全文获取类型
收费全文 | 179136篇 |
免费 | 29264篇 |
国内免费 | 19292篇 |
专业分类
化学 | 121384篇 |
晶体学 | 1978篇 |
力学 | 11600篇 |
综合类 | 1152篇 |
数学 | 23314篇 |
物理学 | 68264篇 |
出版年
2024年 | 191篇 |
2023年 | 3294篇 |
2022年 | 3770篇 |
2021年 | 5800篇 |
2020年 | 6920篇 |
2019年 | 6665篇 |
2018年 | 6013篇 |
2017年 | 5511篇 |
2016年 | 8424篇 |
2015年 | 8061篇 |
2014年 | 10020篇 |
2013年 | 13256篇 |
2012年 | 15882篇 |
2011年 | 16800篇 |
2010年 | 11483篇 |
2009年 | 11092篇 |
2008年 | 11702篇 |
2007年 | 10652篇 |
2006年 | 9870篇 |
2005年 | 8326篇 |
2004年 | 6409篇 |
2003年 | 5085篇 |
2002年 | 4646篇 |
2001年 | 3893篇 |
2000年 | 3433篇 |
1999年 | 3767篇 |
1998年 | 3285篇 |
1997年 | 2994篇 |
1996年 | 3047篇 |
1995年 | 2624篇 |
1994年 | 2470篇 |
1993年 | 2024篇 |
1992年 | 1813篇 |
1991年 | 1635篇 |
1990年 | 1311篇 |
1989年 | 1004篇 |
1988年 | 796篇 |
1987年 | 664篇 |
1986年 | 652篇 |
1985年 | 533篇 |
1984年 | 399篇 |
1983年 | 286篇 |
1982年 | 247篇 |
1981年 | 176篇 |
1980年 | 128篇 |
1979年 | 64篇 |
1978年 | 55篇 |
1976年 | 58篇 |
1975年 | 55篇 |
1974年 | 53篇 |
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
81.
82.
Yi Han Zibo Xue Dr. Guangwu Li Dr. Yanwei Gu Dr. Yong Ni Dr. Shaoqiang Dong Prof. Chunyan Chi 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(23):9111-9116
Incorporation of a non-hexagonal ring into a nanographene framework can lead to new electronic properties. During the attempted synthesis of naphthalene-bridged double [6]helicene and heptagon-containing nanographene by the Scholl reaction, an unexpected azulene-embedded nanographene and its triflyloxylated product were obtained, as confirmed by X-ray crystallographic analysis and 2D NMR spectroscopy. A 5/7/7/5 ring-fused substructure containing two formal azulene units is formed, but only one of them shows an azulene-like electronic structure. The formation of this unique structure is explained by arenium ion mediated 1,2-phenyl migration and a naphthalene to azulene rearrangement reaction according to an in-silico study. This report represents the first experimental example of the thermodynamically unfavorable naphthalene to azulene rearrangement and may lead to new azulene-based molecular materials. 相似文献
83.
Panpan Li Quanbin Liang Eugene Yau-Hin Hong Chin-Yiu Chan Yat-Hin Cheng Ming-Yi Leung Mei-Yee Chan Kam-Hung Low Hongbin Wu Vivian Wing-Wah Yam 《Chemical science》2020,11(42):11601
A class of acceptor–donor–acceptor chromophoric small-molecule non-fullerene acceptors, 1–4, with difluoroboron(iii) β-diketonate (BF2bdk) as the electron-accepting moiety has been developed. Through the variation of the central donor unit and the modification on the peripheral substituents of the terminal BF2bdk acceptor unit, their photophysical and electrochemical properties have been systematically studied. Taking advantage of their low-lying lowest unoccupied molecular orbital energy levels (from −3.65 to −3.72 eV) and relatively high electron mobility (7.49 × 10−4 cm2 V−1 s−1), these BF2bdk-based compounds have been employed as non-fullerene acceptors in organic solar cells with maximum power conversion efficiencies of up to 4.31%. Moreover, bistable resistive memory characteristics with charge-trapping mechanisms have been demonstrated in these BF2bdk-based compounds. This work not only demonstrates for the first time the use of a boron(iii) β-diketonate unit in constructing non-fullerene acceptors, but also provides more insights into designing organic materials with multi-functional properties.Boron(iii) β-diketonates have been demonstrated to serve as multi-functional materials in NFA-based OPVs and organic resistive memories. 相似文献
84.
