全文获取类型
收费全文 | 330篇 |
免费 | 12篇 |
国内免费 | 2篇 |
专业分类
化学 | 175篇 |
晶体学 | 32篇 |
力学 | 3篇 |
数学 | 36篇 |
物理学 | 98篇 |
出版年
2023年 | 2篇 |
2022年 | 4篇 |
2021年 | 16篇 |
2020年 | 8篇 |
2019年 | 9篇 |
2018年 | 8篇 |
2017年 | 9篇 |
2016年 | 20篇 |
2015年 | 8篇 |
2014年 | 13篇 |
2013年 | 20篇 |
2012年 | 19篇 |
2011年 | 21篇 |
2010年 | 10篇 |
2009年 | 8篇 |
2008年 | 18篇 |
2007年 | 13篇 |
2006年 | 15篇 |
2005年 | 9篇 |
2004年 | 8篇 |
2003年 | 7篇 |
2002年 | 7篇 |
2001年 | 6篇 |
2000年 | 3篇 |
1999年 | 4篇 |
1998年 | 4篇 |
1997年 | 6篇 |
1996年 | 4篇 |
1995年 | 4篇 |
1994年 | 4篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1978年 | 2篇 |
1976年 | 2篇 |
1975年 | 3篇 |
1974年 | 3篇 |
1972年 | 3篇 |
1904年 | 1篇 |
1880年 | 1篇 |
排序方式: 共有344条查询结果,搜索用时 31 毫秒
131.
Marcelo Coelho Silva Jeancarlo Pereira dos Anjos Lilian Lefol Nani Guarieiro Bruna A. Souza Machado 《Molecules (Basel, Switzerland)》2021,26(16)
There are a significant number of analytical methodologies employing different techniques to determine phenolic compounds in beverages. However, these methods employ long sample preparation processes and great time consumption. The aim of this paper was the development of a simple method for evaluating the phenolic compounds’ presence in Brazilian craft beers without a previous extraction step. Catechin, caffeic acid, epicatechin, p-coumaric acid, hydrated rutin, trans-ferulic acid, quercetin, kaempferol, and formononetin were analyzed in fifteen different craft beers. The method showed good linearity (R2 ≥ 0.9966). The limit of detection ranged from 0.08 to 0.83 mg L−1, and limits of quantification were between 0.27 and 2.78 mg L−1. The method showed a satisfactory precision (RSD ≤ 16.2%). A good accuracy was obtained by the proposed method for all phenolic compounds in craft beer (68.6% ˂ accuracy ˂ 112%). Catechin showed higher concentrations (up to 124.8 mg L−1) in the samples, followed by epicatechin (up to 51.1 mg L−1) and caffeic acid (up to 8.13 mg L−1). Rutin and formononetin were observed in all analyzed samples (0.52 mg L−1 to 2.40 mg L−1), and kaempferol was less present in the samples. The presence of plant origin products was determinant for the occurrence of the highest concentrations of phenolic compounds in Brazilian craft beers. 相似文献
132.
Pereira Bruna Á. de Bastos Alcione V. Teixeira Wystan K. O. e Silva Sidnei Moura Flores Alex F. C. Flores Darlene C. 《Molecular diversity》2017,21(4):1021-1026
Molecular Diversity - An elegant, efficient, and highly regioselective approach for the synthesis of novel methyl 5-amino-3-(methylthio)-1-differently substituted-1H-pyrazole-4-carboxylates is... 相似文献
133.
134.
135.
