全文获取类型
收费全文 | 1090篇 |
免费 | 29篇 |
国内免费 | 1篇 |
专业分类
化学 | 831篇 |
晶体学 | 11篇 |
力学 | 10篇 |
数学 | 54篇 |
物理学 | 214篇 |
出版年
2021年 | 10篇 |
2020年 | 11篇 |
2019年 | 12篇 |
2018年 | 10篇 |
2017年 | 10篇 |
2016年 | 25篇 |
2015年 | 12篇 |
2014年 | 28篇 |
2013年 | 59篇 |
2012年 | 62篇 |
2011年 | 61篇 |
2010年 | 37篇 |
2009年 | 38篇 |
2008年 | 65篇 |
2007年 | 68篇 |
2006年 | 48篇 |
2005年 | 44篇 |
2004年 | 56篇 |
2003年 | 40篇 |
2002年 | 32篇 |
2001年 | 8篇 |
2000年 | 19篇 |
1999年 | 13篇 |
1998年 | 17篇 |
1997年 | 9篇 |
1996年 | 9篇 |
1995年 | 14篇 |
1994年 | 18篇 |
1993年 | 13篇 |
1992年 | 20篇 |
1991年 | 8篇 |
1990年 | 9篇 |
1989年 | 7篇 |
1988年 | 10篇 |
1986年 | 12篇 |
1985年 | 13篇 |
1984年 | 17篇 |
1983年 | 8篇 |
1982年 | 9篇 |
1981年 | 11篇 |
1980年 | 9篇 |
1979年 | 13篇 |
1978年 | 11篇 |
1977年 | 12篇 |
1975年 | 12篇 |
1974年 | 13篇 |
1973年 | 12篇 |
1972年 | 7篇 |
1970年 | 9篇 |
1969年 | 7篇 |
排序方式: 共有1120条查询结果,搜索用时 15 毫秒
11.
Likelihood estimation of soft-core interaction potentials for Gibbsian point patterns 总被引:3,自引:3,他引:0
Yosihiko Ogata Masaharu Tanemura 《Annals of the Institute of Statistical Mathematics》1989,41(3):583-600
The likelihood method is developed for the analysis of socalled regular point patterns. Approximating the normalizing factor of Gibbs canonical distribution, we simultaneously estimate two parameters, one for the scale and the other which measures the softness (or hardness), of repulsive interactions between points. The approximations are useful up to a considerably high density. Some real data are analyzed to illustrate the utility of the parameters for characterizing the regular point pattern. 相似文献
12.
Tryptophan (Trp) derivatives were selectively separated from 24 kinds of amino acid mixture solutions. Capillary electrophoresis (CE) with UV detection using the described pretreatment system was able to separate and determine 4 kinds of Trp derivatives: 5-hydroxy L-tryptophan, 5-methyl L-tryptophan, 1-methyl L-tryptophan and L-tryptophan. The pretreatment system used a combination of a homogeneous liquid-liquid extraction and a sweeping method, the two are different kinds of powerful preconcentration/separation methods. Trp derivatives were thus separated by two different separation systems. First, these derivatives were selectively extracted at 57-100% by a homogeneous liquid-liquid extraction; secondly, they were respectively separated by micellar electrokinetic chromatography (MEKC) with a sweeping effect. The detection limits following complete separation of the Trp derivatives were 10(-8) mol l(-1) levels, respectively. The proposed method provided a more than 10-fold the improvement in sensitivity compared with fluorescence labeling/fluorophotometric analysis; the proposed method was also applied to the component analysis of nutritious medicine. 相似文献
13.
14.
Hiroyuki Ohno Yoshitaka Ogata Eishun Tsuchida 《Journal of polymer science. Part A, Polymer chemistry》1986,24(11):2959-2969
Small unilamellar liposomes were prepared in an aqueous medium by the sonication of phospholipids containing diene or triene groups in their hydrocarbon acyl chains. These liposomes were polymerized by gamma-ray irradiation. Conversion of polymerization was successively followed by UV spectrometry. Diene-type lipid liposomes were revealed for which a gamma-ray dose of 0.8 Mrad was required for complete polymerization and which were polymerized more easily than triene-type lipid liposomes. Triene-type lipids required 2.3 Mrad gamma ray to polymerize them completely. Contrary to UV-irradiation polymerization, there was no concentration dependence on the polymerization. Structure of the polymerized liposomes were confirmed by electron microscopy as small unilamellar liposomes. Study on the leakage of fluorescein from inner aqueous phase of the polymerized liposomes revealed that polymerized triene-type liposomes were relatively more stable than the polymerized diene-type liposomes. 相似文献
15.
[reaction: see text] Catalytic, enantioselective Mannich-type reactions of alpha-imino esters bearing readily removable substituents on nitrogen are described. Several N-carbamate-protected alpha-imino esters, which are readily prepared from 2-bromoglycine esters using a polymer-supported amine, reacted with silicon enolates to afford the desired adducts in high yields with high enantioselectivity using a copper(II)-diamine complex. Easy deprotection of the product amine and transformation to free alpha-amino acid derivatives have also been demonstrated. 相似文献
16.
