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991.
Divergent Reactivity of Homologue ortho‐Allenylbenzaldehydes Controlled by the Tether Length: Chromone versus Chromene Formation
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Prof. Dr. Benito Alcaide Dr. Pedro Almendros Dr. Israel Fernández Dr. Teresa Martínez del Campo Teresa Naranjo 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(4):1533-1541
The divergent behavior of two homologue allenals, namely, 2‐(buta‐2,3‐dienyloxy)‐ and 2‐(propa‐1,2‐dienyloxy)benzaldehydes, as cyclization substrates is described. 2‐(Buta‐2,3‐dienyloxy)benzaldehydes suffers a formal allenic carbocyclization reaction to afford chromenes, whereas 2‐(propa‐1,2‐dienyloxy)benzaldehydes react to yield chromones. The formation of chromenes is strictly a formal hydroarylation process divided into two parts, namely, allenic Claisen‐type rearrangement and oxycyclization. An unknown N‐heterocyclic carbene (NHC)‐catalyzed allenic hydroacylation reaction must be invoked to account for the preparation of chromones. ortho‐Allenylbenzaldehydes bearing either electron‐donating substituents or electron‐withdrawing substituents worked well to afford both the hydroarylation and hydroacylation products. This unexpected difference in reactivity can be rationalized by means of density functional theory calculations. 相似文献
992.
Guorong Sheng Shicong Ma Songlin Bai Jing Qian Kai Huang Bo Lang Ping Lu Yanguang Wang 《Tetrahedron》2018,74(17):2151-2157
The rhodium-catalyzed reactions of 3-diazoindolin-2-imines with β-enamino esters furnished 2,3-diaminoindoles in excellent yields with wide functional group tolerance. The synthesized 2,3-diaminoindoles could be converted into 5H-pyrazino [2,3-b]indoles via a sequential dehydrogenation/6π-ERC/aromatization process. 相似文献
993.
994.
《Angewandte Chemie (International ed. in English)》2017,56(49):15733-15736
We present the first [2]rotaxane featuring a functional organometallic host. In contrast to the known organic scaffolds, this assembly shows a high post‐synthetic modifiability. The reactivity of the Ag8 pillarplex host is fully retained, as is exemplified by the first transmetalation in a rotaxane framework to provide the respective Au8 analogue. Additionally, a transformation under acidic conditions to give a purely organic [3]rotaxane is demonstrated which is reversible upon addition of a suitable base, rendering the assembly a pH‐dependent switch. Hereby, it is shown that the mechanically interlocked nature of the system enhances the kinetic stability of the NHC host complex by a factor of >1000 and corresponds to the first observation of a stabilizing “rotaxand effect”. 相似文献
995.
996.
Intramolecular CN Bond Activation and Ring‐Expansion Reactions of N‐Heterocyclic Carbenes
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Dr. Patrick Hemberger Dr. Andras Bodi Johannes H. J. Berthel Prof. Dr. Udo Radius 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(4):1434-1438
Intramolecular ring‐expansion reactions (RER) of the N‐heterocyclic carbene 1,3‐dimethylimidazolin‐2‐ylidene were observed upon vacuum ultraviolet (VUV) photoexcitation. Similarly to RERs reported in the solvent phase, for the reaction of NHCs with main‐group‐element hydrides, hydrogen transfer to the NHC carbon atom is the crucial initial step. In an ionization‐mediated protonation, 1,3‐dimethylimidazolin‐2‐ylidene forms an imidazolium ion, which is the rate‐limiting step on the pathway to two six‐membered ring products, namely, methylpyrimidinium and ‐pyrazinium ions. To unravel the reaction path, we have used imaging photoelectron photoion coincidence spectroscopy with VUV synchrotron radiation, as well as high‐level composite method calculations. Similarities and differences between the mechanism in the gas phase and in the condensed phase are discussed. 相似文献
997.
Ana Pereira Dr. Yohan Champouret Dr. Carmen Martín Dr. Eleuterio Álvarez Prof. Dr. Michel Etienne Prof. Dr. Tomás R. Belderraín Prof. Dr. Pedro J. Pérez 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(27):9769-9775
Copper–carbene [TpxCu?C(Ph)(CO2Et)] and copper–diazo adducts [TpxCu{η1‐N2C(Ph)(CO2Et)}] have been detected and characterized in the context of the catalytic functionalization of O?H bonds through carbene insertion by using N2?C(Ph)(CO2Et) as the carbene source. These are the first examples of these type of complexes in which the copper center bears a tridentate ligand and displays a tetrahedral geometry. The relevance of these complexes in the catalytic cycle has been assessed by NMR spectroscopy, and kinetic studies have demonstrated that the N‐bound diazo adduct is a dormant species and is not en route to the formation of the copper–carbene intermediate. 相似文献
998.
Stefan A. Künzi Dr. Juan Manuel Sarria Toro Dr. Tim den Hartog Prof. Dr. Peter Chen 《Angewandte Chemie (International ed. in English)》2015,54(36):10670-10674
Nickel was identified as a catalyst for the cyclopropanation of unactivated olefins by using in situ generated lithiomethyl trimethylammonium triflate as a methylene donor. A mechanistic hypothesis is proposed in which the generation of a reactive nickel carbene explains several interesting observations. Additionally, our findings shed light on a report by Franzen and Wittig published in 1960 that had been retracted later owing to irreproducibility, and provide a rational basis for the systematic development of the reaction for preparative purposes as an alternative to diazomethane or Simmons–Smith conditions. 相似文献
999.
WU Hui JIN Can HUANG GuoLi WANG LianJun JIANG JuLi & WANG LeYong Key Laboratory of Mesoscopic Chemistry of Ministry of Education School of Chemistry Chemical Engineering Nanjing University Nanjing China 《中国科学B辑(英文版)》2011,(6)
Two new bis-imidazolinium salts (4a, 4b) have been synthesized as precursors of N-heterocyclic carbenes (NHCs) from the commercially available (R)-2,2′-dihydroxy-1,1′-binaphthalene. The two bis-imidazolinium salts were used as efficient precursor of NHC ancillary ligands in the palladium-catalyzed Heck reaction. Good to excellent yields and high stereoselectivities were obtained with ethyl acrylate, acrylonitrile, and acrylamide as starting materials. The structure of bis-imidazolinium salt 4b was further c... 相似文献
1000.