全文获取类型
收费全文 | 109篇 |
免费 | 16篇 |
国内免费 | 20篇 |
专业分类
化学 | 82篇 |
晶体学 | 1篇 |
力学 | 1篇 |
数学 | 10篇 |
物理学 | 51篇 |
出版年
2023年 | 1篇 |
2021年 | 1篇 |
2020年 | 3篇 |
2018年 | 1篇 |
2017年 | 1篇 |
2016年 | 3篇 |
2013年 | 5篇 |
2012年 | 5篇 |
2011年 | 2篇 |
2010年 | 6篇 |
2009年 | 7篇 |
2008年 | 7篇 |
2007年 | 4篇 |
2006年 | 3篇 |
2005年 | 8篇 |
2004年 | 8篇 |
2003年 | 10篇 |
2002年 | 16篇 |
2001年 | 11篇 |
2000年 | 11篇 |
1999年 | 5篇 |
1998年 | 1篇 |
1997年 | 2篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1989年 | 4篇 |
1988年 | 2篇 |
1986年 | 1篇 |
1982年 | 3篇 |
1978年 | 1篇 |
1975年 | 1篇 |
1909年 | 2篇 |
1904年 | 1篇 |
排序方式: 共有145条查询结果,搜索用时 8 毫秒
61.
Rong Jian SA Ke Chen WU* Ping LIU Chen Sheng LIN Chao Yong MANG State Key Laboratory of Structural Chemistry Fujian Institute of Research on the Structure of Matter Chinese Academy of Sciences Fuzhou The Graduate school of the Chinese Academy of Sciences Beijing 《中国化学快报》2002,(12)
A series of tri-nuclear transition metal clusters with incomplete cubane-like configurations have been studied by TDDFT method. The calculations show that they have enormously large second-order polarizabilities () and are potential nonlinear optical materials for infrared double frequency conversion1. In this paper some tetra-nuclear transition metal clusters with cubane-like configurations, MCu3X4 (PPh3)3 (M=W, Mo; X= S, O, Cl, Se, Br), were studied by TDDFT method for a reference… 相似文献
62.
Let G be a graph with n(G) vertices and m(G) be its matching number.The nullity of G,denoted by η(G),is the multiplicity of the eigenvalue zero of adjacency matrix of G.It is well known that if G is a tree,then η(G) = n(G)-2m(G).Guo et al.[Jiming GUO,Weigen YAN,Yeongnan YEH.On the nullity and the matching number of unicyclic graphs.Linear Alg.Appl.,2009,431:1293 1301]proved that if G is a unicyclic graph,then η(G)equals n(G)-2m(G)-1,n(G)-2m(G),or n(G)-2m(G) +2.In this paper,we prove that if G is a bicyclic graph,then η(G) equals n(G)-2m(G),n(G)-2m(G)±1,n(G)-2m(G)±2or n(G)-2m(G) + 4.We also give a characterization of these six types of bicyclic graphs corresponding to each nullity. 相似文献
63.
A phenomenological theory for polarization flop in spiral multiferroic TbMnO<Subscript>3</Subscript>
A phenomenological Landau theory has been used to explain magnetic field-driven polarization flop in TbMnO 3. The Néel wall-like magnetic structure in spiral multiferroics induces a space-dependent internal magnetic field which exerts a torque on spins to rotate bc-spiral to ab-spiral. The external magnetic field is argued to be competing with easy axis anisotropy and the system stabilizes when anisotropy is minimum. With the help of Landau free energy with DM magnetoelectric coupling and a general ansatz for magnetization, the phenomenon of polarization flop has been explained. Relation between Tflop and critical magnetic field has been established and found to be in good agreement with the experiment. This could be an indication that anisotropy of the system is temperature- and magnetic field-dependent. 相似文献
64.
65.
Could the New Absorption Cross Section of J/ψ Change the Aspect of Nuclear Absorption Mechanism 下载免费PDF全文
The enlarged new absorption cross sections of J/ψ by π and ρ were put into the hadron and string cascade model, JPCIAE, and the J/ψ suppression factors in P-A, O-U, S-U and Pb-Pb minimum bias collisions at 200A GeV/c were calculated with nuclear absorption mechanism only. The results seem to indicate that, with new enlarged cross section it is still hard to change the aspect that nuclear absorption mechanism itself could not easily account for the J/ψ anomalous suppression in Pb-Pb collisions. 相似文献
66.
Richard D. Chambers Takashi Nakano Graham Sandford Andrei S. Batsanov 《Journal of fluorine chemistry》2008,129(9):811-816
Reactions of 3β-acetoxy-5α-androstan-17-one with elemental fluorine and Selectfluor® are reported and give contrasting results. Fluorine gives a mixture of mono-fluorinated steroids in which fluorine atoms are attached to tertiary carbon sites whereas Selectfluor® gives fluoro-steroid systems arising from electrophilic aliphatic substitution of the most sterically accessible secondary saturated positions. The identities of the fluoro-steroid products were determined by NMR analysis and X-ray crystallography. 相似文献
67.
检验分子晶体非线性光学极化率的可加性,对于确认有向气体模型(Oriented-Gas Model) 具有重要的科学意义,对探索新型实用的分子非线性光学材料也有实际的意义。本文对尿素晶体中分子簇非线性光学极化率的可加性做了详尽的理论研究。首次做到了尿素分子最近邻排布团簇的非线性光学极化率的从头算,从而扩展了前人的工作。研究结果有效地确认了有向气体模型。同时,我们还提出了壳层结构模型 (Shell-Structure Model),用以解决有向气体模型中的缺陷,可实现更为有效可靠地计算晶体宏观非线性光学系数。 相似文献
68.
69.
Annelation reactions between pentafluorobenzonitrile and N,N-dimethylethylene diamine and 3-methyl picoline gave [6,6]-bicyclic and [6,5,6]-tricyclic ring-fused systems, respectively. Reaction of 4-morpholino tetrafluorobenzonitrile with hydrazine and phenyl hydrazine gave [5,6] ring-fused systems arising from a tandem SNAr and cyclisation process involving annelation onto the pendant cyano group providing an indication of the synthetic possibilities for heterocycle formation using the pentafluorobenzonitrile scaffold. 相似文献
70.
使用LUCIAE3.0模型模拟了SPS能区Pb+Pb和C+C在不同能量(Elab=20—200A GeV)和不同中心度下的重离子碰撞.并通过逐个事件的粒子温度涨落提取出了相应粒子的热容,发现对于同一碰撞系统,单位发射粒子的热容随碰撞能量的升高而下降直至饱和,随着碰撞参数b的增大而减小,而且发现单位发射粒子的热容具有随粒子质量的变大而变大的关系.同时还发现不同碰撞系统中同一种粒子具有相同的单位发射粒子热容,并给出了相应的解释. 相似文献