全文获取类型
收费全文 | 305802篇 |
免费 | 17812篇 |
国内免费 | 5528篇 |
专业分类
化学 | 170977篇 |
晶体学 | 3754篇 |
力学 | 10106篇 |
综合类 | 254篇 |
数学 | 27737篇 |
物理学 | 75394篇 |
无线电 | 40920篇 |
出版年
2022年 | 2030篇 |
2021年 | 3279篇 |
2020年 | 4966篇 |
2019年 | 6544篇 |
2018年 | 5741篇 |
2017年 | 5222篇 |
2016年 | 9519篇 |
2015年 | 7653篇 |
2014年 | 9445篇 |
2013年 | 16008篇 |
2012年 | 12747篇 |
2011年 | 13717篇 |
2010年 | 11236篇 |
2009年 | 11340篇 |
2008年 | 13209篇 |
2007年 | 12742篇 |
2006年 | 11738篇 |
2005年 | 10898篇 |
2004年 | 9696篇 |
2003年 | 9069篇 |
2002年 | 9755篇 |
2001年 | 9337篇 |
2000年 | 7709篇 |
1999年 | 5382篇 |
1998年 | 4418篇 |
1997年 | 4298篇 |
1996年 | 3949篇 |
1995年 | 3439篇 |
1994年 | 3475篇 |
1993年 | 3362篇 |
1992年 | 3454篇 |
1991年 | 3518篇 |
1990年 | 3375篇 |
1989年 | 3207篇 |
1988年 | 3053篇 |
1987年 | 2744篇 |
1986年 | 2676篇 |
1985年 | 3348篇 |
1984年 | 3471篇 |
1983年 | 2814篇 |
1982年 | 3038篇 |
1981年 | 2876篇 |
1980年 | 2700篇 |
1979年 | 2884篇 |
1978年 | 2980篇 |
1977年 | 2999篇 |
1976年 | 2959篇 |
1975年 | 2816篇 |
1974年 | 2799篇 |
1973年 | 2929篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
Yang T. L. Kao C. L. Kuo C. E. Yeh H. C. Li W. J. Li H. T. Chen C. Y. 《Chemistry of Natural Compounds》2022,58(5):825-827
Chemistry of Natural Compounds - A novel bibenzyl derivative, hydrangchinenin (1), was isolated from the stems of Hydrangea chinensis Maxim. (Hydrangeaceae). Its structure was determined on the... 相似文献
3.
4.
Xiao Zhu Chen Yanxun Jiang Hongbo Hu Zhenzhen Lui John C. S. Min Geyong Dustdar Schahram 《Wireless Networks》2022,28(7):3305-3322
Wireless Networks - Unmanned aerial vehicles (UAV) have been widely used in various fields because of their high mobility and portability. At the same time, due to the rapid development of... 相似文献
5.
Nonlinear Dynamics - The perovskite solar cell (PSC) is one of the most promising photovoltaic candidates along with the highly increasing demand for green electricity. One of the main concerns... 相似文献
6.
Romanenko G. V. Fokin S. V. Bogomyakov A. S. Zueva E. M. Ovcharenko V. I. 《Journal of Structural Chemistry》2022,63(3):441-450
Journal of Structural Chemistry - The structures of Ni(II), Cu(II), and Zn(II) complexes with anions of 2,5-pyrrolyl-disubstituted nitronyl nitroxide (L1) and iminonitroxide (L2) diradicals (HL1 is... 相似文献
7.
Hassan E. A. M. Elabid A. E. A. Bashier E. O. Elagib T. H. H. 《Mechanics of Composite Materials》2022,58(2):261-270
Mechanics of Composite Materials - Carbon fiber (CF)/ polyamide (PA6) composites are one of the most promising thermoplastic materials for automobile applications. However, the interfacial... 相似文献
8.
Petrov P. A. Filippova E. A. Kompankov N. B. Sukhikh T. S. Sokolov M. N. 《Journal of Structural Chemistry》2022,63(3):470-475
Journal of Structural Chemistry - A new polymorph of the [ReCl3(MeCN)(PPh3)2] complex is synthesized and characterized by single crystal X-ray diffraction (XRD). Its recrystallization from the... 相似文献
9.
Saqib Kamal Arif I. Inamdar Kuan-Ru Chiou Batjargal Sainbileg Muhammad Usman Jenq-Wei Chen Tzuoo-Tsair Luo Michitoshi Hayashi Chen-Hsiung Hung Wen-Feng Liaw Kuang-Lieh Lu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(30):e202103905
The dielectric properties of coordination polymers has been a topic of recent interest, but the role of different functional groups on the dielectric properties of these polymers has not yet been fully addressed. Herein, the effects of electron-donating (R=NH2) and electron-withdrawing (R=NO2) groups on the dielectric behavior of such materials were investigated for two thermally stable and guest-free Zn-based coordination polymers, [Zn(L1)(L2)]n ( 1 ) and [Zn(L1)(L3)]n ( 2 ) [L1=2-(2-pyridyl) benzimidazole (Pbim), L2=5-aminoisophthalate (Aip), and L3=5-nitroisophthalate (Nip)]. The results of dielectric studies of 1 revealed that it possesses a high dielectric constant (κ=65.5 at 1 kHz), while compound 2 displayed an even higher dielectric constant (κ=110.3 at 1 kHz). The electron donating and withdrawing effects of the NH2 and NO2 substituents induce changes in the polarity of the polymers, which is due to the inductive effect from the aryl ring for both NO2 and NH2. Theoretical results from density functional theory (DFT) calculations, which also support the experimental findings, show that both compounds have a distinct electronic behavior with diverse wide bandgaps. The significance of the current work is to provide information about the structure-dielectric property relationships. So, this study promises to pave the way for further research on the effects of different functional groups on coordination polymers on their dielectric properties. 相似文献
10.
Cellulose - In this research, the production of levoglucosan (LG) and levoglucosenone (LGO) was improved from acid-impregnated cellulose via fast pyrolysis. Thermogravimetric and kinetic analysis... 相似文献