全文获取类型
收费全文 | 510篇 |
免费 | 31篇 |
国内免费 | 8篇 |
专业分类
化学 | 319篇 |
晶体学 | 3篇 |
力学 | 32篇 |
数学 | 63篇 |
物理学 | 132篇 |
出版年
2024年 | 1篇 |
2023年 | 8篇 |
2022年 | 5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 | 40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549条查询结果,搜索用时 32 毫秒
451.
452.
453.
Farid Fouad Faycal Khabouchi Alek Nielsen Robert Twieg 《Molecular Crystals and Liquid Crystals》2018,665(1):82-90
A novel series of 3,6-bis(4-hdroxyphenyl)-1,2,4,5-tetrazine alkanoate esters were synthesized and their mesogenic properties were studied using differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). The impact of changing the tail-core linkage from alkyl or alkoxy to ester is profound. Compared to the alkyl or alkoxy linkages, the ester linkage reduced mesogenic properties. Short-tailed compounds are non mesogenic (4a-4e), while long-tailed compounds (4f-4r) exhibit nematic phases. Unlike the alkyl or alkoxy tail series, none of the 18 presented esters in this series exhibits a smectic phase. 相似文献
454.
Nessreen S. Abdelhamid Maimana A. Magdy Basma H. Anwar Nehal F. Farid 《Biomedical chromatography : BMC》2022,36(5):e5343
Recently, prednisolone has been used in treating many medical conditions, such as autoimmune diseases and cancer. It is also prescribed to mitigate the respiratory complications caused by COVID-19 infection. It can cause some health complications, such as GIT ulcers, so it should be co-administered with proton-pump inhibitors, such as esomeprazole, to prevent the risk of ulcers. This work aims to develop an ecofriendly and sensitive TLC method for simultaneous determination of esomeprazole and prednisolone in their binary mixtures and spiked human plasma. Separation was performed using a mixture of ethyl acetate, methanol, and ammonia (9.5:0.5:0.1, v/v/v) as an eluting system with UV scanning at 245 nm. Dapoxetine was used as an internal standard to correct the variation during sampling. The resulting Rf values for plasma, esomeprazole, prednisolone, and dapoxetine were 0.03, 0.51, 0.72 and 0.85, respectively. Four greenness assessment tools—national environmental method index, eco-scale assessments, analytical greenness metric approach (AGREE), and green analytical procedure index (GAPI)—were used to evaluate the greenness characteristics of the proposed method to the environment, and the results were acceptable and satisfactory. Validation parameters were checked according to the US FDA guidelines to achieve the international requirements for bioanalytical method validation, and the results were within the accepted ranges. 相似文献
455.
Greg Albright Mohammed Farid Said Al-Hallaj 《Journal of Thermal Analysis and Calorimetry》2010,101(3):1155-1160
The use of phase change materials (PCMs) in thermal storage is not a new concept, but engineers are continually finding new
ways to utilize them in a wide range of applications. A PCM takes advantage of high latent heat in the phase change process
to store large amounts of heat while undergoing only a small change in temperature. This property makes PCMs suitable for
thermal storage purposes in a wide range of engineering applications. Due to the nature of these applications, it is vital
to have a precise knowledge of the thermal characteristics of any PCM. Unfortunately, due to the low thermal conductivities
and high latent heats found in PCMs, current measuring tools such as differential scanning calorimetry, provide inconsistent
results. This paper conjectures that these errors come from the effects of low thermal diffusivity samples as well as improper
data analysis methods. 相似文献
456.
Zill-e-Huma Maryline Abert VianJean Francois Maingonnat Farid Chemat 《Journal of chromatography. A》2009,1216(45):7700-7707
A solvent free microwave hydrodiffusion and gravity extraction (MHG) of flavonol content from onion (Allium cepa L.) was studied. Effectiveness of this innovative method in extraction of onion total phenolic content, total quercetin (TQ), quercetin aglycon (QA), quercetin-3,4′-diglucoside (QDG), quercetin-4′-monoglucoside (Q4G), quercetin-3-monoglucoside (Q3G), kaempferol (KMF) and myricetin (MRT) have been evaluated and compared with conventional solvent extraction. Microwave extraction offers important advantages like shorter extraction time (23 min), cleaner feature (no solvent or water used) and extraction of valuable onion crude juice retaining fresh organoleptic properties with higher phenolic content (58.29 mg GAE/g DW) at optimized power (500 W). Microwave extraction resulted significant yield (81.5%) with 41.9% of flavonol contents, with better retain of remaining flavonoids (55.9%) in residues of onions. QDG (239.7 mg/100 g DW) and Q4G (82.55 mg/100 g DW) have been reported the main flavonol in this study. Minor quantities of QA (traces), Q3G (4.22 mg/100 g DW) and KMF (3.99 mg/100 g DW) were also detected in microwave onion extracts. 相似文献
457.
Asma Farhat Christian Ginies Mehrez Romdhane Farid Chemat 《Journal of chromatography. A》2009,1216(26):5077-5085
Microwave steam diffusion (MSD) was developed as a cleaner and new process design and operation for isolation of essentials oils and was compared to conventional steam diffusion (SD). The essential oils extracted by MSD for 3 min were quantitatively (yield) and qualitatively (aromatic profile) similar to those obtained by conventional steam diffusion for 20 min. In addition, an optimal operating steam flow rate of 25 g min−1 and microwave power 200 W were found to ensure complete extraction yield with reduced extraction time. To confirm the efficiency of this process a mathematical model was proposed to describe the mass transfer of essential oil from lavender. Solid-steam mass transfer coefficients obtained by MSD were six times higher than obtained by SD. Scanning electronic microscopy was used to confirm the extraction mechanism of the essential oil present in the glandular trichomes of the flowers from lavender outer surface. MSD was better than SD in terms of energy saving, cleanliness and reduced waste water. 相似文献
458.
The reaction of N-Fmoc-aspartic anhydride with glycosyl amines in DMSO selectively leads to the formation of β-substituted products, thus providing a simple and efficient route to N-glycosyl asparagine derivatives, the building blocks for glycopeptide synthesis. 相似文献
459.
460.
Douglas B. Riffel Ferdinand P. Schmidt Francisco A. Belo Antonio P. F. Leite Farid B. Cortés Farid Chejne Felix Ziegler 《Adsorption》2011,17(6):977-984
An application of the original Dubinin-Radushkevitch equation modified with based on Polanyi theory, which taking into consideration
the self-associating molecules in heterogeneous microporous structures at low and high uptake was presented. The Polanyi-Dubinin
models were applied to predicting the behavior of water adsorption on Grace Silica Gel 127B at pressures not yet reported
in the literature. The heat of adsorption, differential entropy, henry ratio was obtained from adsorption isotherm. The resulting
extensions are experimentally and analytically presented. The coefficient of multiple correlation (R
2) between the thermogravimetric measurements and the MDR equation was 0.9924, which is 8.13% better than the best Dubinin-Astakhov
fit. 相似文献