全文获取类型
收费全文 | 17284篇 |
免费 | 2872篇 |
国内免费 | 2375篇 |
专业分类
化学 | 13078篇 |
晶体学 | 251篇 |
力学 | 903篇 |
综合类 | 172篇 |
数学 | 1978篇 |
物理学 | 6149篇 |
出版年
2024年 | 49篇 |
2023年 | 329篇 |
2022年 | 456篇 |
2021年 | 566篇 |
2020年 | 632篇 |
2019年 | 726篇 |
2018年 | 553篇 |
2017年 | 568篇 |
2016年 | 786篇 |
2015年 | 786篇 |
2014年 | 985篇 |
2013年 | 1367篇 |
2012年 | 1549篇 |
2011年 | 1700篇 |
2010年 | 1161篇 |
2009年 | 1137篇 |
2008年 | 1163篇 |
2007年 | 1128篇 |
2006年 | 914篇 |
2005年 | 807篇 |
2004年 | 704篇 |
2003年 | 594篇 |
2002年 | 601篇 |
2001年 | 501篇 |
2000年 | 414篇 |
1999年 | 325篇 |
1998年 | 255篇 |
1997年 | 206篇 |
1996年 | 226篇 |
1995年 | 187篇 |
1994年 | 180篇 |
1993年 | 142篇 |
1992年 | 150篇 |
1991年 | 117篇 |
1990年 | 106篇 |
1989年 | 96篇 |
1988年 | 73篇 |
1987年 | 47篇 |
1986年 | 54篇 |
1985年 | 48篇 |
1984年 | 35篇 |
1983年 | 19篇 |
1982年 | 10篇 |
1981年 | 11篇 |
1980年 | 6篇 |
1979年 | 13篇 |
1977年 | 6篇 |
1976年 | 8篇 |
1975年 | 6篇 |
1957年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Shufang Ji Yang Qu Tao Wang Yuanjun Chen Guofeng Wang Xue Li Juncai Dong QiuYu Chen Wanying Zhang Zedong Zhang Shiyou Liang Rong Yu Yu Wang Dingsheng Wang Yadong Li 《Angewandte Chemie (International ed. in English)》2020,59(26):10651-10657
The solar‐driven photocatalytic reduction of CO2 (CO2RR) into chemical fuels is a promising route to enrich energy supplies and mitigate CO2 emissions. However, low catalytic efficiency and poor selectivity, especially in a pure‐water system, hinder the development of photocatalytic CO2RR owing to the lack of effective catalysts. Herein, we report a novel atom‐confinement and coordination (ACC) strategy to achieve the synthesis of rare‐earth single erbium (Er) atoms supported on carbon nitride nanotubes (Er1/CN‐NT) with a tunable dispersion density of single atoms. Er1/CN‐NT is a highly efficient and robust photocatalyst that exhibits outstanding CO2RR performance in a pure‐water system. Experimental results and density functional theory calculations reveal the crucial role of single Er atoms in promoting photocatalytic CO2RR. 相似文献
992.
Wen‐Jun Yue Jun‐Zhao Xiao Shuai Zhang Liang Yin 《Angewandte Chemie (International ed. in English)》2020,59(18):7057-7062
1,2‐Bisphosphines have been identified as one class of important and powerful chiral ligands in asymmetric catalysis with transition metals. Herein, a copper(I)‐catalyzed asymmetric hydrophosphination of α,β‐unsaturated phosphine sulfides was developed with the assistance of “soft–soft” interaction between copper(I)‐catalyst and the phosphine sulfide moiety, which afforded 1,2‐bisphosphine derivatives with diversified electronic nature and steric hindrance in high to excellent yields with high to excellent enantioselectivity. Moreover, the challenging catalytic asymmetric hydrophosphination/protonation reaction was achieved with excellent enantioselectivity. Strikingly, the dynamic kinetic resolution of racemic diarylphosphines was also successfully carried out with high to excellent diastereo‐ and enantioselectivities. Interestingly, the nucleophilic copper(I)‐diphenylphosphide species was characterized by 31P NMR spectrum and mass spectrum. At last, three products were transformed to chiral 1,2‐bisphosphines, which were employed as ligands in Rh‐catalyzed asymmetric hydrogenation of α‐amino‐α,β‐unsaturated ester. The α‐amino acid derivative was produced in high enantioselectivity, which demonstrated the utility of the present methodology. 相似文献
993.
