全文获取类型
收费全文 | 2020篇 |
免费 | 116篇 |
国内免费 | 58篇 |
专业分类
化学 | 1602篇 |
晶体学 | 12篇 |
力学 | 85篇 |
数学 | 193篇 |
物理学 | 302篇 |
出版年
2024年 | 2篇 |
2023年 | 8篇 |
2022年 | 38篇 |
2021年 | 77篇 |
2020年 | 105篇 |
2019年 | 98篇 |
2018年 | 134篇 |
2017年 | 98篇 |
2016年 | 156篇 |
2015年 | 105篇 |
2014年 | 151篇 |
2013年 | 249篇 |
2012年 | 157篇 |
2011年 | 167篇 |
2010年 | 130篇 |
2009年 | 116篇 |
2008年 | 121篇 |
2007年 | 72篇 |
2006年 | 47篇 |
2005年 | 32篇 |
2004年 | 28篇 |
2003年 | 25篇 |
2002年 | 22篇 |
2001年 | 8篇 |
2000年 | 7篇 |
1999年 | 4篇 |
1998年 | 2篇 |
1997年 | 4篇 |
1996年 | 3篇 |
1995年 | 5篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1987年 | 1篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 4篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 1篇 |
排序方式: 共有2194条查询结果,搜索用时 0 毫秒
951.
952.
953.
Polymerization of ethylene using a series of binuclear and a mononuclear Ni (II)‐based catalysts 下载免费PDF全文
Mostafa Khoshsefat Gholam Hossein Zohuri Navid Ramezanian Saeid Ahmadjo Meisam Haghpanah 《Journal of polymer science. Part A, Polymer chemistry》2016,54(18):3000-3011
A novel series of homo‐, bi‐, and mononuclear Ni(II)‐based catalysts (BNCn n = 1–4, MNC4) were used for ethylene polymerization. The optimum conditions for the catalyst BNC4 (the highest catalytic activity) was obtained at [Al]/[Ni]=2000/1, Tp = 42 °C, and tp = 20 min that was 1073 g PE/mmol Ni h. In theoretical study, steric and electronic effects of substituents and diimine backbone led to prominent influence on the catalyst behavior. The highest MV was resulted from polymerization using BNC4; however, the highest unsaturation content was obtained from BNC1. GPC analysis showed a broad MWD (PDI = 17.8). BNC1 and BNC2 in similar structures showed broad peaks in DSC thermogram, while BNC3 and BNC4 with more electronic effects showed a peak along with a wide shoulder. Monomer pressure increasing showed enhancing in activity of the BNC4, meanwhile a peak with shoulder to a single peak in DSC thermogram and uniformity in morphology of the resulted polymer were observed. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3000–3011 相似文献
954.
Phosphated tungstate as a new, reusable and efficient solid phosphoric acid catalyst was synthesized and used to promote the reaction of diaminoglyoxime with various aromatic aldehydes. The prepared phosphated tungstate was characterized using various techniques including X‐ray diffraction, scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, Fourier transform infrared spectroscopy and thermal analysis. A wide variety of heterocyclic nitrones were obtained under mild reaction conditions and in high yields by using the prepared catalyst. 相似文献
955.
Seyed Jamal Tabatabaei Rezaei Asemeh Mashhadi Malekzadeh Sima Poulaei Ali Ramazani Hossein Khorramabadi 《应用有机金属化学》2018,32(1)
The nitro and nitrile groups in aromatic and aliphatic compounds containing various reducible substituents such as carboxylic acid, ketone, aldehyde and halogen are selectively reduced to the corresponding amines in water as a green solvent with excellent yields by employing NaBH4 in the presence of Fe3O4@PAMAM/Ni(0)‐b‐PEG nanocatalyst. The morphology and structural features of the catalyst were characterized using various microscopic and spectroscopic techniques. The designed catalyst system because of it being covered with hydrophilic polymers is soluble in a wide range of solvents (e.g. water and ethanol) and suitable for immobilizing and stabilizing Ni nanoparticles in aqueous mediums. In addition, the catalyst can be easily recovered from a reaction mixture by applying an external magnetic field and can be reused up to six runs without significant loss of activity. 相似文献
956.
Gold nanoparticles supported on thiol‐functionalized reduced graphene oxide as effective recyclable catalyst for synthesis of tetrahydro‐4H‐chromenes in aqueous media 下载免费PDF全文
Gold nanoparticles supported on thiol‐functionalized reduced graphene oxide (AuNPs@RGO‐SH) were found to be a biocompatible, stable, recyclable heterogeneous catalyst. The catalysts were characterized by field emission scanning electron microscopy (FE‐SEM), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FT‐IR), thermal gravimetric analysis (TGA), and X‐ray diffraction spectroscopy (XRD). The obtained catalyst was used in synthesis of tetrahydro‐4H‐chromenes in aqueous media with excellent yields. The catalysts could be easily separated from the reaction mixture and recovered several times without a significant loss of activity. 相似文献
957.
958.
NH4Fe(SO4)2 was found to be a mild and effective catalyst for the selective synthesis of 2‐aryl‐1‐arylmethyl‐1H‐1,3‐benzimidazoles under solvent‐free conditions. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
959.
960.