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941.
中学阶段常用于检验二氧化硫气体的品红溶液分为酸性品红和碱性品红2种。通过设计集演示、对比于一体的绿色环保二氧化硫性质实验装置,优化实验条件,探讨了酸性品红和碱性品红与SO2、酸碱反应的性质差异及褪色机理,并提出鉴别酸性品红和碱性品红的简便办法。 相似文献
942.
近年来,高性能荧光有机电致发光器件(FOLEDs)的开发受到了广泛关注。由于荧光材料仅能利用25%的单重态激子辐射发光,FOLEDs的外量子效率(EQE)理论极限为5%。通过能量转移,充分利用主体分子的单重态与三重态激子敏化荧光客体发光,可以提高激子利用率。目前敏化型FOLEDs(SFOLEDs)的最高EQE已达26.1%。本文详细介绍了SFOLEDs的敏化原理和机制,并根据敏化机制的不同,系统地总结了热活化延迟荧光敏化、激基复合物敏化、三重态湮灭敏化和局域电荷转移杂化激发态(HLCT)敏化等各类SFOLEDs的材料与器件结构特点及其研究进展。最后本综述对该类器件的研究前景进行了展望,期待吸引更多专业的研究人员的研究兴趣,进而推动该领域的发展。 相似文献
943.
Yu‐Hui Wang Jun‐Song Tian Peng‐Wei Tan Qiang Cao Xue‐Xin Zhang Zhong‐Yan Cao Feng Zhou Xin Wang Jian Zhou 《Angewandte Chemie (International ed. in English)》2020,59(4):1634-1643
Azacycles such as indoles and tetrahydroquinolines are privileged structures in drug development. Reported here is an unprecedented regiodivergent intramolecular nucleophilic addition reaction of imines as a flexible approach to access N‐functionalized indoles and tetrahydroquinolines, by the control of reaction at the N‐terminus and C‐terminus, respectively. Using ketimines derived from 2‐(2‐nitroethyl)anilines with isatins or α‐ketoesters, the regioselective N‐attack reaction gives N‐functionalized indoles, while the catalytic enantioselective C‐attack reaction affords chiral tetrahydroquinolines featuring an α‐tetrasubstituted stereocenter. Mechanistic studies reveal that hydrogen‐bonding interactions may greatly facilitate such unusual N‐attack reactions of imines. The utility of this protocol is highlighted by the catalytic enantioselective formal synthesis of (?)‐psychotrimine, and the construction of various fused aza‐heterocycles. 相似文献
944.
Wenjuan Ji Xinjian Ji Qi Zhang Dhanaraju Mandalapu Zixin Deng Wei Ding Peng Sun Qi Zhang 《Angewandte Chemie (International ed. in English)》2020,59(23):8880-8884
Sulfur‐based homolytic substitution (SH reaction) plays an important role in synthetic chemistry, yet whether such a reaction could occur on the positively charged sulfonium compounds remains unknown. In the study of the anaerobic coproporphyrinogen III oxidase HemN, a radical S‐adenosyl‐l ‐methionine (SAM) enzyme involved in heme biosynthesis, we observed the production of di‐(5′‐deoxyadenosyl)methylsulfonium, which supports a deoxyadenosyl (dAdo) radical‐mediated SH reaction on the sulfonium center of SAM. The sulfonium‐based SH reactions were then investigated in detail by density functional theory calculations and model reactions, which showed that this type of reactions is thermodynamically favorable and kinetically competent. These findings represent the first report of sulfonium‐based SH reactions, which could be useful in synthetic chemistry. Our study also demonstrates the remarkable catalytic promiscuity of the radical SAM superfamily enzymes. 相似文献
945.
Junjun Wu Lu Gem Gao Zoltan Varga Xuefei Xu Wei Ren Donald G. Truhlar 《Angewandte Chemie (International ed. in English)》2020,59(27):10826-10830
Faced with the contradictory results of two recent experimental studies [Jara‐Toro et al., Angew. Chem. Int. Ed. 2017 , 56, 2166 and Chao et al., Angew. Chem. Int. Ed. 2019 , 58, 5013] of the possible catalytic effect of water vapor on CH3OH + OH reaction, we report calculations that corroborate the conclusion made by Chao et al. and extend the rate constant evaluation down to 200 K. The rate constants of the CH3OH + OH reaction catalyzed by a water molecule are computed as functions of temperature and relative humidity using high‐level electronic structure and kinetics calculations. The Wuhan–Minnesota Scaling (WMS) method is used to provide accurate energetics to benchmark a density functional for direct dynamics. Both high‐frequency and low‐frequency anharmonicities are included. Variational and tunneling effects are treated by canonical variational transition state theory with multidimensional small‐curvature tunneling. And, most significantly, we include multistructural effects in the rate constant calculations. Our calculations show that the catalytic effect of water vapor is not observable at 200–400 K. 相似文献
946.
