全文获取类型
收费全文 | 183篇 |
免费 | 6篇 |
国内免费 | 2篇 |
专业分类
化学 | 153篇 |
晶体学 | 2篇 |
力学 | 1篇 |
数学 | 8篇 |
物理学 | 27篇 |
出版年
2023年 | 2篇 |
2022年 | 5篇 |
2021年 | 11篇 |
2020年 | 11篇 |
2019年 | 4篇 |
2018年 | 7篇 |
2017年 | 4篇 |
2016年 | 4篇 |
2015年 | 2篇 |
2014年 | 10篇 |
2013年 | 11篇 |
2012年 | 12篇 |
2011年 | 15篇 |
2010年 | 10篇 |
2009年 | 8篇 |
2008年 | 11篇 |
2007年 | 15篇 |
2006年 | 6篇 |
2005年 | 3篇 |
2004年 | 4篇 |
2003年 | 5篇 |
2002年 | 7篇 |
2001年 | 3篇 |
2000年 | 2篇 |
1998年 | 2篇 |
1997年 | 1篇 |
1995年 | 1篇 |
1992年 | 1篇 |
1985年 | 4篇 |
1984年 | 1篇 |
1981年 | 1篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1978年 | 3篇 |
1977年 | 1篇 |
排序方式: 共有191条查询结果,搜索用时 312 毫秒
1.
I. C. McNeill L. Ackerman S. N. Gupta M. Zulfiqar S. Zulfiqar 《Journal of polymer science. Part A, Polymer chemistry》1977,15(10):2381-2392
In the subambient thermal volatilization analysis (TVA) technique, degradation products initially at ?196°C are allowed to warm up to ambient temperature in a controlled manner under vacuum conditions, and volatilization from the sample tube to a trap at ?196°C is monitored by means of a Pirani gauge. The technique is discussed in relation to earlier TVA work in which volatilization from a heated polymer sample was followed. Design and operation of a subambient TVA system are described, and examples of the application of the technique to the study of the degradation products of seven polymers are considered. 相似文献
2.
Muhammad Ilyas Sarwar Sonia Zulfiqar Zahoor Ahmad 《Colloid and polymer science》2007,285(15):1733-1739
Fluoro-aramid-based sol/gel-derived nanocomposites were synthesized by condensing a mixture of 4,4′-(hexafluoro-isopropylidene)dianiline
and 1,3-phenylenediamine with terephthaloylchloride (TPC) in dimethylacetamide. TPC was added in slight excess to produce
amide chains with carbonyl chloride end groups and then replaced with alkoxy groups using aminophenyltrimethoxysilane to develop
bonding with the silica network. Mechanical, dynamic mechanical thermal, water absorption and morphological measurements were
carried out on the thin hybrid films. Increase in the tensile strength and modulus was observed as compared to pristine polyamide.
The thermal decomposition temperature was found in the range of 400–500 °C. The water absorption was found to be reduced with
higher silica content. The glass transition temperature and the storage moduli increased with increasing silica concentration.
The maximum increase in the T
g value (345 °C) was observed with 20 wt% silica. Scanning electron microscopy revealed the uniform distribution of silica
in the matrix with an average particle size ranging from 8 to 50 nm. 相似文献
3.
Abstract— All- trans - and 13- cis -14,15-dideuterioretinal were synthesized and their solution photochemistry examined. Quantum yields of trans → cis or cis → trans photoisomerization and the number and ratio of primary photoproducts, determined by high pressure liquid chromatographic analysis, are essentially identical to that of their corresponding retinal isomer. The C-14, C-15 carbon-hydrogen modes play no particularly important role in the deactivation of electronically excited linear polyenes related to retinal. 相似文献
4.
N. Grassie M. Zulfiqar M. I. Guy 《Journal of polymer science. Part A, Polymer chemistry》1980,18(1):265-274
A series of polyester polyurethanes with a range of polyester contents was prepared from an ethylene glycol/propylene glycol/adipic acid polyster, butane diol, and methylene bis (4-phenyl isocyanate) (MBPI). They were thermally degraded under vacuum and the products of degradation were identified. The urethane linkages decompose first as the temperature is increased and the stability increases with polyester content. Reaction mechanisms were proposed which account for the principal features of the reaction and the products of degradation. 相似文献
5.
