全文获取类型
收费全文 | 13168篇 |
免费 | 1124篇 |
国内免费 | 700篇 |
专业分类
化学 | 8849篇 |
晶体学 | 116篇 |
力学 | 513篇 |
综合类 | 51篇 |
数学 | 1662篇 |
物理学 | 3801篇 |
出版年
2023年 | 152篇 |
2022年 | 163篇 |
2021年 | 247篇 |
2020年 | 330篇 |
2019年 | 354篇 |
2018年 | 261篇 |
2017年 | 275篇 |
2016年 | 421篇 |
2015年 | 435篇 |
2014年 | 517篇 |
2013年 | 756篇 |
2012年 | 960篇 |
2011年 | 1103篇 |
2010年 | 691篇 |
2009年 | 717篇 |
2008年 | 816篇 |
2007年 | 811篇 |
2006年 | 714篇 |
2005年 | 616篇 |
2004年 | 590篇 |
2003年 | 496篇 |
2002年 | 416篇 |
2001年 | 316篇 |
2000年 | 244篇 |
1999年 | 195篇 |
1998年 | 158篇 |
1997年 | 130篇 |
1996年 | 154篇 |
1995年 | 148篇 |
1994年 | 167篇 |
1993年 | 132篇 |
1992年 | 126篇 |
1991年 | 101篇 |
1990年 | 114篇 |
1989年 | 84篇 |
1988年 | 95篇 |
1987年 | 69篇 |
1986年 | 78篇 |
1985年 | 102篇 |
1984年 | 78篇 |
1983年 | 80篇 |
1982年 | 56篇 |
1981年 | 58篇 |
1980年 | 51篇 |
1979年 | 39篇 |
1977年 | 43篇 |
1976年 | 42篇 |
1975年 | 42篇 |
1974年 | 52篇 |
1973年 | 48篇 |
排序方式: 共有10000条查询结果,搜索用时 125 毫秒
91.
Liangxu Lin Liang Huang Chang Wu Yu Gao Naihua Miao Chao Wu Aaron T. Marshall Yi Zhao Jiazhao Wang Jun Chen Shixue Dou Gordon G. Wallace Wei Huang 《Angewandte Chemie (International ed. in English)》2023,62(49):e202315182
The exploration of inexpensive and efficient catalysts for oxygen reduction reaction (ORR) is crucial for chemical and energy industries. Carbon materials have been proved promising with different catalysts enabling 2 and 4e− ORR. Nevertheless, their ORR activity and selectivity is still complex and under debate in many cases. Many structures of these active carbon materials are also chemically unstable for practical implementations. Unlike the well-discussed structures, this work presents a strategy to promote efficient and stable 2e− ORR of carbon materials through the synergistic effect of lattice distortion and H-passivation (on the distorted structure). We show how these structures can be formed on carbon cloth, and how the reproducible chemical adsorption can be realized on these structures for efficient and stable H2O2 production. The work here gives not only new understandings on the 2e− ORR catalysis, but also the robust catalyst which can be directly used in industry. 相似文献
92.
Dr. Yanbo Mei Prof. Dr. Xiaodan Chen Dr. Rui Wei Dr. Xiao-Yong Chang Prof. Dr. Lizhi Tao Prof. Dr. Liu Leo Liu 《Angewandte Chemie (International ed. in English)》2023,62(52):e202315555
Featuring an extra electron in the π* antibonding orbital, species with a 2-center-3-electron (2c3e) π bond without an underlying σ bond are scarcely known. Herein, we report the synthesis, isolation and characterization of a radical anion salt [K(18-C-6)]+{[(HCNDipp)2Si]2P2}⋅− (i.e. [K(18-C-6)]+ 3 ⋅−) (18-C-6=18-crown-6, Dipp=2,6-diisopropylphenyl), in which 3 ⋅− features a perfectly planar Si2P2 four-membered ring. This species represents the first example of a Si- and P-containing analog of a bicyclo[1.1.0]butane radical anion. The unusual bonding motif of 3 ⋅− was thoroughly investigated via X-ray diffraction crystallography, electron paramagnetic resonance spectroscopy (EPR), and calculations by density functional theory (DFT), which collectively unveiled the existence of a 2c3e π bond between the bridgehead P atoms and no clearly defined supporting P−P σ bond. 相似文献
93.
