全文获取类型
收费全文 | 44篇 |
免费 | 23篇 |
国内免费 | 48篇 |
专业分类
化学 | 80篇 |
数学 | 2篇 |
物理学 | 33篇 |
出版年
2023年 | 1篇 |
2021年 | 2篇 |
2020年 | 2篇 |
2019年 | 1篇 |
2018年 | 5篇 |
2017年 | 3篇 |
2016年 | 5篇 |
2015年 | 5篇 |
2014年 | 1篇 |
2013年 | 2篇 |
2012年 | 6篇 |
2011年 | 8篇 |
2010年 | 3篇 |
2009年 | 4篇 |
2008年 | 4篇 |
2007年 | 9篇 |
2006年 | 8篇 |
2005年 | 5篇 |
2004年 | 5篇 |
2002年 | 1篇 |
2001年 | 5篇 |
2000年 | 1篇 |
1998年 | 2篇 |
1997年 | 4篇 |
1996年 | 1篇 |
1995年 | 2篇 |
1994年 | 7篇 |
1993年 | 6篇 |
1992年 | 3篇 |
1990年 | 2篇 |
1988年 | 1篇 |
1983年 | 1篇 |
排序方式: 共有115条查询结果,搜索用时 515 毫秒
1.
2.
磺酞豚分子是一类极其重要的低毒超高效除草剂,有着十分重要的用途.研究分子的空间结构对于了解分子的构效关系十分重要.最近,我们测定的一系列分子的晶体结构[‘-’1表明,分子1、2、3晶体结构的空间群分别为PZ;儿、Pz、Pz,说明晶体中分别有对称元素(对称面或者对称中心),分子以对映体的形式存在于晶体中.由于磺酸豚分子本身不存在手性原子,由此推断磺酷服分子在晶体中存在的对映异构体是由内旋转阻碍产生的,因而应是构象异构体.本项研究工作的目的是应用分子力学方法,计算阻碍内旋转的能垒,从而找出分子内旋转时的最低… 相似文献
3.
应用分子动力学模拟方法对单嘧磺隆在水、正辛醇和正辛烷3种不同溶剂中的构象行为、单嘧磺隆与3种溶剂之间的相互作用能及氢键相互作用进行了计算研究. 计算结果表明, 在3种不同的溶剂中, 单嘧磺隆的优势构象不同; 其构象转换过程, 特别是转换成活性构象的过程主要发生在水溶液中; 与溶剂分子间的相互作用是分子构象行为的决定因素; 单嘧磺隆的脲桥部分可以和含氢键接受体的溶剂形成氢键, 分子间与分子内氢键的竞争可能是从晶体构象转换成活性构象的主要驱动力. 相似文献
4.
EPR study showed that the semi-quinone radical anion of chloranil (TCQ) was formed in a charge-transfer process between ground state chloranil as acceptor and each one of the following ground state donors,i.e.,N,N'-diethyl aniline (DEA),phenothiazine (PTZ),carbazole (CBZ),pyrene (PY),ferrocene (FRO),triphenylphosphine (TPP),triethylamine (TEA),anthracene (AN) and N,N-diethyl-3-aminophenyl ester of palmitic acid (DPP).Our results indicate that there is a tunneling effect for the ground-state charge-transfer process between chloranil and the donor. 相似文献
5.
Nonextensive effects on QCD chiral phase diagram and baryon-number fluctuations within Polyakov-Nambu-Jona-Lasinio model 下载免费PDF全文
In this paper, a version of the Polyakov-Nambu-Jona-Lasinio (PNJL) model based on nonextensive statistical mechanics is presented. This new statistics summarizes all possible factors that violate the assumptions of the Boltzmann-Gibbs (BG) statistics to a dimensionless nonextensivity parameter q. Thus, when q tends to 1, it returns to the BG case. Within the nonextensive PNJL model, we found that as q increases, the location of the critical end point (CEP) exhibits non-monotonic behavior. That is, for \begin{document}$ q<1.15 $\end{document} ![]()
![]()
, CEP moves in the direction of lower temperature and larger quark chemical potential. However, for \begin{document}$ q>1.15 $\end{document} ![]()
![]()
, CEP turns to move in the direction of lower temperature and lower quark chemical potential. In addition, we studied the moments of the net-baryon number distribution, that is, variance (\begin{document}$ \sigma^{2} $\end{document} ![]()
![]()
), skewness (S), and kurtosis (κ). Our results are generally consistent with the latest experimental data reported, especially for \begin{document}$ \sqrt{S_{NN}}>19.6\ \mathrm{GeV} $\end{document} ![]()
![]()
, when q is set to \begin{document}$ 1.07 $\end{document} ![]()
![]()
. 相似文献
7.
