全文获取类型
收费全文 | 230篇 |
免费 | 10篇 |
专业分类
化学 | 221篇 |
力学 | 1篇 |
数学 | 10篇 |
物理学 | 8篇 |
出版年
2023年 | 2篇 |
2022年 | 2篇 |
2021年 | 5篇 |
2020年 | 3篇 |
2019年 | 6篇 |
2016年 | 4篇 |
2015年 | 8篇 |
2014年 | 2篇 |
2013年 | 6篇 |
2012年 | 9篇 |
2011年 | 11篇 |
2010年 | 14篇 |
2009年 | 6篇 |
2008年 | 13篇 |
2007年 | 6篇 |
2006年 | 3篇 |
2005年 | 7篇 |
2004年 | 6篇 |
2003年 | 6篇 |
2002年 | 4篇 |
2001年 | 3篇 |
2000年 | 2篇 |
1999年 | 2篇 |
1981年 | 1篇 |
1943年 | 4篇 |
1942年 | 2篇 |
1941年 | 4篇 |
1940年 | 2篇 |
1939年 | 6篇 |
1938年 | 5篇 |
1936年 | 2篇 |
1935年 | 7篇 |
1934年 | 7篇 |
1933年 | 2篇 |
1932年 | 4篇 |
1931年 | 6篇 |
1930年 | 4篇 |
1929年 | 9篇 |
1928年 | 1篇 |
1927年 | 6篇 |
1926年 | 3篇 |
1925年 | 2篇 |
1924年 | 7篇 |
1923年 | 4篇 |
1922年 | 9篇 |
1918年 | 1篇 |
1917年 | 1篇 |
1916年 | 3篇 |
1915年 | 1篇 |
1866年 | 1篇 |
排序方式: 共有240条查询结果,搜索用时 527 毫秒
231.
Dr. Jeanne‐Marie Begouin Prof. Dr. Meike Niggemann 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(25):8030-8041
Recently, Lewis acidic calcium salts bearing weakly coordinating anions such as Ca(NTf2)2, Ca(OTf)2, CaF2 and Ca[OCH(CF3)2]2 have been discovered as catalysts for the transformation of alcohols, olefins and carbonyl compounds. High stability towards air and moisture, selectivity and high reactivity under mild reaction conditions render these catalysts a sustainable and mild alternative to transition metals, rare‐earth metals or strong Brønsted acids. 相似文献
232.
Niggemann M Jelonek A Biber N Wuchrer M Plietker B 《The Journal of organic chemistry》2008,73(18):7028-7036
Carbohydrates are an omnipresent class of highly oxygenated natural products. Due to their wide spectra of biological activities, they have been in the center of synthetic organic chemistry for more than 130 years. During the past 50 years non-natural carbohydrates attracted the interest of various chemists in the fields of organic, biological, and medical chemistry. Especially desoxygenated sugars proved to be an important class of compounds. Up to date, most non-natural analogues are synthesized starting from natural, enantiomerically pure carbohydrates in multistep synthesis. In this report, we present a synthetic strategy that allows the selective modular synthesis of natural and non-natural carbohydrates within five synthetic steps starting from readily available starting materials. Due to a sequential introduction of O- or N-functionalities, a regioselective protection of each new functional group is possible. The key step in the carbohydrate synthesis is a RuO4-catalyzed oxidative cyclization via a pH-dependent dehydrogenation-dihydroxylation-cyclization or an oxidative fragmentation-cyclization, leading to highly substituted new carbohydrates, in which each functional group is orthogonally protected and accessible for further synthetic operations. 相似文献
233.
Wolfgang Petz Prof. Dr. Meike Fahlbusch Enrico Gromm Bernhard Neumüller Prof. Dr. 《无机化学与普通化学杂志》2008,634(4):682-687
The betain‐like SOC2(PPh3)2 ( 1a ) reacts with [Mn2(CO)10] in THF to produce the salt‐like complex [(CO)4Mn(SOC2{PPh3}2)2][Mn(CO)5] ( 2 ). 1a is bonded via the sulfur atoms which are arranged in trans position in the octahedral environment of the manganese atom. With InCl3 from CH2Cl2 solution the addition product [Cl3In(SOC2{PPh3}2)] ( 3 ) is obtained along with the salt (H2C{PPh3}2)[InCl4]2 ( 4 ), which is the result of proton abstraction from the solvent. The crystal structures of 2· 0.5THF and 4· CH2Cl2 are reported. The compounds are further characterized by IR and 31P NMR spectroscopy. 相似文献
234.
