全文获取类型
收费全文 | 467篇 |
免费 | 17篇 |
国内免费 | 3篇 |
专业分类
化学 | 362篇 |
晶体学 | 1篇 |
力学 | 12篇 |
数学 | 30篇 |
物理学 | 82篇 |
出版年
2022年 | 4篇 |
2021年 | 5篇 |
2019年 | 5篇 |
2018年 | 4篇 |
2016年 | 5篇 |
2015年 | 13篇 |
2014年 | 6篇 |
2013年 | 24篇 |
2012年 | 28篇 |
2011年 | 26篇 |
2010年 | 10篇 |
2009年 | 15篇 |
2008年 | 27篇 |
2007年 | 20篇 |
2006年 | 18篇 |
2005年 | 29篇 |
2004年 | 18篇 |
2003年 | 14篇 |
2002年 | 23篇 |
2001年 | 12篇 |
2000年 | 7篇 |
1999年 | 13篇 |
1998年 | 9篇 |
1997年 | 10篇 |
1996年 | 8篇 |
1995年 | 5篇 |
1994年 | 11篇 |
1993年 | 4篇 |
1992年 | 3篇 |
1991年 | 6篇 |
1989年 | 2篇 |
1987年 | 2篇 |
1986年 | 4篇 |
1985年 | 8篇 |
1984年 | 12篇 |
1983年 | 2篇 |
1982年 | 8篇 |
1981年 | 3篇 |
1980年 | 5篇 |
1979年 | 4篇 |
1978年 | 5篇 |
1977年 | 2篇 |
1976年 | 4篇 |
1975年 | 2篇 |
1974年 | 7篇 |
1973年 | 11篇 |
1970年 | 4篇 |
1966年 | 2篇 |
1962年 | 3篇 |
1960年 | 2篇 |
排序方式: 共有487条查询结果,搜索用时 31 毫秒
1.
2.
Masamichi Takase 《Topology》2004,43(6):1425-1447
Haefliger has shown that a smooth embedding of the (4k−1)-sphere in the 6k-sphere can be knotted in the smooth sense. In this paper, we give a formula with which we can detect the isotopy class of such a Haefliger knot. The formula is expressed in terms of the geometric characteristics of an extension, analogous to a Seifert surface, of the given embedding. In particular, the Hopf invariant associated to the extension plays a crucial role. This leads us to a new characterisation of Haefliger knots. 相似文献
3.
Both S-(-)- and R-(+)-enantiomers of 5-(p-hydroxyphenyl)-5-phenylhydantoin (p-HPPH), a main oxidative metabolite of the achiral antiepileptic drug phenytoin, could be determined simply, sensitively and accurately using reversed phase high-performance liquid chromatography by using a methanol-monopotassium phosphate eluent containing beta-cyclodextrin. Using this assay procedure, it was determined that an S-(-)-enantiomer was formed predominantly by the oxidation of phenytoin in isolated rat hepatocytes. 相似文献
4.
5.
Yozo Miura Masamichi Dairoku 《Journal of polymer science. Part A, Polymer chemistry》2007,45(18):4364-4376
Dendritic multifunctional macroinitiators having six and 12 TIPNO‐based alkoxyamines, TIPNO‐6 and TIPNO‐12 , were synthesized and used in the living radical polymerization of styrene (St), methyl acrylate (MA), N,N‐dimethylacrylamide (DMAAm), and isoprene (IP). The polymerizations of St initiated with TIPNO‐6 gave 6‐arm star polymers with narrow polydispersities of 1.14–1.18. In the polymerizations of MA initiated with TIPNO‐6 and TIPNO‐12 , the influences of added TIPNO on the polydispersity indexes (PDIs) of the resulting star polymers were first investigated, and this led to the successful formation of poly(MA) star polymers with narrow polydispersities (1.10–1.18). Moreover, the polymerizations of DMAAm and IP from TIPNO‐6 in the presence or absence of TIPNO were briefly investigated. The benzyl ether bonds of the poly(St) and poly(MA) star polymers were cleaved by treating with Me3SiI or Pd/C, and the resulting arm's parts were analyzed with SEC. The PDIs of the resulting arm parts were low (1.19–1.23), and the Mns agreed with the Mn,theor, indicating that the poly(St) and poly(MA) star polymers had well‐controlled arms. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4364–4376, 2007 相似文献
6.
