全文获取类型
收费全文 | 636篇 |
免费 | 15篇 |
国内免费 | 1篇 |
专业分类
化学 | 367篇 |
晶体学 | 4篇 |
力学 | 15篇 |
数学 | 127篇 |
物理学 | 139篇 |
出版年
2022年 | 10篇 |
2021年 | 12篇 |
2020年 | 12篇 |
2019年 | 10篇 |
2018年 | 11篇 |
2017年 | 4篇 |
2016年 | 19篇 |
2015年 | 16篇 |
2014年 | 11篇 |
2013年 | 35篇 |
2012年 | 33篇 |
2011年 | 34篇 |
2010年 | 28篇 |
2009年 | 20篇 |
2008年 | 30篇 |
2007年 | 33篇 |
2006年 | 30篇 |
2005年 | 29篇 |
2004年 | 21篇 |
2003年 | 20篇 |
2002年 | 26篇 |
2001年 | 8篇 |
2000年 | 11篇 |
1999年 | 7篇 |
1997年 | 4篇 |
1996年 | 9篇 |
1995年 | 4篇 |
1994年 | 4篇 |
1993年 | 7篇 |
1992年 | 4篇 |
1991年 | 9篇 |
1989年 | 4篇 |
1988年 | 8篇 |
1986年 | 7篇 |
1985年 | 7篇 |
1984年 | 11篇 |
1983年 | 7篇 |
1982年 | 5篇 |
1981年 | 8篇 |
1980年 | 5篇 |
1979年 | 7篇 |
1978年 | 9篇 |
1977年 | 5篇 |
1975年 | 7篇 |
1974年 | 3篇 |
1970年 | 3篇 |
1969年 | 3篇 |
1967年 | 3篇 |
1909年 | 4篇 |
1908年 | 3篇 |
排序方式: 共有652条查询结果,搜索用时 15 毫秒
51.
[structure: see text] The first examples of epoxy-p-quinol and diepoxy-p-quinol calixarene derivatives have been obtained by base-promoted direct addition of O(2)(oxygenation) to calixarene phenol rings. The regio- and stereochemistry of these derivatives was determined by 2D NMR studies, in conjunction with MM3 calculations, and X-ray crystallography. Both the oxygenation and the subsequent carbonyl reduction occur with a preferential attack to the less hindered exo face of the calixarene rings. 相似文献
52.
Bellezza F Cipiciani A Costantino U Nicolis S 《Langmuir : the ACS journal of surfaces and colloids》2004,20(12):5019-5025
The adsorption and catalytic activity of myoglobin (Mb) on zirconium phosphonates (a-zirconium benzenephosphonate (alpha-ZrBP), a-zirconium carboxyethanephosphonate (alpha-ZrCEP), and a novel layered zirconium fluoride aminooctyl-N,N-bis(methylphosphonate) (ZrC8)) were investigated. The maximum adsorption was reached after 16 h of contact and was greater on hydrophobic supports such as alpha-ZrBP and ZrC8 compared to hydrophilic supports such as alpha-ZrCEP. The equilibrium adsorption isotherms fitted the Langmuir equation, suggesting the presence of a monolayer of protein molecules on the support surfaces. The catalytic activities of free Mb and of the obtained biocomposites were studied in terms of the oxidation of two aromatic substrates, o-phenylenediamine and 2-methoxyphenol (guaiacol), by hydrogen peroxide. The oxidation catalyzed by immobilized myoglobin followed the Michaelis-Menten kinetics, similar to oxidation by free Mb. The kinetic parameters, kcat and KM, were significantly affected by the adsorption process. Mb/alpha-ZrCEP was the most efficient biocatalyst obtained, probably because of the hydrophilic nature of the support. The effect of immobilization on the stability of Mb toward inactivation by hydrogen peroxide was also investigated, and an increased resistance was found. The biocomposites obtained can be stored at 4 degrees C for months without a significant loss of catalytic activity. 相似文献
53.
A combined experimental and theoretical investigation at the DFT and MP2 levels on the boron-to-carbon 1,2-shift in "ate species", coming from the quaternization of boranes (A) and boronate (B), is reported. To discuss the different migratory aptitudes of various alkyl groups, we have examined the migration of primary (R = Me, Et), secondary (R = i-Pr), and tertiary (R = t-Bu) alkyl groups. The effect of the counterion Li(+) and of the solvent (polarized continuous model (PCM) method) has been considered. The following results are relevant: (a) in all cases, the reaction proceeds via a concerted-type mechanism which explains the retention of configuration at the migrating group and the inversion at the migration terminus experimentally observed. (b) The trend of the migration barriers along the direction primary --> secondary --> tertiary alkyl group observed in "ate" species A is reversed in boronate species B, in agreement with the experimental evidences. (c) A simple theoretical model is proposed where the barrier trend is the result of a delicate interplay between two opposite factors: (1) a "steric effect", which favors the most sterically demanding migrating groups, and (2) a "charge effect" associated with the partial carbanionic nature of the migrating carbon atom and which favors the less substituted migrating carbons. 相似文献
54.
Piarulli U Claverie C Daubos P Gennari C Minnaard AJ Feringa BL 《Organic letters》2003,5(23):4493-4496
[reaction: see text] A highly regio-, diastereo-, and enantioselective desymmetrization of five-, six-, and seven-membered meso-cyclic allylic bis-diethyl phosphates (2a, 2b, and 2c, respectively) was obtained with diethylzinc, using catalytic amounts of [Cu(OTf)](2).C(6)H(6) and phosphoramidite ligands 5. Enantiomeric excesses of up to 87, 94, and >98% were obtained for the addition of diethylzinc to cyclopentene, cyclohexene, and cycloheptene bis-diethyl phosphates, respectively. 相似文献
55.
We prove some new degeneracy results for integral points and entire curves on surfaces; in particular, we provide the first examples, to our knowledge, of a simply connected smooth variety whose sets of integral points are never Zariski-dense. Some of our results are connected with divisibility problems, i.e. the problem of describing the integral points in the plane where the values of some given polynomials in two variables divide the values of other given polynomials. 相似文献
56.
57.
58.
Umberto Costantino Maria Antonietta Massucci Aldo La Ginestra Anna Maria Tarola Laura Zampa 《Journal of inclusion phenomena and macrocyclic chemistry》1986,4(2):147-162
The intercalation of imidazole and some organic species containing the imidazole ring, between the layers of crystalline zirconium phosphate has been investigated. Fourteen new, well-ordered intercalation compounds are obtained with the batch procedure at r.t. and/or 60°C. A mechanism of formation of the various compounds is proposed on the basis of the interaction between the guest molecules (with their dimensions and geometries) and the free PO3OH groups available between the layers of the host. The new phases have been characterized by TG and X-ray methods. 相似文献
59.
Engel T. G. Veracka M. J. Neri J. M. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》2010,38(2):194-198
60.
E. Rupp Ph. Nöll L. Krauss F. Lehmann W. F. Schirmer M. de Jong Umberto Saporetti Enrico Rimini Paola Fiora und Albert Fernau 《Fresenius' Journal of Analytical Chemistry》1909,48(7-8):506-514
Ohne Zusammenfassung 相似文献