全文获取类型
收费全文 | 225篇 |
免费 | 21篇 |
国内免费 | 31篇 |
专业分类
化学 | 161篇 |
晶体学 | 5篇 |
力学 | 11篇 |
综合类 | 7篇 |
数学 | 20篇 |
物理学 | 73篇 |
出版年
2024年 | 2篇 |
2023年 | 2篇 |
2022年 | 9篇 |
2021年 | 8篇 |
2020年 | 8篇 |
2019年 | 9篇 |
2018年 | 7篇 |
2017年 | 4篇 |
2016年 | 15篇 |
2015年 | 13篇 |
2014年 | 7篇 |
2013年 | 16篇 |
2012年 | 22篇 |
2011年 | 19篇 |
2010年 | 10篇 |
2009年 | 7篇 |
2008年 | 19篇 |
2007年 | 13篇 |
2006年 | 8篇 |
2005年 | 7篇 |
2004年 | 5篇 |
2003年 | 4篇 |
2002年 | 5篇 |
2001年 | 9篇 |
2000年 | 5篇 |
1999年 | 9篇 |
1998年 | 3篇 |
1997年 | 3篇 |
1996年 | 6篇 |
1995年 | 3篇 |
1994年 | 4篇 |
1993年 | 2篇 |
1992年 | 3篇 |
1991年 | 1篇 |
1990年 | 5篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1985年 | 1篇 |
1982年 | 1篇 |
排序方式: 共有277条查询结果,搜索用时 15 毫秒
91.
Yurong Bian Xiaohong Wang Zhigang Zeng Zhiyu Hu 《Surface and interface analysis : SIA》2013,45(9):1317-1322
Ordered mesoporous titania thin films were synthesized by evaporation induced self‐assembly process in the presence of Pluronic block copolymers P123 (EO20‐PO70‐EO20). The influence of several experimental parameters, including aging humidity, aging temperature, substrate properties and methods for organic templates removal, on the mesostructure of titania thin films was investigated in details. The mesoporous titania thin film supported Pt catalyst was prepared, and its methanol catalytic combustion performance was studied. The results showed that mesoporous titania thin film is an active support for catalyst. Mesoporous titania thin film supported platinum catalysts yields 70% methanol conversion at room temperature and 100% conversion at 100 °C. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
92.
Dr. Mingwei Zhao Dr. Yurong Zhao Prof. Liqiang Zheng Prof. Caili Dai 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(3):1076-1081
Highly ordered supramolecular microfibers were constructed through a simple ionic self‐assembly strategy from complexes of the N‐tetradecyl‐N‐methylpyrrolidinium bromide (C14MPB) surface‐active ionic liquid and the small methyl orange (MO) dye molecule, with the aid of patent blue VF sodium salt. By using scanning electron microscopy and polarized optical microscopy, the width of these self‐assembled microfibers is observed to be about 1 to 5 μm and their length is from tens of micrometers to almost a millimeter. The 1H NMR spectra of the microfibers indicates that the supramolecular complexes are composed of C14MPB and MO in equal molar ratio. The electrostatic, hydrophobic, and π–π stacking interactions are regarded as the main driving forces for the formation of microfibers. Furthermore, through characterization by using confocal fluorescence microscopy, the microfibers were observed to show strong fluorescent properties and may find potential applications in many fields. 相似文献
93.
A novel double-image encryption algorithm is proposed, based on discrete fractional random transform and chaotic maps. The random matrices used in the discrete fractional random transform are generated by using a chaotic map. One of the two original images is scrambled by using another chaotic map, and then encoded into the phase of a complex matrix with the other original image as its amplitude. Then this complex matrix is encrypted by the discrete fractional random transform. By applying the correct keys which consist of initial values, control parameters, and truncated positions of the chaotic maps, and fractional orders, the two original images can be recovered without cross-talk. Numerical simulation has been performed to test the validity and the security of the proposed encryption algorithm. Encrypting two images together by this algorithm creates only one encrypted image, whereas other single-image encryption methods create two encrypted images. Furthermore, this algorithm requires neither the use of phase keys nor the use of matrix keys. In this sense, this algorithm can raise the efficiency when encrypting, storing or transmitting. 相似文献
94.
Rapid separation and identification of Strychnos alkaloids metabolites in rats by ultra high performance liquid chromatography with linear ion trap Orbitrap mass spectrometry
下载免费PDF全文
![点击此处可从《Journal of separation science》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Xiaoyun Liu Shuiqing Zheng Zheng Jiang Chen Liang Rong Wang Zhe Zhou Yurong Zhang Yunqiu Yu 《Journal of separation science》2014,37(7):764-774
An in vivo study of Strychnos alkaloids metabolites in rats by ultra high performance liquid chromatography with linear ion trap Orbitrap MS is reported for the first time. Two major Strychnos alkaloids compounds including strychnine and brucine were investigated. To obtain optimal extraction efficiency, samples were pretreated by using an SPE plate. The structures of metabolites and their fragment ions were characterized based on the accurate mass and MSn data. Forty‐seven metabolites were identified in rat urine, of which 25 were reported for the first time. Four new metabolism pathways were proposed on the basis of the identified metabolites. This study provides a practical approach for rapidly identifying complicated metabolites, a methodology that could be widely applied not only in forensic and clinically toxicological relevant cases, but also for the structural characterization of metabolites of other compounds. 相似文献
95.