994.
Liang‐Jin Xu Sujin Lee Xinsong Lin Logan Ledbetter Michael Worku Haoran Lin Chenkun Zhou He Liu Anna Plaviak Biwu Ma 《Angewandte Chemie (International ed. in English)》2020,59(33):14120-14123
Zero‐dimensional (0D) organic metal halide hybrids, in which organic and metal halide ions cocrystallize to form neutral species, are a promising platform for the development of multifunctional crystalline materials. Herein we report the design, synthesis, and characterization of a ternary 0D organic metal halide hybrid, (HMTA)4PbMn0.69Sn0.31Br8, in which the organic cation N‐benzylhexamethylenetetrammonium (HMTA+, C13H19N4+) cocrystallizes with PbBr42?, MnBr42?, and SnBr42?. The wide band gap of the organic cation and distinct optical characteristics of the three metal bromide anions enabled the single‐crystalline “host–guest” system to exhibit emissions from multiple “guest” metal halide species simultaneously. The combination of these emissions led to near‐perfect white emission with a photoluminescence quantum efficiency of around 73 %. Owing to distinct excitations of the three metal halide species, warm‐ to cool‐white emissions could be generated by controlling the excitation wavelength. 相似文献
995.
Hongjuan Zhang Yuchao Liang Hao Zhao Ruilian Qi Zhuo Chen Huanxiang Yuan Haiyan Liang Lei Wang 《Macromolecular bioscience》2020,20(2)
In this work, dual‐mode antibacterial conjugated polymer nanoparticles (DMCPNs) combined with photothermal therapy (PTT) and photodynamic therapy (PDT) are designed and explored for efficient killing of ampicillin‐resistant Escherichia coli (Ampr E. coli). The DMCPNs are self‐assembled into nanoparticles with a size of 50.4 ± 0.6 nm by co‐precipitation method using the photothermal agent poly(diketopyrrolopyrrole‐thienothiophene) (PDPPTT) and the photosensitizer poly[2‐methoxy‐5‐((2‐ethylhexyl)oxy)‐p‐phenylenevinylene] (MEH‐PPV) in the presence of poly(styrene‐co‐maleic anhydride) which makes nanoparticles disperse well in water via hydrophobic interactions. Thus, DMCPNs simultaneously possess photothermal effect and the ability of sensitizing oxygen in the surrounding to generate reactive oxygen species upon the illumination of light, which could easily damage resistant bacteria. Under combined irradiation of near‐infrared light (550 mW cm?2, 5 min) and white light (65 mW cm?2, 5 min), DMCPNs with a concentration of 9.6 × 10?4 µm could reach a 93% inhibition rate against Ampr E. coli, which is higher than the efficiency treated by PTT or PDT alone. The dual‐mode nanoparticles provide potential for treating pathogenic infections induced by resistant microorganisms in clinic. 相似文献
996.
Tianjiao Qiao Yicheng Wang Sujuan Zheng Huiying Kang Guangxin Liang 《Angewandte Chemie (International ed. in English)》2020,59(33):14111-14114
The first total syntheses of three unusual norrisolide‐type rearranged spongian diterpenes, cheloviolene C, seconorrisolide B, and seconorrisolide C, have been accomplished via a common intermediate through late‐stage ring‐scissoring. The synthesis features a Wolff ring contraction for the synthesis of the trans‐hydrindane system, and a crucial retro Diels–Alder reaction/intramolecular ene cyclization for the rapid stereoselective construction of the furo[2,3‐b]furan system, which is commonly seen in rearranged spongian diterpenes. 相似文献
997.
