全文获取类型
收费全文 | 4825篇 |
免费 | 694篇 |
国内免费 | 283篇 |
专业分类
化学 | 4090篇 |
晶体学 | 15篇 |
力学 | 503篇 |
综合类 | 44篇 |
数学 | 360篇 |
物理学 | 790篇 |
出版年
2024年 | 2篇 |
2023年 | 47篇 |
2022年 | 63篇 |
2021年 | 282篇 |
2020年 | 233篇 |
2019年 | 145篇 |
2018年 | 171篇 |
2017年 | 154篇 |
2016年 | 263篇 |
2015年 | 256篇 |
2014年 | 278篇 |
2013年 | 510篇 |
2012年 | 311篇 |
2011年 | 298篇 |
2010年 | 212篇 |
2009年 | 283篇 |
2008年 | 263篇 |
2007年 | 279篇 |
2006年 | 251篇 |
2005年 | 254篇 |
2004年 | 222篇 |
2003年 | 214篇 |
2002年 | 145篇 |
2001年 | 86篇 |
2000年 | 84篇 |
1999年 | 56篇 |
1998年 | 57篇 |
1997年 | 70篇 |
1996年 | 52篇 |
1995年 | 39篇 |
1994年 | 33篇 |
1993年 | 24篇 |
1992年 | 36篇 |
1991年 | 21篇 |
1990年 | 17篇 |
1989年 | 8篇 |
1988年 | 16篇 |
1987年 | 9篇 |
1986年 | 10篇 |
1985年 | 9篇 |
1984年 | 4篇 |
1982年 | 13篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1979年 | 7篇 |
1978年 | 3篇 |
1975年 | 1篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有5802条查询结果,搜索用时 15 毫秒
111.
S. Y. Fredericks J. M. Pedulla K. D. Jordan T. S. Zwier 《Theoretical chemistry accounts》1997,96(1):51-55
The OH stretch IR spectrum of (H2O)3 is significantly altered upon complexation of the cluster with a benzene molecule. Theoretical calculations show that the
differences in the OH stretch spectra of (H2O)3 and benzene-(H2O)3 are primarily due to mode localization induced by the benzene molecule.
Received: 27 January 1997 / Accepted: 28 January 1997 相似文献
112.
Two natural products databases, the marine natural products database (MNPD) and the traditional Chinese medicines database (TCMD), were used to find novel structures of potent SARS-CoV protease inhibitors through virtual screening. Before the procedure, the databases were filtered by Lipinski's ROF and Xu's extension rules. The results were analyzed by statistic methods to eliminate the bias in target-based database screening toward higher molecular weight compounds for enhancing the hit rate. Eighteen lead compounds were recommended by the screening procedure. They were useful for experimental scientists in prioritizing drug candidates and studying the interaction mechanism. The binding mechanism was also analyzed between the best screening compound and the SARS protein. 相似文献
113.
《Arabian Journal of Chemistry》2020,13(8):6568-6579
In this work, the sol–gel technique was used to prepare a new organic–inorganic hybrid from Epoxidized Natural Rubber (ENR-50) and Titanium dioxide (TiO2) by blending different content of titania precursors (10, 30, and 50 wt%) with an ENR-50 matrix. A wide range of analyses was conducted to understand the nature of this hybrid and also to evaluate its potential uses in applications required high refractive index such as micro optical and optoelectronic devices. Results indicated that the ring-opening reaction of epoxide groups in ENR-50 increased with the increase of titania content in the hybrid resulting a strong bonding between titania and ENR-50 through TiOC bond, which was observed in FTIR spectrum at 1027–1028 cm−1. It is also observed a slight decrease in the intensity of the amorphous peak along with a new crystalline peak appeared at 2θ = 23 and 27° due to the crystalline nature of titania. The hybrids showed three thermal degradation steps in the range of temperature 76 to 769 °C due to the existence of the Ti moieties with the mixture of polymer chains, which in turn shifted the Tg at 24.3, 26.9 and 28.1 °C for the hybrid at 10, 30, and 50 wt% TiO2 compared to the Tg of ENR-50 at −18.4 °C respectively. The morphology of the ENR-50 showed clear changes during of the synthesis of ENR-50/TiO2 hybrids, these changes were proven by SEM, TEM, and AFM analyses. Uv–Vis results showed that the higher wavelength peak at 293 nm has shifted to 296, 298 and 300 nm for the hybrid at 10, 30, and 50 wt% TiO2 respectively due to the strong interaction between titania precursors and ENR-50 matrix. Furthermore, the hybrids showed good optical transparency in the visible light range. 相似文献
114.
