全文获取类型
收费全文 | 519篇 |
免费 | 26篇 |
国内免费 | 1篇 |
专业分类
化学 | 407篇 |
晶体学 | 1篇 |
数学 | 43篇 |
物理学 | 95篇 |
出版年
2023年 | 6篇 |
2022年 | 9篇 |
2021年 | 11篇 |
2020年 | 10篇 |
2019年 | 7篇 |
2018年 | 3篇 |
2017年 | 3篇 |
2016年 | 13篇 |
2015年 | 18篇 |
2014年 | 8篇 |
2013年 | 23篇 |
2012年 | 40篇 |
2011年 | 35篇 |
2010年 | 17篇 |
2009年 | 21篇 |
2008年 | 44篇 |
2007年 | 26篇 |
2006年 | 32篇 |
2005年 | 29篇 |
2004年 | 26篇 |
2003年 | 32篇 |
2002年 | 21篇 |
2001年 | 9篇 |
2000年 | 14篇 |
1999年 | 4篇 |
1998年 | 8篇 |
1997年 | 2篇 |
1996年 | 7篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1993年 | 3篇 |
1992年 | 2篇 |
1991年 | 4篇 |
1989年 | 6篇 |
1988年 | 3篇 |
1987年 | 5篇 |
1986年 | 5篇 |
1985年 | 6篇 |
1984年 | 6篇 |
1982年 | 2篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 2篇 |
1970年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有546条查询结果,搜索用时 31 毫秒
81.
A PCP Pincer Ligand for Coordination Polymers with Versatile Chemical Reactivity: Selective Activation of CO2 Gas over CO Gas in the Solid State
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Junpeng He Nolan W. Waggoner Samuel G. Dunning Dr. Alexander Steiner Dr. Vincent M. Lynch Prof. Simon M. Humphrey 《Angewandte Chemie (International ed. in English)》2016,55(40):12351-12355
A tetra(carboxylated) PCP pincer ligand has been synthesized as a building block for porous coordination polymers (PCPs). The air‐ and moisture‐stable PCP metalloligands are rigid tetratopic linkers that are geometrically akin to ligands used in the synthesis of robust metal–organic frameworks (MOFs). Here, the design principle is demonstrated by cyclometalation with PdIICl and subsequent use of the metalloligand to prepare a crystalline 3D MOF by direct reaction with CoII ions and structural resolution by single crystal X‐ray diffraction. The Pd?Cl groups inside the pores are accessible to post‐synthetic modifications that facilitate chemical reactions previously unobserved in MOFs: a Pd?CH3 activated material undergoes rapid insertion of CO2 gas to give Pd?OC(O)CH3 at 1 atm and 298 K. However, since the material is highly selective for the adsorption of CO2 over CO, a Pd?N3 modified version resists CO insertion under the same conditions. 相似文献
82.
Kieran?Griffiths Albert?EscuerView authors OrcID profile George?E.?KostakisEmail author 《Structural chemistry》2016,27(6):1703-1714
This article presents the syntheses, crystal structures, topological features and magnetic properties of two NiII/NaI coordination clusters formulated [Ni 3 II Na(L1)3(HL1)(MeOH)2] (1) and [Ni 6 II Na(L1)5(CO3)(MeO)(MeOH)3(H2O)3]·4(MeOH) 2(H2O) [2 4(MeOH) 2(H2O)] where H2L1 is the semi-rigid Schiff base ligand (E)-2-(2-hydroxy-3-methoxybenzylideneamino)-phenol). Compound 1 possesses a rare Ni 3 II NaI cubane (3M4-1) topology, and compound 2 is the first example in polynuclear Ni/Na chemistry that exhibits a 2,3,4M7-1 topology. 相似文献
83.
Clavier H Grela K Kirschning A Mauduit M Nolan SP 《Angewandte Chemie (International ed. in English)》2007,46(36):6786-6801
Ruthenium-catalyzed olefin metathesis reactions represent an attractive and powerful transformation for the formation of new carbon-carbon double bonds. This area is now quite familiar to most chemists as numerous catalysts are available that enable a plethora of olefin metathesis reactions. Nevertheless, with the exception of uses in polymerization reactions, only a limited number of industrial processes use olefin metathesis. This is mainly due to difficulties associated with removing ruthenium from the final products. In this context, a number of studies have been carried out to develop procedures for the removal of the catalyst or the products of catalyst decomposition, however, none are universally attractive so far. This situation has resulted in tremendous activity in the area dealing with supported or tagged versions of homogeneous catalysts. This Review summarizes the numerous studies focused on developing cleaner ruthenium-catalyzed metathesis processes. 相似文献
84.
Marion N Díez-González S Nolan SP 《Angewandte Chemie (International ed. in English)》2007,46(17):2988-3000
Organocatalyzed reactions represent an attractive alternative to metal-catalyzed processes notably because of their lower cost and benign environmental impact in comparison to organometallic catalysis. In this context, N-heterocyclic carbenes (NHCs) have been studied for their ability to promote primarily the benzoin condensation. Lately, dramatic progress in understanding their intrinsic properties and in their synthesis have made them available to organic chemists. This has resulted in a tremendous increase of their scope and in a true explosion of the number of papers reporting NHC-catalyzed reactions. Here, we highlight the ever-increasing number of reactions that can be promoted by N-heterocyclic carbenes. 相似文献
85.