Methodology and Computing in Applied Probability - In this paper, we consider the least squares estimators of the Ornstein-Uhlenbeck process with a constant drift... 相似文献
96.
97.
用电化学腐蚀法制备出多孔硅系列样品.室温下具有明亮可见的光致发光.增大电解电流或延长腐蚀时间,发光光谱明显地“蓝移”;提高样品测量温度,发光光谱也明显地“蓝移”。红外吸收光谱表明多孔硅中除了硅丝骨架以外,还含有H、F及O等元素,随着腐蚀时间的增加,F和O原子的相对含量增加.实验结果表明,多孔硅在可见光区的发光现象是一种量子尺寸效应. 相似文献
98.
用 NaD_2线激发钠蒸汽(T=523°K),探测3P→3S,5S→3P,4D→3P 的荧光强度,得到 Na(3P)+Na(3P)→Na(4D)+Na(3S)碰撞激发能量转移截面为2.4×10~(-15)(cm)~2.并将本文和国内外文献数值作了比较,结果相符. 相似文献
99.
A Multifunctional Nanocrystalline CaF2:Tm,Yb@mSiO2 System for Dual‐Triggered and Optically Monitored Doxorubicin Delivery
下载免费PDF全文
![点击此处可从《Particle & Particle Systems Characterization》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Yangyang Li Yurong Zhou Tongxu Gu Gang Wang Zhaohui Ren Wenjian Weng Xiang Li Gaorong Han Chuanbin Mao 《Particle & Particle Systems Characterization》2016,33(12):896-905
Daunting challenges in investigating the controlled release of drugs in complicated intracellular microenvironments demand the development of stimuli‐responsive drug delivery systems. Here, a nanoparticle system, CaF2:Tm,Yb@mSiO2, made of a mesoporous silica (mSiO2) nanosphere with CaF2:Tm,Yb upconversion nanoparticles (UCNPs) is developed, filling its mesopores and with its surface‐modified with polyacrylic acid for binding the anticancer drug molecules (doxorubicin, DOX). The unique design of CaF2:Tm,Yb@mSiO2 enables us to trigger the drug release by two mechanisms. One is the pH‐triggered mechanism, where drug molecules are preferentially released from the nanoparticles at acidic conditions unique for the intracellular environment of cancer cells compared to normal cells. Another is the 808 nm near infrared (NIR)‐triggered mechanism, where 808 nm NIR induces the heating of the nanoparticles to weaken the electrostatic interaction between drug molecules and nanoparticles. In addition, luminescence resonance energy transfer occurs from the UCNPs (the energy donor) to the DOX drug (the energy acceptor) in the presence of 980 nm NIR irradiation, allowing us to monitor the drug release by detecting the vanishing blue emission from the UCNPs. This study demonstrates a new multifunctional nanosystem for dual‐triggered and optically monitored drug delivery, which will facilitate the rational design of personalized cancer therapy. 相似文献
100.
Determination of volatile chlorinated hydrocarbons in water samples by static headspace gas chromatography with electron capture detection
下载免费PDF全文
![点击此处可从《Journal of separation science》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Tiejun Li Yuanming Guo Hongmei Hu Xiaoning Zhang Yanjian Jin Xiaojun Zhang Yurong Zhang 《Journal of separation science》2016,39(2):358-366
A simple, efficient, solvent‐free, and commercial readily available approach for determination of five volatile chlorinated hydrocarbons in water samples using the static headspace sampling and gas chromatography with electron capture detection has been described. The proposed static headspace sampling method was initially optimized and the optimum experimental conditions found were 10 mL water sample containing 20% w/v sodium chloride placed in a 20 mL vial and stirred at 50ºC for 20 min. The linearity of the method was in the range of 1.2–240 μg/L for dichloromethane, 0.2–40 μg/L for trichloromethane, 0.005–1 μg/L for perchloromethane, 0.025–5 μg/L for trichloroethylene, and 0.01–2 μg/L for perchloroethylene, with coefficients of determination ranging between 0.9979 and 0.9990. The limits of detection were in the low μg/L level, ranging between 0.001 and 0.3 μg/L. The relative recoveries of spiked five volatile chlorinated hydrocarbons with external calibration method at different concentration levels in pure, tap, sea water of Jiaojiang Estuary, and sea water of waters of Xiaomendao were in the range of 91–116, 96–105, 86–112, and 80–111%, respectively, and with relative standard deviations of 1.9–3.6, 2.3–3.5, 1.5–2.7, and 2.3–3.7% (n = 5), respectively. The performance of the proposed method was compared with traditional liquid–liquid extraction on the real water samples (i.e., pure, tap, and sea water, etc.) and comparable efficiencies were obtained. It is concluded that this method can be successfully applied for the determination of volatile chlorinated hydrocarbons in different water samples. 相似文献