Tetsuro Ito Toshiyuki TanakaMunekazu Iinuma Ibrahim IliyaKen-ichi Nakaya Zulfiqar AliYoshikazu Takahashi Ryuichi SawaYoshiaki Shirataki Jin MurataDedy Darnaedi 《Tetrahedron》2003,59(28):5347-5363
Five new resveratrol oligomers; pauciflorols A-C (1-3), isovaticanols B (6) and C (8), and three new oligostilbene glucosides; pauciflorosides A (11), B (13), C (14), were isolated from the stem bark of Vatica pauciflora (Dipterocarpaceae) together with known 17 resveratrol oligomers (4, 5, 7, 9, 10, 12 and 15-25) and bergenin (26). The structures of isolates were established on the basis of detailed spectroscopic analysis. The typical and characteristic spectral properties of some resveratrol oligomers were also discussed. 相似文献
6.
Lamia T. Abou El-Kassem Usama W. Hawas Mohamed S. Abdelfattah Ayat A. Mostafa 《Natural product research》2020,34(5):613-620
AbstractA new rotenoid named 12-O-methylrotenolol along with five known rotenoid and isoflavone metabolites were isolated from the seeds of Dalbergia lanceolaria subsp. paniculata, collected from Egypt. The structures of these compounds were identified by physical and spectroscopic data measurements ([α]D, UV, 1D- and 2D-NMR and MS). The methanol extract of the seeds exhibited strong antioxidant activity with IC50 value 0.7?µg/µl against DPPH radical, in respect to quercetin as antioxidant reference (IC50 1.5?μM), while the tested compounds from this extract showed weak activities with IC50 values ranged from 19.6 to 33.0?µM. 相似文献
7.
8.
Chemical fingerprint analysis and quantitative determination of steroidal compounds from Dioscorea villosa,Dioscorea species and dietary supplements using UHPLC‐ELSD
下载免费PDF全文
![点击此处可从《Biomedical chromatography : BMC》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Bharathi Avula Yan‐Hong Wang Zulfiqar Ali Troy J. Smillie Ikhlas A. Khan 《Biomedical chromatography : BMC》2014,28(2):281-294
Ultra high‐performance liquid chromatography (UHPLC) with evaporative light scattering detection was used for the quantification of steroidal saponins and diosgenin from the rhizomes or tubers of various Dioscorea species and dietary supplements that were purported to contain Dioscorea. The analysis was performed on an Acquity UPLC? system with an UPLC? BEH Shield RP18 column using a gradient elution with water and acetonitrile. Owing to their low UV absorption, the steroidal saponins were observed by evaporative light scattering detection. The 12 compounds could be separated within 15 min using the developed UHPLC method with detection limits of 5–12 µg/mL with 2 μL injection volume. The analytical method was validated for linearity, repeatability, accuracy, limits of detection and limits of quantification. The relative standard deviations for intra‐ and inter‐day experiments were <3.1%, and the recovery efficiency was 97–101%. The total content of standard compounds was found to be in the ranges 0.01–14.5% and 0.9–28.6 mg daily intake for dry plant materials and solid commercial preparations, respectively. UHPLC–mass spectrometry with a quadrupole mass analyzer and ESI source was used only for confirmation of the identity of the various saponins. The developed method is simple, rapid and especially suitable for quality control analysis of commercial products. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
9.
Compounds belonging to the stilbene family have gained remarkable significance in pharmaceutical as well as material chemistry. The current review covers the various synthetic approaches for the syntheses of stilbene scaffold and related structures over last 30 years. In addition, this review also highlights the role of stilbene intermediates used in the synthesis of important molecules with diverse applications in the field of pharmaceutics and material science. 相似文献
10.
Usama Fathy Mariam A. Azzam Fathia Mahdy Somia El-Maghraby Rasha M. Allam 《Journal of heterocyclic chemistry》2020,57(5):2108-2120
A new series of tetrahydroquinoline derivatives having pyrazol and hydrazide moieties were synthesized for the purpose of anticancer cell line evaluation. Syntheses of these compounds were firstly achieved by one pot four reactions. The reaction of 3-amino-tetrahydro-1H-pyrazolo [3,4-b]quinolin with aldehydes, indoline-2,3-dione derivatives to give 9a-c , 11a-c , and 13a,b , respectively. In similar manner for biological comparison, the reactions of compound 5 with the same aldehydes and indoline-2,3-dione derivatives to give 19a-c and 20a-c . The newly synthesized compounds were examined in vitro for their cytotoxic activity against HepG-2 and A549 cancer cells. The compounds 11a-c and 20a-c showed promising activity as anticancer agents against HepG-2 and A549 cancer cells. 相似文献