Chang Liu Yunci Zhang Shanshan Tang Yi Wang Jing Tian Dongyu Gu Yi Yang 《Journal of separation science》2023,46(10):2200958
Robinia pseudoacacia flowers have attracted much attention because of numerous bioactivities. In this study, its extract showed the potential scavenging ability for 2,2′-azinobis-(3-ethylbenzthiazoline-6-sulphonate) and 1,1-diphenyl-2-picrylhydrazyl free radicals. Under the guidance of antioxidant activity, the antioxidant extract was enriched by liquid-liquid extraction. The partition coefficients of the two main components in antioxidant extracts differed greatly, so in this study, elution-extrusion counter-current chromatography with the solvent system of n-hexane-ethyl acetate-methanol-water (2.5:5:2.5:5, v/v) was used to enhance the separation efficiency, and the two main components were successfully obtained. Among them, kaempferol showed strong antioxidant activity, which can be responsible for the activity of the extract. In order to deeply understand the antioxidant mechanism of kaempferol, the thermodynamics, frontier molecular orbital, and kinetics of scavenging free radicals were investigated by density functional theory. The results showed that 4′-OH in kaempferol was the most active group, which can scavenge free radicals by hydrogen atom transfer in non-polar solvents and activate 3-OH to generate double hydrogen atom transfer in the gas phase. But in polar solvents, it was more inclined to clear radicals through single electron transfer and proton transfer. The kinetic result showed that kaempferol needed 9.17 kcal/mol of activation energy to scavenge free radicals. 相似文献
94.
Nina Wei Dandan Song Chang Lu Yong Jiang Qin Liu Lunyuan Liu Liu Xu Linwei Chen Zhipeng Chen 《Journal of separation science》2023,46(17):2300235
Aconitum carmichaelii is widely used to treat chronic and intractable diseases due to its remarkable curative effect, but it is also a highly toxic herb with severe cardiac and neurotoxicity. It has been combined with honey for thousands of years to reduce toxicity and enhance efficacy, but there has been no study on the chemical constituent changes in the honey-processing so far. In this study, the chemical constituents of A. carmichaelii before and after honey-processing were characterized by ultra-high-performance liquid chromatography-quadrupole time-of-flight tandem mass spectrometry. The results showed that a total of 118 compounds were identified, of which six compounds disappeared and five compounds were newly produced after honey-processing, and the cleavage pathway of main components was elucidated. At the same time, 25 compounds were found to have significant effects on different products, among which four compounds with the biggest difference were selected for quantitative analysis by ultra-high-performance liquid chromatography-tandem mass spectrometry. This study not only explained the chemical differences between the different products, but also helped to control the quality of the honey-processed products more effectively, and laid a foundation for further elucidating the mechanism of chemical constituent change during the honey-processing of A. carmichaelii. 相似文献
95.
In this study, the possibility of using Tween 80 to disturb the microstructures of 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF4) and 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]PF6) was investigated under high pressures. The imidazolioum C H absorptions of pure ionic liquids (ILs) are significantly blue-shifted under high pressures. However, mild changes in imidazolioum C H stretching frequencies were observed for IL/Tween 80 mixtures. Tween 80 may hinder cations of ILs to form network structures with anions under high pressures via pressure-enhanced cation-Tween 80 interactions. Based on the experimental results, Tween 80-[BMIM]PF6 interactions are more effective in disturbing the local structure of imidazolium C H than Tween 80-[BMIM]BF4 interactions. 相似文献
96.
Zhen Zhu Hsiang-Ning Luk Yi-Min Huang Yu-Cheng Zhang Xu-Jia Chang Ren-Jang Wu 《中国化学会会志》2023,70(4):928-937
This study used a facile method to develop a novel silver/Graphene–polypyrrole (Ag/G–PPy)-modified electrode that can be used as an electrochemical sensor for levosimendan detection. The properties of the synthesized Ag/G–PPy-modified electrode were examined through field-emission scanning electron microscopy, x-ray diffraction, and transmission electron microscopy. The Ag/G–PPy-modified electrode exhibited satisfactory current signals toward levosimendan concentrations ranging from 0.21 to 6.88 μM and exhibited a low detection limit (0.12 μM). Accordingly, the proposed electrode can serve as a simple and inexpensive electrochemical sensor for levosimendan detection. 相似文献
97.
