全文获取类型
收费全文 | 3119篇 |
免费 | 64篇 |
国内免费 | 257篇 |
专业分类
化学 | 2907篇 |
晶体学 | 9篇 |
力学 | 2篇 |
综合类 | 6篇 |
数学 | 5篇 |
物理学 | 511篇 |
出版年
2024年 | 10篇 |
2023年 | 109篇 |
2022年 | 41篇 |
2021年 | 40篇 |
2020年 | 52篇 |
2019年 | 52篇 |
2018年 | 52篇 |
2017年 | 64篇 |
2016年 | 68篇 |
2015年 | 80篇 |
2014年 | 98篇 |
2013年 | 262篇 |
2012年 | 233篇 |
2011年 | 206篇 |
2010年 | 145篇 |
2009年 | 190篇 |
2008年 | 146篇 |
2007年 | 201篇 |
2006年 | 193篇 |
2005年 | 192篇 |
2004年 | 195篇 |
2003年 | 95篇 |
2002年 | 86篇 |
2001年 | 68篇 |
2000年 | 51篇 |
1999年 | 66篇 |
1998年 | 40篇 |
1997年 | 43篇 |
1996年 | 36篇 |
1995年 | 49篇 |
1994年 | 42篇 |
1993年 | 25篇 |
1992年 | 23篇 |
1991年 | 30篇 |
1990年 | 23篇 |
1989年 | 32篇 |
1988年 | 17篇 |
1987年 | 20篇 |
1986年 | 5篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1983年 | 6篇 |
1982年 | 12篇 |
1981年 | 8篇 |
1980年 | 7篇 |
1979年 | 6篇 |
1978年 | 4篇 |
1974年 | 2篇 |
1970年 | 3篇 |
1967年 | 1篇 |
排序方式: 共有3440条查询结果,搜索用时 31 毫秒
991.
Faouzi Guenadil Houcine Aichaoui 《Phosphorus, sulfur, and silicon and the related elements》2013,188(11):2633-2638
The use of polyphosphoric acid and the complex AlCl 3 -DMF in 6-acylation of 2(3H)-benzothiazolones previously have been reported. Instead of the frequently used AlCl 3 as a catalyst in the Friedl-Crafts reactions, we conducted the acylation of 2(3H)-benzothiazones using zinc chloride as a catalyst in DMF as solvent and acid chlorides or anhydrides as acylating agents. 相似文献
992.
Razium Ali Soomro Ayman Nafady Keith Richard Hallam Sana Jawaid Abdullah Al Enizi Syed Tufail Hussain Sherazi Sirajuddin Zafar Hussain Ibupoto Magnus Willander 《Analytica chimica acta》2016
This study describes sensitive determination of atropine using glassy carbon electrodes (GCE) modified with Co3O4 nanostructures. The as-synthesised nanostructures were grown using cysteine (CYS), glutathione (GSH) and histidine (HYS) as effective templates under hydrothermal action. The obtained morphologies revealed interesting structural features, including both cavity-based and flower-shaped structures. The as-synthesised morphologies were noted to actively participate in electro-catalysis of atropine (AT) drug where GSH-assisted structures exhibited the best signal response in terms of current density and over-potential value. The study also discusses the influence of functional groups on the signal sensitivity of atropine electro-oxidation. The functionalisation was carried with the amino acids originally used as effective templates for the growth of Co3O4 nanostructures. The highest increment was obtained when GSH was used as the surface functionalising agent. The GSH-functionalised Co3O4-modified electrode was utilised for the electro-chemical sensing of AT in a concentration range of 0.01–0.46 μM. The developed sensor exhibited excellent working linearity (R2 = 0.999) and signal sensitivity up to 0.001 μM of AT. The noted high sensitivity of the sensor is associated with the synergy of superb surface architectures and favourable interaction facilitating the electron transfer kinetics for the electro-catalytic oxidation of AT. Significantly, the developed sensor demonstrated excellent working capability when used for AT detection in human urine samples with strong anti-interference potential against common co-existing species, such as glucose, fructose, cysteine, uric acid, dopamine and ascorbic acid. 相似文献
993.
Mohammad Ali Zolfigol Arash Ghorbani Choghamarani 《Phosphorus, sulfur, and silicon and the related elements》2013,188(7):1623-1629
A combination of silica sulfuric acid and sodium nitrite in the presence of wet SiO 2 was used as an effective nitrosating agent for the nitrosation of g -diketones to their corresponding f -nitroso or f -oximinoketones under mild and heterogenous conditions in moderate to excellent yields. 相似文献
994.
