全文获取类型
收费全文 | 249篇 |
免费 | 19篇 |
国内免费 | 2篇 |
专业分类
化学 | 227篇 |
晶体学 | 2篇 |
力学 | 2篇 |
数学 | 14篇 |
物理学 | 25篇 |
出版年
2024年 | 2篇 |
2023年 | 3篇 |
2022年 | 8篇 |
2021年 | 13篇 |
2020年 | 16篇 |
2019年 | 11篇 |
2018年 | 16篇 |
2017年 | 13篇 |
2016年 | 34篇 |
2015年 | 16篇 |
2014年 | 16篇 |
2013年 | 23篇 |
2012年 | 32篇 |
2011年 | 18篇 |
2010年 | 11篇 |
2009年 | 10篇 |
2008年 | 5篇 |
2007年 | 6篇 |
2006年 | 2篇 |
2005年 | 1篇 |
2004年 | 1篇 |
2003年 | 1篇 |
2001年 | 1篇 |
2000年 | 2篇 |
1999年 | 1篇 |
1998年 | 1篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1992年 | 1篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1982年 | 1篇 |
排序方式: 共有270条查询结果,搜索用时 15 毫秒
21.
Samira Ouardad Sergei V. Kostjuk François Ganachaud Judit E. Puskas Alain Deffieux Frederic Peruch 《Journal of polymer science. Part A, Polymer chemistry》2011,49(23):4948-4954
The polymerization of isoprene initiated by dimethylallyl alcohols (DMAOH) in the presence of Lewis acids (LAs) as coinitiators has been selected as a potential model of the proposed cationic mechanisms involved in natural rubber (NR) biosynthesis. In view to investigate the activation/ionization mechanism of the allyl alcohol chain terminus (PIAllOH), which was shown to exist in NR, different isomers of DMAOH were used as simple models of polyisoprene chain‐end structures in the presence of tris(pentafluorophenyl)borane (BLA) as a LA. It is shown that cationation of 3,3‐DMAOH by BLA proceeds by direct OH abstraction. However, this process is strongly retarded in the presence of 2,6‐di‐tert‐butylpyridine (dtBP), due to the formation of different BLA complexes, one with 3,3‐DMAOH, active for cationation, and a dormant one involving its ionized form 3,3‐DMAO?. The monomer generated in situ by ionization/proton elimination steps subsequently adds on the primary allylic carbocation form, then resulting in the formation of oligoisoprenes, whereas the tertiary carbocation form of the allylic carbocation yields exclusively to proton elimination and isoprene formation, a possible mechanism of chain‐end termination. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011. 相似文献
22.
Abedinifar Fahimeh Babazadeh Rezaei Elham Biglar Mahmood Larijani Bagher Hamedifar Halleh Ansari Samira Mahdavi Mohammad 《Molecular diversity》2021,25(4):2571-2604
Molecular Diversity - Thiophene-based analogs have been fascinated by a growing number of scientists as a potential class of biologically active compounds. Furthermore, they play a vital role for... 相似文献
23.
24.
25.
In this paper the concept of lower and upper solutions combined with the fixed point theorem of Bohnnenblust–Karlin is used to investigate the existence of solutions for a class of the initial value problem for impulsive differential inclusions involving the Caputo fractional derivative. 相似文献
26.
Samira Karoune Hanen Falleh Mohamed Seif Allah Kechebar Youcef Halis Khaoula Mkadmini Mohamed Belhamra 《Natural product research》2015,29(5):452-454
This study compared phenolic contents and antioxidant activity in different organs of Acacia albida (leaves and bark) and focuses on identification of phenolic compounds of leaves by HPLC-DAD. The analysed organs exhibited differences in total polyphenol contents (100 and 59.5 mg GAE g? 1 DW). Phenolic contents of leaves were two times higher than those in bark. Ethanolic extracts exhibited good antioxidant activities with IC50 = 26 μg mL? 1 for DPPH and EC50 = 50 μg mL? 1 for FRAP. Identification by HPLC-DAD revealed the presence of nine phenolic compounds known for their high antioxidant activity. The results suggested that this species can be used as source of natural antioxidants. 相似文献
27.
28.
Functionalization of Graphene Oxide with 3‐Mercaptopropyltrimethoxysilane and Its Electrocatalytic Activity in Aqueous Medium 下载免费PDF全文
In this work, a highly dispersed graphene oxide (GO) was successfully functionalized with 3‐mercaptopropyltrimethoxysilane (MPTS) molecule by silanization method. The chemically generated GO and MPTS functionalized GO (MPTS‐GO) were structurally characterized by thermogravimetric analysis (TGA), X‐ray diffraction analysis (XRD), scanning electron microscope (SEM), energy dispersive X‐ray (EDAX), fourier transform infrared spectroscopy (FT‐IR) and ultraviolet visible spectroscopy (UV‐Vis) techniques. The MPTS‐GO is highly suspensable in water. The thermal and conductivity results for MPTS‐GO are significantly increased compared to GO. Moreover, glassy carbon electrode modified with MPTS‐GO hybrid (MPTS‐GO/GCE) was prepared by casting of the MPTS‐GO solution on GCE. The MPTS‐GO/GCE showed an excellent electrocatalytic activity towards methionine (Met). This was understood from the observed less positive oxidation potential and higher oxidation current when compared to bare GC electrode. The MPTS‐GO has excellent electrocatalytic activity, making it an ideal candidate for sensor applications. 相似文献
29.
Cymbopogon is an aromatic plant valued for its citrus scent aroma. In this article, the effect of saline irrigation water on yield and quality of Cymbopogon schoenanthus L. was evaluated. Compounds of essential oils were identified by gas chromatography-mass spectrometry and/or (13)C-NMR spectroscopy. Results showed that the growth of the aerial part was not affected at a concentration of 50 mmol NaCl. Under salt stress, the content of major chemical compounds was affected differently by the treatment level. 相似文献
30.
Samira El Moumen Rachid EllaiaRajae Aboulaich 《Applied mathematics and computation》2011,218(7):3265-3276
In this paper we present a new hybrid method, called the SASP method. The purpose of this method is the hybridization of the simulated annealing (SA) with the descent method, where we estimate the gradient using simultaneous perturbation. Firstly, the new hybrid method finds a local minimum using the descent method, then SA is executed in order to escape from the currently discovered local minimum to a better one, from which the descent method restarts a new local search, and so on until convergence.The new hybrid method can be widely applied to a class of global optimization problems for continuous functions with constraints. Experiments on 30 benchmark functions, including high dimensional functions, show that the new method is able to find near optimal solutions efficiently. In addition, its performance as a viable optimization method is demonstrated by comparing it with other existing algorithms. Numerical results improve the robustness and efficiency of the method presented. 相似文献