全文获取类型
收费全文 | 79篇 |
免费 | 24篇 |
国内免费 | 17篇 |
专业分类
化学 | 69篇 |
力学 | 3篇 |
数学 | 21篇 |
物理学 | 27篇 |
出版年
2023年 | 2篇 |
2022年 | 2篇 |
2021年 | 12篇 |
2020年 | 3篇 |
2019年 | 2篇 |
2018年 | 1篇 |
2017年 | 7篇 |
2016年 | 2篇 |
2015年 | 1篇 |
2014年 | 7篇 |
2013年 | 17篇 |
2012年 | 17篇 |
2011年 | 10篇 |
2010年 | 10篇 |
2009年 | 3篇 |
2008年 | 6篇 |
2007年 | 3篇 |
2006年 | 3篇 |
2005年 | 2篇 |
2004年 | 1篇 |
2002年 | 2篇 |
2001年 | 2篇 |
2000年 | 2篇 |
1999年 | 1篇 |
1994年 | 1篇 |
1991年 | 1篇 |
排序方式: 共有120条查询结果,搜索用时 718 毫秒
61.
Sheng Ouyang Lei Wang Qing-Wen ZhangGuo-Cai Wang Ying WangXiao-Jun Huang Xiao-Qi ZhangRen-Wang Jiang Xin-Sheng YaoChun-Tao Che Wen-Cai Ye 《Tetrahedron》2011,67(26):4807-4813
Six new monoterpenoid indole alkaloids along with four known analogues were isolated from the aerial part of Gelsemium elegans. Their structures with absolute configurations were elucidated by NMR, HRESIMS, X-ray diffraction, CD spectra, and molecular modeling calculation. Among them, gelselenidine (1) is a new gelsedine-type alkaloid with a 2,3-epoxybutane unit. Gelseziridine (2) is the first example of monoterpenoid indole alkaloids with an oxaziridine residue. Compounds 6 and 7 are a pair of N4 epimers of humantenine N4-oxide. A plausible biogenetic pathway for compounds 1-4 was also proposed. 相似文献
62.
Qing-Wen WangShao-Wen Yu 《Applied mathematics and computation》2011,218(6):2761-2771
We in this paper consider the bisymmetric nonnegative definite solution with extremal ranks and inertias to a system of quaternion matrix equations AX = C, XB = D. We derive the extremal ranks and inertias of the common bisymmetric nonnegative definite solution to the system. The general expressions of the bisymmetric nonnegative definite solution with extremal ranks and inertias to the system mentioned above are also presented. In addition, we give a numerical example to illustrate the results of this paper. 相似文献
63.
Chen Zhuo-Ling Dong Youzhen Liu Qing-Wen Bian Rong-Rong Cheng Wei-Wei Xue Yun-Shan Liu Mei-Pin 《Transition Metal Chemistry》2019,44(5):445-454
Transition Metal Chemistry - Two coordination polymers based on 1,4-bis(benzimidazo-1-ly)benzene (L) and O-donor linking co-ligands, namely {[ZnL(mipa)(H2O)]}n (1) and {[Cd2L2(sdba)Cl2]}n (2)... 相似文献
64.
In this paper, a mixed terminal structure for the 4H-SiC merged PiN/Schottky diode (MPS) is investigated, which is a combination of a field plate, a junction termination extension and floating limiting rings. Optimization is performed on the terminal structure by using the ISE-TCAD. Further analysis shows that this structure can greatly reduce the sensitivity of the breakdown voltage to the doping concentration and can effectively suppress the effect of the interface charge compared with the structure of the junction termination extension. At the same time, the 4H-SiC MPS with this termination structure can reach a high and stable breakdown voltage. 相似文献
65.
66.
Baeyer-Villiger反应是酮在过氧酸氧化下形成酯的反应,是有机反应中合成酯的主要方法,这一反应可应用在环酮扩环形成含氧杂环内酯的反应上.由于反应是立体控制的,已广泛应用于天然产物,例如:抗生素、类固醇和信息素中间体的合成,某些用其它方法难以合成的羟基酸可由内酯水解得到。 相似文献
67.
Study of a double epi-layers SiC junction barrier Schottky rectifiers embedded P layer in the drift region
下载免费PDF全文
![点击此处可从《中国物理 B》网站下载免费的PDF全文](/ch/ext_images/free.gif)
<正>This paper proposes a double epi-layers 4H—SiC junction barrier Schottky rectifier(JBSR) with embedded P layer (EPL) in the drift region.The structure is characterized by the P-type layer formed in the n-type drift layer by epitaxial overgrowth process.The electric field and potential distribution are changed due to the buried P-layer,resulting in a high breakdown voltage(BV) and low specific on-resistance(R_(on,sp)).The influences of device parameters,such as the depth of the embedded P+ regions,the space between them and the doping concentration of the drift region,etc.,on BV and R_(on,sp) are investigated by simulations,which provides a particularly useful guideline for the optimal design of the device.The results indicate that BV is increased by 48.5%and Baliga's figure of merit(BFOM) is increased by 67.9%compared to a conventional 4H-SiC JBSR. 相似文献
68.
该文给出了四元数矩阵方程组X_1B_1=C_1,X_2B_2=C2,A_1X_1B_3+A_2X_2B_4=C_b可解的充要条件及其通解的表达式,利用此结果建立了四元数矩阵方程组XB_a=C_a,A_bXB_b=C_b有广义(反)反射解的充要条件及其有此种解时通解的表达式. 相似文献
69.
报道了一种结构简单、运转稳定并可以输出高脉冲能量的被动锁模光纤激光器.激光器的增益介质为掺Yb3 双包层大模场面积光纤,具有非常低的非线性系数.利用非线性偏振旋转效应和半导体可饱和吸收镜结合实现自启动锁模,获得了平均功率为160 mW、重复频率为55.9 MHz(对应于3 nJ的单脉冲能量)、脉冲宽度为10.6 ps的激光脉冲输出. 相似文献
70.
A new drimane sesquiterpenoid was isolated from the heartwood of the Japanese yew, Taxus cuspidata Sieb. et Zucc. Its structure was established as 1beta-acetoxyisodrimeninol (1beta-acetoxy-11,12-epoxy-7-drimen-11-ol, 1). This compound was gradually oxidized to give y-lactone (1beta-acetoxy-8-drimeno-11,12-lactone, 4). 相似文献