全文获取类型
收费全文 | 184篇 |
免费 | 3篇 |
国内免费 | 3篇 |
专业分类
化学 | 129篇 |
晶体学 | 2篇 |
力学 | 10篇 |
数学 | 13篇 |
物理学 | 36篇 |
出版年
2023年 | 1篇 |
2022年 | 3篇 |
2021年 | 10篇 |
2020年 | 3篇 |
2019年 | 4篇 |
2018年 | 10篇 |
2017年 | 9篇 |
2016年 | 19篇 |
2015年 | 6篇 |
2014年 | 13篇 |
2013年 | 22篇 |
2012年 | 12篇 |
2011年 | 14篇 |
2010年 | 7篇 |
2009年 | 10篇 |
2008年 | 10篇 |
2007年 | 5篇 |
2006年 | 2篇 |
2005年 | 5篇 |
2004年 | 6篇 |
2003年 | 1篇 |
2002年 | 3篇 |
1999年 | 1篇 |
1998年 | 1篇 |
1996年 | 2篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1973年 | 1篇 |
排序方式: 共有190条查询结果,搜索用时 0 毫秒
1.
Jocelyne Hellou Raymond J. Andersen Shahin Rafii Edward Arnold Jon Clardy 《Tetrahedron letters》1981,22(42):4173-4176
The structure of luteone (), a twenty three carbon terpenoid, has been solved by performing a single crystal x-ray analysis on a 3,4-dinitrophenylhydrazone derivative. 相似文献
2.
Three new Δ3-norcycloartene triterpenoids, with differing side chain functionalities, have been isolated from the tropical green alga collected in Guam. The structures of these new compounds were secured by x-ray crystallography and by chemical interconversion. 相似文献
3.
Kazem D. Safa Mohammad Shahrivar Shahin Tofangdarzadeh Akbar Hassanpour 《Tetrahedron》2007,63(15):3189-3194
Metalation of (HSiMe2)3CH with lithium diisopropylamide (LDA) in THF gives (HSiMe2)3CLi, which reacts with ethylene oxide, propylene oxide, 1,2-epoxy butane, 1,2-epoxy pentane, 1,2-epoxy hexane, and epichlorohydrin to give the corresponding 1-oxa-2-silacyclopentane derivatives. Then, glycidylmethacrylate (GM) random copolymers with styrene (St) (in a 1:1 and 1:3 mol ratio) were synthesized by solution free radical polymerization at 70(±1) °C using α,α′-azobis(isobutyronitrile) (AIBN) as an initiator. Both types of copolymers were treated with (HSiMe2)3CLi to give new modified copolymers. The reaction of (HSiMe2)3CLi with epoxides on the side chains of the copolymers does not lead to intramolecular nucleophilic attack contrary to simple epoxides. All the products have been characterized by spectroscopic techniques. 相似文献
4.
A very simple, selective and sensitive spectrophotometric method for the determination of dodecyl benzene sulfonate (DBS) has been investigated. In this method, the ion pair of DBS and methylene blue was adsorbed onto plasticized poly(vinylchloride) membrane as a solid phase extraction medium. The absorbance of the blue membrane was measured at 660nm against a blank membrane using a spectrophotometer. The influence of type and amount of plasticizer, pH, concentration of methylene blue, temperature of sample solution and time of extraction on the absorbance of membrane was studied. Linear calibration was obtained over a concentration range of 0.1 to 6.5µgmL–1 of DBS. The method was applied to the determination of DBS in different commercial detergents. The precision and accuracy of the method is comparable with the conventional standard method. This method is cost-effective, and the use of organic solvent such as chloroform is completely eliminated. 相似文献
5.