M. Toba S. Tanaka S. Niwa F. Mizukami Z. Koppány L. Guczi 《Journal of Sol-Gel Science and Technology》1998,13(1-3):1037-1041
In order to achieve functional group selective hydrogenation, the layer structure of Ru-Sn-Al2O3 catalysts was controlled by using sol-gel, powder impregnation and combined sol-gel impregnation methods. The properties of the catalysts and effectiveness in hydrogenation of dimethyl terephthalate were examined. The surface Sn contents of the catalysts characterized by X-ray photoelectron spectroscopy depended on the preparation method, in spite of almost the same bulk Ru and Sn compositions measured by X-ray fluorescence analyses. TPR and CO adsorption of the catalysts also depended on the preparation method. With regard to the conversion rate of dimethyl terephthalate and the rate of product conversion from methyl 4-hydroxy methylbenzoate to p-xylene via methyl p-toluate, Ru impregnation catalysts had higher rates than the other catalysts. 相似文献
7.
Ken-Ichi Ito Masamichi Nishimura Minoru Sashio Masahiro Tsunooka 《Journal of polymer science. Part A, Polymer chemistry》1994,32(11):2177-2185
It was found that amines were formed efficiently by the photolysis of O-acyloximes followed by hydrolysis in polystyrene films and the relationship between structures of O-acyloximes and yields of amines were investigated. O-phenylacetyl acetophenone oxime (PaApO), O-pivaloyl acetophenone oxime (PApO), and O-benzoyl acetophenone oxime (BApO) as monofunctional O-acyloximes and O,O′-succinyl diacetophenone oxime (SDApO) and O,O′-glutaryl diacetophenone oxime (GDApO) as bifunctional O-acyloximes were examined. The yields of amines for PaApO and SDApO under N2 were ca. 70%, which was the highest among O-acyloximes examined in this experiment. On the other hand, the yields for PApO, BApO, and GDApO were less than 15% and it was verified that the hydrogen abstraction by imino radicals via 6-membered cyclic intermediates resulted in the lowering of yields. Although the effect of oxygen under photolysis on the yields of amine for PaApO was negligible under 50% conversion of PaApO, the yield decreased with further increase in the conversion and was 50% at 90% conversion. © 1994 John Wiley & Sons, Inc. 相似文献
8.
Palladium-diethylzinc or palladium-triethylborane catalytically promotes self-allylation of 2-(allyloxy)tetrahydrofurans, 2-(allyloxy)tetrahydropyrans, and their hydroxy derivatives on the rings (ribose, glucose, mannose, deoxyribose, deoxyglucose). All the reactions proceed at room temperature and provide polyhydroxyl products, sharing a structural motif of a homoallyl alcohol, in good to excellent yields with high levels of stereoselectivity. Useful C3-unit elongation, which makes the best use of an allyl ether as a protecting group and a nucleophilic allylation agent, is demonstrated. Mechanisms for the umpolung reaction (of an allyl ether into an allylic anion) and stereoselectivity associated with allylation of aldehydes are discussed. 相似文献
9.
Masamichi Furukawa 《Analytica chimica acta》1982,140(1):281-289
2-(2-ThiazolyIazo)-5-dimethylaminobenzoic acid (TAMB) and 2-(2-benzothiazolylazo)-5-dimethylaminobenzoic acid (BTAMB) have been synthesized, and their potential for determinations of metals has been studied spectrophotometrically. Both are extremely sensitive chromogenic reagents for the determination of nickel. Molar absorptivities in aqueous methanol are 0.95 × 105 (TAMB) and 1.2 × 105 (BTAMB). In aqueous methanol, at apparent pH 5–9.5, the system conforms to Beer's law for 0.05–0.5 ppm nickel; Cu, Cr, Co, Pd and Fe interfere, but they can easily be masked. 相似文献
10.
A Yamamoto A Matsunaga E Mizukami K Hayakawa M Miyazaki 《Journal of chromatography. A》1991,585(2):315-317
An ion chromatographic separation with photometric detection using a chiral copper(II) complex as the eluent has been developed for the resolution of enantiomers of malic acid in commercially available apple juices. The results obtained by this method were in good agreement with those by an enzymatic method with separation by high-performance liquid chromatography. 相似文献