全文获取类型
收费全文 | 212篇 |
免费 | 7篇 |
国内免费 | 2篇 |
专业分类
化学 | 111篇 |
晶体学 | 6篇 |
力学 | 15篇 |
数学 | 60篇 |
物理学 | 29篇 |
出版年
2023年 | 6篇 |
2022年 | 4篇 |
2021年 | 6篇 |
2020年 | 6篇 |
2019年 | 7篇 |
2018年 | 7篇 |
2017年 | 9篇 |
2016年 | 12篇 |
2015年 | 4篇 |
2014年 | 3篇 |
2013年 | 18篇 |
2012年 | 19篇 |
2011年 | 18篇 |
2010年 | 10篇 |
2009年 | 8篇 |
2008年 | 5篇 |
2007年 | 11篇 |
2006年 | 13篇 |
2005年 | 2篇 |
2004年 | 7篇 |
2003年 | 6篇 |
2002年 | 9篇 |
2001年 | 2篇 |
2000年 | 2篇 |
1999年 | 2篇 |
1998年 | 4篇 |
1997年 | 2篇 |
1996年 | 4篇 |
1994年 | 2篇 |
1993年 | 5篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1975年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有221条查询结果,搜索用时 531 毫秒
131.
Saliha Loughmari Abderrafia Hafid Aicha Bouazza Abdelaziz El Bouadili Philippe Zinck Marc Visseaux 《Journal of polymer science. Part A, Polymer chemistry》2012,50(14):2898-2905
Polymerization of β‐myrcene with neodymium borohydride‐based coordination catalysts is very efficient, affording poly‐β‐myrcene (polymyrcene, PMy) with high selectivity. With stoichiometric amounts of n‐butylethyl magnesium (BEM) as co‐catalyst, good control over macromolecular data along with cis‐stereoselectivity up to 98.5%, are obtained. In the presence of excess BEM, high level of transfer reactions efficiency between neodymium and magnesium is clearly evidenced whereas the selectivity switches to 3,4‐rich. Combining the neodymium pre‐catalyst with triisobutyl aluminum in the presence of a boron activator affords PMy in good yield, but the polymer material displays low solubility, likely due to the occurrence of crosslinking. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 相似文献
132.
133.
134.
Anna Canale Rosa Maria Mininni Abdelaziz Rhandi 《Mathematical Methods in the Applied Sciences》2017,40(13):4982-4992
We present an analytic approach to solve a degenerate parabolic problem associated with the Heston model, which is widely used in mathematical finance to derive the price of an European option on an risky asset with stochastic volatility. We give a variational formulation, involving weighted Sobolev spaces, of the second‐order degenerate elliptic operator of the parabolic PDE. We use this approach to prove, under appropriate assumptions on some involved unknown parameters, the existence and uniqueness of weak solutions to the parabolic problem on unbounded subdomains of the half‐plane. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
135.
Achelhi K Masse S Laurent G Roux C Laghzizil A Saoiabi A Coradin T 《Langmuir : the ACS journal of surfaces and colloids》2011,27(24):15176-15184
Zirconia-hydroxyapatite nanocomposites were prepared by sol-gel deposition of zirconium oxide from a zirconium alkoxide in the presence of apatite colloidal suspension under ultrasonication. The material porosity evolves from mainly microporous zirconia to mesoporous hydroxyapatite, with decreasing surface area and increasing pore volume. XRD studies indicate that the apatite phase is well-preserved within the composite materials. The homogeneous dispersion of apatite colloids within the zirconia network was supported by TEM observations and nitrogen sorption measurements. (31)P solid-state NMR studies suggest that partial dissolution of apatite may have occurred during the preparation, leading to the adsorption of phosphate species on zirconia particles. This is confirmed by XRD studies of nanocomposites after thermal treatment that demonstrate the preferred formation of tetragonal over monoclinic ZrO(2) in the presence of hydroxyapatite. In order to investigate the surface properties of these novel materials, the adsorption of Pb(2+), Cr(3+), and Cr(2)O(7)(2-) was evaluated. Metal cations were preferentially adsorbed on apatite-rich composites, whereas Cr(2)O(7)(2-) shows a good affinity for the zirconia-rich phases. Zirconia-apatite materials showed the most promising performance in terms of recyclability. These nanocomposites that combine microporosity, mesoporosity and dual sorption properties for these species appear as interesting materials for metal ion remediation and may also find applications as biomaterials. 相似文献
136.
