全文获取类型
收费全文 | 59篇 |
免费 | 21篇 |
国内免费 | 14篇 |
专业分类
化学 | 48篇 |
晶体学 | 4篇 |
力学 | 1篇 |
综合类 | 3篇 |
数学 | 15篇 |
物理学 | 23篇 |
出版年
2023年 | 1篇 |
2022年 | 1篇 |
2019年 | 2篇 |
2018年 | 2篇 |
2017年 | 3篇 |
2016年 | 2篇 |
2015年 | 5篇 |
2014年 | 3篇 |
2013年 | 8篇 |
2012年 | 5篇 |
2011年 | 2篇 |
2010年 | 6篇 |
2009年 | 5篇 |
2008年 | 3篇 |
2007年 | 2篇 |
2006年 | 4篇 |
2005年 | 2篇 |
2004年 | 4篇 |
2003年 | 5篇 |
2002年 | 1篇 |
2000年 | 3篇 |
1999年 | 1篇 |
1998年 | 1篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 3篇 |
1993年 | 1篇 |
1992年 | 2篇 |
1991年 | 1篇 |
1990年 | 3篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1983年 | 1篇 |
1981年 | 1篇 |
排序方式: 共有94条查询结果,搜索用时 15 毫秒
61.
A variety
of universal algebras is said to be congruence permutable if for every algebra A of
and every pair of congruences α, β from A we have αβ = βα. We show that if
is locally finite (i.e., every finitely generated member of
is finite) then congruence permutability is equivalent to a local property of the finite members of
, expressible in the language of tame congruence theory. This answers a question of R. McKenzie and D. Hobby. 相似文献
62.
单质碘掺杂纳米TiO2光催化剂的制备及性能 总被引:2,自引:0,他引:2
以钛酸四异丙酯和单质碘为起始原料,用改进的溶胶-凝胶法制备了掺碘的纳米TiO2的前驱体,经500 ℃煅烧得到棕黄色TiO2/I2纳米粉末.采用X射线衍射(XRD),紫外-可见(UV-Vis)漫反射光谱,透射电镜(TEM)等手段对TiO2/I2粉末进行了表征,并研究了其光催化性能.结果表明,掺杂的碘存在于TiO2内部纳米孔洞中,不会因为高温而被氧化;光催化降解甲基橙反应是一级反应;TiO2掺杂碘单质后对光响应波长拓展至可见光范围,对甲基橙的降解效率可提高15%以上. 相似文献
63.
In this paper we determine those locally finite varieties that generate decidable discriminator varieties when augmented by a ternary discriminator term.Dedicated to Bjarni Jonsson on the occasion of his 70th birthdayPresented by G. McNulty.The first author gratefully acknowledges the support of NSERC. 相似文献
64.
+-Kalkitoxin, a metabolite of the marine cyanobacterium Lyngbya majuscula, was synthesized from (R)-2-methylbutyric acid, (R)-cysteine, and (3S, 4S, 6S)-3,4,6-trimethyl-8-(methylamino)octanoic acid. A key step in the synthesis was installation of the anti,anti methyl stereotriad by means of a tandem asymmetric conjugate addition of an organocopper species to an alpha,beta-unsaturated N-acyl oxazolidin-2-one followed in situ by alpha-methylation of the resultant enolate. The thiazoline portion of kalkitoxin was assembled by titanium tetrachloride catalyzed cyclization of a vinyl substituted amido thiol. 相似文献
65.
66.
67.
Johnson TA Amagata T Oliver AG Tenney K Valeriote FA Crews P 《The Journal of organic chemistry》2008,73(18):7255-7259
A reinvestigation of a Fijian collection of Cacospongia mycofijiensis has yielded the known mycothiazole and a novel heterocyclic, CTP-431 (1). Its structure including absolute configuration as 8R,9R,10S,13S was established using NMR data, calculated DFT (13)C chemical shifts and results from X-ray crystallography. It is possible that the tricyclic skeleton of CTP-431 (1) is biosynthetically related to the macrolide latrunculin A, however the thiopyrone moiety of 1 has no previous precedent in natural products chemistry. 相似文献
68.
基于液体阵列味觉仿生传感器鉴别白酒香型的新方法 总被引:2,自引:0,他引:2
通过模拟哺乳动物的味觉系统, 建立了交叉响应的液体阵列传感器, 为鉴别白酒香型提供了新方法. 选用7种染料和1种卟啉化合物作为传感单元, 构建液体阵列传感器, 集合8个传感单元的光谱响应信号构成分析物的指纹图谱, 达到识别的目的. 使用96孔板酶标仪采集响应数据, 结合主成分分析(PCA)、分层聚类分析(HCA)和判别分析(LDA)等模式识别方法进行数据处理, 对9种具有代表性的不同香型白酒样品进行了鉴别分析. PCA结果表明, 该方法对于白酒的检测主要基于酒体微量成分, 其中酸类物质对识别的贡献最大(贡献率达54.3%), 芳香类物质贡献率为18.6%; 同时, 仅用63.4%的数据信息量即可对白酒香型进行区分. HCA结果表明, 平行样均正确归类, 各白酒之间的相似程度在聚类图上得到体现. LDA结果表明, 该阵列对于9种白酒样品香型识别的准确率达到100%. 相似文献
69.
ZHANG Ya QIAN Linlin YIN Wei HE Bin LIU Fangmei HOU Changjun HUO Danqun FA Huanbao 《高等学校化学研究》2016,32(5):725-730
Molecularly imprinted membrane-zinc porphyrin-mathacrylate(MIM-Zn-MAA), a dual read-out sensor based on a molecularly imprinted membrane, was developed to recognize and detect dimethyl methylphosphonate (DMMP) as an intermediate molecule of organophosphorus pesticides. The membranes were prepared via thermal polymerization of two functional monomers(zinc porphyrin and mathacrylate) on the surface of a glass slide functionalized with ethylene glycol dimethacrylate and azobisisobutyronitrile. The morphology of the as-synthesized MIM-Zn-MAA was determined with scanning electronic microscopy. The composite membranes exhibited macrovoid morphologies, which were affected by the functional monomers. These membranes were selectively adsorbed onto the template molecule and displayed higher adsorbing capacity toward DMMP compared with their structural analogs. Changes in the fluorescent spectra were qualitatively and quantitatively monitored via fluorescence photometry. Difference maps were also obtained using colorimetry before and after the reaction between MIM-Zn-MAA and DMMP at various concentrations. The maps showed a wide linear range varying from 0.1 μmol/L to 10 mmol/L with a low detection limit of 0.1 μmol/L. These preliminary results demonstrate that the as-fabricated dual read-out sensor displays good sensitivity and selectivity toward DMMP, indicating its considerable potential in DMMP detection in practical applications. 相似文献
70.
IntroductionPorphyrin possesses some unique properties.Incomparison with the porphyrin monomer,porphyrin oli-gomers are much attracting owing to their much betterproperties in some aspects,such as light harvest,ener-gy transformation and electron transiti… 相似文献