全文获取类型
收费全文 | 669篇 |
免费 | 96篇 |
国内免费 | 140篇 |
专业分类
化学 | 816篇 |
晶体学 | 5篇 |
力学 | 3篇 |
综合类 | 4篇 |
数学 | 8篇 |
物理学 | 69篇 |
出版年
2024年 | 1篇 |
2023年 | 15篇 |
2022年 | 13篇 |
2021年 | 35篇 |
2020年 | 33篇 |
2019年 | 27篇 |
2018年 | 27篇 |
2017年 | 25篇 |
2016年 | 42篇 |
2015年 | 41篇 |
2014年 | 49篇 |
2013年 | 69篇 |
2012年 | 33篇 |
2011年 | 37篇 |
2010年 | 33篇 |
2009年 | 40篇 |
2008年 | 24篇 |
2007年 | 33篇 |
2006年 | 27篇 |
2005年 | 35篇 |
2004年 | 38篇 |
2003年 | 33篇 |
2002年 | 33篇 |
2001年 | 29篇 |
2000年 | 20篇 |
1999年 | 14篇 |
1998年 | 12篇 |
1997年 | 10篇 |
1996年 | 13篇 |
1995年 | 10篇 |
1994年 | 9篇 |
1993年 | 9篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 7篇 |
1989年 | 5篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1979年 | 3篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有905条查询结果,搜索用时 15 毫秒
81.
Chunqiao Zhang Yajie Jiang Hongbin Ju Yakui Wang 《Journal of Dispersion Science and Technology》2017,38(12):1817-1823
The obvious different aggregation and adsorption behavior of six newly quaternary ammonium surfactants with different lipophilic counterions has been discoverd by measurements of equilibrium and dynamic surface tension, fluorescence and conductivity. Interestingly, the critical micelle concentration (CMC) and its surface tension γCMC decrease with the increasing counterion chain length. However, three methods have confirmed that an exception of CMC increases slightly from C16NC1 to C16NC2. According to experimental results, a balanced mechanism between hydrophobicity and electrostatic of counterion is proposed. Besides, the dynamic surface tension results show the diffusion coefficient increases with the increasing counterion length both at a short time (Dt?→?0) and long time (Dt?→?∞), which indicates a faster adsorption process. Unlike the inorganic counterion, the diffusion coefficient decreases with the increase of hydrophobic chain length. This is attributed to the strong electrostatic interactions between counterions and cationic headgroups. 相似文献
82.
83.
对壳聚糖氨基和羟基进行化学改性,合成了水溶性双功能化壳聚糖衍生物O-季铵化-N-壳聚糖Schiff碱(O-HTCCS);用红外光谱表征了产物的结构;确定了O-HTCCS的最佳合成条件,并测定了其溶解性能.结果表明,合成O-HTCCS的最佳条件为:壳聚糖Schiff碱/缩水甘油三甲基氯化铵(GTMAc)摩尔比为1∶5;反应时间24 h;反应温度70℃.在最佳条件下合成O-HTCCS的产率为78.5%,季铵化度为89.7%.与此同时,O-HTCCS的水溶性随季铵化度的增大而提高,季铵化度达到70%以上能溶于水;且其在有机溶剂中的溶解性优于壳聚糖. 相似文献
84.
A nonenzymatic amperometric sensor for sensitive and selective detection of glucose has been constructed by using highly dispersed Pt nanoparticles supported onto mesoporous carbons (MCs). The Pt nanoparticles/mesoporous carbons (Pt/MCs) composites modified electrode displayed high electrocatalytic activity towards the oxidation of glucose. At an applied potential of 0.1 V, the Pt/MCs electrode has a linear dependence (R=0.996) in the glucose concentration up to 7.5 mM with a sensitivity of 8.52 mA M?1 cm?2. The Pt/MCs electrode has also shown highly resistant toward poisoning by chloride ions and without interference from the oxidation of common interfering species. 相似文献
85.
86.
YUAN DaoYi ZHANG YongQiang TU YongQiang CHEN ZhiHua & ZHAO Xiong State Key Laboratory of Applied Organic Chemistry 《中国科学:化学》2010,(1)
Construction of the polyaryl quaternary unit through a ZnBr2 catalyzed tandem coupling/semipinacol rearrangement participated by allylic cations was reported for the first time. 相似文献
87.
88.
89.
Yong Mei Hu Guang Hai Su Stephen Cho‐Wing Sze Wencai Ye Yao Tong 《Biomedical chromatography : BMC》2010,24(4):438-453
A simple method based on liquid chromatography coupled with diode array detection and electrospray ionization mass spectrometry (LC‐DAD‐ESI‐MS) was developed for the quality assessment of Cortex Phellodendri (CP), which was mainly derived from two species of Phellodendron chinense Schneid and Phellodendron amurense Rupr. Total 41 compounds, including 14 phenols, 24 alkaloids and three liminoidal triterpenes were identified or tentatively characterized from the 75% methanol extract of CP samples by online ESI‐MSn fragmentation and UV spectra analysis. Among them, two phenols and six alkaloids were simultaneously quantified using HPLC‐DAD method. The validated HPLC‐DAD method showed a good linearity, precision, repeatability and accuracy for the quantification of eight marker compounds. Furthermore, the plausible fragmentation pathway of the representative compounds were proposed in the present study. The differences of the chemical constituents content and the comprehensive HPLC profiles between the two CP species using LC‐DAD‐ESI‐MS method are reported for the first time, indicating that the CP drugs from different resources should be used separately in the clinic. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
90.
Eva Sjöblom Thomas Edberg Per Stenius 《Journal of Dispersion Science and Technology》2013,34(2):123-145
The phase diagrams for the system TRS 10-80/ butanol/Petrol D/sodium chloride show that the weight ratio B = TRS/butanol is very important for the stability of the microemulsion. R = 1 results in a very limited microemulsion region. Provided the ratio is >1.22 the minimum amount of (TRS+butanol) necessary to form a microemulsion, with equal amounts of water and Petrol D, is 15% and approximately independent of R.However, as R is increased the solubility of water in the (TRS+butanol) mixture is reduced and a liquid crystalline phase is formed. Its presence increases the viscosity and the kinetic stability of the emulsions formed at low content of Petrol D. Addition of electrolyte reduces the minimum amount of (TRS+butanol) necessary to form a microemulsion. Furthermore, systems rich in water separate into two phases; an upper microemulsion phase and a lower aqueous phase. This can be explained in terms of a redistribution of the butanol from the aqueous phase to the oil phase. It is shown that, although the studied system contains unpurified technical products, the phase behaviour is very similar to that of model systems of pure chemicals. X-ray diffraction showed that the liquid crystal line phase was lamellar. The thickness of the amphiphilie layer was 26-28 Å. It is more difficult to obtain direct information of the structure of the microemulsion. However, conductivity data indicated a “bicontinuous” structure or at least, the occurrence of highly dynamic aggregates over a large concentration range. 相似文献