全文获取类型
收费全文 | 120篇 |
免费 | 0篇 |
专业分类
化学 | 70篇 |
晶体学 | 9篇 |
力学 | 1篇 |
数学 | 6篇 |
物理学 | 34篇 |
出版年
2015年 | 1篇 |
2014年 | 1篇 |
2013年 | 1篇 |
2012年 | 2篇 |
2011年 | 1篇 |
2010年 | 3篇 |
2009年 | 6篇 |
2008年 | 9篇 |
2007年 | 4篇 |
2006年 | 3篇 |
2005年 | 3篇 |
2004年 | 4篇 |
2003年 | 3篇 |
2002年 | 11篇 |
2001年 | 9篇 |
2000年 | 18篇 |
1999年 | 11篇 |
1998年 | 8篇 |
1997年 | 2篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 6篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有120条查询结果,搜索用时 15 毫秒
81.
82.
Manuela Ramos Silva Ana Matos Beja Susana H. Lopes Jos Antnio Paixo Abílio J. F. N. Sobral A. M. d'A. Rocha Gonsalves 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(11):o685-o687
In the title compound, C16H17NO3·H2O, the pyrrole ring is distorted slightly from ideal C2v symmetry. Three strong hydrogen bonds link the substituted pyrrole and water molecules to form infinite chains, in which the hydrogen bonds form rings and chain patterns. Two intermolecular C—H?π interactions maintain the internal cohesion between these chains. The molecular structure differs slightly from that of the isolated molecule calculated by ab initio quantum‐mechanical calculations. In the latter model, the non‐H substituent atoms share the plane of the pyrrole ring, except for the phenyl group, which lies almost perpendicular to this plane. 相似文献
83.
Manuela Ramos Silva Ana Matos Beja Jose Antonio Paixo Abilio J. F. N. Sobral Susana H. Lopes A. M. d'A. Rocha Gonsalves 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(9):o572-o574
The title compound, C21H37NO2, is a new amphiphilic pyrrole with a long hydrocarbon chain, which will be used as a precursor for the synthesis of Langmuir–Blodgett films of porphyrins. Molecules related by an inversion centre are joined head‐to‐head into dimers by strong N—H?O hydrogen bonds. The dimers pack in the structure with their carbon chains parallel to one another, thereby forming alternating layers of carbon chains and pyrrole heads. The structure is further stabilized by two weak C—H?π intermolecular interactions, thereby saturating the hydrogen‐bonding capability of the aromatic π‐electron clouds. 相似文献
84.
M. Ramos Silva J.A. Paixão A. Matos Beja L. Alte da Veiga J. Martín-Gil 《Journal of chemical crystallography》2001,31(3):167-171
[Cu2(bet)4Cl2]Cl2·4H2O (bet = betaine: IUPAC name: trimethylammonioacetate) is monoclinic, space group P21/c, a = 11.0510(10) Å, b = 14.7140(4) Å, c = 11.1620(15) Å, = 107.40(2)°. The dinuclear copper(II) cation [Cu2(bet)4Cl2]2+ is counterbalanced by two naked Cl– ions. The copper(II) ions have a square bipyramidal environment with oxygen atoms from the acetato groups in the basal planes and a chlorine and a copper atom occupying the apical positions. The metal atoms are 2-bridged by four acetato groups and the molecular symmetry is close to C
2h. The two symmetry-independent chelating betaine molecules are present in their zwitterionic, neutral form. 相似文献
85.
86.
87.
Manuela Ramos Silva Ana Matos Beja Jesus Martín-Gil 《Journal of solid state chemistry》2006,179(7):2054-2058
A new 1D complex has been prepared and characterized. X-ray single crystal structure confirms that the Mn(II) ions assemble in alternating chains with Mn-Mn distances of 3.8432(13) and 4.4428(14) Å. A 3D network of hydrogen bonds links the chains together. The temperature dependence of the magnetic susceptibility reveals that this compound undergoes a magnetic transition and exhibits an antiferromagnetic interaction in the low-temperature phase with two alternating exchange interactions of −2.32(1) and −5.55(1) cm−1. 相似文献
88.
Much is known about the connection between the growth and decayof subharmonic functions. The results indicate that there isa general principle: asubharmonic function cannot decay toofast relative to its growth.Three theorems are provedwhich, together with work previously published elsewhere, givea fairly complete account of how this principle works out fora subharmonic function having extremal decay along a ray. 1991Mathematics Subject Classification: 30D20, 31A05. 相似文献
89.
Jarmelo S Reva I Rozenberg M Silva MR Beja AM Fausto R 《The journal of physical chemistry. B》2008,112(27):8032-8041
The structure of dl-serine.HCl was studied by three complementary techniques. Experimental Fourier transform infrared (FT-IR) spectra of pure NH/OH polycrystalline dl-serine.HCl [HO-CH2-CH(NH3+)-COOH.Cl(-)] and the respective deuterated derivatives [ND/ODAlcohol/Acid (<10% and ca. 60% D)] were recorded in the region 4000-400 cm(-1) in the temperature range 300-10 K and interpreted. The assignments were confirmed by comparison with the vibrational spectra of crystalline dl- and l-serine zwitterions [HO-CH 2-CH(NH3+)-COO(-)]. Further insight into the structure of the title compound was provided by theoretical DFT(B3LYP)/6-311++G(d,p) calculations of the infrared spectra and energies of 13 different conformers. Potential energy distributions resulting from normal co-ordinate analysis were calculated for the most stable conformer ( I) in its hydrogenated and deuterated modification. Frequencies of several vibrational modes were used in the estimation of enthalpies of individual H-bonds present in the crystal, using empirical correlations between enthalpy and the frequency shift that occurs as a result of the establishment of the H-bonds. X-ray crystallography data for dl-serine.HCl were recorded for the first time and, together with the experimental vibrational spectra and the theoretical calculations, allowed a detailed characterization of its molecular structure. 相似文献
90.
V. H. Rodrigues J. A. Paixo M. M. R. R. Costa A. Matos Beja 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(4):417-420
In the title compound, C4H10NO2+·C2F3O2?, the main N—C—COOH skeleton of the protonated amino acid is nearly planar. The C=O/C—N and C=O/O—H bonds are syn and the two methyl groups are gauche to the methylene H atoms. The conformation of the cation in the crystal is compared to that given by ab initio calculations (Hartree–Fock, self‐consistent field molecular‐orbital theory). The trifluoroacetate anion has the typical staggered conformation with usual bond distances and angles. The cation and anion form dimers through a strong O—H?O hydrogen bond which are further interconnected in infinite zigzag chains running parallel to the a axis by N—H?O bonds. Weaker C—H?O interactions involving the methyl groups and the carboxy O atoms of the cation occur between the chains. 相似文献