Determination of taurine in human tear fluid by capillary electrophoresis with indirect amperometric detection based on electrogenerated bromine 下载免费PDF全文
Fuying Du Wenfeng Zhao Shunan Cao Ying‐Sing Fung 《Journal of separation science》2015,38(18):3271-3278
A new method for the determination of taurine was developed based on indirect amperometric detection after capillary electrophoresis. A serial dual‐electrode detector comprising an on column Pt film electrode (upstream electrode) and an end column Pt microdisk electrode (downstream electrode) was utilized to conduct the indirect amperometric detection. Bromide is oxidized to bromine at upstream electrode and reduced back to bromide at downstream electrode. Since taurine can react with bromine quantitatively and rapidly, its concentration can therefore be determined by the decrease of the current for bromine reduction at the downstream electrode. Principal experimental parameters governing the analytical performance were investigated and optimized. Under the optimal conditions, taurine can be baseline separated from interfering amino acids and the detection limit of 0.18 μM was obtained with a linear correlation coefficient of 0.999 over the concentration range of 0.5–60 μM. The developed method has been successfully applied in the determination of taurine in human tear fluid. The taurine level obtained was in good agreement with previous reports and recoveries for taurine spiked ranged from 92–95% with relative standard deviations within 4.6%, demonstrating the reliability of the developed method in the determination of taurine in human tear fluid. 相似文献
995.
Zitao WangWeizhi Geng Hanliu WangShaoguang Zhang Wen-Xiong ZhangZhenfeng Xi 《Tetrahedron letters》2011,52(51):6997-6999
Benzothiophene derivatives were synthesized in high yields from readily available o-(alkynyllithio)aryllithio compounds, sulfur, and 2 equiv of acid chlorides or other electrophiles. An acid chloride-induced electrophilic cyclization resulted in the formation of the thiophene ring. 相似文献
996.
《Physics and Chemistry of Liquids》2012,50(4):479-485
The removal of chemical oxygen demand (COD) and color from simulated dye wastewater containing organic dyes, direct yellow 4, C26H20N4O8S2Na2 and acid yellow 17, C16H10O7N4S2Cl2Na2 experimentally investigated using an electrochemical undivided cell reactor with Pt as anode and steel as cathode. Particular attention was paid to probe the effect of supporting electrolyte (NH4Cl), cell voltage, pH, and treatment time on the electrochemical treatment efficiency. Experiments were also carried out using 0.2?M NH4Cl as supporting electrolyte under the condition of free pH. The experimental results showed that the process could efficiently remove the color and COD from simulated dye waste water. The overall COD removal reached at 69.9% by using supporting electrolyte and increasing voltage. The process can be described by pseudo first-order kinetics for the removal of COD. 相似文献
997.
Ramu Tadikonda Mangarao Nakka Mahaboob Basha Gajula Srinuvasarao Rayavarapu Padma Rao Gollamudi 《合成通讯》2014,44(13):1978-1986
Silica-supported perchloric acid (HClO4-SiO2) was found to be a new, highly efficient, inexpensive, and reusable catalyst for a rapid and efficient synthesis of various 1,2,4-oxadiazoles with good to excellent yields under solvent-free conditions. The present methodology has been effectively utilized for the synthesis of oxolamine, an anti-inflammatory drug. 相似文献
998.
Elisabetta Schievano Ileana Menegazzo Ester Marotta Stefano Mammi 《Magnetic resonance in chemistry : MRC》2011,49(8):523-528
The chemistry of dyes and pigments is relevant to the textile industry, because of the importance to establish the best conditions for the finishing process and to understand the interactions among various compounds to yield the correct hue and nuances. For this reason, the molecular structure of a monoazo acid dye, C.I. Acid Red 131, was elucidated and characterized by homo‐ and hetero‐nuclear NMR, MS, IR and UV spectroscopy techniques. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
999.
Alexandra M. Webster Christopher R. CoxonAlan M. Kenwright Graham SandfordSteven L. Cobb 《Tetrahedron》2014
Dehydrobutyrine is an amino acid that is present in a range of peptide natural products. Reaction of pentafluoropyridine with threonine and subsequent E1cb-type elimination allowed the preparation of novel dehydrobutyrine-containing amino acids under mild conditions. 相似文献
1000.
《Tetrahedron letters》2017,58(13):1273-1275
Herein we report the stereoselective total synthesis of first occurrence distaminolyne A via aminolytic kinetic resolution, Corey-Fuch’s reaction for alkyne formation and Cardiot-Chodkiewicz cross coupling followed by Wittig olefination as the key steps. 相似文献