全文获取类型
收费全文 | 600篇 |
免费 | 40篇 |
国内免费 | 17篇 |
专业分类
化学 | 450篇 |
晶体学 | 1篇 |
力学 | 39篇 |
数学 | 87篇 |
物理学 | 80篇 |
出版年
2023年 | 1篇 |
2022年 | 14篇 |
2021年 | 20篇 |
2020年 | 25篇 |
2019年 | 39篇 |
2018年 | 35篇 |
2017年 | 30篇 |
2016年 | 65篇 |
2015年 | 36篇 |
2014年 | 35篇 |
2013年 | 99篇 |
2012年 | 49篇 |
2011年 | 43篇 |
2010年 | 40篇 |
2009年 | 24篇 |
2008年 | 23篇 |
2007年 | 28篇 |
2006年 | 7篇 |
2005年 | 12篇 |
2004年 | 7篇 |
2003年 | 7篇 |
2002年 | 6篇 |
2001年 | 2篇 |
2000年 | 1篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1980年 | 1篇 |
排序方式: 共有657条查询结果,搜索用时 15 毫秒
651.
In this study, a selective method for the determination of atropine in pharmaceutical formulations was proposed. L-cysteine capped Mn-doped ZnS quantum dots (QDs) were prepared in an in-situ method using sodium thiosulfate precursor and characterized by spectrofluorometer, Fourier transform infrared spectroscopy (FT-IR), transmission electron microscope (TEM) and X-ray diffractometer (XRD). Dopamine hydrochloride was used as a precursor for preparation of poly dopamine-coated molecularly imprinted Mn-doped ZnS quantum dots. Finally, these prepared molecularly imprinted Mn-doped ZnS quantum dots were used for determination of atropine in pharmaceutical formulations. The obtained linear range for determination of atropine was in the range of 2 × 10?8 – 7 × 10?6 M, with a correlation coefficient (R2) of 0.9889; and the detection limit (S/N = 3) was 3.2 nM. 相似文献
652.
Ghasemi Y Rasoul-Amini S Morowvat MH Raee MJ Ghoshoon MB Nouri F Negintaji N Parvizi R Mosavi-Azam SB 《Molecules (Basel, Switzerland)》2008,13(10):2416-2425
A unicellular microalga, Chlamydomonas reinhardtii, was isolated from rice paddy-field soil and water samples and used in the biotransformation of hydrocortisone (1). This strain has not been previously tested for steroid bioconversion. Fermentation was carried out in BG-11 medium supplemented with 0.05% substrate at 25 degrees C for 14 days of incubation. The products obtained were chromatographically purified and characterized using spectroscopic methods. 11b,17 beta-Dihydroxyandrost-4-en-3-one (2), 11 beta-hydroxyandrost-4-en-3,17-dione (3), 11 beta,17 alpha,20 beta,21-tetrahydroxypregn-4-en-3-one (4) and prednisolone (5) were the main products of the bioconversion. The observed bioreaction features were the side chain degradation of the substrate to give compounds 2 and 3 and the 20-ketone reduction and 1,2-dehydrogenation affording compounds 4 and 5, respectively. A time course study showed the accumulation of product 2 from the second day of the fermentation and of compounds 3, 4 and 5 from the third day. All the metabolites reached their maximum concentration in seven days. Microalgal 18S rRNA gene was also amplified by PCR. PCR products were sequenced to confirm their authenticity as 18S rRNA gene of microalgae. The result of PCR blasted with other sequenced microalgae in NCBI showed 100% homology to the 18S small subunit rRNA of two Chlamydomonas reinhardtii spp. 相似文献
653.
Ahmad Reza Massah Roozbeh Javad Kalbasi Anahita Shafiei 《Monatshefte für Chemie / Chemical Monthly》2012,141(10):643-652
Abstract
ZSM-5 has been modified as supported sulfuric acid (ZSM-5-SO3H) and introduced for the first time as a mild, convenient, reusable, and heterogeneous catalyst. Various types of aldehydes were efficiently converted to their 1,1-diacetates using a catalytic amount of ZSM-5-SO3H in excellent yields under solvent-free and heterogeneous conditions at room temperature. The deprotection of 1,1-diacetates has also been achieved using this novel catalyst in ethanol. The procedure is operationally simple, environmentally benign, and only a stoichiometric amount of anhydride is used. 相似文献654.
The effect of shear strain on the iron α-ε phase transformation has been studied using a rotational diamond anvil cell (RDAC). The initial transition is observed to take place at the reduced pressure of 10.8?GPa under pressure and shear operation. Complete phase transformation was observed at 15.4?GPa. The rotation of an anvil causes limited pressure elevation and makes the pressure distribution symmetric in the sample chamber before the phase transition. However, it causes a significant pressure increase at the centre of the sample and brings about a large pressure gradient during the phase transformation. The resistance to the phase interface motion is enhanced due to strain hardening during the pressure and shear operations on iron and this further increases the transition pressure. The work of macroscopic shear stress and the work of the pressure and shear stress at the defect tips account for the pressure reduction of the iron phase transition. 相似文献
655.
Javad Azizian Farhad Hatamjafari Ali Reza Karimi 《Journal of heterocyclic chemistry》2006,43(5):1349-1352
A series of some new spiro‐1,4‐dihydropyridine derivatives have been synthesized in good yields in a four component, and solvent‐free process by condensation of isatins, primary amines, ethyl cyanoacetate and cyclohexanone on solid support montmorillonite K10 相似文献
656.
Javad Azizian Ali A. Mohammadi Ebrahim Soleimani Ali R. Karimi Mohammad R. Mohammadizadeh 《Journal of heterocyclic chemistry》2006,43(1):187-190
A mild and stereoselective three‐component one‐step synthesis of cis‐isoquinolonic acid using silica sulfuric acid as a heterogeneous catalyst from an aldehyde, amine and homophthalic anhydride in acetonitrile is described. This new method produces pure products in high yields (81‐91%). 相似文献
657.
Javad Safari Shiva Dehghan Khalili Mehran Rezaei Sayed Hossein Banitaba Fereshteh Meshkani 《Monatshefte für Chemie / Chemical Monthly》2010,122(3):1339-1345