947.
Joji Tanaka Satu Hkkinen Parker T. Boeck Yidan Cong Sbastien Perrier Sergei S. Sheiko Wei You 《Angewandte Chemie (International ed. in English)》2020,59(18):7203-7208
An orthogonal combination of cationic and radical RAFT polymerizations is used to synthesize bottlebrush polymers using two distinct RAFT agents. Selective consumption of the first RAFT agent is used to control the cationic RAFT polymerization of a vinyl ether monomer bearing a secondary dormant RAFT agent, which subsequently allows side‐chain polymers to be grafted from the pendant RAFT agent by a radical‐mediated RAFT polymerization of a different monomer, thus completing the synthesis of bottlebrush polymers. The high efficiency and selectivity of the cationic and radical RAFT polymerizations allow both polymerizations to be conducted in one‐pot tandem without intermediate purification. 相似文献
948.
Yaqi Wu Shu Zeng Danhua Yuan Jiacheng Xing Hanbang Liu Shutao Xu Yingxu Wei Yunpeng Xu Zhongmin Liu 《Angewandte Chemie (International ed. in English)》2020,59(17):6765-6768
Propene/propane separation is challenging due to the very small difference in molecular sizes, boiling points and condensabilities between these molecules. Herein, we report a strategy of introducing ZIF fragments into traditional mordenite (MOR) zeolite to decorate the 12‐membered ring of MOR. After decoration, the originally ineffective zeolite MOR exhibited high kinetic propene/propane selectivities (139 at 25 °C) and achieved efficient propene/propane separation. The propene/propane separation potentials of the resulting adsorbents were further confirmed by breakthrough experiments with equimolar propene/propane (50/50) mixtures. 相似文献
949.
Xing‐Ben Wang Zhan‐Jiang Zheng Jia‐Le Xie Xing‐Wei Gu Qiu‐Chao Mu Guan‐Wu Yin Fei Ye Zheng Xu Li‐Wen Xu 《Angewandte Chemie (International ed. in English)》2020,59(2):790-797
A novel and unusual palladium‐catalyzed [4+2] annulation of cyclopropenes with benzosilacyclobutanes is reported. This reaction occurred through chemoselective Si?C(sp2) bond activation in synergy with ring expansion/insertion of cyclopropenes to form new C(sp2)?C(sp3) and Si?C(sp3) bonds. An array of previously elusive bicyclic skeleton with high strain, silabicyclo[4.1.0]heptanes, were formed in good yields with excellent diastereoselectivity under mild conditions. An asymmetric version of the reaction with a chiral phosphoramidite ligand furnished a variety of chiral bicyclic silaheterocycle derivatives with good enantioselectivity (up to 95.5:4.5 er). Owing to the mild reaction conditions, the good stereoselectivity profile, and the ready availability of the functionalized precursors, this process constitutes a useful and straightforward strategy for the synthesis of densely functionalized silacycles. 相似文献
950.
Kai Wu Kang Li Sha Chen Ya‐Jun Hou Yu‐Lin Lu Jing‐Si Wang Mei‐Juan Wei Mei Pan Cheng‐Yong Su 《Angewandte Chemie (International ed. in English)》2020,59(7):2639-2643
A nanocage coupling effect from a redox RuII‐PdII metal–organic cage (MOC‐16) is demonstrated for efficient photochemical H2 production by virtue of redox–guest modulation of the photo‐induced electron transfer (PET) process. Through coupling with photoredox cycle of MOC‐16, tetrathiafulvalene (TTF) guests act as electron relay mediator to improve the overall electron transfer efficiency in the host–guest system in a long‐time scale, leading to significant promotion of visible‐light driven H2 evolution. By contrast, the presence of larger TTF‐derivatives in bulk solution without host–guest interactions results in interference with PET process of MOC‐16, leading to inefficient H2 evolution. Such interaction provides an example to understand the interplay between the redox‐active nanocage and guest for optimization of redox events and photocatalytic activities in a confined chemical nanoenvironment. 相似文献