全文获取类型
收费全文 | 3457篇 |
免费 | 139篇 |
国内免费 | 26篇 |
专业分类
化学 | 2424篇 |
晶体学 | 16篇 |
力学 | 53篇 |
数学 | 561篇 |
物理学 | 568篇 |
出版年
2024年 | 5篇 |
2023年 | 20篇 |
2022年 | 21篇 |
2021年 | 96篇 |
2020年 | 86篇 |
2019年 | 105篇 |
2018年 | 118篇 |
2017年 | 83篇 |
2016年 | 137篇 |
2015年 | 128篇 |
2014年 | 145篇 |
2013年 | 201篇 |
2012年 | 240篇 |
2011年 | 262篇 |
2010年 | 172篇 |
2009年 | 112篇 |
2008年 | 242篇 |
2007年 | 241篇 |
2006年 | 214篇 |
2005年 | 189篇 |
2004年 | 148篇 |
2003年 | 119篇 |
2002年 | 99篇 |
2001年 | 44篇 |
2000年 | 30篇 |
1999年 | 36篇 |
1998年 | 34篇 |
1997年 | 21篇 |
1996年 | 32篇 |
1995年 | 23篇 |
1994年 | 29篇 |
1993年 | 15篇 |
1992年 | 11篇 |
1991年 | 10篇 |
1989年 | 7篇 |
1988年 | 11篇 |
1987年 | 4篇 |
1986年 | 7篇 |
1985年 | 6篇 |
1984年 | 9篇 |
1983年 | 8篇 |
1982年 | 8篇 |
1981年 | 6篇 |
1980年 | 9篇 |
1979年 | 8篇 |
1977年 | 4篇 |
1976年 | 12篇 |
1975年 | 11篇 |
1973年 | 7篇 |
1954年 | 5篇 |
排序方式: 共有3622条查询结果,搜索用时 328 毫秒
111.
Brauer B Gerber RB Kabelác M Hobza P Bakker JM Abo Riziq AG de Vries MS 《The journal of physical chemistry. A》2005,109(31):6974-6984
The results of harmonic and anharmonic frequency calculations on a guanine-cytosine complex with an enolic structure (a tautomeric form with cytosine in the enol form and with a hydrogen at the 7-position on guanine) are presented and compared to gas-phase IR-UV double resonance spectral data. Harmonic frequencies were obtained at the RI-MP2/cc-pVDZ, RI-MP2/TZVPP, and semiempirical PM3 levels of electronic structure theory. Anharmonic frequencies were obtained by the CC-VSCF method with improved PM3 potential surfaces; the improved PM3 potential surfaces are obtained from standard PM3 theory by coordinate scaling such that the improved PM3 harmonic frequencies are the same as those computed at the RI-MP2/cc-pVDZ level. Comparison of the data with experimental results indicates that the average absolute percentage deviation for the methods is 2.6% for harmonic RI-MP2/cc-pVDZ (3.0% with the inclusion of a 0.956 scaling factor that compensates for anharmonicity), 2.5% for harmonic RI-MP2/TZVPP (2.9% with a 0.956 anharmonicity factor included), and 2.3% for adapted PM3 CC-VSCF; the empirical scaling factor for the ab initio harmonic calculations improves the stretching frequencies but decreases the accuracy of the other mode frequencies. The agreement with experiment supports the adequacy of the improved PM3 potentials for describing the anharmonic force field of the G...C base pair in the spectroscopically probed region. These results may be useful for the prediction of the pathways of vibrational energy flow upon excitation of this system. The anharmonic calculations indicate that anharmonicity along single mode coordinates can be significant for simple stretching modes. For several other cases, coupling between different vibrational modes provides the main contribution to anharmonicity. Examples of strongly anharmonically coupled modes are the symmetric stretch and group torsion of the hydrogen-bonded NH2 group on guanine, the OH stretch and torsion of the enol group on cytosine, and the NH stretch and NH out-of-plane bend of the non-hydrogen-bonded NH group on guanine. 相似文献
112.
