全文获取类型
收费全文 | 522篇 |
免费 | 29篇 |
国内免费 | 2篇 |
专业分类
化学 | 370篇 |
晶体学 | 1篇 |
力学 | 17篇 |
数学 | 75篇 |
物理学 | 90篇 |
出版年
2023年 | 8篇 |
2022年 | 10篇 |
2021年 | 24篇 |
2020年 | 19篇 |
2019年 | 17篇 |
2018年 | 15篇 |
2017年 | 7篇 |
2016年 | 30篇 |
2015年 | 22篇 |
2014年 | 16篇 |
2013年 | 27篇 |
2012年 | 37篇 |
2011年 | 35篇 |
2010年 | 23篇 |
2009年 | 22篇 |
2008年 | 38篇 |
2007年 | 38篇 |
2006年 | 27篇 |
2005年 | 33篇 |
2004年 | 19篇 |
2003年 | 21篇 |
2002年 | 14篇 |
2001年 | 3篇 |
2000年 | 4篇 |
1999年 | 3篇 |
1997年 | 2篇 |
1995年 | 4篇 |
1994年 | 1篇 |
1993年 | 4篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 3篇 |
1987年 | 2篇 |
1985年 | 2篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1981年 | 4篇 |
1978年 | 1篇 |
1976年 | 3篇 |
1957年 | 1篇 |
1940年 | 1篇 |
1935年 | 3篇 |
1906年 | 1篇 |
排序方式: 共有553条查询结果,搜索用时 343 毫秒
181.
Lilian Geniller Dr. Marc Taillefer Dr. Florian Jaroschik Dr. Alexis Prieto 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(43):e202201495
The first photo-mediated process enabling the generation of halide radicals by Halogen-Atom Transfer (XAT) is described. Contrary to radical transformations involving XAT reactivity, which exploit stable carbon radicals, this unique approach uses 1,2-dihaloethanes for the generation of unstable carbon radicals by XAT. These transient radicals then undergo β-scission with release of ethylene and formation of more stable halide radicals which have been used in selective hydrohalogenations of a large number of unsaturated hydrocarbons, including Michael acceptors, unactivated alkenes and alkynes. This hydrohalogenation is tolerant of a broad range of functionalities and is believed to proceed through a radical-chain manifold that propagates by the use of silane derivatives. 相似文献
182.
A sensor with potential for the development of a “chemical barcode” for real-time monitoring of fish freshness is described. This on-package sensor contains a pH sensitive dye, bromocresol green, that responds through visible colour change to basic volatile spoilage compounds, such as trimethylamine (TMA), ammonia (NH3) and dimethylamine (DMA) collectively known as Total Volatile Basic Nitrogen (TVB-N). The sensor characteristics were studied as well as its response with standard ammonia gas. Trials on cod and under-utilised species have verified that the sensor response correlates with bacterial growth patterns in fish samples thus enabling the “real-time” monitoring of spoilage in various fish species. The sensor response can be interrogated with a simple, inexpensive reflectance colorimeter that we have developed based on two light emitting diodes (LEDs) and a photodetector. 相似文献
183.
Catalytic Upgrading of Biomass‐Derived Methyl Ketones to Liquid Transportation Fuel Precursors by an Organocatalytic Approach 下载免费PDF全文
Dr. Shylesh Sankaranarayanapillai Dr. Sanil Sreekumar Joseph Gomes Adam Grippo George E. Arab Prof. Martin Head‐Gordon Prof. F. Dean Toste Prof. Alexis T. Bell 《Angewandte Chemie (International ed. in English)》2015,54(15):4673-4677
A highly efficient water‐tolerant, solid‐base catalyst for the self‐condensation of biomass‐derived methyl ketones to jet‐diesel fuel precursors was developed by grafting site‐isolated secondary amines on silica‐alumina supports. It is shown that apart from the nature and density of amine groups and the spatial separation of the acidic and basic sites, the acidity of the support material plays a critical role in defining the catalytic activity. It is also found that a combination of weakly acidic silanol/aluminol with secondary amine groups can mimic proline catalysts and are more effective in catalyzing the selective dimerization reaction than the combination of amines with organic acids. In situ FTIR measurements demonstrate that acidic groups activate methyl ketones through their carbonyl groups leading to a favorable C? C bond formation step involving an enamine intermediate. DFT analysis of the reaction pathway confirms that C? C bond formation is the rate‐limiting step. 相似文献
184.
Déchirures de variétés de dimension trois et la conjecture de Nash de rationalité en dimension trois
Sans résumé
Dédié à Heisuke Hironaka 相似文献
185.
We consider the full system of compressible Navier–Stokes equations for heat conducting fluid. We show that the temperature
is uniformly positive for t ≥ t
0 (for any t
0 > 0) for any solutions with finite initial entropy. The assumptions on the viscosity and conductivity coefficients are minimal
(for instance, the solutions constructed by Feireisl in (Oxford Lecture Series in Mathematics and its Applications, vol 26,
2004) verify all the requirements).
相似文献
186.
Brutchey RL Drake IJ Bell AT Tilley TD 《Chemical communications (Cambridge, England)》2005,(29):3736-3738
A new pseudo-tetrahedral Co(II) complex has been grafted onto the surface of SBA-15 and successfully utilized for the catalytic oxidization of alkylaromatic substrates with tert-butyl hydroperoxide (TBHP)via an H-atom transfer mechanism. 相似文献
187.
In this short note we give a characterization of extremal principally polarized abelian varieties determining an isolated point in Sing
The case g = 5 is treated in depth.Received: 14 June 2004 相似文献
188.
Consider the operator
in
where q is a real function with q′ and
bounded. The spectrum of T is purely discrete and consists of simple eigenvalues. We determine their asymptotics
and we extend these results for complex q.Communicated by Bernard Helffersubmitted 23/04/04, accepted 26/10/04 相似文献
189.
We present the first experimental demonstration of noiseless amplification of images, where noise refers to spatial quantum fluctuations on the pixels of single shot images. Phase-sensitive and phase-insensitive schemes are compared and the noise figures are in good agreement with theory, inasmuch this theory includes the quantum efficiency of the whole system and the pixel size. 相似文献
190.
Solvent effects on the kinetics for hydrogen abstraction from a lactone antioxidant were determined for alkoxyl and nitroxyl radicals; their reactivity differ by about 7 orders of magnitude. A decrease by approximately 12 and approximately 35 were determined for H-abstraction by tert-butoxyl and nitroxyl radicals, respectively, upon changing the solvent from hexane to acetonitrile. Results of solvent and isotope studies indicate that the antioxidant properties of lactone antioxidants should be attributed to the enol, not the lactone. [reaction: see text] 相似文献