全文获取类型
收费全文 | 216篇 |
免费 | 11篇 |
专业分类
化学 | 88篇 |
力学 | 8篇 |
数学 | 84篇 |
物理学 | 47篇 |
出版年
2023年 | 3篇 |
2022年 | 3篇 |
2021年 | 2篇 |
2020年 | 3篇 |
2019年 | 6篇 |
2018年 | 4篇 |
2017年 | 2篇 |
2016年 | 15篇 |
2015年 | 10篇 |
2014年 | 12篇 |
2013年 | 21篇 |
2012年 | 19篇 |
2011年 | 12篇 |
2010年 | 10篇 |
2009年 | 12篇 |
2008年 | 15篇 |
2007年 | 9篇 |
2006年 | 8篇 |
2005年 | 16篇 |
2004年 | 5篇 |
2003年 | 5篇 |
2002年 | 5篇 |
2001年 | 4篇 |
2000年 | 4篇 |
1999年 | 4篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1992年 | 4篇 |
1991年 | 3篇 |
1990年 | 1篇 |
1988年 | 3篇 |
排序方式: 共有227条查询结果,搜索用时 750 毫秒
71.
Nicolae Hurduc Cristina Damian Anca Tarus Violeta Toader Natalia Hurduc 《Central European Journal of Chemistry》2005,3(1):53-62
The main objective of this paper is to study the thermal stability of some aromatic copolyethers containing a propylenic spacer.
Some of the investigated copolyethers displayed a liquid crystalline (LC) behavior, with the presence of the mesogenic groups
in the main chain, inducing high values of the thermal transition temperatures. As a consequence, a thermal stability study
was necessary to establish the maximum temperature value for the LC behavior characterization. A thermal degradation mechanism
is proposed, taking into consideration the azobenzenic unit as the weakest link in the polymer chain and thus, the starting
point of the thermal degradation process. The degradation mechanisms were correlated with the chemical structure and the polarity
and conformation of the chains. Conformational analysis was performed using molecular simulations. Freeman-Caroll and Coats-Redfern
methods were used to calculate some kinetic characteristics. 相似文献
72.
Ovidiu I. Covaci Gabriel L. Radu 《International journal of environmental analytical chemistry》2013,93(3):325-334
This paper presents the effect of acrolein on three dehydrogenases and proposes a fast spectrometric method for acrolein analysis. We have found that alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (AlDH) are inhibited by low acrolein concentrations (0.2?mM) while inhibition of glutamate dehydrogenase (GDH) is not observed even at higher acrolein concentrations (1?mM). Acrolein is a suicide substrate for AlDH and ADH inhibition by acrolein is competitive. Cysteine (L-Cys) and glutathione (GSH) react with acrolein and thus reduce its expected inhibitory effect. ADH was chosen to develop a spectrophotometric method for acrolein analysis based on enzyme inhibition. The calibration curve is linear between 0.2 and 1.0?mM acrolein. 相似文献
73.
74.
In the setting of antiplane linearized elasticity, we show the existence of the stress intensity factor and its relation with the energy release rate when the crack path is a C1,1 curve. Finally, we show that the energy release rate is continuous with respect to the Hausdorff convergence in a class of admissible cracks. 相似文献
75.
76.
Mădălina Mihalache Ovidiu Oprea Cornelia Guran Alina M. Holban 《Comptes Rendus Chimie》2018,21(1):32-40
The four divalent nickel complexes having α-ketoglutaric acid (H2A) and 1-(o-tolyl)biguanide (TB) ligands have been synthesized, characterized, and tested for antibacterial and antitumor activity.The proposed formulas for these complexes are [Ni(TB)(HA)(H2O)2]Cl (C1), [Ni(TB)(HA)(H2O)2]Br (C2), [Ni(TB)(HA)]NO3·H2O (C3), and [Ni(TB)(HA)]CH3COO (C4), where HA represents deprotonated H2A.For the four complexes and for the ligands used in the synthesis, the antibacterial activity against Staphylococcus aureus ATCC 25923 and Pseudomonas aeruginosa ATCC 27853 and antitumor activity in HeLa tumor cells were tested. A moderate cytotoxic effect of C3 and C4 complexes has been observed on the development and metabolic activity of HeLa cells, whereas C1 and C2 ligands have a very low effect on them.The synthesized complexes (obtained) inhibit adherence to the inert substrate of bacterial strains S. aureus and P. aeruginosa; therefore, they may be candidates for (potential) therapeutic applications. 相似文献
77.
78.
We investigate integration of classes of real-valued continuous functions on (0,1]. Of course difficulties arise if there is a non-L1 element in the class, and the Hadamard finite part integral (p.f.) does not apply. Such singular integrals arise naturally in many contexts including PDEs and singular ODEs. 相似文献
79.
The activities of Pt/WO2, Ir/WO2 and Pt–Ir/WO2 toward the conversion of methylcyclopentane (MCP) were investigated. The catalysts were prepared using impregnation and co-impregnation methods and were characterized by SEM, XRD, N2-sorption and TEM investigations. The most active catalyst toward the conversion of MCP, irrespective of the temperature, was Ir/WO2. The order of the reactivity was Ir/WO2 > Pt–Ir/WO2 > Pt/WO2. Strong metal–support interactions (SMSI) were observed for all the catalysts over the entire investigated temperature range. At 400 °C, the Pt and Pt–Ir showed 100% selectivity toward ring-enlargement reactions associated with the presence of electron-deficient adduct sites on the reducible acidic WO2 support. Ring opening occurred over all the catalysts in three positions, resulting in the formation of 2-methylpentane (2-MP), 3-methylpentane (3-MP), and n-hexane (n-H). Difficulty in breaking the secondary – tertiary carbon bonds was observed predominantly on the Ir catalyst, which opens the MCP ring via a selective mechanism. 相似文献
80.
Toader M Knupfer M Zahn DR Hietschold M 《Journal of the American Chemical Society》2011,133(14):5538-5544
The adsorption of lutetium(III) bis-phthalocyanine (LuPc(2)) on Ag(111) was investigated using scanning tunneling microscopy and spectroscopy (STM/STS). A comprehensive study was carried out toward understanding the driving mechanism responsible for the formation of the first and second monolayers (MLs). In both MLs, the adsorbed molecules are found to exhibit different in-plane orientations arranged according to a "chess-board" like pattern. Highly resolved STM images allowed an exact determination of the corresponding angle mismatch, which differs for the first and second MLs. The tunneling transport through individual molecules reveals a negative differential resistance (NDR) effect detectable within the current-voltage curves. The corresponding density of states (DOS) representation is consistent with a resonant tunneling mechanism sustained by the valence band (VB) states close to the Fermi energy (E(F)) recorded via highly resolved ultraviolet photoemission spectroscopy (UPS). 相似文献