Wintjes N Hornung J Lobo-Checa J Voigt T Samuely T Thilgen C Stöhr M Diederich F Jung TA 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(19):5794-5802
The self-assembly of three porphyrin derivatives was studied in detail on a Cu(111) substrate by means of scanning tunneling microscopy (STM). All derivatives have two 4-cyanophenyl substituents in diagonally opposed meso-positions of the porphyrin core, but differ in the nature of the other two meso-alkoxyphenyl substituents. At coverages below 0.8 monolayers, two derivatives form molecular chains, which evolve into nanoporous networks at higher coverages. The third derivative self-assembles directly into a nanoporous network without showing a one-dimensional phase. The pore-to-pore distances for the three networks depend on the size and shape of the alkoxy substituents. All observed effects are explained by 1) different steric demands of the alkoxy residues, 2) apolar (mainly dispersion) interactions between the alkoxy chains, 3) polar bonding involving both cyanophenyl and alkoxyphenyl substituents, and 4) the entropy/enthalpy balance of the network formation. 相似文献
235.
236.
Behnken HN Fellenberg M Koetzler MP Jirmann R Nagel T Meyer B 《Analytical and bioanalytical chemistry》2012,404(5):1427-1437
Chromatographic overlap is a common problem in the analysis of complex mixtures. As a result, it is not possible to identify the components because each resulting NMR or MS spectrum contains multiple components. We introduce three-dimensional cross correlation (3DCC) that dissects NMR spectra of a mixture into spectra of the individual components without actually separating them. Correlation of peaks from MS and NMR profiles along a common LC time domain yields 3DCC NMR spectra of pure components correlated with a mass and a retention time. The method requires an LC run followed by fractionation and recording of MS and NMR spectra. The method is applicable to mixtures of any classes of molecules. Here, we demonstrate its application to a mixture of complex glycans obtained from a glycoprotein. Fourteen glycans eluting within only 3 min showed heavy overlap in the chromatographic run. 3DCC allowed their direct characterization without separation. Some of these structures from the glycoprotein bovine fibrinogen had not previously been described. The 3DCC procedure has been implemented in standard software. Actually, 3DCC can be used for any combination of separation techniques, like LC or GC, combined with two characterization methods like UV, IR, Raman, NMR or MS. 相似文献
237.
238.
239.
Meike Niggemann 《Nachrichten aus der Chemie》2007,55(10):1053-1054
240.
Kai-Oliver Brenske Dr. Meike Emondts Sven T. Hörnig Sinan Panitz Maria I. Pieper Aron Ligori Alexander Schacht Johanna Henkel Prof. Dr. Jürgen Klankermayer Prof. Dr. Andreas Herrmann 《Angewandte Chemie (International ed. in English)》2023,62(22):e202300531
Enhancing NMR signals of biomacromolecules by hyperpolarization offers exciting opportunities for diagnostic applications. However, their hyperpolarization via parahydrogen remains challenging as specific catalytic interactions are required, which are difficult to tune due to the large size of the biomolecule and its insolubility in organic solvents. Herein, we show the unprecedented hyperpolarization of the cancer-targeting DNA aptamer AS1411. By screening different molecular motifs for an unsaturated label in nucleosides and in DNA oligomers, we were able to identify structural prerequisites for the hyperpolarization of AS1411. Finally, adjusting the polarity of AS1411 by complexing the DNA backbone with amino polyethylene glycol chains allowed the hydrogenation of the label with parahydrogen while the DNA structure remains stable to maintain its biological function. Our results are expected to advance hyperpolarized molecular imaging technology for disease detection in the future. 相似文献