全文获取类型
收费全文 | 233篇 |
免费 | 13篇 |
专业分类
化学 | 152篇 |
晶体学 | 1篇 |
力学 | 4篇 |
数学 | 21篇 |
物理学 | 68篇 |
出版年
2023年 | 2篇 |
2022年 | 2篇 |
2021年 | 4篇 |
2020年 | 2篇 |
2019年 | 6篇 |
2018年 | 6篇 |
2017年 | 3篇 |
2016年 | 6篇 |
2015年 | 6篇 |
2014年 | 8篇 |
2013年 | 16篇 |
2012年 | 9篇 |
2011年 | 15篇 |
2010年 | 8篇 |
2009年 | 8篇 |
2008年 | 17篇 |
2007年 | 14篇 |
2006年 | 9篇 |
2005年 | 13篇 |
2004年 | 8篇 |
2003年 | 8篇 |
2002年 | 7篇 |
2001年 | 4篇 |
2000年 | 3篇 |
1999年 | 4篇 |
1998年 | 2篇 |
1996年 | 5篇 |
1995年 | 3篇 |
1994年 | 5篇 |
1993年 | 5篇 |
1992年 | 4篇 |
1991年 | 3篇 |
1990年 | 4篇 |
1989年 | 1篇 |
1988年 | 3篇 |
1986年 | 1篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1885年 | 2篇 |
1884年 | 1篇 |
排序方式: 共有246条查询结果,搜索用时 0 毫秒
241.
Amaral JS Valentão P Andrade PB Martins RC Seabra RM 《Molecules (Basel, Switzerland)》2008,13(6):1321-1332
Walnut leaves from nine different cultivars (Arco, Franquette, Hartley, Lara, Marbot, Mayette, Meylannaise, Parisienne and Rego) were studied for their phenolic compounds. Samples were harvested along three consecutive years, at two different geographical locations, in order to evaluate if significant differences in the phenolics composition can be related with genetic, climatic or geographical factors. Nine compounds (3-caffeoylquinic, 3-p-coumaroylquinic and 4-p-coumaroylquinic acids, quercetin 3- galactoside, quercetin 3-arabinoside, quercetin 3-xyloside, quercetin 3-rhamnoside, a quercetin 3-pentoside derivative and a kaempferol 3-pentoside derivative) were quantified using an HPLC-DAD methodology. The qualitative profiles were identical for all samples, but differences were observed in terms of individual compounds' contents. Multivariate statistical analysis was carried out, showing that significant differences exist among production years, which can be related to climatic reasons. 相似文献
242.
Cid-Ruiz Yairon Homs Roser Sturmfels Bernd 《Foundations of Computational Mathematics》2021,21(5):1363-1399
Foundations of Computational Mathematics - An ideal in a polynomial ring encodes a system of linear partial differential equations with constant coefficients. Primary decomposition organizes the... 相似文献
243.
Patricia Rodríguez-Salamanca Prof. Rosario Fernández Dr. Valentín Hornillos Prof. José M. Lassaletta 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(28):e202104442
Molecules with restricted rotation around a single bond or atropisomers are found in a wide number of natural products and bioactive molecules as well as in chiral ligands for asymmetric catalysis and smart materials. Although most of these compounds are biaryls and heterobiaryls displaying a C−C stereogenic axis, there is a growing interest in less common and more challenging axially chiral C−N atropisomers. This review offers an overview of the various methodologies available for their asymmetric synthesis. A brief introduction is initially given to contextualize these axially chiral skeletons, including a historical background and examples of natural products containing axially chiral C−N axes. The preparation of different families of C−N based atropisomers is then presented from anilides to chiral five- and six-membered ring heterocycles. Special emphasis has been given to modern catalytic asymmetric strategies over the past decade for the synthesis of these chiral scaffolds. Applications of these methods to the preparation of natural products and biologically active molecules will be highlighted along the text. 相似文献
244.
Jesus M. Arsuaga Mercedes Caceres-Alonso Valentín G. Baonza Javier Nuñez 《Journal of solution chemistry》1991,20(6):613-621
The osmotic coefficients of dilute aqueous solutions of [Co(pn)3]X3 [pn=1,2-diaminopropane and X=Cl–, Br– and (NO3)–] and [Co(tn)3]X3 (tn=1,3-diaminopropane and X=Cl– and Br–) have been measured from 0.00 to 0.02 mol-kg–1 at 0°C by the freezing point method. The results have been compared with those obtained from the numerical integration of the Poisson-Boltzmann equation. 相似文献
245.
Galliano Valent 《General Relativity and Gravitation》2012,44(5):1103-1127
We present the derivation, for these vacuum metrics, of the Painlevé VI equation first obtained by Christodoulakis and Terzis, from the field equations for both minkowskian and euclidean signatures. This allows to give the precise connection with some old results due to Kinnersley. The hyperkähler metrics are shown to belong to the Multi-Centre class and for the cases exhibiting an integrable geodesic flow the relevant Killing tensors are given. We conclude by the proof that for the Bianchi B family, excluding type III, there are no hyperkähler metrics. 相似文献
246.
Dr. Amàlia Monge‐Marcet Dr. Xavier Cattoën Dr. Philippe Dieudonné Prof. Dr. Roser Pleixats Dr. Michel Wong Chi Man 《化学:亚洲杂志》2013,8(9):2235-2241
The transformation by hydrolysis/condensation of four new mesityl‐(bis or tris)imidazolium‐based alkoxysilane precursors into their corresponding bridged silsesquioxanes has been investigated. These precursors feature urea groups and either short or long alkylene chains, which are known to favor self‐assembly. The most regular nanostructures were obtained by a combination of the tripodal precursors with C10H20 alkylene chains, as shown by powder X‐ray diffraction (PXRD) analysis, independent of the reaction conditions. 相似文献