Chiaki Azuma Takao Mitsuboshi Kohei Sanui Naoya Ogata 《Journal of polymer science. Part A, Polymer chemistry》1980,18(3):781-797
cis-1,4-Polybutadiene and polypentenamer having pendant functional groups such as formyl, aldoxime, hydroxymethyl, or cinnamoyloxymethyl groups have been prepared, and some of their properties were investigated in terms of structural effect on physical properties of these polymers. cis-1, 4-Polybutadiene and polypentenamer having a different content of formyl group were prepared by the hydroformylation reaction with rhodium catalyst under mild conditions. The pendant formyl group was reduced to a hydroxymethyl group by using various reducing agents such as sodium borohydride or sodium trimethoxyborohydride which were effective to avoid a crosslinking reaction among the formyl groups. Glass transition temperature of polypentenamer having hydroxymethyl groups increased with increasing the content of the hydroxymethyl groups in the polymer. Cinnamoyl group was introduced into the polypentenamer having hydroxymethyl groups by reacting with cinnamoyl chloride so as to prepare a photosensitive rubber. The relationships between the photosensitivity of the cinnamoylated polypentenamer and the mobility of polymer main chains have been elucidated. A linear relationship between the photodimerization rate constant and the difference between ultraviolet (UV) irradiation temperature and the glass transition temperature of the polymer was found. It has become apparent that the photosensitivity of cinnamoylated polypentenamer can be estimated by the glass transition temperature of the original polymer, UV irradiation temperature, activation energy of the dimerization, and γ, which is a coefficient of the relationship between the photosensitive group concentration and the glass transition temperature of the polymer. 相似文献
17.
Yoshitaka Gotoh Yutaka Kohno Wakichi Fukuda Masao Tomoi 《Journal of polymer science. Part A, Polymer chemistry》1994,32(8):1543-1550
Soluble polystyrenes with crown ether structures and hydroxyl groups adjacent to the macrorings were prepared by the reaction of epoxide-containing polystyrenes with monoaza-15-crown-5 or monoaza-18-crown-6. Rate of formation of the polymer-bound alkali cation-crown alkoxide ion pair from the soluble polystyrenes and aqueous NaOH or KOH depended on the loading of crown ether and hydroxyl units and on the size of the macroring. The elimination of HCl from less reactive 2-chloroethylbenzene with aqueous NaOH or KOH in the presence of the soluble polystyrene catalysts under two-phase conditions was limited mainly by the intrinsic reaction rate. The elimination of HBr from more reactive 2-bromoethylbenzene in the presence of the less (11%) ring-substituted polymer catalyst with 18-crown unit was limited by the alkoxide formation rate. © 1994 John Wiley & Sons, Inc. 相似文献
18.
Yoshitaka Ogiwara Hitoshi Kubota Yuji Kimura 《Journal of polymer science. Part A, Polymer chemistry》1978,16(11):2865-2873
The influence of ferric acetylacetonate [Fe(acac)3] on the photodegradation of model compounds of polyethylene (PE) was examined. By studying electron-spin-resonance (ESR) spectra of photoirradiated compounds such as 1-octene and 1,7-octadiene, which contain carbon double bonds, Fe(acac)3 was found to accelerate the formation of allyl radical by contact with them. On the other hand, Fe(acac)3 suppressed the radical formation based on Norrish type I reaction in a carbonyl group of compounds such as 2-octanone and 3-octanone. Based on the study of ultraviolet (UV) spectra as well as ESR spectra on photoirradiated samples, the influence of Fe(acac)3 on the photodecomposition of model compounds of PE was discussed. Finally, the discussion turned to the mechanism of photodecomposition of PE in the presence of ferric salt. 相似文献
19.
A cationic CpRu(II) complex in combination with quinaldic acid shows high reactivity and chemoselectivity for the catalytic deprotection of hydroxyl groups protected as allyl ethers. The catalyst operates in alcoholic solvents without the need for any additional nucleophiles, satisfying the practical requirements of operational simplicity, safety, and environmental friendliness. The wide applicability of this deprotection strategy to a variety of multifunctional molecules, including peptides and nucleosides, may provide new opportunities in protective group chemistry. [structure: see text] 相似文献
20.
Yoshikatsu Ito Meng Ji-Ben Shin Suzuki Yoshitaka Kusunaga Teruo Matsuura Keiichi Fukuyama 《Tetrahedron letters》1985,26(17):2093-2096
In contrast to simple imidazoles, 1-methy1–2,4,5-triphenylimidazole () produced stable oxetane photoadducts - with good efficiency upon irradiation in the presence of benzophenone derivatives - in acetonitrile solution. Irradiation in the solid-phase was also studied. The oxetanes - readily underwent cycloreversion by acid catalysis or by heating. 相似文献