Sushko I Novotarskyi S Körner R Pandey AK Rupp M Teetz W Brandmaier S Abdelaziz A Prokopenko VV Tanchuk VY Todeschini R Varnek A Marcou G Ertl P Potemkin V Grishina M Gasteiger J Schwab C Baskin II Palyulin VA Radchenko EV Welsh WJ Kholodovych V Chekmarev D Cherkasov A Aires-de-Sousa J Zhang QY Bender A Nigsch F Patiny L Williams A Tkachenko V Tetko IV 《Journal of computer-aided molecular design》2011,25(6):533-554
137.
El Bouzidi L Larhsini M Markouk M Abbad A Hassani L Bekkouche K 《Natural product communications》2011,6(10):1447-1450
In the present study, we report for the first time the antioxidant and antimicrobial activities of Withania frutescens (L.) Pauquy roots and leaves. Total phenolic content was determined using the Folin-Ciocalteu method and antioxidant activity was evaluated by the DPPH free radical scavenging and reducing power methods. Antimicrobial activity tests were carried out against ten bacterial species involved in nosocomial infections and two opportunistic clinical yeast isolates. The ethyl acetate and n-butanol leaf fractions exhibited the highest DPPH radical scavenging activity with IC50 = 4.53 +/- 0.12 and 8.49 +/- 0.46 microg/mL, respectively. The n-butanol root fraction showed the greatest reducing power comparable with that of quercetin at 0.4 mg/mL. The dichloromethane leaf fraction exhibited the highest antibacterial activity against both Gram-positive and Gram-negative bacteria with MIC values ranging between 50 and 400 microg/mL, depending on the tested bacteria. However, none of the examined extracts exhibited anticandidal activity. The polyphenol and glycowithanolide constituents appeared to be responsible for the antioxidant capacity of W. frutescens, whereas the observed antimicrobial activity may be due to the presence of withanolides. 相似文献
138.
El Maatougui A Crespo A Silva AM Coelho A 《Combinatorial chemistry & high throughput screening》2011,14(7):570-582
An efficient solution-phase parallel procedure to perform the structural diversification of some formyl-nitrogen heterocycles (A) using the reusable TBD supported base is described. The library synthesis is based in a consecutive Alkylation-Knoevenagel functionalisation that uses alkyl halides (B), Michael acceptors (C) and activated methylene compounds (D) as diversity elements. 相似文献
139.
A series of carboxyphosphonate-derivatives of (Zn, Al) layered double hydroxide (LDH) was prepared and characterized by a combination of techniques including powder X-ray diffraction, FTIR spectroscopy and solid-state 13C CP-MAS and 31P MAS NMR spectroscopies. The number of carbon atoms, n=1 or 2 in HO2C(CH2)nPO3H2, was found to have an influence on the accommodation of the interleaved molecule, the carboxylate function lying perpendicular or parallel to the inorganic sheets of the LDH host material. These observations are in agreement with NMR results which evidence an interaction of the interlayered molecules through either the carbonyl or the phosphonate group or both in the case of the larger molecule, N-(phosphonomethyl)iminodiacetic acid. The variation of the basal spacing of the hybrid materials as a function of the temperature indicates a rearrangement of the molecule within the host material gap. 相似文献
140.
In this paper we are concerned with a multidimensional Timoshenko system subjected to boundary conditions of memory type. We establish general rate decay results. The usual exponential and polynomial decay rates are only special cases. 相似文献