全文获取类型
收费全文 | 3136篇 |
免费 | 144篇 |
国内免费 | 9篇 |
专业分类
化学 | 2441篇 |
晶体学 | 28篇 |
力学 | 39篇 |
数学 | 129篇 |
物理学 | 652篇 |
出版年
2023年 | 21篇 |
2022年 | 13篇 |
2021年 | 46篇 |
2020年 | 54篇 |
2019年 | 59篇 |
2018年 | 38篇 |
2017年 | 35篇 |
2016年 | 77篇 |
2015年 | 89篇 |
2014年 | 103篇 |
2013年 | 181篇 |
2012年 | 187篇 |
2011年 | 220篇 |
2010年 | 128篇 |
2009年 | 108篇 |
2008年 | 207篇 |
2007年 | 165篇 |
2006年 | 189篇 |
2005年 | 165篇 |
2004年 | 160篇 |
2003年 | 118篇 |
2002年 | 130篇 |
2001年 | 56篇 |
2000年 | 65篇 |
1999年 | 59篇 |
1998年 | 27篇 |
1997年 | 42篇 |
1996年 | 38篇 |
1995年 | 31篇 |
1994年 | 37篇 |
1993年 | 32篇 |
1992年 | 39篇 |
1991年 | 24篇 |
1990年 | 15篇 |
1989年 | 24篇 |
1988年 | 23篇 |
1987年 | 25篇 |
1986年 | 16篇 |
1985年 | 25篇 |
1984年 | 23篇 |
1983年 | 16篇 |
1982年 | 21篇 |
1981年 | 19篇 |
1980年 | 12篇 |
1979年 | 20篇 |
1978年 | 10篇 |
1977年 | 14篇 |
1976年 | 15篇 |
1974年 | 13篇 |
1973年 | 13篇 |
排序方式: 共有3289条查询结果,搜索用时 93 毫秒
71.
Cao B Wakahara T Tsuchiya T Kondo M Maeda Y Aminur Rahman GM Akasaka T Kobayashi K Nagase S Yamamoto K 《Journal of the American Chemical Society》2004,126(30):9164-9165
A new metallofullerene, La2@C78, has been synthesized by DC arc discharge method, isolated by high-performance liquid chromatography, and characterized by laser desorption time-of-flight mass spectrometry, UV-vis-NIR absorption, differential pulse voltammetry, 13C NMR spectroscopy, and theoretical calculations. The La2@C78/CS2 solution is dark violet and presents several characteristic absorption features at 647, 561, 533, and 386 nm, with an onset around 1000 nm. With respect to empty D3-C78, the capability of La2@C78 as an electron acceptor or donor is stronger. Addition of 1,1,2,2-tetrakis(2,4,6-trimethylphenyl)-1,2-disirane to La2@C78 photochemically, as well as thermally, affords bis- and mono-adducts. Theoretical studies and 13C NMR spectroscopic analysis of La2@C78 indicate that it possesses a D3h-C78 cage (78:5). 相似文献
72.
Sinomenine, an alkaloid of the Japanese plant Sinomenium acutum, was converted to the 4-phenylether by the Ullmann reaction in a good yield. The Clemmensen reduction of sinomenine-phenylether and of its derivatives gave (+)-3-methoxy-4-phenoxy-N-methyl-Δx-morphinan.
Hydrogenation and successive sodium-liquid ammonia reduction of (+)-3-methoxy-4-phenoxy-N-methyl-Δx-morphinan gave (+)-3-methoxy-N-methylmorphinan. 相似文献
73.
Juglomycin A has been synthesized in four steps from 5-methoxy-1-naphthol. 相似文献
74.
75.
76.
Recently, high-performance nano-scale flow pumping systems have been developed for micro and miniaturized analysis systems. A novel device capable of measuring and monitoring nanoliter scale flow rates has been required for the further development of the pumping system. In this study, an atomic emission detector using helium radio-frequency plasma (RFP-AED) was used for the measurement of the nanoliter scale flow rate of water by quantitatively detecting the emission from hydrogen in the water molecules. Monitoring nano-flow rates of water in the range up to 1.0 microl min(-1), and the change in the flow rate by the indication of the ratio of the emissions of H (656.3 nm) and He (667.8 nm) were successful. At present, the lowest flow rate that could be determined reproducibly was 4 nl min(-1) calculated as five times the standard deviation of the background noise. Additionally, similar evaluations for the deviation of each flow rate by using the RFP-AED and a flow-injection system were produced. 相似文献
77.
