全文获取类型
收费全文 | 790篇 |
免费 | 14篇 |
国内免费 | 2篇 |
专业分类
化学 | 634篇 |
晶体学 | 14篇 |
力学 | 11篇 |
数学 | 50篇 |
物理学 | 97篇 |
出版年
2023年 | 5篇 |
2022年 | 4篇 |
2021年 | 7篇 |
2020年 | 10篇 |
2019年 | 10篇 |
2018年 | 5篇 |
2017年 | 5篇 |
2016年 | 9篇 |
2015年 | 10篇 |
2014年 | 18篇 |
2013年 | 37篇 |
2012年 | 35篇 |
2011年 | 47篇 |
2010年 | 24篇 |
2009年 | 23篇 |
2008年 | 36篇 |
2007年 | 36篇 |
2006年 | 44篇 |
2005年 | 38篇 |
2004年 | 40篇 |
2003年 | 38篇 |
2002年 | 44篇 |
2001年 | 14篇 |
2000年 | 17篇 |
1999年 | 14篇 |
1998年 | 6篇 |
1997年 | 11篇 |
1996年 | 12篇 |
1995年 | 5篇 |
1994年 | 13篇 |
1993年 | 10篇 |
1992年 | 4篇 |
1991年 | 7篇 |
1989年 | 6篇 |
1988年 | 7篇 |
1987年 | 12篇 |
1986年 | 9篇 |
1985年 | 18篇 |
1984年 | 16篇 |
1983年 | 4篇 |
1982年 | 16篇 |
1981年 | 10篇 |
1980年 | 14篇 |
1979年 | 12篇 |
1978年 | 9篇 |
1977年 | 4篇 |
1976年 | 7篇 |
1975年 | 4篇 |
1973年 | 5篇 |
1968年 | 3篇 |
排序方式: 共有806条查询结果,搜索用时 0 毫秒
141.
Naomichi Furukawa Toshiaki Yoshimura Masami Ohtsu Takeshi Akasaka Shigeru Oae 《Tetrahedron》1980,36(1):73-80
The Michael type additions of diphenyl N-unsubstituted sulfimide (free sulfimide) to various electrophilic olefins were carried out. The reaction with cis- and trans-dibenzoylethylene, dimethyl-fumarate, dimethylmaleate, benzalacetophenone and benzalacetone gave mainly the corresponding trans-2-acylaziridines and trans-enaminoketones. However, phenyl vinyl sulfone or acrylonitrile afforded not the corresponding aziridine but diphenyl-N-2-cyano or N-2-phenylsulfonylethylsulfimide, a simple Michael adduct When optically active (+)-(R)-o-methoxyphenyiphenyl free sulfimide was treated with such an α,β-unsaturated carbonyl compound as benzalacetopbenone, an optically active 2-acylazindine, i.e., (-)-trans-2-benzoyl-3-phenylaziridine was obtained in ca 30% optical purity and its absolute configuration was assigned as (2R,3S) upon chemical transformation to the configuration-ally known 2-phenyl-2-benzoylamino-1-ethanol or by comparing its CD spectrum with that of (1R,2R)-1-phenyl-2-benzoyl-cyclopropane. Meanwhile, (-)-(S)-o-methoxyphenylphenyl free sulfimide was found to react with benzalacetophenone to afford (+)-trans-2-benzoyl-3-phenylaziridine of 25% optical purity. Effects of solvent and temperature on both die distribution of the products ratio and the optical yield were examined. 相似文献
142.
143.
