全文获取类型
收费全文 | 4043篇 |
免费 | 568篇 |
国内免费 | 400篇 |
专业分类
化学 | 2861篇 |
晶体学 | 34篇 |
力学 | 178篇 |
综合类 | 45篇 |
数学 | 594篇 |
物理学 | 1299篇 |
出版年
2024年 | 12篇 |
2023年 | 77篇 |
2022年 | 134篇 |
2021年 | 131篇 |
2020年 | 146篇 |
2019年 | 157篇 |
2018年 | 152篇 |
2017年 | 126篇 |
2016年 | 197篇 |
2015年 | 185篇 |
2014年 | 261篇 |
2013年 | 294篇 |
2012年 | 330篇 |
2011年 | 315篇 |
2010年 | 233篇 |
2009年 | 219篇 |
2008年 | 259篇 |
2007年 | 213篇 |
2006年 | 207篇 |
2005年 | 168篇 |
2004年 | 140篇 |
2003年 | 122篇 |
2002年 | 145篇 |
2001年 | 125篇 |
2000年 | 71篇 |
1999年 | 68篇 |
1998年 | 61篇 |
1997年 | 41篇 |
1996年 | 38篇 |
1995年 | 43篇 |
1994年 | 48篇 |
1993年 | 35篇 |
1992年 | 34篇 |
1991年 | 41篇 |
1990年 | 30篇 |
1989年 | 16篇 |
1988年 | 15篇 |
1987年 | 14篇 |
1986年 | 9篇 |
1985年 | 16篇 |
1984年 | 8篇 |
1983年 | 6篇 |
1982年 | 6篇 |
1981年 | 8篇 |
1980年 | 6篇 |
1979年 | 6篇 |
1978年 | 5篇 |
1977年 | 5篇 |
1971年 | 5篇 |
1962年 | 3篇 |
排序方式: 共有5011条查询结果,搜索用时 15 毫秒
991.
Antioxidant coumarin and pyrone derivatives from the insect-associated fungus Aspergillus Versicolor
Tian-Xiao Li Dan-Dan Meng Ying Wang Jin-Lu An Jia-Feng Bai Xue-Wei Jia 《Natural product research》2020,34(10):1360-1365
AbstractTwo new compounds, versicolones A and B (1 and 2), and three known pyrone derivatives (3?5) were isolated from the insect-associated fungus Aspergillus versicolor. Their structures were elucidated through a combination of HRESIMS and NMR spectroscopic analysis. Versicolone A (1) was revealed as a coumarin derivative with the rare 5-alkyl side chain substitution. Compound 5 exhibited significant antioxidant activity with EC50 value of 8.0?μM in the ABTS (2,2-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid) assay, which was more than 2-fold potency of the positive control trolox. 相似文献
992.
Ming-Hua Zheng Tie Wang Dong-Yang Wang Cheng-Hua Bai Shou Zhang Cheng-Shou An Hong-Fu Wang 《中国科学:物理学 力学 天文学(英文版)》2019,(5)
We study the generation of quadruple-transparency windows and the implementation of a conversion between slow and fast light in a hybrid optomechanical system. By demonstrating the generation of these transparency windows one by one, we analyze the physical mechanism through which each transparency window forms in detail. Additionally, we discuss how the system parameters affect the formation of transparency windows and conclude that the location, width, and absorption of each transparency window can be arbitrarily manipulated by varying the appropriate parameters. Moreover, when the pump field is changed from red to blue detuning, conversions between slow and fast light occur in the output field. These interesting properties of the output field can be applied to achieve the coherent control and manipulation of light pulses using cavity optomechanical system. 相似文献
993.
994.
强反馈光纤光栅外腔半导体激光器 总被引:5,自引:0,他引:5
在理论上对强外腔反馈情形的半导体激光器线宽压窄效应进行了分析,对消反膜剩余反射率,外腔反射率,外腔腔长对线宽压缩的影响进行了研究,在实验上采用光纤光栅作为反馈元件,与一端镀有消反膜的1.5μm波段的常规多纵模交导体激光器耦合,构成强反馈光纤光栅外腔半导体激光器,得到单频窄线宽的激光输出,静态下边模抑制比大于30dB,线宽小于120kHz。 相似文献
995.
Analytical expressions of the exciton-exciton interaction in 3D and 2D laser-excited semiconductors are approximately derived in rather easy-to-handle forms which enable us to study in detail their dependences on the exciton momenta, the momentum transferred between two excitons and the electron-hole mass ratio.We would like to thank Prof. Nguyen Van Hieu and Prof. Dao Vong Due for their support given to us in the research of highly excited media. 相似文献
996.
安军 《武汉大学学报(理学版)》1996,(3)
对两个相依方程组成的回归系统,当设计矩阵呈病态时,提出了回归系数的一个主成分估计β_1**(k)及其相应的两步估计β_1**(k,T),并在均方误差意义下研究了它们的优良性质。 相似文献
997.
998.
We classify the radical subgroups and chains of the Harada-Norton simple group HN and verify the Alperin weight conjecture
and the refined Dade conjecture due to Uno for the group. This implies the Isaacs-Navarro and Dade reductive conjectures for
the group.
This work was supported in part by the Marsden Fund of New Zealand via grant #9144/3368248. 相似文献
999.
We report a flexible all-optical gain controlled bidirectional optical amplifier. The device achieves constant gain and low noise figure over a large input power range. Moreover, the device removes Rayleigh backscattered light and amplifier noise. 相似文献
1000.
Nano-TiO2 is modified by a method, by which nano-TiO2 first reacts with silane coupling agent WD-70 with double bond group which subsequently copolymerizes with methyl methacrylate and butyl acrylate to produce a thin polymer shell on the nanoparticles. The modified nanoparticles have stable organophilicity. They are applied to polyacrylate coating and performances of the coating are measured by different methods. The modification of nano-TiO2 particles can improve their dispersibility in coating, enhance hardness of coating and reduce water absorption and permeability of polyacrylate coating. The mechanism has been analyzed in this paper. 相似文献