全文获取类型
收费全文 | 428篇 |
免费 | 17篇 |
国内免费 | 4篇 |
专业分类
化学 | 283篇 |
晶体学 | 1篇 |
力学 | 12篇 |
数学 | 54篇 |
物理学 | 99篇 |
出版年
2022年 | 7篇 |
2021年 | 9篇 |
2020年 | 11篇 |
2019年 | 8篇 |
2018年 | 8篇 |
2017年 | 4篇 |
2016年 | 10篇 |
2015年 | 14篇 |
2014年 | 11篇 |
2013年 | 27篇 |
2012年 | 25篇 |
2011年 | 33篇 |
2010年 | 18篇 |
2009年 | 15篇 |
2008年 | 26篇 |
2007年 | 19篇 |
2006年 | 15篇 |
2005年 | 23篇 |
2004年 | 14篇 |
2003年 | 14篇 |
2002年 | 10篇 |
2001年 | 5篇 |
2000年 | 9篇 |
1999年 | 14篇 |
1998年 | 10篇 |
1996年 | 9篇 |
1994年 | 6篇 |
1993年 | 8篇 |
1992年 | 9篇 |
1991年 | 9篇 |
1990年 | 6篇 |
1988年 | 6篇 |
1987年 | 1篇 |
1985年 | 6篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1974年 | 3篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1970年 | 1篇 |
1969年 | 1篇 |
1968年 | 4篇 |
1959年 | 1篇 |
排序方式: 共有449条查询结果,搜索用时 31 毫秒
91.
92.
Esther García G. Virgilio Mendoza G. Jos Agustín Guzmn‐B. Luis Angel Maldonado Graniel Simn Hernndez‐Ortega 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(6):o336-o338
In the molecule of the title compound, C13H18O3, there is a syn relationship between the two vicinal methyl groups. The six‐membered ring adopts a chair conformation, with one equatorial and two axial groups, and the furyl group is almost parallel to the ketone group. Intermolecular hydrogen bonds [O—H?O=C 2.814 (3) Å] form chains along [100]. 相似文献
93.
Iglesias-Sánchez JC Souto B Pastor CJ de Mendoza J Prados P 《The Journal of organic chemistry》2005,70(25):10400-10407
[structure: see text] In this article we describe the selective O-benzylation of para-unsubstituted calix[6]arene 1 in rings 1 and 4 (2a-c) and the subsequent alkylation of phenol groups with alpha-haloesters (methyl esters 3a, 3c, and 3e; tert-butyl esters 3b, 3d, and 3f) to determine the effect of these groups on their conformational behavior. 2D NMR studies at 188 K reveal that compounds 2a-c, 3b, 3d, and 3f are less flexible, showing a 1,2,3-alternate conformation. The same conformation has been observed in the solid state. 相似文献
94.
M. T. Alonso O. Juanes J. de Mendoza J. C. Rodríguez-Ubis 《Journal of organometallic chemistry》1992,430(3):349-355
The synthesis and characterization of a number of new coordination compounds of PdII with the nitrogen donor 1-tert-butylpyrazole (tBuPzH) are described. Compounds are trans-[Pd(tBuPzH)2Cl2] and the cyclometallated structures [Pd2(tBuPz)2(AcO)2] and [Pd3(tBuPz)2(AcO)4]. All these complexes are mixtures of syn and anti isomers. Also, the chloro-bridged complex [Pd2(tBuPz)2Cl2] has been isolated as an equilibrium mixture of cis and trans isomers. The compounds have been studied by variable temperature 1H- and 13C-NMR spectroscopy. 相似文献
95.
Breccia P Van Gool M Pérez-Fernández R Martín-Santamaría S Gago F Prados P de Mendoza J 《Journal of the American Chemical Society》2003,125(27):8270-8284
A number of artificial carriers for the transport of zwitterionic aromatic amino acids across bulk model membranes (U-tube type) have been prepared and evaluated. 1,2-Dichloroethane and dichloromethane were employed in the organic phase. All compounds are based on a bicyclic chiral guanidinium scaffold that ideally complements the carboxylate function. The guanidinium central moiety was attached to crown ethers or lasalocid A as specific subunits for ammonium recognition as well as to aromatic or hydrophobic residues to evaluate their potential interaction with the side chains of the guest amino acids. The subunits were linked to the guanidinium through ester or amide connectors. Amides were found to be better carriers than esters, though less enantioselective. On the other hand, crown ethers were superior to lasalocid derivatives. As expected, transport rates were dependent on the carrier concentration in the liquid membrane. Reciprocally, enantioselectivities were much higher at lower carrier concentrations. The results show that our previously proposed three-point binding model (J. Am. Chem. Soc. 1992, 114, 1511-1512), involving the participation of the aromatic or hydrophobic residue to interact with the side chains of the amino acid guest, is unnecessary to explain the high enantioselectivities observed. Molecular dynamics fully support a two-point model involving only the guanidinium and crown ether moieties. These molecules constitute the first examples of chiral selectors for underivatized amino acids acting as carriers under neutral conditions. 相似文献
96.
[reaction: see text] A shape-persistent, conjugated o-phenylene ethynylene cyclic trimer was prepared in one step from tetrasubstituted benzene monomer 4 in 86% isolated yield through precipitation-driven alkyne metathesis. The template-free, selective generation of the molecular triangle 5 is a thermodynamically favored process and under equilibrium control. A novel tetrameric macrocycle 7 was generated via scrambling metathesis between tricycle 5 and hexacycle 6 using this dynamic covalent chemistry. 相似文献
97.
p-(1H-phenanthro[9,10-d]imidazol-2-yl)- substituted calix[4]arene, a deep cavity for guest inclusion
The reaction of tetra-p-formyltetra-O-propylcalix[4]arene with phenanthrenequinone in the presence of NH(4)OAc affords compound 2, a new class of calixarene with an expanded aromatic cavity, that could be stabilized by hydrogen-bonded bridges and/or ion pairing, thus preventing collapse into fully stacked pinched cone conformations as depicted. Two partially protonated calixarenes interdigitate in the solid state to give rise to a self-assembled face-to-face dimer, stabilized by pi-pi stacking interactions. 相似文献
98.
Oscar RomeroAlejandro Castro Joel L. TeránDino Gnecco María L. OreaÁngel Mendoza Marcos FloresLuis F. Roa Jorge R. Juárez 《Tetrahedron letters》2011,52(45):5947-5950
The diastereoselective substitution of 3-bromolactam derived from (R)-(−)-2-phenylglycinol with a variety of arylcuprate reagents is presented. The stereochemical outcome of the substitution reaction is discussed. The method provides an efficient and straightforward route to enantiopure 3-arylpiperidines. 相似文献
99.
H.-J. Fan M. D. Carducci C. Grittini A. Mendoza D. L. Lichtenberger 《Acta Crystallographica. Section C, Structural Chemistry》1999,55(11):IUC9900154-IUC9900154