全文获取类型
收费全文 | 2131篇 |
免费 | 69篇 |
国内免费 | 192篇 |
专业分类
化学 | 1008篇 |
晶体学 | 5篇 |
力学 | 271篇 |
综合类 | 4篇 |
数学 | 699篇 |
物理学 | 405篇 |
出版年
2023年 | 34篇 |
2022年 | 36篇 |
2021年 | 49篇 |
2020年 | 63篇 |
2019年 | 46篇 |
2018年 | 41篇 |
2017年 | 53篇 |
2016年 | 55篇 |
2015年 | 56篇 |
2014年 | 100篇 |
2013年 | 226篇 |
2012年 | 83篇 |
2011年 | 141篇 |
2010年 | 95篇 |
2009年 | 143篇 |
2008年 | 132篇 |
2007年 | 139篇 |
2006年 | 109篇 |
2005年 | 86篇 |
2004年 | 74篇 |
2003年 | 52篇 |
2002年 | 42篇 |
2001年 | 40篇 |
2000年 | 35篇 |
1999年 | 30篇 |
1998年 | 50篇 |
1997年 | 37篇 |
1996年 | 28篇 |
1995年 | 24篇 |
1994年 | 36篇 |
1993年 | 45篇 |
1992年 | 35篇 |
1991年 | 23篇 |
1990年 | 18篇 |
1989年 | 18篇 |
1988年 | 10篇 |
1987年 | 19篇 |
1986年 | 8篇 |
1985年 | 8篇 |
1984年 | 12篇 |
1983年 | 10篇 |
1982年 | 11篇 |
1981年 | 5篇 |
1980年 | 6篇 |
1979年 | 8篇 |
1975年 | 3篇 |
1973年 | 2篇 |
1972年 | 2篇 |
1970年 | 4篇 |
1968年 | 2篇 |
排序方式: 共有2392条查询结果,搜索用时 375 毫秒
41.
Heinz Günter Viehe Robert Mernyi Lucien Stella Zdenek Janousek 《Angewandte Chemie (International ed. in English)》1979,18(12):917-932
The 100 yers old Wurster's salts have long been recognized as compounds with redical cations. Their unusual stabilization derives partly form capto-dative (cd) substitution. This principle is now discussed as one factor of radical stabilization and it is applied to simple methine derivatives. cd-Substitution has synthetically useful applications: cd-substituents on a carbon atom allow its selective dehydrodimerization. Olefines with geminal and thus cross-conjugated cd-substituents are “radicophilic” and permit twofold carbon radical addition. cd-Substituted olefines are useful antioxidants, polymerization inhibitors and are promising agents in the control of biological radical reactions. Generally, many reactions of cd-substituted molecules appear to involve radicals. 相似文献
42.
The possibility of coulometric titrations of cysteine, 2-thio-uracil, 6-mercaptopurine, and 6-thioguanine with iodine and bromine in methanol and with bromine in acetic acid has been investigated. Conditions have been found for the direct titration of the test substances with iodine in methanol based on their 1-electron oxidation to the corresponding disulphides and for their direct and indirect determination with bromine in acetic acid based on their 6-electron oxidation to the corresponding sulphonic acids.On leave from Department of Analytical Chemistry, Charles University, Prague, Czechoslovakia 相似文献
43.
44.
John A. McNaney Franz M. Zimmerman Howard K. Zimmerman 《Monatshefte für Chemie / Chemical Monthly》1984,115(8-9):1039-1045
The solubilities of potassium acetate and benzoate in aqueous 1,4-dioxane at a temperature of 85°C are reported together with a quasi-thermodynamic general treatment of the experimental results.This brief contribution is a second report upon the results of systematic solubility measurements, commenced with Ref.1, which have been performed by Dr.John A. McNaney during his abruptly truncated lifetime. 相似文献
45.
Polyazoamide(PAA) was used as initiator to prepare block copolymer P(MMA-b-St) byfree radical polymerization. The fraction of block copolymer was about 50%. The structureof the block-copolymer was characterized by IR and the results of ~1H-NMR and GPCshowed that the content of the block and the molecular weight (M_w) of the prepolymerand block copolymer could be controlled by varying the mol ratio of styrene/PAA andMMA/prepolymer. DSC and TEM results revealed that the block copolymer has twoseparated glass transition temperatures and phase separation within the domain structure. 相似文献
46.
Ramin Ghorbani‐Vaghei Mohammad Ali Zolfigol Nasrin Moshfeghifar Nadiya Koukabi Gholamabbas Chehardoli 《中国化学会会志》2007,54(3):791-794
An efficient method for the oxidative coupling of thiols to their corresponding disulfides by new reagents poly(N‐bromobenzene‐1,3‐disulfonylamide) PBBS , N,N,N′,N′‐tetrabromobenzene‐1,3‐disulfonylamide TBBDA and DABCO‐bromine complex is described. The reaction was applicable to a variety of thiols with high chemoselectivity. 相似文献
47.
Summary Tokaj wines (Szamorodni and Aszu wines) of Hungarian origin were investigated on the basis of free amino acids and biogenic
amines. The separation and determination of these compounds was performed by an amino acid analyser equipped with an ion-exchange
resin column. The total amount of free amino acids and biogenic amines was higher in Aszu wines than in Szamorodni wines.
The main amino acids were proline and arginine, while the major biogenic amines were tyramine and putrescine. The free amino
acid and biogenic amine content of Aszu wines depended on the vineyards the wines originated from.
Presented at Balaton Symposium '01 on High-Performance Separation Methods, Siófok, Hungary, September 2–4, 2001 相似文献
48.
新型螺环单体的合成和自由基聚合反应的研究王宏鲁剑涛冯品珍(中国科学技术大学研究生院化学部北京100039)关键词自由基聚合,新单体合成,螺环单体,自由基共聚虽然离子型开环聚合早已为人熟知,但是自由基开环聚合反应的研究和应用开发还刚刚起步.... 相似文献
49.
Oxidative free radical reactions of enamino esters are described. Electrophilic carbon-centered radicals produced by the cerium(IV) ammonium nitrate (CAN) oxidation of β-dicarbonyl compounds undergo efficient addition to the C-C double bond of enamino esters. This CAN mediated free radical reaction between enamino esters and β-dicarbonyl compounds provides a novel method for the synthesis of highly substituted pyrroles. The direct CAN oxidation of β-enaminocinnamates gave the dimerization products effectively. 相似文献
50.
S. G. Zlotin O. V. Prokshits N. F. Karpenko Yu. A. Strelenko O. A. Luk'yanov 《Russian Chemical Bulletin》1992,41(8):1400-1413
We have worked out a method for the synthesis of 1,3,3-trisubstituted triazene 1-oxides based upon reaction of 1,1-disubstituted hydrazines with bromine in the presence of aryl- and heteroarylnitroso compounds in acid media. Obtained are a broad range of triazene 1-oxides, among which hitherto unknown compounds of the series of pyrazole and 3,3-dialkyltriazene 1-oxides that contain functional groups at the alkyl part of the molecule. We propose a reaction scheme which includes in situ formation of diazenium cations and reaction of them with nitroso compounds that are present in the system. By means of PMR,13C, and14N NMR spectroscopy, and mass spectroscopy, it has been shown that in all the prepared compounds the oxidated nitrogen atom is at the N1 position of the triazene N-oxide group.N. D. Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, 117913 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 8, pp. 1804–1820, August, 1992. 相似文献