全文获取类型
收费全文 | 239篇 |
免费 | 13篇 |
国内免费 | 37篇 |
专业分类
化学 | 235篇 |
力学 | 3篇 |
综合类 | 1篇 |
数学 | 23篇 |
物理学 | 27篇 |
出版年
2023年 | 5篇 |
2022年 | 7篇 |
2021年 | 14篇 |
2020年 | 8篇 |
2019年 | 12篇 |
2018年 | 3篇 |
2017年 | 10篇 |
2016年 | 5篇 |
2015年 | 19篇 |
2014年 | 13篇 |
2013年 | 21篇 |
2012年 | 21篇 |
2011年 | 15篇 |
2010年 | 10篇 |
2009年 | 8篇 |
2008年 | 12篇 |
2007年 | 14篇 |
2006年 | 15篇 |
2005年 | 8篇 |
2004年 | 8篇 |
2003年 | 4篇 |
2002年 | 6篇 |
2001年 | 5篇 |
2000年 | 6篇 |
1999年 | 15篇 |
1998年 | 9篇 |
1997年 | 3篇 |
1996年 | 5篇 |
1995年 | 5篇 |
1993年 | 1篇 |
1990年 | 2篇 |
排序方式: 共有289条查询结果,搜索用时 15 毫秒
11.
12.
Partitioned difference families (PDFs) arise from constructions of optimum constant composition codes. In this paper, a number of infinite classes of PDFs are constructed, based on known cyclotomic difference families in GF(q). A general approach which obtains PDFs from difference packings and coverings in abelian group is also presented. 相似文献
13.
The rigid [6]ferrocenophane, L1, was synthesised by condensation of 1,1′-ferrocene dicarbaldehyde with trans-1,2-diaminocyclohexane in high dilution at r.t. followed by reduction. When other experimental conditions were employed, the [6,6,6]ferrocenephane (L2) was also obtained. Both compounds were characterised by single crystal X-ray crystallography. The protonation of L1 and its metal complexation were evaluated by the effect on the electron-transfer process of the ferrocene (fc) unit of L1 using cyclic voltammetry (CV) and square wave voltammetry (SWV) in anhydrous CH3CN solution and in 0.1 M nBu4NPF6 as the supporting electrolyte. The electrochemical process of L1 between −300 and 900 mV is complicated by amine oxidation. On the other hand, an anodic shift from the fc/fc+ wave of L1 of 249, 225, 81 and 61 mV was observed by formation of Zn2+, Ni2+, Pd2+ and Cu2+ complexes, respectively. Whereas Mg2+ and Ca2+ only have with L1 weak interactions and they promote the acid-base equilibrium of L1. This reveals that L1 is an interesting molecular redox sensor for detection of Zn2+ and Ni2+, although the kinetics of the Zn2+ complex formation is much faster than that of the Ni2+ one. The X-ray crystal structure of [PdL1Cl2] was determined and showed a square–planar environment with Pd(II) and Fe(II) centres separated by 3.781(1) Å. The experimental anodic shifts were elucidated by DFT calculations on the [ML1Cl2] series and they are related to the nature of the HOMO of these complexes and a four-electron, two-orbital interaction. 相似文献
14.
柚皮苷分子印迹膜的水相制备与识别 总被引:2,自引:0,他引:2
以柚皮苷为印迹分子,PEG为致孔剂,在水相中制备了柚皮苷分子印迹壳聚糖膜.分别讨论了交联剂、致孔剂和印迹分子的用量对印迹膜结构和性能的影响.用SEM观察了致孔剂对印迹膜形貌及孔径的影响.紫外吸收光谱分析、柚皮苷在不同体系中的溶解度变化,以及红外光谱分析的结果表明功能聚合物壳聚糖和模板分子柚皮苷间形成了氢键.膜的渗透实验结果表明,在水相中,柚皮苷分子印迹膜能有效地从新橙皮苷和柚皮苷的混合液中分离出印迹分子柚皮苷,选择透过率为11.16%. 相似文献
15.
Mesoporous TiO2/SiO2 composite nanofibers with a diameter of 100-200 nm and silica shell thickness of 5-50 nm have been fabricated by a sol-gel combined two-capillary co-electrospinning method; the composite nanofibers exhibited selective photocatalytic activity based on the decomposition of Methylene Blue, Active Yellow and Disperse Red. 相似文献
16.
17.
Effect of mixed eluents which contain zwitterions such as 2-(N-morpholino)ethanesulfonic acid (MES), 3-(N-morpholino)propanesulfonic acid (MOPS), 2-(cyclohexylamino)ethanesulfonic acid (CHES) and 3-(cyclohexylamino)-1-propanesulfonic acid (CAPS) and carbonate for suppressed conductivity ion chromatography (IC) were studied. The retention behaviors of all species were affected with different anion exchange columns when adding some zwitterion into carbonate eluent. The retention time of all species, especially those of strong retetion, was substantially shortened in AS14A column with either Na(2)CO(3)/CHES or Na(2)CO(3)/CAPS as eluent while a general increase in retetion time was noticed in AS9-HC column. Low pH of eluent was achieved when zwitterion was added. Without much changes in the background conductivity after suppressed, CHES could be used as suppressed conductivity ion chromatography eluent for determination of species unstable in strong alkaline, such as determination of phosphate in heteropoly acid (HPA) samples in AS14 column. The mixed eluent could also affect the selectivity when it was applied to the study of simultaneous separation of anions and cations in AS9-HC column by suppressed ion chromatography. 相似文献
18.
利用标量化方法建立对称向量拟均衡问题有效解的存在性定理.作为标量化方法的应用,利用这一方法得到向量变分不等式和拟向量变分不等式有效解的存在性定理. 相似文献
19.
Chloride‐bridged palladacycle dimers 1 have been evaluated as catalysts for the aza‐Claisen rearrangement of allylic imidates 2 to the corresponding allyl amides 3 . Cyclopalladated complexes 1b–e bearing electron‐donating substituents on imidazoline ring were identified as being superior catalysts because excellent yields were obtained without using silver salts for activation. In addition, a correlation between substituents on the imidazoline ring and catalytic activity of palladacycles was established. The electron‐deficient ligands and good solubility of catalysts in the reaction solution increase the catalytic activity. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
20.
Kun Xu Xiuling Li Pengzuo Chen Dan Zhou Changzheng Wu Yuqiao Guo Lidong Zhang Jiyin Zhao Xiaojun Wu Yi Xie 《Chemical science》2015,6(1):283-287
Ferromagnetic two-dimensional (2D) ultrathin nanosheets hold great promise for next generation electronics. Ferromagnetic metal-free materials that usually possess only an s/p electronic configuration with weak spin–orbit coupling and a large spin relaxation time, would play an important role in constructing future spintronic devices. However, the absence of an intrinsic spin ordering structure in most metal-free materials greatly hampers the widening scope of ferromagnetic 2D nanostructures as well as in-depth understanding of their ferromagnetic nature. Herein, the induction of intrinsic ferromagnetism in 2D metal-free g-C3N4 ultrathin nanosheets has been achieved through a new effective strategy whereby hydrogen dangling bonds are introduced. In our case, g-C3N4 ultrathin nanosheets with hydrogen dangling bonds showed obvious room temperature ferromagnetic behavior that could even be tuned by the concentration of hydrogen. This work will pave a new pathway to engineer the properties of 2D nanomaterial systems. 相似文献