全文获取类型
收费全文 | 120篇 |
免费 | 7篇 |
专业分类
化学 | 93篇 |
力学 | 10篇 |
数学 | 8篇 |
物理学 | 16篇 |
出版年
2023年 | 2篇 |
2022年 | 6篇 |
2021年 | 4篇 |
2020年 | 8篇 |
2019年 | 5篇 |
2018年 | 5篇 |
2017年 | 1篇 |
2016年 | 5篇 |
2015年 | 7篇 |
2014年 | 4篇 |
2013年 | 11篇 |
2012年 | 5篇 |
2011年 | 11篇 |
2010年 | 6篇 |
2009年 | 7篇 |
2008年 | 5篇 |
2007年 | 7篇 |
2006年 | 7篇 |
2005年 | 3篇 |
2004年 | 3篇 |
2003年 | 1篇 |
2001年 | 1篇 |
2000年 | 1篇 |
1999年 | 1篇 |
1997年 | 2篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1984年 | 1篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有127条查询结果,搜索用时 15 毫秒
101.
102.
103.
Polypropylene–wood fiber composites were prepared in the optimal mixture conditions determined in a previous work (180°C, 60 rpm, 10 min). Tensile, impact and three-point bending tests were performed in order to evaluate the adhesion between matrix and wood fibers. Other than mixture conditions, drying temperature of treated wood fiber is also an important factor to obtain good performance composites as shown in this work. Tensile properties of composites submitted to two extreme conditions (immersion in water at ambient temperature for 90 days and immersion in boiling water for 1 h) were determined. Heat deflection temperature and thermal analysis of composites were evaluated. 相似文献
104.
Andr M. Marques Alexandre Siqueira da Rocha Queiroz Elsie F. Guimares Ana Carolina Mafud Paulo de Sousa Carvalho Yvonne Primerano Mascarenhas Thais da Silva Barenco Pmella Dourila N. Souza David William Provance Jos Hamilton M. do Nascimento Cristiano G. Ponte Maria Auxiliadora C. Kaplan Davyson de Lima Moreira Maria Raquel Figueiredo 《Molecules (Basel, Switzerland)》2022,27(4)
The Piper species are a recognized botanical source of a broad structural diversity of lignans and its derivatives. For the first time, Piper tectoniifolium Kunth is presented as a promising natural source of the bioactive (−)-grandisin. Phytochemical analyses of extracts from its leaves, branches and inflorescences showed the presence of the target compound in large amounts, with leaf extracts found to contain up to 52.78% in its composition. A new HPLC-DAD-UV method was developed and validated to be selective for the identification of (−)-grandisin being sensitive, linear, precise, exact, robust and with a recovery above 90%. The absolute configuration of the molecule was determined by X-ray diffraction. Despite the identification of several enantiomers in plant extracts, the major isolated substance was characterized to be the (−)-grandisin enantiomer. In vascular reactivity tests, it was shown that the grandisin purified from botanical extracts presented an endothelium-dependent vasorelaxant effect with an IC50 of 9.8 ± 1.22 μM and around 80% relaxation at 30 μM. These results suggest that P. tectoniifolium has the potential to serve as a renewable source of grandisin on a large scale and the potential to serve as template for development of new drugs for vascular diseases with emphasis on disorders related to endothelial disfunction. 相似文献
105.
106.
First-passage time problems for continuous-time birth–death chains are considered. Recursive formulas for the moments of the first-exit time and of the first-passage time in terms of the potential coefficients are explicitly obtained. Making use of the probability current, some functional relations between transition probabilities for unrestricted and restricted continuous-time birth–death chains are determined. Finally, two continuous-time birth–death chains with constant rates are taken in account; for them, closed form results on the first-exit time and on the first-passage time are explicitly obtained.
相似文献107.
Roccaldo Sardella Federica Ianni Lina Cossignani Giancarlo Aldini Andrea Carotti 《Journal of separation science》2020,43(9-10):1728-1736
In the present study, an in silico methodology able to define the binding modes adopted by carnosine enantiomers in the setting of the chiral recognition process is described. The inter‐ and intramolecular forces involved in the enantioseparation process with the Teicoplanin A2‐2 chiral selector and carnosine as model compound are successfully identified. This approach fully rationalizes, at a molecular level, the (S) < (R) enantiomeric elution order obtained under reversed‐phase conditions. Consistent explanations were achieved by managing molecular dynamics results with advanced techniques of data analysis. As a result, the time‐dependent identification of all the interactions simultaneously occurring in the chiral selector‐enantiomeric analyte binding process was obtained. Accordingly, it was found that only (R)‐carnosine is able to engage a stabilizing charge–charge interaction through its ionized imidazole ring with the carboxylate counter‐part on the chiral selector. Instead, (S)‐carnosine establishes intramolecular contacts between its ionized functional groups, that limit its conformational freedom and impair the association with the chiral selector unit. 相似文献
108.
Federica Ianni Andrea Carotti Maura Marinozzi Gloria Marcelli Alessandro Di Michele Roccaldo Sardella Wolfgang Lindner Benedetto Natalini 《Analytica chimica acta》2015
A chiral chromatography method enabling the simultaneous diastereo- and enantioseparation of Nα-Boc-N4-(hydroorotyl)-4-aminophenylalanine [Boc-Aph(Hor)-OH, 1] was optimized with a quinine-based zwitterionic stationary phase. The polar-ionic eluent system consisting of ACN:MeOH:water—49.7:49.7:0.6 (v/v/v) with formic acid (4.0 mM) and diethylamine (2.5 mM), allowed the successful separation of the four acid stereoisomers: αd,d-/d,l-1 = 1.08; αd,l-/l,d-1 = 1.08; αl,d-/l,l-1 = 1.40. 相似文献
109.
The principle of material frame-indifference (MFI) is a fundamental and controversial principle of continuum mechanics that has been invoked recently to derive nonlinear algebraic models for stresses of viscoelastic liquids. The purpose of the present study is to identify regions of a flow field where MFI should be considered. Such regions are identified by computing the angular velocity of the principal directions of the rate-of-deformation tensor in order to obtain an Euclidean objective vorticity tensor. An analysis is carried out for uniform shear and extensional flows, and for a Couette flow. The method is then applied to the planar flow through an abrupt 4:1 contraction and to the two-dimensional stream past a circular cylinder. The main results are: (1) MFI should be taken into account in regions characterized by the transition between two different kinematics and a significant velocity magnitude, and (2) MFI can be safely ignored in regions of pure viscometric behaviour as well as in recirculation regions. The consequences of MFI being taken into account are then examined upon using the Euclidean objective vorticity tensor in a simple algebraic constitutive law for viscoelastic fluids. 相似文献