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排序方式: 共有451条查询结果,搜索用时 15 毫秒
441.
Elena Michel Fabian F. Grieser Alexandra V. Mackenroth Michael Schukin Petra Krämer Shaista Tahir Dr. Frank Rominger Dr. Matthias Rudolph Prof. Dr. A. Stephen K. Hashmi 《Angewandte Chemie (International ed. in English)》2023,62(42):e202309274
The chemistry of alkynyl triazenes is an emerging field for organic chemists and especially acid-induced nucleophilic functionalizations, either directly, or after a prior reaction towards aromatic triazenes under extrusion of nitrogen, paved the way for fruitful strategies. In contrast, the chemical behavior of alkynyl triazenes upon irradiation with light is still unknown. Herein we present the first photoactivation of alkynyl triazenes that triggers an uncommon reactivity pattern involving the cleavage of the N1−N2 bond of the triazene moiety resulting in a unique approach to cyanocarbenes from a readily available, stable, and insensitive precursor. This allows to access various nitrile compounds without the use of a toxic cyanating agent by exploiting the reactivity pattern of carbenes. By variation of the reaction conditions and light sources, different substitution patterns can be obtained selectively in good yields under mild and metal-free conditions, thus introducing the alkynyl triazene unit as a photo accessible methylene nitrile synthon. Using this synthon, subclasses like α-alkoxynitriles, α-aminonitriles and α-cyanohydrazones become easily available. These exhibit synthetically valuable substitution patterns for the synthesis of pharmaceuticals, intermediates for total synthesis and amino acid synthesis. 相似文献
442.
Kouakou Eric Konan Prof. Abollé Abollé Prof. François-Xavier Felpin 《European journal of organic chemistry》2023,26(1):e202201055
In this work, we describe ultra-fast continuous flow photo-thiol-ene reactions on cinchona alkaloids derivatives through a control of the reactive conformation in solution. Flow thiol-ene reactions proceed at 32 °C under light irradiation at 365 nm and require only 2.5 minutes of residence time to reach completion. The short path length of the tubular flow photochemical reactor, which maximizes and homogenizes the photon flux, associated to the fine tuning of the reactive conformation of cinchona alkaloids in solution are the main reasons for the high rates observed. The predominant conformation in solution of cinchona alkaloids was adjusted through the substitution of the hydroxyl group at C9 by a phenyl carbamate function. 相似文献
443.
Daniel Lin Matthew Coe Vinayak Krishnamurti Xanath Ispizua-Rodriguez G. K. Surya Prakash 《Chemical record (New York, N.Y.)》2023,23(9):e202300104
In the last few years, many reagents and protocols have been developed to allow for the efficient fluorofunctionalization of a diverse set of scaffolds ranging from alkanes, alkenes, alkynes, and (hetero)arenes. The concomitant rise of organofluorine chemistry and visible light-mediated synthesis have synergistically expanded the fields and have mutually benefitted from developments in both fields. In this context, visible light driven formations of radicals containing fluorine have been a major focus for the discovery of new bioactive compounds. This review details the recent advances and progress made in visible light-mediated fluoroalkylation and heteroatom centered radical generation. 相似文献
444.
Dr. Grant J. Sherborne Dr. Paul Kemmitt Callum Prentice Prof. Dr. Eli Zysman-Colman Prof. Dr. Andrew D. Smith Dr. Charlene Fallan 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2023,135(2):e202207829
Condensation of 2-vinylanilines and conjugated aldehydes followed by an efficient light-mediated cyclisation selectively yields either substituted tetrahydroquinolines with typically high dr, or in the presence of an iridium photocatalyst the synthesis of quinoline derivatives is demonstrated. These atom economical processes require mild conditions, with the substrate scope demonstrating excellent site selectivity and functional group tolerance, including azaarene-bearing substrates. A thorough experimental mechanistic investigation explores multiple pathways and the key role that imine and iminium intermediates play in the absorption of visible light to generate reactive excited states. The synthetic utility of the reactions is demonstrated on gram scale quantities in both batch and flow, alongside further manipulation of the medicinally relevant products. 相似文献
445.
Dr. Ya-Ming Tian Evamaria Hofmann Dr. Wagner Silva Xiang Pu Dr. Didier Touraud Prof. Dr. Ruth M. Gschwind Prof. Dr. Werner Kunz Prof. Dr. Burkhard König 《Angewandte Chemie (International ed. in English)》2023,62(17):e202218775
The amino alcohol meglumine solubilizes organic compounds in water and enforces the formation of electron donor acceptor (EDA) complexes of haloarenes with indoles, anilines, anisoles or thiols, which are not observed in organic solvents. UV-A photoinduced electron transfer within the EDA complexes induces the mesolytic cleavage of the halide ion and radical recombination of the arenes leading, after rearomatization and proton loss to C−C or C−S coupling products. Depending on the substitution pattern selective and unique cross-couplings are observed. UV and NMR measurements reveal the importance of the assembly for the photoinduced reaction. Enforced EDA aggregate formation in water allows new activation modes for organic photochemical synthesis. 相似文献
446.
