全文获取类型
收费全文 | 493篇 |
免费 | 19篇 |
国内免费 | 1篇 |
专业分类
化学 | 422篇 |
晶体学 | 5篇 |
力学 | 7篇 |
数学 | 44篇 |
物理学 | 35篇 |
出版年
2023年 | 2篇 |
2022年 | 6篇 |
2021年 | 9篇 |
2020年 | 11篇 |
2019年 | 8篇 |
2018年 | 6篇 |
2017年 | 5篇 |
2016年 | 13篇 |
2015年 | 18篇 |
2014年 | 18篇 |
2013年 | 24篇 |
2012年 | 35篇 |
2011年 | 35篇 |
2010年 | 23篇 |
2009年 | 32篇 |
2008年 | 33篇 |
2007年 | 28篇 |
2006年 | 39篇 |
2005年 | 35篇 |
2004年 | 25篇 |
2003年 | 30篇 |
2002年 | 17篇 |
2001年 | 4篇 |
2000年 | 10篇 |
1999年 | 7篇 |
1998年 | 7篇 |
1997年 | 3篇 |
1996年 | 4篇 |
1995年 | 4篇 |
1994年 | 4篇 |
1993年 | 4篇 |
1992年 | 2篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1978年 | 2篇 |
1965年 | 1篇 |
1964年 | 1篇 |
排序方式: 共有513条查询结果,搜索用时 31 毫秒
91.
Dr. Emilio Brunetti Dr. Lionel Marcelis Dr. Fedor E. Zhurkin Prof. Michel Luhmer Prof. Ivan Jabin Prof. Olivia Reinaud Prof. Kristin Bartik 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(55):13730-13738
In this study, the ligand exchange mechanism at a biomimetic ZnII centre, embedded in a pocket mimicking the possible constrains induced by a proteic structure, is explored. The residence time of different guest ligands (dimethylformamide, acetonitrile and ethanol) inside the cavity of a calix[6]arene-based tris(imidazole) tetrahedral zinc complex was probed using 1D EXchange SpectroscopY NMR experiments. A strong dependence of residence time on water content was observed with no exchange occurring under anhydrous conditions, even in the presence of a large excess of guest ligand. These results advocate for an associative exchange mechanism involving the transient exo-coordination of a water molecule, giving rise to 5-coordinate ZnII intermediates, and inversion of the pyramid at the ZnII centre. Theoretical modelling by DFT confirmed that the associative mechanism is at stake. These results are particularly relevant in the context of the understanding of kinetic stability/lability in Zn proteins and highlight the key role that a single water molecule can play in catalysing ligand exchange and controlling the lability of ZnII in proteins. 相似文献
92.
Banita D. White Dennis M. Dishong Carlo Minganti Kristin A. Arnold D.M. Goli George W. Gokel 《Tetrahedron letters》1985,26(2):151-154
The efficient synthesis of several 12-membered ring, N-pivot lariat ethers are reported and it is shown that binding to sodium cations is generally weak except when an oligoethyleneoxy sidearm is long enough to provide additional solvation. 相似文献
93.
The design and synthesis of a new cross-linkable amphiphile is reported. Solutions of the amphiphile in a toluene/water mixture form reverse micelles as indicated by dynamic light scattering and NMR spectroscopy. As indicated by dynamic light scattering, TEM, and NMR spectroscopy data, these reverse micelles can be cross-linked without drastically changing the radius of the reverse micelles. Mixed reverse micelles are also characterized and cross-linked. The cross-linked reverse micelles are demonstrated to facilitate phase transfer and can be used to site isolate a catalyst. 相似文献
94.
95.
