全文获取类型
收费全文 | 5484篇 |
免费 | 310篇 |
国内免费 | 57篇 |
专业分类
化学 | 4111篇 |
晶体学 | 22篇 |
力学 | 99篇 |
综合类 | 1篇 |
数学 | 918篇 |
物理学 | 700篇 |
出版年
2023年 | 49篇 |
2022年 | 90篇 |
2021年 | 105篇 |
2020年 | 148篇 |
2019年 | 123篇 |
2018年 | 104篇 |
2017年 | 85篇 |
2016年 | 183篇 |
2015年 | 155篇 |
2014年 | 200篇 |
2013年 | 276篇 |
2012年 | 448篇 |
2011年 | 475篇 |
2010年 | 230篇 |
2009年 | 170篇 |
2008年 | 399篇 |
2007年 | 373篇 |
2006年 | 375篇 |
2005年 | 339篇 |
2004年 | 311篇 |
2003年 | 233篇 |
2002年 | 206篇 |
2001年 | 81篇 |
2000年 | 39篇 |
1999年 | 39篇 |
1998年 | 38篇 |
1997年 | 46篇 |
1996年 | 45篇 |
1995年 | 33篇 |
1994年 | 35篇 |
1993年 | 32篇 |
1992年 | 31篇 |
1991年 | 34篇 |
1990年 | 21篇 |
1989年 | 16篇 |
1988年 | 19篇 |
1987年 | 23篇 |
1986年 | 24篇 |
1985年 | 25篇 |
1984年 | 15篇 |
1983年 | 19篇 |
1982年 | 15篇 |
1981年 | 19篇 |
1980年 | 19篇 |
1979年 | 17篇 |
1978年 | 14篇 |
1976年 | 11篇 |
1975年 | 11篇 |
1974年 | 11篇 |
1973年 | 8篇 |
排序方式: 共有5851条查询结果,搜索用时 15 毫秒
181.
182.
183.
Marc A. Little Jonathan J. Loughrey Amedeo Santoro Malcolm A. Halcrow Michaele J. Hardie 《Tetrahedron letters》2014
The synthesis of four 3,4-di(alkylsulfanyl)benzyl alcohol derivatives is described, in five steps from methyl 3,4-di(hydroxy)benzoate via a Newman–Kwart rearrangement. Incubation of these derivatives in formic acid affords 2,3,7,8,12,13-hexakis(alkylsulfanyl)-10,15-dihydro-5H-tribenzo[a,d,g]cyclononene products, which are hexa-sulfanyl analogues of the well-known supramolecular cavitand host, cyclotriveratrylene (CTV). The yield of this cyclization depends strongly on the alkylsulfanyl substituents present, in the order SMe > SEt ≈ SiPr ? SBn. A crystal structure determination of one of the cyclotrimers shows a mode of self-association that is commonly exhibited by CTV itself. 相似文献
184.
185.
186.
Dr. Carmine D'Agostino Dr. Tatyana Kotionova Dr. Jonathan Mitchell Dr. Peter J. Miedziak Prof. David W. Knight Dr. Stuart H. Taylor Prof. Graham J. Hutchings Prof. Lynn F. Gladden Dr. Mick D. Mantle 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(35):11725-11732
In recent work, it was reported that changes in solvent composition, precisely the addition of water, significantly inhibits the catalytic activity of Au/TiO2 catalyst in the aerobic oxidation of 1,4‐butanediol in methanol due to changes in diffusion and adsorption properties of the reactant. In order to understand whether the inhibition mechanism of water on diol oxidation in methanol is generally valid, the solvent effect on the aerobic catalytic oxidation of 1,3‐propanediol and its two methyl‐substituted homologues, 2‐methyl‐1,3‐propanediol and 2,2‐dimethyl‐1,3‐propanediol, over a Au/TiO2 catalyst has been studied here using conventional catalytic reaction monitoring in combination with pulsed‐field gradient nuclear magnetic resonance (PFG‐NMR) diffusion and NMR relaxation time measurements. Diol conversion is significantly lower when water is present in the initial diol/methanol mixture. A reactivity trend within the group of diols was also observed. Combined NMR diffusion and relaxation time measurements suggest that molecular diffusion and, in particular, the relative strength of diol adsorption, are important factors in determining the conversion. These results highlight NMR diffusion and relaxation techniques as novel, non‐invasive characterisation tools for catalytic materials, which complement conventional reaction data. 相似文献
187.
Bharat Kumar Ruth L. Viboh Margel C. Bonifacio William B. Thompson Jonathan C. Buttrick Babe C. Westlake Min‐Soo Kim Robert W. Zoellner Sergey A. Varganov Philipp Mrschel Jaroslav Teteruk Martin U. Schmidt Benjamin T. King 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2012,124(51):13071-13071
188.
Xin Chen Aleksandra M. Krajewska Dr. Cormac McGuinness Amy Lynes David McAteer Nina Berner Prof. Georg Duesberg Prof. Jonathan N. Coleman Prof. Aidan R. McDonald 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(3):984-992
Covalently tethering photosensitizers to catalytically active 1T-MoS2 surfaces holds great promise for the solar-driven hydrogen evolution reaction (HER). Herein, we report the preparation of two new RuII-complex-functionalized MoS2 hybrids [RuII(bpy)2(phen)]-MoS2 and [RuII(bpy)2(py)Cl]-MoS2. The influence of covalent functionalization of chemically exfoliated 1T-MoS2 with coordinating ligands and RuII complexes on the HER activity and photo-electrochemical performance of this dye-sensitized system was studied systematically. We find that the photo-electrochemical performance of this RuII-complex-sensitized MoS2 system is highly dependent on the surface extent of photosensitizers and the catalytic activity of functionalized MoS2. The latter was strongly affected by the number and the kind of functional groups. Our results underline the tunability of the photovoltage generation in this dye-sensitized MoS2 system by manipulation of the surface functionalities, which provides a practical guidance for smart design of future dye-sensitized MoS2 hydrogen production devices towards improved the photofuel conversion efficiency. 相似文献
189.
Christian A. Malapit Donald R. Caldwell Irungu K. Luvaga Dr. Jonathan T. Reeves Dr. Ivan Volchkov Dr. Nina C. Gonnella Dr. Zhengxu S. Han Dr. Carl A. Busacca Prof. Dr. Amy R. Howell Dr. Chris H. Senanayake 《Angewandte Chemie (International ed. in English)》2017,56(24):6999-7002
β-Ketonitriles bearing a quaternary carbon at the 2-position were prepared through Rh-catalyzed addition of aryl boronic acids to 2,2-disubstituted malononitriles. In contrast to the previously described transnitrilative cyanation of aryl boronic acids with dialkylmalononitriles, the present reaction avoids retro-Thorpe collapse of the intermediate addition product through the use of a milder base. The reaction was amenable to a variety of aryl boronic acids and disubstituted malononitriles, providing a diverse array of β-ketonitriles. The products could be further derivatized to valuable chiral α,α-disubstituted-β-aminonitriles through addition reactions to the corresponding N-tert-butanesulfinyl imines. 相似文献
190.
Gerald A. Miller Anthony W. Thomas Jonathan D. Carroll Johann Rafelski 《Few-Body Systems》2012,52(3-4):357-366
The existence and importance of the proton radius puzzle, observed via a Lamb shift measurement in muonic atoms, is discussed. Possible resolutions of the puzzle are discussed. Then the broader question of the meaning of the proton radius is addressed and examples of correctly defined charge densities are presented. 相似文献