全文获取类型
收费全文 | 516篇 |
免费 | 31篇 |
国内免费 | 8篇 |
专业分类
化学 | 324篇 |
晶体学 | 3篇 |
力学 | 32篇 |
数学 | 63篇 |
物理学 | 133篇 |
出版年
2024年 | 1篇 |
2023年 | 8篇 |
2022年 | 12篇 |
2021年 | 19篇 |
2020年 | 8篇 |
2019年 | 20篇 |
2018年 | 25篇 |
2017年 | 15篇 |
2016年 | 26篇 |
2015年 | 23篇 |
2014年 | 30篇 |
2013年 | 63篇 |
2012年 | 48篇 |
2011年 | 39篇 |
2010年 | 20篇 |
2009年 | 15篇 |
2008年 | 23篇 |
2007年 | 13篇 |
2006年 | 13篇 |
2005年 | 19篇 |
2004年 | 14篇 |
2003年 | 8篇 |
2002年 | 13篇 |
2001年 | 2篇 |
2000年 | 1篇 |
1999年 | 2篇 |
1998年 | 4篇 |
1997年 | 4篇 |
1995年 | 1篇 |
1994年 | 4篇 |
1993年 | 8篇 |
1992年 | 5篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 5篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1978年 | 6篇 |
1977年 | 1篇 |
1976年 | 4篇 |
1973年 | 2篇 |
排序方式: 共有555条查询结果,搜索用时 281 毫秒
541.
Nadia Abdel Aal Ahmed A. Al-Ghamdi Farid El-Tantawy F. Yakuphanoglu W. A. Farooq 《Journal of Sol-Gel Science and Technology》2014,70(1):14-18
Novel magnesium oxide (MgO) nanobelt structures were successfully synthesized on a large scale, low cost and catalyst free by a microwave hydrothermal route using the magnesium metal and potassium hydroxide precursors at 200 °C for 10 min. The synthesized MgO nanobelts were systemically characterized by power X-ray diffraction (XRD), scanning electron microscopy, energy dispersion spectroscopy and transmission-high resolution electron microscopy. The XRD results indicate that the MgO nanobelts have the well-crystalline cubic phase. The detailed morphological studies revealed that the synthesized products were nanobelts and were grown in large quantity. The optical energy gap of MgO nanobelts was found to be 3.1 eV. The photoluminescence spectra of the MgO nanobelts show a strong and broad green emission band, a weak ultraviolet emission band, and a weak red emission band. This novel method will open new dimensions for synthesized 1-D metal oxide and can be easily extended to the synthesis and assembly of other inorganic nanocrystals. 相似文献
542.
A useful and green method for the extraction of fats and oils with a new procedure combining Soxhlet extraction and Clevenger distillation using d-limonene (bio-solvent) as a substitute for n-hexane (petroleum solvent) is reported. This method using green solvent is a laboratory exercise which easily teaches fundamental green analytical chemical lessons and successfully incorporates green “analytical chemistry” into the teaching and the research laboratory to both developed and developing nations. 相似文献
543.
Microwave hydrodiffusion and gravity, a new technique for extraction of essential oils 总被引:1,自引:0,他引:1
A new process design and operation for the extraction of essential oils was developed. Microwave hydrodiffusion and gravity (MHG) is a combination of microwaves for hydrodiffusion of essential oils from the inside to the exterior of biological material and earth gravity to collect and separate. MHG is performed at atmospheric pressure without adding any solvent or water. MHG has been compared with a conventional technique, hydrodistillation (HD), for the extraction of essential oil from two aromatic herbs: spearmint (Mentha spicata L.) and pennyroyal (Mentha pulegium L.) belonging to the Labiatae family. The essential oils extracted by MHG for 15 min were quantitatively (yield) and qualitatively (aromatic profile) similar to those obtained by conventional hydrodistillation for 90 min. MHG also prevents pollution through potential 90% of energy saved which can lead to greenhouse gas emission benefits. 相似文献
544.
Farid Bozorgnia 《Numerical Functional Analysis & Optimization》2016,37(11):1378-1384
In this article, convergence of an iterative scheme to approximate the first eigenfunction and related eigenvalue for p-Laplace operator is shown. Moreover, numerical examples are presented that show the e?ciency and accuracy of the algorithm. 相似文献
545.
546.
Farid Madani 《Bulletin des Sciences Mathématiques》2008,132(7):575
Let (Mn,g) be a compact riemannian manifold of dimension n?3. Under some assumptions, we prove that there exists a positive function φ solution of the Yamabe equation
547.
Fouzi Douak Farid Melgani Naif Alajlan Edoardo Pasolli Yakoub Bazi Nabil Benoudjit 《Journal of Chemometrics》2012,26(7):374-383
In this work, we introduce an active learning approach for the estimation of chemical concentrations from spectroscopic data. Its main objective is to opportunely collect training samples in such a way as to minimize the error of the regression process while minimizing the number of training samples used, and thus to reduce the costs related to training sample collection. In particular, we propose two different active learning strategies developed for regression approaches based on partial least squares regression, ridge regression, kernel ridge regression, and support vector regression. The first strategy uses a pool of regressors in order to select the samples with the greatest disagreements among the different regressors of the pool, while the second one is based on adding samples that are distant from the current training samples in the feature space. For support vector regression, a specific strategy based on the selection of the samples distant from the support vectors is proposed. Experimental results on three different real data sets are reported and discussed. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
548.
Farid Jahouh Rina Saksena Pavol Kováč Joseph Banoub 《Journal of mass spectrometry : JMS》2012,47(7):890-900
549.
550.
C Dejoye Tanzi M Abert Vian C Ginies M Elmaataoui F Chemat 《Molecules (Basel, Switzerland)》2012,17(7):8196-8205
Herein is described a green and original alternative procedure for the extraction of oil from microalgae. Extractions were carried out using terpenes obtained from renewable feedstocks as alternative solvents instead of hazardous petroleum solvents such as n-hexane. The described method is achieved in two steps using Soxhlet extraction followed by the elimination of the solvent from the medium using Clevenger distillation in the second step. Oils extracted from microalgae were compared in terms of qualitative and quantitative determination. No significant difference was obtained between each extract, allowing us to conclude that the proposed method is green, clean and efficient. 相似文献