Mohammad Ali Karimi Rasul Shahin Sayed Zia Mohammadi Abdolhamid Hatefi‐Mehrjardi Javad Hashemi Javad Yarahmadi 《中国化学会会志》2013,60(11):1339-1346
A new solid phase extraction (SPE) method has been developed for the speciation of Cr(III) and Cr(VI). This method is based on the adsorption of Cr(VI) on modified alumina‐coated magnetite nanoparticles (ACMNPs). Total chromium in different samples was determined as Cr(VI) after oxidation of Cr(III) to Cr(VI) using H2O2. The chromium concentration has been determined by flame atomic absorption spectrometric (FAAS) technique and amount of Cr(III) was calculated by substracting the concentration of Cr(VI) from total chromium concentration. The effect of parameters such as pH, amount of adsorbent, contact time, sample volume, eluent type, H2O2 concentration and cetyltrimethylammonium bromide (CTAB) concentration as modifier on the quantitative recovery of Cr(VI) were investigated. Under the optimal experimental conditions, the preconcentration factor, detection limit, linear range and relative standard deviation (RSD) of Cr(VI) were 140 (for 350 mL of sample solution), 0.083 ng mL?1, 0.1‐10.0 ng mL?1 and 4.6% (for 5.0 ng mL?1, n = 7), respectively. This method avoided the time‐consuming column‐passing process of loading large volume samples in traditional SPE through the rapid isolation of CTAB@ACMNPs with an adscititious magnet. The proposed method was successfully applied to the determination and speciation of chromium in different water and wastewater samples and suitable recoveries were obtained. 相似文献
6.
An environmentally benign, three-component, one-pot integrated chemical process has been developed for the synthesis of 12-aryl-8,9,10,12-tetrahydrobenzoxanthene-11-one by nucleophilic addition reaction between aldehyde and β-naphthol followed by Michael addition of dimedone, catalyzed by thiamine hydrochloride in aqueous micellar medium with excellent yield. Simple reaction conditions, no requirement of chromatographic separation, short reaction time, ease of isolation, use of inexpensive, easily recoverable and reusable catalyst makes this protocol very interesting from an economic and environmental perspective. 相似文献
7.
A simple, green, and efficient protocol is reported for the preparation of aryl-7,8-dihydro[1,2,4]triazolo[4,3-a]-pyrimidine-6-carbonitriles through one-pot multi component reaction using substituted aromatic aldehydes, malononitrile, and 3-amino[1,2,4]triazole. The reaction is catalyzed by boric acid in aqueous micellar condition. Present protocol incorporates environmentally non-hazardous reaction condition, easy work-up, and use of recyclable catalytic system with associated benefits like excellent yield (84–96%) and shorter reaction time (20 min). Proposed methodology offers rapid access to substituted aryl-7,8-dihydro[1,2,4]triazolo[4,3-a]pyrimidine-6-carbonitriles with high atom-economy and catalytic efficiency. 相似文献
8.
Shamsabadi Amir Shahin Tavanai Hossein Ranjbar Mehdi 《Journal of Cluster Science》2021,32(5):1121-1127
Journal of Cluster Science - This work reports on the outcome of the calcination of gold nanoparticles incorporated polyacrylonitrile nanofibers in air which results in the formation of gold... 相似文献
9.
Sara Sobhani Zahra Pakdin Parizi Soodabeh Rezazadeh 《Journal of organometallic chemistry》2011,696(3):813-817
3-Aminopropylated silica gel, which is prepared from commercially available and cheap starting materials, is introduced as an efficient and recyclable catalyst for the phospha-Michael addition of phosphorus nucleophiles to α,β-unsaturated malonates. Short reaction times, mild reaction conditions, ease of recovery and catalyst reusability make this method a new, economic and waste-free chemical process for the synthesis of β-phosphonomalonates. 相似文献
10.
Joseph C. Ferguson Sadaf Sobhani Matthias Ihme 《Proceedings of the Combustion Institute》2021,38(2):2127-2134
Porous media combustion (PMC) is an active field of research with a number of potential advantages over free-flame combustors. A key contributor to these phenomena is the interphase heat exchange and heat recirculation from the products upstream to the reactants. In this paper, we present a network model that captures the conjugate heat transfer in pore-resolved 2D simulations of PMC. A series of simulations are presented with varying solid conduction and inlet velocity to isolate the role of conjugate heat transfer on the salient features of the burner, including flame stability, axial temperature profiles, and flame structure. We show that both the flame stabilization and the propagation behavior are strongly related to the conjugate heat transfer, and the flame stability regime is shifted to higher velocities as the conductivity of the solid material is increased. 相似文献