The synthesis of a series of ruthenium 1,5-disubstituted 1,2,3-triazolato complexes, 1,5-disubstituted 1,2,3-triazoles, and a triazolium salt is reported. Treatment of the ruthenium azido complex [Ru]-N3 ( 1 , [Ru] = (η5-C5H5)(dppe)Ru, dppe = Ph2PCH2CH2PPh2) with an excess of ethyl propiolate results in the formation of a mixture of the Z- and E-forms of zwitterionic N(1)-bound N(3)-ethyl acryl-4-carboxylate triazolato complexes [Ru]N3(CH=CHCO2Et)C2H(CO2) ( Z - 2 ) and ( E - 2 ). The arylation of 2 with aromatic bromides gives a series of cationic N(1)-bound N(3)-ethyl acryl-4-alkoxycarbonyl triazolato complexes {[Ru]N3(CH=CHCO2Et)C2H(CO2CH2R)}[Br] ( 3a , R = Ph ; 3b , R = C6F5; 3c , R = 4-C6H4CN, 3d , R = 2,6-C6H3F2) and the subsequent cleavage of the Ru-N bond of 3a–d gives 1,5-disubstituted 1,2,3-triazoles N3(CH=CHCO2Et)C2H(CO2CH2R) ( 4a , R = Ph; 4b , R = C6F5; 4c , R = 4-C6H4CN; 4d , R = 2,6-C6H3F2) and [Ru]-Br. A 1,2,3-triazolium salt [N3(CH=CHCO2Et)(CH2C6F5)C2H2][Br] ( 5 ) was formed by transformation of 4b in BrCH2C6F5/chloroform mixture. The structures of Z-3a and Z-5 were confirmed by single-crystal x-ray diffraction analysis and both complexes participate in non-covalent aromatic interactions in the solid-state structures which can be favorable in the binding of DNA/biomolecular targets and have shown great potential in the application of biologically active anticancer drugs. 相似文献
98.
Bo-Hao Chen Jun-Jia Xu Wei-Ren Lai Chung-Kai Chang Jeng-Lung Chen Jyh-Fu Lee Jin-Ming Chen Hwo-Shuenn Sheu Jey-Jau Lee Yoshiki Kubota Ming-Hsi Chiang Yasutaka Kitagawa Yu-Chun Chuang I-Jui Hsu 《中国化学会会志》2023,70(5):1187-1199
Two cobalt(II) halide complexes with 1,2,4-triazole as a ligand were synthesized. Their structures were determined by extended x-ray absorption fine structure (EXAFS) and powder x-ray diffraction (XRD). Both complexes [Co(Htrz)Cl2]n ( 1 ) and {[Co(Htrz)2(trz)]BF4}n ( 2 ) form one-dimensional polymeric chain and the distances of Co⋯Co are 3.3521(2) Å and 3.8629(2) Å, respectively. The Htrz and Cl− are bridging ligands to connect two Co(II) ions in 1 , and the local environment of Co site is in a distorted octahedron with {CoN2Cl4} core. In complex 2 , two Htrz and one trz are bridging ligands to connect two Co(II) ions, and the local geometry of Co is in a pseudo octahedron with {CoN6} core. The analysis of Co LII,III-edge XAS indicates that the Co(II) of both complexes are at high spin state with t2g5eg2 configuration and the crystal field strength (10Dq) is about 1.2 eV. The broken-symmetry DFT calculations indicate that antiferromagnetic coupling state of Co⋯Co is the most stable state in both complexes; and the coupling constants of 1 and 2 are −0.32 cm−1 and −3.70 cm−1, respectively. Based on the distances of Co⋯Co and coupling constants, such antiferromagnetic interaction is achieved through triazole ligands. 相似文献
99.
Ruyi Xu Zhaorui Chang Dan Wen Yi Liu Chudong Wang Weifeng Qu Xuan Tang Hongtao Jia Jienan Li Jifeng Cai Guanlin Li Bowei Jiang Lagabaiyila Zha 《Electrophoresis》2023,44(19-20):1579-1587
100.
Jing-Xiang Wang Dr. Avery C. Vilbert Dr. Chang Cui Dr. Evan N. Mirts Lucas H. Williams Wantae Kim Prof. Dr. Y. Jessie Zhang Prof. Dr. Yi Lu 《Angewandte Chemie (International ed. in English)》2023,62(52):e202314019
The key to type 1 copper (T1Cu) function lies in the fine tuning of the CuII/I reduction potential (E°′T1Cu) to match those of its redox partners, enabling efficient electron transfer in a wide range of biological systems. While the secondary coordination sphere (SCS) effects have been used to tune E°′T1Cu in azurin over a wide range, these principles are yet to be generalized to other T1Cu-containing proteins to tune catalytic properties. To this end, we have examined the effects of Y229F, V290N and S292F mutations around the T1Cu of small laccase (SLAC) from Streptomyces coelicolor to match the high E°′T1Cu of fungal laccases. Using ultraviolet-visible absorption and electron paramagnetic resonance spectroscopies, together with X-ray crystallography and redox titrations, we have probed the influence of SCS mutations on the T1Cu and corresponding E°′T1Cu. While minimal and small E°′T1Cu increases are observed in Y229F- and S292F-SLAC, the V290N mutant exhibits a major E°′T1Cu increase. Moreover, the influence of these mutations on E°′T1Cu is additive, culminating in a triple mutant Y229F/V290N/S292F-SLAC with the highest E°′T1Cu of 556 mV vs. SHE reported to date. Further activity assays indicate that all mutants retain oxygen reduction reaction activity, and display improved catalytic efficiencies (kcat/KM) relative to WT-SLAC. 相似文献