全文获取类型
收费全文 | 89篇 |
免费 | 82篇 |
国内免费 | 62篇 |
专业分类
化学 | 126篇 |
晶体学 | 4篇 |
数学 | 3篇 |
物理学 | 100篇 |
出版年
2023年 | 1篇 |
2022年 | 6篇 |
2020年 | 1篇 |
2019年 | 2篇 |
2018年 | 3篇 |
2016年 | 1篇 |
2015年 | 1篇 |
2014年 | 4篇 |
2013年 | 19篇 |
2012年 | 10篇 |
2011年 | 19篇 |
2010年 | 17篇 |
2009年 | 25篇 |
2008年 | 21篇 |
2007年 | 14篇 |
2006年 | 9篇 |
2005年 | 19篇 |
2004年 | 4篇 |
2003年 | 9篇 |
2002年 | 8篇 |
2001年 | 9篇 |
2000年 | 8篇 |
1999年 | 4篇 |
1998年 | 5篇 |
1997年 | 1篇 |
1996年 | 2篇 |
1994年 | 3篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有233条查询结果,搜索用时 15 毫秒
1.
In order to contribute to the Apparent Polar Wander Path (APWP) of the North China Block (NCB) , we collected paleomagnetic samples of Late Paleozoic rocks from the northern and southern margins of the Alashan (Alxa) terrane (the western part of Inner Mongolia and northern parts of Gansu and Ningxia Provinces) and adjacent regions. Laboratory work revealed different types of demagnetization behavior and isolated a higher temperature characteristic component in most of the samples. Results of IRM experiments show high thermal stability and high coercivities for the magnetic carriers in these rocks. The characteristic component passed the fold and/or reversal tests, suggesting that the characteristic components were probably primary. On the basis of comparing the paleomagnetic results with the geologic evidence, we discuss the tectonic implications. In the Late Paleozoic, the Alashan region had been part of the NCB and was not connected with the northern and southern blocks. During the Carboniferous Alash 相似文献
2.
Hong-Wen Hu Xu-Dong Wei Cun Li Hong-Zhe Sun Yi-Ming Yao Zhong-Yuan Zhou Kai-Bei Yu 《中国化学》1992,10(3):278-284
The reaction of m-chlorobenzaldoxime dehydrodimer with styrene gives two 1:1 adducts.The main product 7 is a bisnitrone. The minor product 8 has been shown by X-ray diffraction anal-ysis to possess the structure: ArCH(N=O)CH_2CH (Ph)O--N=CHAr. The two C=N bonds areall in Z configuration. The structure of the adducts from benzaldoxime dehydrodimer and styrene isalso assigned. 相似文献
3.
在合成[Co(bpma)(tn)Cl]2+体系配合物的实验中,得到[Co(ptma)(amp)Cl]2+体系的一反式(ptma中仲胺上的氢相对于Cl)经式异构体(m3[ZnCl4]·0.5H2O),其中bpma=N,N′-二(2-吡啶基甲基)胺,tn=1,3丙二胺,ptma=N-(2-吡啶基甲基)丙二胺,amp=2-(氨基甲基)吡啶。此配合物异构体构型选择性形成的原因可能主要是其结构中配体间C-H…π相互作用使之更稳定的结果。利用单晶X-射线衍射法测定的晶体学参数:单斜晶系,空间群C2/c,a=1.55978(19)nm,b=1.33324(16)nm,c=2.2077(3)nm,β=94.832(3)°,V=4.5748(10)nm3,Dc=1.696g·cm-3,Z=8,F000=2360,μ(MoKα)=23.72cm-1,R=0.0475,Rw=0.1204。配合物离子中Co3+为六配位。晶胞中含8个配合物阳离子,8个[ZnCl4]2-阴离子及4个水分子,对映体的比例为1∶1。 相似文献
4.
Liang Hong Chen Zhen-Feng Hu Rui-Xiang Yu Qing Zhou Zhong-Yuan Zhou Xiang-Ge 《Transition Metal Chemistry》2002,27(1):102-104
(n-Bu4N)4[Mo8O26] reacts with the Na salt of 2-mercaptopyridine N-oxide (NaPT) in MeCN to give the complex (n-Bu4N)2[MoO2(PT)2·Mo4O8(-O)2(3-O)2(PT)2] (1) which contains two metal centres: one being mononuclear molybdenum chelating to two PT ligands, and the other a tetranuclear oxomolybdenum cluster with two PT ligands at the terminal point. The i.r. spectrum of the title complex exhibits absorption bands at 911.5 and 881.9 cm–1, characteristic of the [cis-MoO2]2+ fragment. 相似文献
5.
