全文获取类型
收费全文 | 1237篇 |
免费 | 116篇 |
国内免费 | 29篇 |
专业分类
化学 | 780篇 |
晶体学 | 22篇 |
力学 | 58篇 |
数学 | 114篇 |
物理学 | 408篇 |
出版年
2024年 | 4篇 |
2023年 | 15篇 |
2022年 | 25篇 |
2021年 | 76篇 |
2020年 | 54篇 |
2019年 | 53篇 |
2018年 | 45篇 |
2017年 | 39篇 |
2016年 | 65篇 |
2015年 | 56篇 |
2014年 | 61篇 |
2013年 | 102篇 |
2012年 | 90篇 |
2011年 | 98篇 |
2010年 | 68篇 |
2009年 | 48篇 |
2008年 | 51篇 |
2007年 | 44篇 |
2006年 | 39篇 |
2005年 | 32篇 |
2004年 | 39篇 |
2003年 | 26篇 |
2002年 | 25篇 |
2001年 | 17篇 |
2000年 | 18篇 |
1999年 | 7篇 |
1998年 | 5篇 |
1997年 | 9篇 |
1996年 | 12篇 |
1995年 | 5篇 |
1994年 | 10篇 |
1993年 | 7篇 |
1992年 | 6篇 |
1991年 | 14篇 |
1990年 | 11篇 |
1989年 | 8篇 |
1988年 | 9篇 |
1987年 | 10篇 |
1986年 | 13篇 |
1985年 | 12篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1982年 | 12篇 |
1981年 | 3篇 |
1980年 | 5篇 |
1978年 | 3篇 |
1977年 | 5篇 |
1974年 | 4篇 |
1973年 | 4篇 |
1971年 | 2篇 |
排序方式: 共有1382条查询结果,搜索用时 15 毫秒
81.
(+)-Parviflorine (), found in Lam. (Fumariaceae), is the first known glycosidic spirobenzylisoquinoline alkaloid. Its acid hydrolysis yields (+)-parfumine () and D-glucose. Klyne's rule indicates that is a β-D-glucoside. The absolute configuration shown in expressions is predominant among spirobenzylisoquinolines. A generalization has been drawn between plant source and the oxygenation pattern of ring C for the spirobenzylisoquinoline alkaloids. 相似文献
82.
Ahmad VU Hussain J Hussain H Farooq U Farmanullah Lodhi MA Choudhary MI 《Natural product research》2005,19(3):267-274
Two new myrsinol-type diterpene polyesters 3,5,13,17-tetra-O-acetyl-7-O-benzoyl-15-hydroxymyrsinol (1) and 3,5,13,17-tetra-O-acetyl-7-O-butanoyl-13-hydroxymyrsinol (2), with a tricyclic carbon skeleton have been isolated from Euphorbia decipiens Boiss. & Buhse. The structure elucidation of the isolated compounds was based primarily on HREIMS, EIMS, IR, UV, ID-, and 2D-NMR analyses, including COSY, HMQC, HMBC, and NOESY correlations. Compounds 1 and 2 also showed activity against urease enzyme. 相似文献
83.
Rösch O Gunnarsson O Zhou XJ Yoshida T Sasagawa T Fujimori A Hussain Z Shen ZX Uchida S 《Physical review letters》2005,95(22):227002
We present angle-resolved photoemission spectroscopy (ARPES) data on undoped La2CuO4, indicating polaronic coupling between bosons and charge carriers. Using a shell model, we calculate the electron-phonon coupling and find that it is strong enough to give self-trapped polarons. We develop an efficient method for calculating ARPES spectra in undoped systems. Using the calculated couplings, we find the width of the phonon sideband in good agreement with experiment. We analyze reasons for the observed dependence of the width on the binding energy. 相似文献
84.
Hussain HA Ansari AA Iftikhar K 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2004,60(4):873-884
The optical absorption and NMR studies of trivalent lanthanide chloride complexes with 2,2'-bipyridine (bpy) are presented and discussed. The NMR spectra of paramagnetic complexes exhibit lower as well as higher field shifts of bpy resonances that reflect change in geometry and reveals importance of the factor (3 cos2 theta - 1 ) in changing sign of the shift. The paramagnetic shifts recorded have been analyzed and the intramolecular shift ratios suggest that the paramagnetic shift is predominantly dipolar in origin. Electronic spectral studies of the Pr, Nd, Ho, Er and Dy complexes in different solvents (viz. methanol, pyridine, DMSO and DMF), which differ with respect to donor atoms, reveal that the chemical environment around the lanthanide ion has great impact on f-f transitions and any change in the environment results in modifications of the spectra. The oscillator strength for the hypersensitive and non-hypersensitive transitions have been determined and changes in the oscillator strength and band shape with respect to solvent type is rationalized in terms of ligand (solvent) structure and coordination properties. 相似文献
85.
86.
Brouet V Yang WL Zhou XJ Choi HJ Louie SG Cohen ML Goldoni A Parmigiani F Hussain Z Shen ZX 《Physical review letters》2004,93(19):197601
We observe, with angle-resolved photoemission, a dramatic change in the electronic structure of two C60 monolayers, deposited, respectively, on Ag (111) and (100) substrates, and similarly doped with potassium to half filling of the C60 lowest unoccupied molecular orbital. The Fermi surface symmetry, the bandwidth, and the curvature of the dispersion at Gamma point are different. Orientations of the C60 molecules on the two substrates are known to be the main structural difference between the two monolayers, and we present new band-structure calculations for some of these orientations. We conclude that orientations play a key role in the electronic structure of fullerides. 相似文献
87.
Thin films of molybdenum trioxide were deposited on glass substrates employing direct current (DC) magnetron sputtering by
sputtering of molybdenum at different oxygen partial pressures in the range 8 × 10−5–1 × 10−3 mbar and at a substrate temperature of 473 K. The glow discharge characteristics of magnetron cathode target of molybdenum
were studied. The influence of oxygen partial pressure on the structural and optical properties of molybdenum trioxide films
was investigated. The films formed at an optimum oxygen partial pressure of 2 × 10−4 mbar were polycrystalline in nature with orthorhombic α- phase and an optical band gap of 3.16 eV. The refractive index of
the films formed at an oxygen partial pressure of 2 × 10−4 mbar decreased from 2.08 to 1.89 with increase of wavelength from 450 to 1,000 nm, respectively.
Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, Dec. 7–9, 2006. 相似文献
88.
S. Hussain 《Applied Surface Science》2007,253(7):3649-3657
Diamond-like carbon films containing Ag and Cu in nanocrystalline form were deposited onto SnO2-coated glass substrates by electrochemical technique. Relative amount of silver and copper to be incorporated in the DLC matrix was tailored by varying the amount of silver and copper containing salts in the electrolyte. Current density was adjusted to obtain films with different crystallite size while the volume fraction of the metal nanocrystallites was altered by varying the dilution of the solution containing the salts. Raman studies indicated the presence of two peaks located at ∼1350 cm−1 (D-line) and 1566 cm−1 (G-line) for all the films and the relative intensities of these peaks changed with the amount of metal incorporation in it. The FTIR spectra were seen to be dominated by a peak at 975 cm−1 for C-H out of plane deformation modes along with peaks for C-H bending, C-H stretching and C-C stretching modes at 858, 1113 and 1189 cm−1, respectively. The optical absorption spectra showed a single plasmon band instead of two characteristic bands for Ag and Cu. We ascribe this to nanophase limited interfacial alloying at the Ag-Cu interface. The experimental observation was analyzed in the light of Mie theory. 相似文献
89.
90.