全文获取类型
收费全文 | 415篇 |
免费 | 23篇 |
国内免费 | 11篇 |
专业分类
化学 | 279篇 |
晶体学 | 4篇 |
力学 | 19篇 |
数学 | 59篇 |
物理学 | 84篇 |
综合类 | 4篇 |
出版年
2023年 | 1篇 |
2022年 | 8篇 |
2021年 | 17篇 |
2020年 | 14篇 |
2019年 | 28篇 |
2018年 | 32篇 |
2017年 | 26篇 |
2016年 | 29篇 |
2015年 | 13篇 |
2014年 | 26篇 |
2013年 | 56篇 |
2012年 | 39篇 |
2011年 | 28篇 |
2010年 | 12篇 |
2009年 | 22篇 |
2008年 | 20篇 |
2007年 | 22篇 |
2006年 | 13篇 |
2005年 | 8篇 |
2004年 | 5篇 |
2003年 | 3篇 |
2002年 | 1篇 |
2001年 | 5篇 |
1997年 | 2篇 |
1994年 | 1篇 |
1989年 | 2篇 |
1985年 | 2篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1978年 | 5篇 |
1977年 | 2篇 |
1975年 | 1篇 |
1974年 | 2篇 |
排序方式: 共有449条查询结果,搜索用时 15 毫秒
351.
352.
4-Formylphenyl benzoate was utilized as a versatile precursor for the construction of new series of heterocyclic scaffolds that contain thiazole and thiazolidin-5-one rings. The antibacterial activity of these scaffolds against two types of bacteria was screened and most of them exhibited good activity. Among the synthesized thiazole derivatives, compounds 5, 6, and 8a showed antibacterial activity close to the standard chemotherapeutic (Ampicillin). 相似文献
353.
Mina Yarazavi Ebrahim Noroozian Mehdi Mousavi 《Journal of the Iranian Chemical Society》2018,15(11):2593-2603
Sol–gel coating technology for the preparation of solid-phase microextraction fibers involves a single-step procedure and allows for in situ creation of chemically bonded coatings which are characterized by high thermal and solvent stabilities. A novel titania sol–gel coating was prepared for the first time on a stainless steel fiber and applied for the headspace solid-phase microextraction (HS-SPME) of menthol with gas chromatography and flame ionization detection. Important parameters influencing the efficiency of SPME process, such as extraction time, extraction temperature and ionic strength, were optimized by central composite design. An extraction time of 40 min at 60 °C gave maximum extraction efficiency, when NaCl (10% w/v) was added to the aqueous sample. The analytical characteristics of the proposed method were comparable with other reported fibers. Under optimized conditions, the linearity was between 0.05 and 100 µg mL??1. The relative standard deviations (RSDs) determined at 0.5 µg mL??1 concentration level (n?=?5) were as follows: intra-day RSD 7.26%; inter-day RSD 10.87%; fiber-to-fiber RSD 9.05%. The relative recoveries determined after spiking a mint distillate sample at three concentration levels from 0.067 to 50.0 µg mL??1 varied from 86 to 102%. The proposed method was successfully applied for the analysis of menthol in peppermint samples. 相似文献
354.
Atom transfer radical polymerization of (meth)acrylates and their novel block copolymers with vinyl acetate 总被引:1,自引:0,他引:1
Mohammad Ali Semsarzadeh Ahmad Mirzaei Ebrahim Vasheghani-Farahani 《European Polymer Journal》2003,39(11):2193-2201
Homopolymerization of methyl acrylate (MA) and methyl methacrylate (MMA) by atom transfer radical polymerization (ATRP) were carried out at 90 °C using methyl-2-bromopropionate (MBP) as initiator, copper halide (CuX, X=Cl, Br) as catalyst, 2,2′-bipyridine (bpy) or N,N,N′,N′,N″-pentamethyldiethylenetriamine (PMDETA) as ligand in 1-butanol (less polar and containing OH) and acetonitrile (more polar) solvents. It was found that with CuCl/bpy catalyst ATRP of MA and MMA in 1-butanol proceeded faster than that in acetonitrile. The rate of ATRP of MA and MMA in acetonitrile and 1-butanol was comparable when CuCl/PMDETA used as catalyst system. The number-average molecular weights increased with conversion and polydispersities were low . The ATRP of MA and MMA with vinyl acetate telomer having trichloromethyl end group (PVAc-CCl3) were also used to synthesize new block copolymers. The structures and molecular weight of synthesized PVAc-b-PMA and PVAc-b-PMMA were characterized by 1H NMR, FTIR spectroscopy and gel permeation chromatography (GPC) and shown that the block copolymers were novel. 相似文献
355.