S.A. da S. Corradini G.G. Lenzi M.K. Lenzi C.M.F. Soares O.A.A. Santos 《Journal of Non》2008,354(42-44):4865-4870
The hydrogenation of methyl oleate over 2%Ru/TiO2, 4.7%Sn/TiO2 and 2%Ru–4.7%Sn–TiO2 catalysts was studied. The catalysts were prepared by the impregnation method. The characterization techniques used were: (i) specific surface area (B.E.T. method); (ii) pore volume and mean pore diameter; (iii) thermogravimetric analysis (TGA); (iv) temperature programed reduction (TPR); (v) X-ray diffraction (DRX); and (vi) scanning electron microscopy (SEM). The results indicate that the presence of tin increases the difficulty of the ruthenium reduction, evidencing a possible metal–metal interaction. However, tin addition to the TiO2 and the catalysts calcinations did not significantly influence the values obtained for the surface area and mean pore diameter. The DRX analyses showed that the catalysts have a crystalline structure, mostly in the anatase form. The metal-support interaction occurred probably due to the formation of RuTi of Ru/TiO2 catalyst. In Ru–Sn/TiO2 catalyst, the metal–metal interaction occurs between ruthenium and tin, resulting in Ru3Sn7. The catalysts reaction revealed that tin addition in ruthenium affects the activity of catalyst considerably in the hydrogenation of methyl oleate reaction. However, the activity decrease is accompanied by a considerable increase of alcohols yield, in particular of unsaturated alcohols. 相似文献
136.
Three amorphous steel alloys, Fe71.2?xC7.0Si3.3B5.5P8.7Cr2.3Al2.0Mox (x = 0, 4.5 and 6.5 at.%), have been produced by the melt-spinning technique and characterized by X-ray diffraction and transmission Mössbauer spectrometry (TMS). TMS allows us to study the local environments of the Fe atoms in the glassy state, showing the changes in the amorphous structure due to the addition of Mo. A reduction of the mean hyperfine field is observed as the amount of Mo increases. With intermediate Mo content, this reduction is associated to the substitution of Fe by Mo in a disordered magnetic Fe-rich structure, whereas for high Mo content, this structure is destroyed leading to an increase of paramagnetic environments. Finally, the relationship between the glass forming ability (GFA) of these alloys and their local structure determined by TMS will be discussed. 相似文献
137.
Epixenosomes, epibiontic organisms living on the protozoon ciliate Euplotidium itoi, like prokaryotes, lack a true nucleus surrounded by a nuclear envelope. However, their cytoplasm, at least in the mature state, is somehow compartmentalized by the presence of a complex extrusive apparatus surrounded by a form of basket consisting of bundles of tubules (BT), 20–24 nm in diameter, delineated by a wall made of globular subunits. The nature of these tubules was investigated by means of in vivo experiments, ultrastructural analysis and immunocytochemistry by both fluorescence and electron microscopy. It has been found that BT, besides being well preserved when fixed in the presence of tannic acid, are sensitive to factors known to depolymerize cytoplasmic microtubules in a variety of cells such as nocodazole and cold and show a positive immunoreaction against different antitubulin antibodies. On the basis of all the results obtained, the hypothesis that the epixenosomal BT consist of tubulin acquires a strong credibility. This is particularly interesting if we consider that tubulin in prokaryotes has never been conclusively demonstrated. 相似文献
138.
We prove that, if γ is a simple smooth curve in the unit sphere inC
n, the space o pluriharmonic functions in the unit ball, continuous up to the boundary, has a trace of finite cof dimension
in the space of all continuous functions on the curve.
First author partially supported by the Swedish Natural Science Research Council. Second author partially supported by CICYT
grant PB85-0374. 相似文献
139.
Kinetics of dehydrogenation of propan-2-ol on the most active catalyst found in the mixed calcium-cobalt orthophosphate system,
Ca3-xCox(PO4)2, with x=0.32, has been studied. The activation energy of the reaction was also determined. 相似文献
140.
We study the zero-varieties of holomorphic functions in the unit ball satisfying the growth condition log |f(z)|≤c
fλ(|z|), where λ:(0,1)→ℝ+ is a positive increasing function. We obtain some sufficient conditions on an analytic variety to be defined by such a function.
Some results for the particular case λ(r)=log(e/(1−r)), corresponding to the classA
−∞, generalize those of B. Korenblum in one variable.
Both authors supported by DGICYT grant PB92-0804-C02-02. 相似文献