Youxin Fu Jun.-Prof. Dr. Nadja A. Simeth Dr. Ryojun Toyoda Dr. Robert Brilmayer Prof. Dr. Wiktor Szymanski Prof. Dr. Ben L. Feringa 《Angewandte Chemie (International ed. in English)》2023,62(16):e202218203
Light-induced 9,10-phenanthrenequinone-electron-rich alkene ( PQ-ERA ) photocycloadditions are an attractive new type of photoclick reaction, featuring fast conversions and high biocompatibility. However, the tunability of the reaction was hardly investigated up to now. To this end, we explored the influence of substituents on both reaction partners and the reaction rate between the PQs and ERAs . We identified new handles for functionalization and discovered that using enamines as ERAs leads to drastically enhanced rates (>5400 times faster), high photoreaction quantum yields ( ΦP , up to 65 %), and multicolor emission output as well as a high fluorescence quantum yield of the adducts ( ΦF , up to 97 %). Further investigation of the photophysical and photochemical properties provided insights to design orthogonal reaction systems both in solution and on nanoparticle surfaces for ultrafast chemoselective functionalization by photoclick reactions. 相似文献
447.
A visible-light-induced C-5 selective C—H borylation of imidazo[1,2-a]pyridines with NHC-BH3 via Minisci-type radical borylation reaction has been developed for the first time. The present sustainable protocol provides a new family of regioselectively C5-borylated imidazopyridines that would otherwise be difficult to prepare. It is a supplement to site-selective borylation of azines (nitrogen-containing aromatic heterocycles) and the assembly of sp2 carbon-boron bond. 相似文献
448.
Dr. Bo Lu Dr. Lina Wang Xin Jiang Prof. Dr. Guntram Rauhut Prof. Dr. Xiaoqing Zeng 《Angewandte Chemie (International ed. in English)》2023,62(10):e202217353
The simplest diphosphene HPPH and isomeric diphosphinyldene PPH2 features prototype phosphorus-phosphorus multiple bonding properties that have been of long-standing interest in main-group chemistry. Herein, we report the observation of cis-HPPH, trans-HPPH, and PPH2 among the respective laser photolysis products of phosphine (PH3) and diphosphine (P2H4) in solid N2- and Ar-matrices at 10 K. The identification of these P2H2 isomers with matrix-isolation IR and UV/Vis spectroscopy is supported by D-isotope labeling and the quantum chemical calculations at the CCSD(T)-F12a/cc-pVTZ-F12 level using configuration-selective vibrational configuration interaction theory (VCI). Bonding analyses suggest that the two conformers of HPPH contain standard PP double bonds, whereas, PPH2 resembles P2 in having partial PP triple bond due to the H2P←P π bonding interaction. 相似文献
449.
Alessandro Marotta Hao Fang Callum E. Adams Kailey Sun Marcus Constantin G. Daniliuc Dr. John J. Molloy 《Angewandte Chemie (International ed. in English)》2023,62(34):e202307540
Operationally simple strategies to assemble boron containing organic frameworks are highly enabling in organic synthesis. While conventional retrosynthetic logic has engendered many platforms focusing on the direct formation of C−B bonds, α-boryl radicals have recently reemerged as versatile open-shell alternatives to access organoborons via adjacent C−C bond formation. Direct light-enabled α-activation is currently contingent on photo- or transition metal-catalysis activation to efficiently generate radical species. Here, we disclose a facile activation of α-halo boronic esters using only visible light and a simple Lewis base to enable homolytic scission. Intermolecular addition to styrenes facilitates the rapid construction of highly versatile E-allylic boronic esters. The simplicity of activation permits the strategic merger of this construct with selective energy transfer catalysis to enable the complimentary stereodivergent synthesis of Z-allylic boronic esters. 相似文献
450.
Graham C. R. Ellis-Davies 《Angewandte Chemie (International ed. in English)》2023,62(9):e202206083
Light passes through biological tissue, and so it is used for imaging biological processes in situ. Such observation is part of the very essence of science, but mechanistic understanding requires intervention. For more than 50 years a “second function” for light has emerged; namely, that of photochemical control. Caged compounds are biologically inert signaling molecules that are activated by light. These optical probes enable external instruction of biological processes by stimulation of an individual element in complex signaling cascades in its native environment. Cause and effect are linked directly in spatial, temporal, and frequency domains in a quantitative manner by their use. I provide a guide to the basic properties required to make effective caged compounds for the biological sciences. 相似文献