传统量子系统的哈密顿是自伴算子,哈密顿的自伴性不仅保证系统遵循酉演化和保持概率守恒,而且也保证了它自身具有实的能量本征值,这类系统称为自伴量子系统.然而,确实存在一些物理系统(如PT-对称量子系统),其哈密顿不是自伴的,这类系统称为非自伴量子系统.为了深入研究PT-对称量子系统,并考虑到算子PT的共轭线性性,首先讨论了共轭线性算子的一些性质,包括它们的矩阵表示和谱结构等;其次,分别研究了具有共轭线性对称性和完整共轭线性对称性的线性算子,通过它们的矩阵表示,给出了共轭线性对称性和完整共轭线性对称性的等价刻画;作为应用,得到了关于PT-对称及完整PT-对称算子的一些有趣性质,并通过一些具体例子,说明了完整PT-对称性对张量积运算不具有封闭性,同时说明了完整PT-对称性既不是哈密顿算子在某个正定内积下自伴的充分条件,也不是必要条件. 相似文献
85.
86.
87.
Lijuan Shen Li Li Sheng Lu Xiaohan Zhang Jie Liu Junlin An Guojun Zhang Bo Wu Fei Wang 《中国颗粒学报》2015,(3):10-15
We conducted measurements of black carbon(BC) aerosol in Jiaxing,China during autumn from September 26 to November 30,2013.We investigated temporal and diurnal variations of BC,and its correlations with meteorological parameters and other major pollutants.Results showed that hourly mass concentrations of BC ranged from 0.2 to 22.0 μg/m3,with an average of 5.1 μg/m3.The diurnai variation of BC exhibited a bimodal distribution,with peaks at 07:00 and 18:00.The morning peak was larger than the evening peak.The mass percentages of BC in PM2.5 and PM10 were 7.1%and 4.8%,respectively.The absorption coefficient of BC was calculated to be 44.4 Mm-1,which accounted for 11.1%of the total aerosol extinction.BC was mainly emitted from local sources in southwestern Jiaxing where BC concentrations were generally greater than 11 μg/m3 during the measurement period.Correlation analysis indicated that the main sources of BC were motor vehicle exhaust,and domestic and industrial combustion. 相似文献
88.
JPC – Journal of Planar Chromatography – Modern TLC - A new high-performance thin-layer chromatographic (HPTLC) method has been developed for the simultaneous estimation of... 相似文献
89.
90.
Xiaoxia Yang Hongyan Xie Zhiguang Xu Jiabing Feng Qiwei Fu Haidong Li Yongtang Jia 《Journal of polymer science. Part A, Polymer chemistry》2021,59(9):813-823
An efficient, atom-economic, oxygen-tolerant, and water-tolerant strategy has been established to synthesize cyano-rich polyesters. Four kinds of organic bases, 1,1,3,3-tetramethylguanidine (TMG), 4-dimethylaminopyridine, triethylamine, and 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) were explored for accelerating Michael addition polymerization of malononitrile and 1,4-butandiol diacrylate. TMG can promote the polymerization efficiently under mild conditions to quantitatively afford polyester with high-molecular weight and moderate polydispersity. The comparison of the kinetic studies of TMG and TBD reveals that TMG shows better catalytic performance, while the catalysis of TBD brings about oligomers in spite of the higher efficiency at early age of the polymerization. Moreover, other diacrylate compounds could also be quantitatively polymerized to afford polyesters with high molecular weight. When dimethacrylate is chose as the monomer, the polymerization becomes sluggish. All the afforded polyesters display programmable thermal and mechanical properties that are closely related to their chemical structures. 相似文献