Busby M Gabrielsson A Matousek P Towrie M Di Bilio AJ Gray HB Vlcek A 《Inorganic chemistry》2004,43(16):4994-5002
The nature and dynamics of the lowest excited states of fac-[Re(I)(L)(CO)(3)(phen)](+) and fac-[Re(I)(L)(CO)(3)(5-NO(2)-phen)](+) [L = Cl(-), 4-ethyl-pyridine (4-Etpy), imidazole (imH); phen = 1,10-phenanthroline] have been investigated by picosecond visible and IR transient absorption spectroscopy in aqueous (L = imH), acetonitrile (L = 4-Etpy, imH), and MeOH (L = imH) solutions. The phen complexes have long-lived Re(I) --> phen (3)MLCT excited states, characterized by CO stretching frequencies that are upshifted relative to their ground-state values and by widely split IR bands due to the out-of-phase A'(2) and A"nu(CO) vibrations. The lowest excited states of the 5-NO(2)-phen complexes also have (3)MLCT character; the larger upward nu(CO) shifts accord with much more extensive charge transfer from the Re(I)(CO)(3) unit to 5-NO(2)-phen in these states. Transient visible absorption spectra indicate that the excited electron is delocalized over the 5-NO(2)-phen ligand, which acquires radical anionic character. Similarly, involvement of the -NO(2) group in the Franck-Condon MLCT transition is manifested by the presence of an enhanced nu(NO(2)) band in the preresonance Raman spectrum of [Re(I)(4-Etpy)(CO)(3)(5-NO(2)-phen)](+). The Re(I) --> 5-NO(2)-phen (3)MLCT excited states are very short-lived: 7.6, 170, and 43 ps for L = Cl(-), 4-Etpy, and imH, respectively, in CH(3)CN solutions. The (3)MLCT excited state of [Re(I)(imH)(CO)(3)(5-NO(2)-phen)](+) is even shorter-lived in MeOH (15 ps) and H(2)O (1.3 ps). In addition to (3)MLCT, excitation of [Re(I)(imH)(CO)(3)(5-NO(2)-phen)](+) populates a (3)LLCT (imH --> 5-NO(2)-phen) excited state. Most of the (3)LLCT population decays to the ground state (time constants of 19 (H(2)O), 50 (MeOH), and 72 ps (CH(3)CN)); in a small fraction, however, deprotonation of the imH.+ ligand occurs, producing a long-lived species, [Re(I)(im.)(CO)(3)(5-NO(2)-phen).-]+. 相似文献
113.
114.
115.
Frontispiece: Probing Transient Conformational States of Proteins by Solid‐State R1ρ Relaxation‐Dispersion NMR Spectroscopy 下载免费PDF全文
116.
117.
Eduard E. Karslyan Andrew I. Konovalov Alexandra O. Borissova Pavel V. Petrovskii Alexander R. Kudinov 《Mendeleev Communications》2012,22(4):189-191
The [2 + 2] photodimerization of the complex [(C5Me4CH2OMe)Ru(η6-C12H8)]+ under visible-light irradiation leads to a mixture of the head-to-head heptacyclene products [(μ-η6: η6-C24H16)Ru2(C5Me4CH2OMe)2]2+ (syn- and anti-) with the predominant formation of the syn-isomer; the structures of both isomers were established by X-ray diffraction analysis. 相似文献
118.
Yulia S. Kudyakova Yanina V. Burgart Pavel A. Slepukhin Victor I. Saloutin 《Mendeleev Communications》2012,22(5):284-286
Condensation of two moles of ethyl 2-[(2-aminophenylamino)methylidene]-3-oxo-3-(polyfluoroalkyl)propionates with 2,5-thiophene-dicarboxaldehyde results in new heteroatomic podands. X-ray data showed that in the solid state these molecules arrange in two independent chelating fragments of b-amino enone type, thiophene fragment being a spacer. 相似文献
119.
120.
Asanbaeva Nargiz B. Rychkov Denis A. Tyapkin Pavel Yu. Arkhipov Sergey G. Uvarov Nikolay F. 《Structural chemistry》2021,32(3):1261-1267
Structural Chemistry - The crystal and molecular structure of tris(tetrabutylammonium) pentanitratoplumbate(II) was determined and characterized by single-crystal and powder X-ray diffraction and... 相似文献