Ahmad Shaabani Ebrahim Soleimani Zahra Badri 《Monatshefte für Chemie / Chemical Monthly》2006,137(2):181-184
Summary. Silica sulfuric acid as an inexpensive and recyclable solid acid efficiently catalyzes the Fridedl?nder synthesis of quinolines through a condensation reaction of a 2-aminoaryl ketone with an activated α-CH acid compound under
solvent-free conditions in high yields at 100°C. 相似文献
356.
MOHAMMAD-HUSSEIN Sorouraddin MOHAMMAD-REZA Rashidi BEHROOZ Shabani EBRAHIM Ghorbani-Kalhor 《中国化学》2005,23(2):160-165
A new synthesized fluorogenic reagent,8-[(2-pyridine)methylideneamino] quinoline
(PMAQ), was utilized for spectrofluorimetric determination of Cu(II) at trace levels. PMAQ, a good fluorogenic reagent, though insoluble in water, but is soluble in ethanol and 20% ethanol-water. The excitation and the fluorescence wavelengths of PMAQ were 310 and 434 nm respectively. When the reagent was complexed with Cu(II), the fluorescence intensity decreased proportionally with the concentration of Cu(II) at pH 4.5 by a static quenching effect. The highest sensitivity to Cu2+ determination was shown to be at PMAQ
concentration of 1.0×10-5mol•L-1. In order to enhance the quenching effect, the Cu(II)-PMAQ complex solution was kept at 22 ℃ for 20 min. Though the interferences by Co(II) and Fe(III) were very serious, they were however, completely eliminated by being masked with oxalate and ascorbate ions respectively. The linear dynamic range for Cu(II) determination was between 25—441 µg•L-1 with the detection limit of 18 µg•L-1 (RSD=3.7%, n=6). The proposed method was successfully applied to the determination of Cu(II) in real samples including
human blood serum, commercial tea and wheat flour. 相似文献
357.
Ahmad Shaabani Ebrahim Soleimani Ralf-Dieter Hoffmann Rainer Pöttgen 《Tetrahedron letters》2006,47(31):5493-5496
A three-component condensation reaction between an isocyanide, an electron-deficient acetylenic ester and (ethoxycarbonylmethyl)triphenylphosphonium bromide efficiently provides fully substituted N-alkyl-2-triphenylphosphoranylidene glutarimides in a one-pot reaction without any activation or modification. 相似文献
358.
A novel isocyanide-based four-component reaction between a 2-hydroxybenzaldehyde, Meldrum's acid, an isocyanide, and an aromatic or an aliphatic alcohol efficiently provide 3,4-dihydrocoumarin derivatives in good to excellent yields without using any catalyst or activation. The reaction can be carried out as a simple one-pot protocol at room temperature. 相似文献
359.
Mothi Mohamed Ebrahim Helen Stoeckli-Evans 《Journal of organometallic chemistry》2007,692(11):2168-2174
Organotin(IV) complexes of the type [RSnCl3(cis-Ph2PCHCHPPh2)] [R = Me (1), nBu (2), Ph (3)] were prepared by the reaction of RSnCl3 with the rigid bisphosphine ligand, cis-1,2-bis(diphenylphosphino)ethylene in dichloromethane. The complexes have been characterized both in solution and the solid state. Low temperature 31P and 119Sn NMR studies indicate two different phosphorus environments. The crystal structures indicate a weak but chelating mode of coordination of the two phosphorus atoms to tin, leading to a distorted octahedral geometry. In solution the complexes 1-3 undergo a redistribution reaction to form [SnCl4(cis-Ph2PCHCHPPh2)] (4) as one of the products. In order to confirm the redistribution, complex 4 has been prepared separately and characterized both structurally and spectrally. 相似文献
360.
Ebrahim Samei 《Proceedings of the American Mathematical Society》2007,135(7):2045-2049
Let be an open connected subset of the plane, and let be a Banach algebra of analytic functions on . We show that the space of bounded derivations from into is not reflexive. We also obtain similar results when for .