixed layer in the upper ocean (its thickness, bulk eddy viscosity and... 相似文献