Neidig ML Brown CD Light KM Fujimori DG Nolan EM Price JC Barr EW Bollinger JM Krebs C Walsh CT Solomon EI 《Journal of the American Chemical Society》2007,129(46):14224-14231
The alpha-ketoglutarate (alpha-KG)-dependent oxygenases are a large and diverse class of mononuclear non-heme iron enzymes that require FeII, alpha-KG, and dioxygen for catalysis with the alpha-KG cosubstrate supplying the additional reducing equivalents for oxygen activation. While these systems exhibit a diverse array of reactivities (i.e., hydroxylation, desaturation, ring closure, etc.), they all share a common structural motif at the FeII active site, termed the 2-His-1-carboxylate facial triad. Recently, a new subclass of alpha-KG-dependent oxygenases has been identified that exhibits novel reactivity, the oxidative halogenation of unactivated carbon centers. These enzymes are also structurally unique in that they do not contain the standard facial triad, as a Cl- ligand is coordinated in place of the carboxylate. An FeII methodology involving CD, MCD, and VTVH MCD spectroscopies was applied to CytC3 to elucidate the active-site structural effects of this perturbation of the coordination sphere. A significant decrease in the affinity of FeII for apo-CytC3 was observed, supporting the necessity of the facial triad for iron coordination to form the resting site. In addition, interesting differences observed in the FeII/alpha-KG complex relative to the cognate complex in other alpha-KG-dependent oxygenases indicate the presence of a distorted 6C site with a weak water ligand. Combined with parallel studies of taurine dioxygenase and past studies of clavaminate synthase, these results define a role of the carboxylate ligand of the facial triad in stabilizing water coordination via a H-bonding interaction between the noncoordinating oxygen of the carboxylate and the coordinated water. These studies provide initial insight into the active-site features that favor chlorination by CytC3 over the hydroxylation reactions occurring in related enzymes. 相似文献
86.
Marion N Carlqvist P Gealageas R de Frémont P Maseras F Nolan SP 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(22):6437-6451
The [(NHC)AuI]-catalyzed (NHC=N-heterocyclic carbene) formation of alpha,beta-unsaturated carbonyl compounds (enones and enals) from propargylic acetates is described. The reactions occur at 60 degrees C in 8 h in the presence of an equimolar mixture of [(NHC)AuCl] and AgSbF6 and produce conjugated enones and enals in high yields. Optimization studies revealed that the reaction is sensitive to the solvent, the NHC, and, to a lesser extent, to the silver salt employed, leading to the use of [(ItBu)AuCl]/AgSbF6 in THF as an efficient catalytic system. This transformation proved to have a broad scope, enabling the stereoselective formation of (E)-enones and -enals with great structural diversity. The effect of substitution at the propargylic and acetylenic positions has been investigated, as well as the effect of aryl substitution on the formation of cinnamyl ketones. The presence or absence of water in the reaction mixture was found to be crucial. From the same phenylpropargyl acetates, anhydrous conditions led to the formation of indene compounds via a tandem [3,3] sigmatropic rearrangement/intramolecular hydroarylation process, whereas simply adding water to the reaction mixture produced enone derivatives cleanly. Several mechanistic hypotheses, including the hydrolysis of an allenol ester intermediate and SN2' addition of water, were examined to gain an insight into this transformation. Mechanistic investigations and computational studies support [(NHC)AuOH], produced in situ from [(NHC)AuSbF6] and H2O, instead of cationic [(NHC)AuSbF6] as the catalytically active species. Based on DFT calculations performed at the B3LYP level of theory, a full catalytic cycle featuring an unprecedented transfer of the OH moiety bound to the gold center to the C[triple chemical bond]C bond leading to the formation of a gold-allenolate is proposed. 相似文献
87.
(NHC)-Cu (NHC = N-heterocyclic carbene) complexes efficiently catalyzed the methylenation of a variety of aliphatic and aromatic aldehydes and ketones in the presence of trimethylsilyldiazomethane, triphenylphosphine, and 2-propanol. The copper catalysts are not only inexpensive compared to rhodium complexes, but they also exhibit better functional group compatibility with aromatic aldehydes and ketones. Indeed very high yields were obtained for the formation of styrenes containing nitro, trifluoromethyl, amino, and ester groups, as well as for pyridine-, pyrrole-, and indole-substituted alkenes. 相似文献
88.
89.
90.
Kieran F. Scott Timothy J. Mann Shadma Fatima Mila Sajinovic Anshuli Razdan Ryung Rae Kim Adam Cooper Aflah Roohullah Katherine J. Bryant Kasuni K. Gamage David G. Harman Fatemeh Vafaee Garry G. Graham W. Bret Church Pamela J. Russell Qihan Dong Paul de Souza 《Molecules (Basel, Switzerland)》2021,26(23)
Phospholipase A2 (PLA2) enzymes were first recognized as an enzyme activity class in 1961. The secreted (sPLA2) enzymes were the first of the five major classes of human PLA2s to be identified and now number nine catalytically-active structurally homologous proteins. The best-studied of these, group IIA sPLA2, has a clear role in the physiological response to infection and minor injury and acts as an amplifier of pathological inflammation. The enzyme has been a target for anti-inflammatory drug development in multiple disorders where chronic inflammation is a driver of pathology since its cloning in 1989. Despite intensive effort, no clinically approved medicines targeting the enzyme activity have yet been developed. This review catalogues the major discoveries in the human group IIA sPLA2 field, focusing on features of enzyme function that may explain this lack of success and discusses future research that may assist in realizing the potential benefit of targeting this enzyme. Functionally-selective inhibitors together with isoform-selective inhibitors are necessary to limit the apparent toxicity of previous drugs. There is also a need to define the relevance of the catalytic function of hGIIA to human inflammatory pathology relative to its recently-discovered catalysis-independent function. 相似文献