全文获取类型
收费全文 | 463篇 |
免费 | 10篇 |
国内免费 | 1篇 |
专业分类
化学 | 321篇 |
晶体学 | 9篇 |
力学 | 6篇 |
数学 | 93篇 |
物理学 | 45篇 |
出版年
2021年 | 4篇 |
2020年 | 5篇 |
2019年 | 6篇 |
2018年 | 4篇 |
2016年 | 7篇 |
2015年 | 8篇 |
2014年 | 3篇 |
2013年 | 19篇 |
2012年 | 18篇 |
2011年 | 21篇 |
2010年 | 7篇 |
2009年 | 15篇 |
2008年 | 40篇 |
2007年 | 32篇 |
2006年 | 20篇 |
2005年 | 22篇 |
2004年 | 23篇 |
2003年 | 15篇 |
2002年 | 13篇 |
2001年 | 9篇 |
2000年 | 9篇 |
1999年 | 7篇 |
1998年 | 11篇 |
1997年 | 8篇 |
1996年 | 7篇 |
1995年 | 10篇 |
1994年 | 10篇 |
1993年 | 4篇 |
1992年 | 3篇 |
1991年 | 3篇 |
1990年 | 5篇 |
1989年 | 5篇 |
1988年 | 6篇 |
1986年 | 3篇 |
1984年 | 8篇 |
1981年 | 7篇 |
1980年 | 6篇 |
1978年 | 5篇 |
1977年 | 3篇 |
1975年 | 3篇 |
1973年 | 3篇 |
1971年 | 3篇 |
1970年 | 4篇 |
1966年 | 2篇 |
1964年 | 5篇 |
1963年 | 2篇 |
1960年 | 2篇 |
1959年 | 4篇 |
1954年 | 3篇 |
1942年 | 2篇 |
排序方式: 共有474条查询结果,搜索用时 156 毫秒
1.
Technical cellulose-2.5-acetates (CA 2.5) were characterized regarding their carbohydrate composition in comparison to the raw material. The association of the CA 2.5 samples in acetone was studied by size exclusion chromatography (SEC) using various acetone grades and styrene divinylbenzene copolymer columns. In HPLC grade acetone with and without addition of 1% water up to three different pre-humps eluted in front of the main fraction of the polymer. The evaluation of the main peak by light scattering measurements resulted in high molar masses indicating that for these technical CA 2.5 samples even the main fraction is not dissolved without association. No pre-humps or association phenomena were observed after addition of 1 ppm LiBr to HPLC grade acetone or with p.a. grade acetone. In addition pre-hump enriched and pre-hump free fractions were isolated by fractionated precipitation. The carbohydrate composition of these fractions was determined and correlated with their association pattern in SEC investigations. 相似文献
2.
3.
4.
Bodo Dittmar 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》1988,39(3):351-366
Zusammenfassung Es wird ein neues Verfahren zur numerischen Berechnung des ersten nichttrivialen Stekloffschen Eigenwertes beschrieben. Dieses Verfahren arbeitet nur mit oberen Schranken.
We describe a new procedure for the numerical evaluation of the first nontrivial Stekloff eigenvalue. This procedure works only with upper bounds.相似文献
5.
6.
Tetramethyldisilane-1,2-diyl bridged Dicyclopentadienyl and Diindenyl Metal Dichlorides of the Group 4 Metals – Crystal Structure of Dicyclopentadienyl and diindenyl metal dichlorides of the type Cp′? SiMe2SiMe2? Cp′MCl2 (Cp′ = C5H4, M = Ti ( 1 ), Zr ( 2 ), Hf ( 3 ); Cp′ = C9H7, M = Zr ( 4 ), Hf ( 5 )) were synthesized and characterized by means of their 1H, 13C, 29Si-n.m.r., MS, and IR spectra. The crystal structure of 2 was determined. 相似文献
7.
Egon Fanghnel Hagen Bartossek Ute Baumeister Matthias Biedermann Helmut Hartung 《Journal of heterocyclic chemistry》1998,35(6):1449-1454
The first synthesis of substituted 2,2-dioxo-1-phenyl-1H-thieno[3,4-c][1,2]thiazines 2 and some of their reactions are achieved. Compounds 2 were prepared from the 3,5-dimethyl-1,1-dioxo-1,2-thiazine-4-carbaldehydes 1 by reaction with sulfur and triethyl amine in dimethylformamide under mild conditions. They were characterized spectroscopically and by X-ray structure analysis. The formylation, chlorination and oxidation of 2 are reported. 相似文献
8.
Triphenylphosphane Nickel(0) Complexes with Isocyanide Ligands — [(RNC)nNi(PPh3)4–n] (n = 1–3) Synthesis and properties of the isocyanide triphenylphosphane nickel(0) complexes [(RNC)Ni(PPh3)3], [(RNC)2Ni(PPh3)2] and [(RNC)3Ni(PPh3)] (R = tBu, Cy, PhCH2, p-TosCH2) are described. I.r. and 31P n.m.r. spectra were recorded and the X-ray crystal structure of [(PhCH2NC)2Ni(PPh3)2] was determined. 相似文献
9.
Lehmann B 《Photochemistry and photobiology》2005,81(6):1246-1251
The skin is the only tissue yet known in which the complete ultraviolet-B (UV-B)-induced pathway from 7-dehydrocholesterol to hormonally active calcitriol (1alpha,25-dihydroxyvitamin D(3)) occurs under physiological conditions. Epidermal synthesis of calcitriol could be of fundamental relevance because calcitriol regulates important cellular functions in keratinocytes and immunocompetent cells. Because of their antiproliferative and prodifferentiating effects, calcitriol and other vitamin D analogs are highly efficient in the treatment of psoriasis vulgaris. The known antipsoriatic effect of UV-B light could, at least in part, be mediated via UV-B-induced synthesis of calcitriol. In addition, mounting evidence indicates that cutaneous vitamin D(3) synthesis is of high importance for the prevention of a broad variety of diseases, including various malignancies. New but controversially discussed sun-protection guidelines were established for the prevention of internal cancers. A better understanding of the metabolism of vitamin D in the skin opens new perspectives for therapeutic applications of vitamin D analogs. 相似文献
10.