Hu Xue-Lei Luo Qin-Hui Wang Zhi-Lin Wang Yi-Ning Zhou Zhong-Yuan 《Transition Metal Chemistry》2003,28(6):640-643
A new heterodinuclear cryptate [AgCuL](ClO4
–)2 was synthesized by transmetallation via its precursor [Ag2L](ClO4
–)2 (L = ligand). The electrospray mass spectrum (ES-MS) showed that the heterodinuclear entity exists in the solution. The X-Ray structure analysis shows that the AgI ion has tetrahedral geometry while CuI lies in a three-coordinate environment. 相似文献
6.
7.
8.
Hydrogen Passivation Effect on Enhanced Luminescence from Nanocrystalline Si/SiO2 Multilayers 下载免费PDF全文
Nanocrystalline Si/SiO2 multilayers are prepared by thermally annealing amorphous Si/SiO2 stacked structures. The photoluminescence intensity is obviously enhanced after hydrogen passivation at various temperatures. It is suggested that the hydrogen trapping and detrapping processes at different temperatures strongly influence the passivation effect. Direct experimental evidence is given by electron spin resonance spectra that hydrogen effectively reduces the nonradiative defect states existing in the Si nanocrystas/SiO2 system which enhances the radiative recombination probability. The luminescence characteristic shows its stability after hydrogen passivation even after aging eight months. 相似文献
9.
The crystal structures of a pair isomers of [Co(3,3-tri)(amp)Cl][ZnCl4] (here 3,3-tri = N-(3-Aminoprop- yl)-1,3-propanediamine; amp=2-(Aminomethyl)pyridine) have been determined by single crystal X-ray diffrac-tion. They are the epimers with the only difference of the orientation of the Sec-NH proton in 3,3-tri ligand. The crystals with the anti-epimer (m1[ZnCl4]·CH3OH·H2O) are monoclinic, space group C2/c with eight molecules in a unit cell of dimensions a=30.401(5)?,b=8.0469(13)?,c=18.817(3)?,β=93.346(3)°,V=4595.3(12)?3,Dc=1.708g·cm-3,Z=8,F000=2416,R=0.0462,Rw=0.1304. The crystals of the syn-epimer (m2[ZnCl4]·H2O) are triclinic, space group P1 with two molecules in a unit cell of dimensions a=8.9752(12)?,b=9.8855(12)?,c=12.6886(16)?,α=89.228(3)°,β=76.447(2)°,γ=80.428(3)°,V=1078.8(2)nm3,Dc=1.721g·cm-3,Z=2,F000=568,R=0.0313,Rw=0.0929. The crystal parameters, such as bond lengths and angles, are well consistent with the data of an ab initio computational result (RHF/LANL2DZ opti-mised structure). The average error for bond length is about 1.6%, only two of them in the isomer m3 (Co-N2 and Co-N4) are over 3%, (3.09% and 4.28% respectively). The errormax for bond angle is 2.52%, the bond angles with an over 2% error are only 3.6% out of all bond angles. 相似文献
10.
CdSe纳米线阵列的制备及其表征(英) 总被引:1,自引:0,他引:1
通过在含有SeSO32-和Cd2+的室温水溶液中,用模板-电沉积法在纳米孔阵列阳极氧化铝膜(AAM)模板中制备了高有序性的CdSe纳米线阵列,并对其形貌、结构和组分进行了表征。扫描电子显微镜(SEM)和透射电子显微镜(TEM)结果表明,纳米线阵列中的CdSe纳米线具有相同的长度和直径,分别对应于使用的AAM模板的厚度和孔径;X-射线衍射(XRD)和X-射线能谱(EDAX)结果表明,CdSe纳米线中Cd和Se的化学组成非常接近于1∶1,其结构为立方CdSe。另外,对模板-电沉积法制备CdSe纳米线的机理进行了讨论。 相似文献