全文获取类型
收费全文 | 937篇 |
免费 | 48篇 |
国内免费 | 23篇 |
专业分类
化学 | 846篇 |
晶体学 | 4篇 |
力学 | 20篇 |
数学 | 59篇 |
物理学 | 79篇 |
出版年
2024年 | 4篇 |
2023年 | 7篇 |
2022年 | 26篇 |
2021年 | 37篇 |
2020年 | 64篇 |
2019年 | 55篇 |
2018年 | 81篇 |
2017年 | 40篇 |
2016年 | 74篇 |
2015年 | 54篇 |
2014年 | 72篇 |
2013年 | 126篇 |
2012年 | 69篇 |
2011年 | 74篇 |
2010年 | 53篇 |
2009年 | 47篇 |
2008年 | 43篇 |
2007年 | 30篇 |
2006年 | 9篇 |
2005年 | 13篇 |
2004年 | 6篇 |
2003年 | 7篇 |
2002年 | 6篇 |
2001年 | 3篇 |
1999年 | 1篇 |
1994年 | 1篇 |
1991年 | 1篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1976年 | 1篇 |
排序方式: 共有1008条查询结果,搜索用时 312 毫秒
851.
852.
A simple and highly efficient one-pot protocol for the synthesis of novel polysubstituted 1,2-dihydronaphtho[2,1-b] furans has been developed by three-component coupling reaction of 2-aminopyridines, naphthols, and glyoxal in the presence of guanidinium chloride as a polyfunctional organocatalyst under solvent-free conditions. The protocol avoids the use of expensive catalysts, toxic solvents, and chromatographic separation and provides a wide range of novel dihydronaphthofurans in good to excellent yields. 相似文献
853.
Three-component, one-pot synthesis of 4,6-diarylpyrimidin-2(1H)-ones and 9-phenyl-8-oxa-10,12-diaza-tricyclo[7.3.1.02,7]trideca-2(7),3,5-trien-11-one by condensing acetophenone derivatives, aldehydes, and urea in the presence of trimethylsilyl chloride using a catalytic amount of H6P2W18O62-18H2O under solvent-free conditions is reported. 相似文献
854.
Rahim Hekmatshoar Sodeh Sadjadi Samaheh Sadjadi Majid M. Heravi Yahya S. Beheshtiha Fatemeh F. Bamoharram 《合成通讯》2013,43(11):1708-1716
An efficient synthetic method of six- and five-member nitrogen heterocyclic compounds was developed. Nitrogen heterocyclic compounds were prepared by condensation of the β-dicarbonyl compounds with the corresponding β- or γ-amino alcohols, subsequent cyclization, and spontaneous aromatization in the presence of a catalytic amount of Keggin-type heteropoly acids under very mild conditions. 相似文献
855.
Majid M. Heravi Fatemeh Derikvand Hossein A. Oskooie Rahim Hekmat Shoar Mahmood Tajbakhsh 《合成通讯》2013,43(3):513-517
An efficient and convenient method for the oxidation of thiols mediated by silica‐supported bis (trimethylsilyl) chromate (BTSC) in acetonitrile is reported. 相似文献
856.
Maryam Kaabipour Saeid Khodadoust Fatemeh Zeraatpisheh 《Journal of separation science》2020,43(5):912-919
In this work, core/shell magnetic molecularly imprinted polymer nanoparticles were synthesized for extraction and pre‐concentration of valsartan from different samples and then it was measured with high‐performance liquid chromatography. For preparation of molecularly imprinted polymer nanoparticles, Fe3O4 nanoparticles were coated with tetraethyl orthosilicate and then functionalized with 3‐(trimethoxysilyl) propyl methacrylate. In the next step, molecularly imprinted polymer nanoparticles were synthesized under reflux and distillation conditions via polymerization of methacrylic acid, valsartan (as a template), azobisisobutyronitrile and ethylene glycol dimethacrylate as cross linking. The properties of molecularly imprinted polymer nanoparticle were investigated by FTIR spectroscopy, field emission scanning electron microscopy, and X‐ray diffraction. Box‐Behnken design with the aid of desirability function was used for optimizing the effect of variables such as the amounts of molecularly imprinted polymer nanoparticles, time of sonication, pH, and volume of methanol on the extraction percentage of valsartan. According to the obtained results, the affecting variables extraction condition were set as 10 mg of adsorbent, 16 min for sonication, pH = 5.5 and 0.6 mL methanol. The obtained linear response (r2 > 0.995) was in the range of 0.005–10 µg/mL with detection limit 0.0012 µg/mLand extraction recovery was in the range of 92–95% with standard deviation less than 6% (n = 3). 相似文献
857.
Motaharesadat Hosseini Karim Dadashi‐Noshahr Maryam Islami Ehsan Saburi Amin R. Nikpoor Amir Mellati Majid Mossahebi‐Mohammadi Fatemeh Soleimanifar Seyed E. Enderami 《先进技术聚合物》2020,31(8):1857-1864
Using stem cells to replace the lost beta cells is a hopeful strategy in the treatment of diabetic patients. Furthermore, during stem cell culture and therapy, it is a need to use a substrate to act as a supportive matrix to mimic 3D in vivo microenvironment. Therefore, in this study, human adipose‐derived stem cells were used to differentiate into insulin‐producing cells (IPCs) on a silk/polyethersulfone (PES) scaffold. After exposing to the differentiation media, 2D and 3D (silk/PES) cultured cells were gradually aggregated and formed spherical shaped clusters. The viability of cells was comparable in both 3D and 2D culture. As the results of gene expression assay in both RNA and protein level showed, the differentiation efficiency was higher in 3D culture. Furthermore, ELISA revealed that the release of C‐peptide and insulin was higher in 3D than 2D culture. It seems that silk/PES nanofibrous hybrid scaffold could provide an appropriate matrix to mimic in vivo microenvironment and therefore increases the IPC differentiation potency of stem cells. 相似文献
858.
One-pot synthesis of organo-silica hybrids with high thermal properties via a simple sol–gel process
Javanbakht Fatemeh Razavi Bahareh Salami-Kalajahi Mehdi Roghani-Mamaqani Hossein Ommati Masoud 《Journal of Thermal Analysis and Calorimetry》2020,140(5):2267-2274
Journal of Thermal Analysis and Calorimetry - Organic–inorganic hybrid composites have received much attention of scientists in the recent years due to the notable improvement of thermal... 相似文献
859.
Masoumeh Vafaei-Nezhad Ghiasi Reza Shafiei Fatemeh 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2020,94(4):772-777
Russian Journal of Physical Chemistry A - This research aimed at exploring the stabilities of the conformers of 2-methoxy-2-oxo-1,3,2-dioxaphosphorinane and its methylthio and methylselenyl analogs... 相似文献
860.
Heravi Majid M. Janati Fatemeh Zadsirjan Vahideh 《Monatshefte für Chemie / Chemical Monthly》2020,151(4):439-482
Monatshefte für Chemie - Chemical Monthly - The Knoevenagel condensation reaction is a prominent organic reaction commonly being utilized in the total synthesis of natural and biologically... 相似文献