Wang W Rusin O Xu X Kim KK Escobedo JO Fakayode SO Fletcher KA Lowry M Schowalter CM Lawrence CM Fronczek FR Warner IM Strongin RM 《Journal of the American Chemical Society》2005,127(45):15949-15958
At elevated levels, homocysteine (Hcy, 1) is a risk factor for cardiovascular diseases, Alzheimer's disease, neural tube defects, and osteoporosis. Both 1 and cysteine (Cys, 3) are linked to neurotoxicity. The biochemical mechanisms by which 1 and 3 are involved in disease states are relatively unclear. Herein, we describe simple methods for detecting either Hcy or Cys in the visible spectral region with the highest selectivity reported to date without using biochemical techniques or preparative separations. Simple methods and readily available reagents allow for the detection of Cys and Hcy in the range of their physiologically relevant levels. New HPLC postcolumn detection methods for biological thiols are reported. The potential biomedical relevance of the chemical mechanisms involved in the detection of 1 is described. 相似文献
96.
Kang SO Llinares JM Powell D VanderVelde D Bowman-James K 《Journal of the American Chemical Society》2003,125(34):10152-10153
An anion receptor derived from a tren-based amide cryptand with pyridine spacers has been synthesized and characterized. Two crystal structures are reported: the hydrochloride salt and the fluoride complex. The cryptand shows extremely high binding with fluoride ion in DMSO-d6. Both the crystal structure and solution 19F NMR data indicate an encapsulated fluoride ion with very high symmetry. 相似文献
97.
Broadwater SJ Roth SL Price KE Kobaslija M McQuade DT 《Organic & biomolecular chemistry》2005,3(16):2899-2906
Creating one-pot synthetic routes is a challenge that is already spawning new chemistry, enzymes, materials, and mechanistic insight. Through one-pot reactions, the chemical products that add value to our lives can be produced with less waste and greater economic benefits. Within this Emerging Area, we describe models for designing one-pot reactions as well as advanced catalysts created to facilitate their realization. 相似文献
98.
Hofstadler SA Drader JJ Gaus H Hannis JC Sannes-Lowery KA 《Journal of the American Society for Mass Spectrometry》2003,14(12):1413-1423
In this work we present variations on in-hexapole infrared multiphoton dissociation (IRMPD) for the characterization of modified oligonucleotides using an ESI-FTICR spectrometer. We demonstrate that IRMPD in the external ion reservoir provides a comprehensive series of fragments allowing thorough characterization of a wide range of oligonucleotides containing alternative backbones and 2′ substitutions. An alternative pulse sequence is presented that allows alternating MS and IRMPD MS/MS spectra to be acquired on a chromatographic timescale without loss in ionization duty cycle. Ions are excited to a larger cyclotron radius such that they “dodge” the IR laser beam that travels through the center of the trapped ion cell and impinges on the external ion reservoir creating IRMPD fragments that will be detected in the next scan. An alternative approach for directing IR radiation into the external ion reservoir using a hollow fiber waveguide as a photon conduit is presented. This approach offers a simple and robust alternative to the previously utilized on-axis scheme and may allow effective implementation with lower power lasers owing to the inherent increase in power density achieved by focusing the nascent laser beam into the hollow fiber waveguide. 相似文献
99.
Ammonium based anion receptors 总被引:2,自引:0,他引:2
Jos M. Llinares Douglas Powell Kristin Bowman-James 《Coordination chemistry reviews》2003,240(1-2):57-2003
Selective anion recognition has been a tremendous challenge to chemists over the decades. However, with the advent of the concepts inherent in ‘supramolecular chemistry,’ the field now flourishes. Of the major types of receptors, polyamines have been studied widely as anion hosts by a number of researchers. Both electrostatic interactions and hydrogen bonds between protonated amines and the anion guests govern the binding in these systems. Exceptions to this rule are found in the quaternary ammonium systems, which utilize primarily electrostatic interactions and topological complementarity for binding purposes. This review focuses only on amine-based hosts, and is divided into acyclic and macrocyclic categories, the latter of which are based on cyclic dimension. The resulting four categories are: acyclic, monocyclic, bicyclic, and polycyclic. Within the major categories, binding is discussed according to the nature of the anion target, i.e. ‘simple’ inorganic anions, organic anions, and anionic metal complexes. 相似文献