全文获取类型
收费全文 | 844篇 |
免费 | 41篇 |
国内免费 | 11篇 |
专业分类
化学 | 472篇 |
晶体学 | 18篇 |
力学 | 15篇 |
数学 | 255篇 |
物理学 | 136篇 |
出版年
2023年 | 4篇 |
2022年 | 6篇 |
2021年 | 10篇 |
2020年 | 9篇 |
2019年 | 16篇 |
2018年 | 23篇 |
2017年 | 10篇 |
2016年 | 24篇 |
2015年 | 18篇 |
2014年 | 21篇 |
2013年 | 40篇 |
2012年 | 47篇 |
2011年 | 66篇 |
2010年 | 34篇 |
2009年 | 47篇 |
2008年 | 60篇 |
2007年 | 64篇 |
2006年 | 45篇 |
2005年 | 46篇 |
2004年 | 40篇 |
2003年 | 36篇 |
2002年 | 28篇 |
2001年 | 9篇 |
2000年 | 12篇 |
1999年 | 13篇 |
1998年 | 8篇 |
1997年 | 6篇 |
1996年 | 14篇 |
1994年 | 4篇 |
1993年 | 10篇 |
1992年 | 5篇 |
1991年 | 7篇 |
1990年 | 7篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1987年 | 9篇 |
1986年 | 5篇 |
1985年 | 11篇 |
1984年 | 6篇 |
1983年 | 4篇 |
1982年 | 7篇 |
1981年 | 6篇 |
1980年 | 7篇 |
1979年 | 5篇 |
1978年 | 7篇 |
1975年 | 4篇 |
1973年 | 4篇 |
1971年 | 3篇 |
1970年 | 3篇 |
1967年 | 4篇 |
排序方式: 共有896条查询结果,搜索用时 31 毫秒
91.
John CJ Amalanathan M Sajan D Lakshmi KU Joe IH 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2011,78(1):264-272
FT-Raman and FT-IR spectra of the nonlinear optical crystal 1-(4-N,N-dimethylaminopyridinium) acetic acid bromide monohydrate have been recorded and analyzed. The equilibrium geometry, vibrational wavenumbers and the first order hyperpolarizability of the crystal have been calculated with the help of density functional theory computations. The assignments of the vibrational spectra have been carried out with the help of Scaled Quantum Mechanic force field theory. Optimized geometry gives the charge transfer interaction of the pyridine ring and the amino group in the electron-donor side of the nonlinear optic chromophore. Electron–phonon coupling and O–H?O interactions in making the molecule nonlinear optical active have been analyzed based on the vibrational spectral features. The Natural Bond Orbital analysis confirms the occurrence of strong intermolecular O–H?O hydrogen bonding. 相似文献
92.
Dhas DA Joe IH Roy SD Balachandran S 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2011,79(5):993-1003
Vibrational analysis of the thionocarbamate fungicide tolnaftate which is antidermatophytic, antitrichophytic and antimycotic agent, primarily inhibits the ergosterol biosynthesis in the fungus, was carried out using NIR FT-Raman and FTIR spectroscopic techniques. The equilibrium geometry, various bonding features, harmonic vibrational wavenumbers and torsional potential energy surface (PES) scan studies have been computed using density functional theory method. The detailed interpretation of the vibrational spectra has been carried out with the aid of VEDA.4 program. Vibrational spectra, natural bonding orbital (NBO) analysis and optimized molecular structure show the clear evidence for electronic interaction of thionocarbamate group with aromatic ring. Predicted electronic absorption spectrum from TD-DFT calculation has been compared with the UV-vis spectrum. The Mulliken population analysis on atomic charges and the HOMO-LUMO energy were also calculated. Vibrational analysis reveals that the simultaneous IR and Raman activation of the C-C stretching mode in the phenyl and naphthalene ring provide evidence for the charge transfer interaction between the donor and acceptor groups and is responsible for its bioactivity as a fungicide. 相似文献
93.
Amalanathan M Rastogi VK Joe IH Palafox MA Tomar R 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2011,78(5):1437-1444
The FT-IR and Raman spectra of 3,5-dinitrobenzoic acid (DNBA) have been recorded and analyzed. The equilibrium geometry, various bonding and harmonic vibrational wavenumbers have been calculated with the help of density functional theory (DFT) method. Most of the vibrational modes are observed in the expected range. Mulliken population analysis shows the interactions C-N-O?H-C and C-O?H-C. The most possible interaction is explained using natural bond orbital (NBO) analysis. The strengthening and polarization of the CO bond increases due to the degree of conjugation. HOMO-LUMO energy and the thermodynamic properties are also evaluated. 相似文献
94.
95.
Corrections to Lee's visibility polygon algorithm 总被引:2,自引:0,他引:2
We present a modification and extension of the (linear time) visibility polygon algorithm of Lee. The algorithm computes the visibility polygon of a simple polygon from a viewpoint that is either interior to the polygon, or in its blocked exterior (the cases of viewpoints on the boundary or in the free exterior being simple extensions of the interior case). We show by example that the original algorithm by Lee, and a more complex algorithm by El Gindy and Avis, can fail for polygons that wind sufficiently. We present a second version of the algorithm, which does not extend to the blocked exterior case.This work was partially supported by grants from the Central Research Fund of the University of Alberta and the Natural Sciences and Engineering Research Council of Canada. 相似文献
96.
97.
98.
Athar Ata Joe Ackerman Abdelhamid Bayoud Parvataneni Radhika 《Helvetica chimica acta》2004,87(3):592-597
From the methanolic extract of Cladiella sp., collected from the Andaman Island, India, a new sesquiterpene, cladidiol ( 2 ), and three known diterpenes, cladiellaperoxide ( 3 ), (6E)‐2α,9α‐epoxyeunicella‐6,11(12)‐dien‐3β‐ol ( 4 ), and polyanthellin A ( 5 ) were isolated. The structures of these compounds were established by extensive spectroscopic studies. Compound 2 exhibited modest acetylcholinesterase‐inhibition activity, and compounds 3 – 5 showed antibacterial activities against Streptococcus pyogenes, Escherichia coli, and Pseudomonas aeruginosa. 相似文献
99.
100.