8.
Behaviour of Self-Standing CVD Diamond Film with Different Dominant Crystalline Surfaces in Thermal-Iron Plate Polishing 下载免费PDF全文
Self-standing CVD diamond films with different dominant crystalline surfaces are polished by the thermal-iron plate polishing method. The influence of the dominant crystalline surfaces on polishing etfficiency is investigated by measuring the removal rate and final roughness. The smallest rms roughness of 0.14 μm is measured with smallest removal rate in the films with the initial (220) dominant crystalline surface. Activation energy for the polishing is analysed by the Arrhenius relation. It is found that the values are 170kJ/mol, 222kJ/mol and 214kJ/mol for the film with three different dominant crystalline surfaces. Based on these values, the polishing cause is regarded as the graphitization-controlling process. In the experiment, we find that transformation of the dominant crystalline surfaces from (111) to (220) always appears in the polishing process when we polish the (111) dominant surface. 相似文献
9.
Electrogenerated chemiluminescence (ECL) of luminol on a gold-nanorod-modified gold electrode was studied, and five ECL peaks were obtained under conventional cyclic voltammetry in both neutral and alkaline solutions. Among them, four ECL peaks (ECL-1-4) were also observed on a gold-nanosphere-modified gold electrode, but the intensities of these ECL peaks were enhanced about 2-10-fold on a gold-nanorod-modified gold electrode in neutral solution. One new strong ECL peak (ECL-5) was obtained at -0.28 V (vs SCE) on a gold-nanorod-modified gold electrode in both neutral and alkaline solutions and enhanced with an increase in pH. In strong alkaline solutions, ECL-1 and ECL-2 on a gold-nanosphere-modified electrode were much stronger than those on a gold-nanorod-modified gold electrode, while ECL-3-5 appeared to only happen on a gold-nanorod-modified gold electrode. The emitter of all the ECL peaks was identified as 3-aminophthalate. The ECL peaks were found to depend on the scan direction, the electrolytes, the pH, and the presence of O(2) and N(2). The reaction pathways for ECL-4 have been further elucidated, and the mechanism of the new ECL peak (ECL-5) has been proposed. The results indicate that a gold-nanorod-modified gold electrode has a catalytic effect on luminol ECL different from that of a gold-nanosphere-modified gold electrode, revealing that the shape of the metal nanoparticles has an important effect on the luminol ECL behavior. The strong ECL of luminol in neutral solution obtained on a gold-nanorod-modified electrode may be used for the sensitive detection of biologically important compounds in physiological conditions. 相似文献
10.
The photodissociation dynamics of various aromatic molecules, studied using multimass ion imaging techniques, is reviewed. The experimental data reveals new isomerization and dissociation mechanisms. Our investigation of benzene, pyridine, and pyrimidine finds that H-atom elimination thresholds remain the same for the three molecules. We also notice that ring-opening dissociation thresholds decrease rapidly with the increase of the number of nitrogen atoms in the aromatic ring. Hydrogen atom elimination is the sole dissociation channel for benzene at 193 nm. Along with H-atom elimination, we observe five distinct ring-opening dissociation channels for pyridine at 193 nm. No dissociation channels were observed for benzene and pyridine at 248 nm. Ring-opening dissociation channels are the major channels for pyrimidine, which dissociates at 193 nm and also at 248 nm. A six-membered to seven-membered ring isomerization was observed for photodissociation processes involving toluene, m-xylene, aniline, 4-methylpyridine, alpha-fluorotoluene, and 4-fluorotoluene, indicating a general isomerization mechanism for all such aromatic molecules. What is significant, is that during the isomerization, atoms (i.e., carbon, nitrogen, fluorine, and hydrogen) belonging to respective alkyl or amino groups are involved in an exchange with atoms within the aromatic ring. This type of isomerization is not observed in other aromatic isomerization mechanisms. For small tyrosine chromophores, such as phenol, 4-methylphenol, and 4-ethylphenol, H-atom elimination from a repulsive excited state plays a key role. However, dissociation is quenched in large chromophores like 4-(2-aminoethyl)-phenol. Our work demonstrates the capability and high sensitivity of multimass ion imaging techniques in the study of aromatic compounds. 相似文献