Chai OH Lee HK Lee YC Lee MS Han EH Kim HT Song CH 《Experimental & molecular medicine》2005,37(5):408-417
Trimellitic anhydride (TMA) is widely used industrially to make epoxy and alkyd resins, plasticizers and surfactants. The purpose of this study was to investigate whether contact hypersensitivity (CHS) is induced by repeated TMA challenge and the role of TNF-alpha and IgE in the TMA-induced CHS. The repetition of the challenge enlarged the extent of an early and a late phase of CHS in TNF-alpha+/+ (B6129SF2/J) and Balb/c mice. In the late phase of TMA-induced CHS, the peak of ear swelling responses by single challenge showed at 24 h after challenge, but the peak was observed at 8 h after repeated challenge. In the TNF-alpha knockout TNF-alpha-/- (B6;129S-Tnftm1Gk1) mice, the repetition of the TMA challenges enlarged the extent of the late phase of CHS, but less than those in TNF-alpha+/+ mice. Injection of anti-TNF-alpha antibody into the peritoneal cavity of Balb/c mice significantly decreased the extent of the late phase of CHS. Subcutaneous injection of anti-IgE antibody into Balb/c mice also decreased the extent of the late phase of CHS in dose-dependent manner. Histologically, infiltration of polymorphonuclear leukocytes and eosinophils was more pronounced in repeatedly TMA-challenged TNF-alpha+/+ and Balb/c mice than in the TNF-alpha-/- mice and anti-TNF-alpha or anti-IgE antibodies treated Balb/c mice. These results indicate that mice sensitized by TMA could possibly offer a useful model to study the mechanism of CHS, and TNF-alpha and IgE may act as potential modulators in the late phase of TMA-induced CHS. Neutralization of TNF-alpha and IgE by anti-TNF-alpha or anti-IgE antibodies may provide therapeutic tools for the treatment of TMA-induced CHS. 相似文献
78.
Dihydrothebaine-φ, dihydrothebainone-Δ5-enol methylether and dihydrothebainone were converted to the respective 4-phenylethers by Ullmann reaction in good yields. These phenylether derivatives were reduced to 4-desoxy compounds by sodium-liquid ammonia reduction.
Clemmensen reduction of the phenylether and the desoxy derivatives gave (-)-3-methoxy-4-phenoxy-N-methyl-morphinan and (-)-3-methoxy-N-methylmorphinan respectively. 相似文献
79.
Sang Chul Shim Chil Hoon Doh Tae Jeong Kim Hak Ki Lee Ki Doo Kim 《Journal of heterocyclic chemistry》1988,25(5):1383-1385
Ethanolic tetracarbonylhydridoferrate combined with adipaldehyde is very efficient for the selective transformation of an amino group into perhydroazepine. A large variety of both aliphatic and aromatic amines react with adipaldehyde in the presence of tetracarbonylhydridoferrate at room temperature and carbon monoxide to give the corresponding N-alkyl- and N-arylperhydroazepines in good to excellent yields. 相似文献
80.
Jae Ha Kim Young Tae Jeong Seong Ihl Woo 《Journal of polymer science. Part A, Polymer chemistry》1994,32(15):2979-2987
Highly active catalysts for copolymerization have been prepared by the precipitation of MgCl2/ToCl4 complex with or without high surface area silica. Copolymerization of ethylene and 1-butene has been tested by using the prepared catalysts at various concentrations of 1-butene. The catalytic activities are 20–80 kg/g Ti h. The rate of copolymerization is strongly affected by the addition of 1-butene. The decay rate of copolymerization is first order with respect to time. Analyses of copolymers with solvent extraction, DSC, IR, XRD, and NMR were performed. Ethylene reactivity ratio (k11) for TiCl4/MgCl2/THF catalyst is calculated to be about 26 by NMR spectrum. © 1994 John Wiley & Sons, Inc. 相似文献