Issei Kasahara Masami Kanai Masako Taniguchi Ayako Kakeba Noriko Hata Shigeru Taguchi Katsumi Goto 《Analytica chimica acta》1989
The singly charged complex anion bis[2-(5-bromo-2-pyridylazo)-5-(N-propyl-N-sulphopropylamino)phenolato]cobaltate(III) is intensely purple-violet and is stable over the pH range 1–13. Its absorption spectrum remains the same over this pH range. At pH2, it forms extractable ion pairs with long-chain quaternary ammonium ions and protonated alkylamines. Only the quaternary ammonium ions are extracted into chloroform at pH 11, hence separate extractions allow both types to be determined. The absorbance of the organic phase is measured at 594 nm. The apparent molar absorptivity is 7.0 × 104 l mol?1 cm?1. Calibration graphs for zephiramine, benzethonium and hexadecylpyridinium ions are linear over the range 0.1–2 × 10?6 M. The only interference found was from anionic surfactants. The method is applied to hair and fabric conditioners. 相似文献
144.
The calcium salts of -sulfonated fatty acid methyl esters were prepared, and the physico-chemical properties such as solubility, critical micelle concentration, aggregation number, and precipitation phase boundary were studied to clarify the reasons for the good hardness tolerance manifested by -sulfonated fatty acid methyl esters.The Krafft point of the calcium salts of -sulfonated fatty acid methyl esters were not necessarily lower than room temperature, but the rate of crystallization in hard water was extremely slow compared with the calcium salt of dodecyl sulfate, which has been known as an insufficient surfactant in terms of hardness tolerance. 相似文献
145.
146.
R. Fujiyoshi A. Aono M. Katayama 《Journal of Radioanalytical and Nuclear Chemistry》1992,164(3):193-201
A metal exchange reaction between*Zn-EDTA and Mn-PAN complexes has been investigated to evaluate the possibility of Mn determination in geological samples radiometrically. Exchange ratios (E) of Mn(II) to Zn(II) were obtained from measuring the activity of65ZnPAN2 extracted into an organic phase. Values of E increased rapidly with increasing pH of the aqueous solution. Suitable conditions for the determination of Mn(II) in soil samples are considered. 相似文献
147.
148.
Moriuchi T Mao L Wu HL Ohmura SD Watanabe M Hirao T 《Dalton transactions (Cambridge, England : 2003)》2012,41(31):9519-9525
The tripodal ligands composed of the 1,3,5-trisubstituted cyclohexyl moiety as a molecular scaffold and 2-phenylpyridyl moieties as a coordination site were designed. The homoleptic cyclometalated fac-Ir(C^N)(3) complexes could be obtained by the reaction of IrCl(3)·nH(2)O with the designed tripodal ligands. The single crystal X-ray structure determination confirmed the fac configuration and a distorted octahedral geometry with three intramolecular cyclometalated 2-phenylpyridyl ligands surrounding the iridium metal center. Also, the cyclohexyl scaffold was found to serve as a flexible scaffold to induce the fac configuration. The thus-obtained homoleptic cyclometalated fac-Ir(C^N)(3) complexes exhibited a broad emission band in the emission spectra at 298 K. 相似文献
149.
Hisashi Miyazaki Hiroaki Takiguchi Masami Aono Yoichi Okamoto 《Journal of Non》2012,358(17):2103-2106
Multilayered a-Ge/Au was investigated to realize low-temperature formation of poly-Ge films on insulator. Increasing Au layer thicknesses, peak intensity of crystalline Ge–Ge TO mode increased and amorphous Ge–Ge TO mode decreased. When Au composition ratio is high, the samples are crystallized under eutectic temperature. Annealing temperature at 673 K, all samples with Au layer are crystallized. Crystalline Ge has no strain evaluated by X-ray diffraction and Raman scattering spectroscopy. However, the Au is compressed or expanded in the films with various annealing temperature. It is thought that this phenomenon changes depending on the size of the space in the film. The behavior of electrical resistivity is changed at eutectic temperature. 相似文献
150.
Georgia Pagona Takayuki Aono Hisanori Shinohara Nikos Tagmatarchis 《Tetrahedron letters》2010,51(45):5896-5912
La@C82 is recognized by an isophthaloyl-bridged porphyrin dimer forming a stable 1:1 supramolecular complex with an association constant Kassoc = (67.3 ± 3.2) × 103 M−1. 相似文献