全文获取类型
收费全文 | 1402篇 |
免费 | 36篇 |
国内免费 | 242篇 |
专业分类
化学 | 1532篇 |
晶体学 | 12篇 |
力学 | 2篇 |
综合类 | 7篇 |
数学 | 1篇 |
物理学 | 126篇 |
出版年
2023年 | 7篇 |
2022年 | 23篇 |
2021年 | 20篇 |
2020年 | 27篇 |
2019年 | 31篇 |
2018年 | 33篇 |
2017年 | 21篇 |
2016年 | 23篇 |
2015年 | 20篇 |
2014年 | 49篇 |
2013年 | 155篇 |
2012年 | 83篇 |
2011年 | 80篇 |
2010年 | 59篇 |
2009年 | 74篇 |
2008年 | 85篇 |
2007年 | 102篇 |
2006年 | 98篇 |
2005年 | 85篇 |
2004年 | 69篇 |
2003年 | 68篇 |
2002年 | 49篇 |
2001年 | 54篇 |
2000年 | 35篇 |
1999年 | 49篇 |
1998年 | 35篇 |
1997年 | 28篇 |
1996年 | 25篇 |
1995年 | 24篇 |
1994年 | 21篇 |
1993年 | 21篇 |
1992年 | 17篇 |
1991年 | 15篇 |
1990年 | 13篇 |
1989年 | 17篇 |
1988年 | 11篇 |
1987年 | 16篇 |
1986年 | 5篇 |
1985年 | 2篇 |
1984年 | 6篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1972年 | 2篇 |
排序方式: 共有1680条查询结果,搜索用时 62 毫秒
121.
《合成通讯》2013,43(20):3575-3581
Abstract The nucleophilic substitution of the benzotriazolyl group in the N-(α-benzotriazol-1-ylalkyl)amides and N-(α-benzotriazol-1-ylalkyl) sulfonamides with allylsamarium bromide was investigated, and the corresponding homoallylamides or homoallylsulfonamides were obtained in good to excellent yields. 相似文献
122.
A facile,one-pot synthesis of N-aryl propargylamine from aromatic boronic acid,aqueous ammonia,and propargyl bromide has been achieved under microwave-assisted conditions.The reactions can be smoothly completed within a total 10 min through a two-step procedure,including copper-catalyzed coupling of aromatic boronic acids with aqueous ammonia and following propargylation by propargyl bromide. 相似文献
123.
Martín A. Iglesias Arteaga Roxana Pérez Gil Vivian Leliebre Lara Carlos S. Pérez Martinez Francisco Coll Manchado Arístides Rosado Pérez 《合成通讯》2013,43(8):1381-1386
The synthesis of a plant growth promoter furostanol which bears the characteristic functionality of teasterone on rings A and B is described. 相似文献
124.
Rydberg transitions for the interhalogen IBr, are reported in the wavelength region 160-130 nm. 相似文献
125.
An expeditious synthesis of aryl substituted E‐homoallylic bromides has been accomplished by the cleavage of cyclopropylcarbinols with phosphorus tribromide. 相似文献
126.
Controlled dilithiation of propargyl bromide with two equivalents of n-butyllithium, in the presence of TMEDA, produces the operational equivalent of the dianion 1,3-dilithiopropyne. The latter reacts efficiently with acid chlorides to produce bishomopropargylic alcohols in a single step route and with high regioselectivity and moderate yields. 相似文献
127.
The electrochemical bromination of 4-methoxy toluene by two-phase electrolysis yields 3-bromo 4-methoxy toluene at first, which subsequently undergoes side-chain bromination to give 3-bromo 4-methoxy benzyl bromide as a final product in 86% yield. The two-phase electrolysis consists of 25–50% NaBr as aqueous electrolyte and CHCl3 containing aromatic compound as organic phase. The reaction temperature is maintained at 10–25 °C. The probable orientation of bromine atom in an alkyl aromatic compound (nuclear versus side chain) is explained from the experimental result. 相似文献
128.
Xiaoyi Yang Binbin Zhang Chaohua Guo Jianbo Li Xingang Wang 《Journal of Dispersion Science and Technology》2018,39(10):1518-1523
The present work aimed at research the physic-chemical properties of the interaction of N-decyl-O-chitosan sulfate (an amphiphilic chitosan derivative, C10-OCHS) with cetyltrimetylammonium bromide (CTAB) by the steady-state fluorescent, static/dynamic surface tension, turbidity and transmission electron microscopy (TEM). The results showed that the complex of C10-OCHS/CTAB had high surface activity and lower critical aggregation concentration. Besides, the C10-OCHS/CTAB could self-assemble into various aggregates like irregular spherical aggregates, vesicles or polydisperse aggregates from lower to higher concentrations of CTAB with a mixed C10-OCHS concentration of 200?mg/L. 相似文献
129.
A simple and efficient synthesis of highly substituted pyrroles was achieved in water medium via multi-component strategy, using amine,DMAD/DEAD as well as phenacyl bromide catalyzed by β-CD.Utilizing this protocol various pyrrole derivatives were synthesized in good to excellent yields. 相似文献
130.
《Analytical letters》2012,45(8):1531-1543
ABSTRACT Three simple and sensitive spectrophotometric methods for the determination of ipratropium bromide (IPB) in liquid for nebulization are described. Method A, is based on the formation of a charge transfer complex with iodine. The reaction product is measured spectrophotometrically at 278 nm. Method B, is based oh the formation of an ion – association complex between the drug and an acidic dye, Bromocresol green (BCG), which is extractable into chloroform and has an absorption maximum at 418 nm. Method C, uses derivative spectrophotometry for the determination of IPB by measuring the D2-value at 232 nm. Beer's law is obeyed over the concentration range 1-10, 2-16 and 5-30 μg ml? for method A, B and C, respectively. The optimum conditions for the formation of the charge transfer or ion-association complexes were optimized. The proposed methods were applied for the determination of IPB in liquid for nebulization. Evaporation to dryness and extraction of the residue with isopropanol, were performed before application of methods A & B. Mean percentage recoveries were found to be 99.67 ± 0.79, 99.26 ± 1.06 and 100.21 ± 0.85 for method A, B, and C, respectively. 相似文献