Volker Staemmler 《Theoretical chemistry accounts》1982,62(1):69-80
Ab initio calculations for the 2 ground states of SF and SCl have been performed on Hartree-Fock level and with inclusion of valence shell correlation effects by means of the CI and CEPA approaches. The calculated properties are: Equilibrium distances, vibration frequencies, and dipole moment curves in the vicinity of the respective equilibrium geometries. Our best estimates for the 0 1 infrared absorption frequencies o for SF and SCl are 786 cm–1 and 520 cm–1, respectively, both with an uncertainty of about 10 cm–1. This confirms a recent experimental value obtained by Willner for SF (791 cm–1), but indicates that for SCl both experimental values reported previously in the literature (617 cm–1 and 574 cm–1) are wrong. The S—F and S—Cl bonds in SF and SCl are very similar to the ones in SF2 and SCl2, being essentially single p-bonds in either case. In the analogous oxygen-halogen molecules the situation is different, the O—F and O—Cl bonds in the diatomic radicals OF and OCl have partial double bond character and are much stronger than those in OF2 and OCl2 or in HOF and HOCl. 相似文献
115.
116.
{[Cu^Ⅱ(Hpb)(mal)]H=O}n (Hpb=2-2'-pyridylbenzimidazole, mal=maleic acid) is a helical chain-like polymer complex. In order to investigate the electronic structure of the complex, the monomer Cu^Ⅱ(Hpb)(mal) was obturated with different functional groups respectively. For these selective segments, the geometry optimizations were conducted by using hybrid DFT (B3LYP)methods to find that the structure obturated with H2O was better consistent with the experiment, and then this model would be used to latter calculations, such as the frontier molecular orbital and the NBO charge population analysis. In addition the magnetic behaviors of this complex were analyzed by experiments and the weak antiferromagnetic couple between copper(Ⅱ) ions was observed. The exchange coupling constant was calculated by DFT based on the spin broken symmetry formalism. The calculated coupling constants were in good agreement with the experimental data. 相似文献
117.
Maria Kolympadi 《Tetrahedron》2005,61(8):2003-2010
A synthesis of the marine labdane furanoditerpene (−)-marginatone 1 has been accomplished by a short sequence of reactions starting from (+)-coronarin E 5. The key step is the stereocontrolled-intramolecular electrophilic cyclisation of the (+)-dihydrocoronarin E 6, to the tetracyclic marginatane skeleton 7, which is subsequently functionalized by allylic oxidation to give 1. As (+)-coronarin E 5 was previously synthesized from (−)-sclareol 10, the herein reported preparation constitutes the first formal total synthesis of (−)-marginatone 1, by which its absolute configuration has been confirmed. 相似文献
118.
119.
综述了亚甲胺叶立德的制备、它参与的[3+2]环加成反应的反应机理、反应选择性及在天然产物全合成中的应用等方面的最新进展. 相似文献
120.
CHANG Nein Chen DAY Huo-Muh CHIU Chih-Tsao CHANG Chi-Peng HSU Lung-Fu Department of Chemistry National Sun Yat-Sen University Kaohsiung Taiwan 《有机化学》1993,(2)
Approaches toward the synthesis of iridoids and 9-isocyanopupukeanane starting from cy-clopentadiene are discussed. 相似文献