Qihao Wu Song‐Wei Li Heng Xu Hong Wang Pei Hu Hao Zhang Cheng Luo Kai‐Xian Chen Bastien Nay Yue‐Wei Guo Xu‐Wen Li 《Angewandte Chemie (International ed. in English)》2020,59(29):12105-12112
Placobranchus ocellatus is well known to produce diverse and complex γ‐pyrone polypropionates. In this study, the chemical investigation of P. ocellatus from the South China Sea led to the discovery and identification of ocellatusones A–D, a series of racemic non‐γ‐pyrone polyketides with novel skeletons, characterized by a bicyclo[3.2.1]octane ( 1 , 2 ), a bicyclo[3.3.1]nonane ( 3 ) or a mesitylene‐substituted dimethylfuran‐3(2H)‐one core ( 4 ). Extensive spectroscopic analysis, quantum chemical computation, chemical synthesis, and/or X‐ray diffraction analysis were used to determine the structure and absolute configuration of the new compounds, including each enantiomer of racemic compounds 1 – 4 after chiral HPLC resolution. An array of new and diversity‐generating rearrangements is proposed to explain the biosynthesis of these unusual compounds based on careful structural analysis and comparison with six known co‐occurring γ‐pyrones ( 5 – 10 ). Furthermore, the successful biomimetic semisynthesis of ocellatusone A ( 1 ) confirmed the proposed rearrangement through an unprecedented acid induced cascade reaction. 相似文献
998.
Biwei Xiao Hanshuo Liu Ning Chen Mohammad Norouzi Banis Haijun Yu Jianwen Liang Qian Sun Tsun‐Kong Sham Ruying Li Mei Cai Gianluigi A. Botton Xueliang Sun 《Angewandte Chemie (International ed. in English)》2020,59(34):14313-14320
Li‐ and Mn‐rich layered oxides are among the most promising cathode materials for Li‐ion batteries with high theoretical energy density. Its practical application is, however, hampered by the capacity and voltage fade after long cycling. Herein, a finite difference method for near‐edge structure (FDMNES) code was combined with in situ X‐ray absorption spectroscopy (XAS) and transmission electron microscopy/electron energy loss spectroscopy (TEM/EELS) to investigate the evolution of transition metals (TMs) in fresh and heavily cycled electrodes. Theoretical modeling reveals a recurring partially reversible LiMn2O4‐like sub‐nanodomain formation/dissolution process during each charge/discharge, which accumulates gradually and accounts for the Mn phase transition. From the modeling of spectra and maps of the valence state over large regions of the cathodes, it was found that the phase change is size‐dependent. After prolonged cycling, the TMs displayed different levels of inactivity. 相似文献
999.
Qun‐Liang Zhang Qin Xiong Miao‐Miao Li Wei Xiong Bin Shi Yu Lan Liang‐Qiu Lu Wen‐Jing Xiao 《Angewandte Chemie (International ed. in English)》2020,59(33):14096-14100
Higher‐order cycloadditions, particularly [8+2] cycloadditions, are a straightforward and efficient strategy for constructing significant medium‐sized architectures. Typically, configuration‐restrained conjugated systems are utilized as 8π‐components for higher‐order concerted cycloadditions. However, for this reason, 10‐membered monocyclic skeletons have never been constructed via catalytic asymmetric [8+2] cycloaddition with high peri‐ and stereoselectivity. Here, we accomplished an enantioselective [8+2] dipolar cycloaddition via the merger of visible‐light activation and asymmetric palladium catalysis. This protocol provides a new route to 10‐membered monocyclic architectures bearing chiral quaternary stereocenters with high chemo‐, peri‐, and enantioselectivity. The success of this strategy relied on the facile in situ generation of Pd‐containing 1,8‐dipoles and their enantioselective trapping by ketene dipolarophiles, which were formed in situ via a photo‐Wolff rearrangement. 相似文献
1000.
Lin Yu Leiyang Lv Zihang Qiu Zhangpei Chen Ze Tan Yu‐Feng Liang Chao‐Jun Li 《Angewandte Chemie (International ed. in English)》2020,59(33):14009-14013
We have developed an unprecedented Pd‐catalyzed formal hydroalkylation of alkynes with hydrazones, which are generated in situ from naturally abundant aldehydes, as both alkylation reagents and hydrogen donors. The hydroalkylation proceeds with high regio‐ and stereoselectivity to form (Z)‐alkenes, which are more difficult to generate compared to (E)‐alkenes. The reaction is compatible with a wide range of functional groups, including hydroxy, ester, ketone, nitrile, boronic ester, amine, and halide groups. Furthermore, late‐stage modifications of natural products and pharmaceutical derivatives exemplify its unique chemoselectivity, regioselectivity, and synthetic applicability. Mechanistic studies indicate the possible involvement of Pd‐hydride intermediates. 相似文献