全文获取类型
收费全文 | 4092篇 |
免费 | 192篇 |
国内免费 | 101篇 |
专业分类
化学 | 3080篇 |
晶体学 | 16篇 |
力学 | 216篇 |
数学 | 479篇 |
物理学 | 594篇 |
出版年
2024年 | 4篇 |
2023年 | 21篇 |
2022年 | 88篇 |
2021年 | 118篇 |
2020年 | 176篇 |
2019年 | 198篇 |
2018年 | 268篇 |
2017年 | 184篇 |
2016年 | 341篇 |
2015年 | 222篇 |
2014年 | 302篇 |
2013年 | 537篇 |
2012年 | 347篇 |
2011年 | 305篇 |
2010年 | 251篇 |
2009年 | 197篇 |
2008年 | 212篇 |
2007年 | 147篇 |
2006年 | 83篇 |
2005年 | 74篇 |
2004年 | 77篇 |
2003年 | 55篇 |
2002年 | 41篇 |
2001年 | 18篇 |
2000年 | 21篇 |
1999年 | 17篇 |
1998年 | 10篇 |
1997年 | 3篇 |
1996年 | 7篇 |
1995年 | 7篇 |
1994年 | 1篇 |
1993年 | 6篇 |
1992年 | 7篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1989年 | 4篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1977年 | 3篇 |
1975年 | 3篇 |
1963年 | 1篇 |
排序方式: 共有4385条查询结果,搜索用时 15 毫秒
101.
Today the synthesis of silver nanoparticles is very common due to their numerous applications in various fields. Silver nanoparticles have unique properties such as: optical and catalytic properties, which, depend on the size and shape of the produced nanoparticles. So, today the production of silver nanoparticles with different shapes which have various uses in different fields such as medicine, are noted by many researchers. This article, is an attempt to present an overview of the shape-controlled synthesis of silver nanoparticles using various methods. 相似文献
102.
In this study, natural‐based ionic liquid (IL) using caffeine (Caff), trietahnolamine (TEA) and ZnBr2, [Caff‐TEA]+[ZnBr3]?, which features high catalytic activity and environmentally‐friendly nature was synthesized with melting point of 76 °C by a facile method. The synthesized [Caff‐TEA]+[ZnBr3]? has high catalytic activity as both of catalyst and solvent in condensation reactions for the synthesis of benzylidenes, bis‐hydroxyenones and xanthenes. Synthesized IL was characterized by proton nuclear magnetic resonance (1HNMR), Fourier transform infrared spectroscopy (FT‐IR), X‐ray diffraction (XRD) and Energy‐dispersive X‐ray spectroscopy (EDX) analysis. Also synthesized heterocycles were characterized by FT‐IR, proton nuclear magnetic resonance (1HNMR) and carbon nuclear magnetic resonance (13CNMR). 相似文献
103.
Vahid Beigi-Somar Seyed Saied Homami Majid Ghazanfarpour-Darjani Amirhossein Monzavi 《Journal of heterocyclic chemistry》2020,57(1):140-150
In situ generated copper acetylides react with isocyanates and oxiranes to form a decent range of morpholine derivatives. The reactions proceeded with acceptable yields and excellent regioselectivity. The presence of oxygen and moisture completely inhibited the reaction. The scope of the reaction is wide and the reactions involve consecutive C–C, C–N, and C–O bond formations. 相似文献
104.
Ali Reza Kiasat Simin Nazari 《Journal of inclusion phenomena and macrocyclic chemistry》2013,76(3-4):363-368
This paper presents a feasible protocol for the preparation of β-cyclodextrin conjugated Fe3O4 magnetic nanoparticles as an efficient microvessel and host system for nucleophilic substitution reaction of benzyl halides in water. No evidence for the formation of by-product for example isothiocyanate or benzyl alcohol was observed and the products were obtained in pure form without further purification. The characteristics results of FT-IR, XRD, TGA and SEM shows that β-CD is grafted onto Fe3O4 nanoparticles. The nanomagnetic catalyst could be readily separated from solution via application of an external magnet, allowing straightforward recovery and reuse. 相似文献
105.
Reza Takjoo Alireza Akbari Mehdi Ahmadi Hadi Amiri Rudbari Giuseppe Bruno 《Central European Journal of Chemistry》2013,11(11):1844-1851
A new Schiff base ligand of 5-bromo-2-hydroxybenzaldehyde S-ethyl-isothiosemicarbazone (H2L) was synthesized and its mixed-ligand Cu(II) complex was also prepared by reaction of Cu(NO3)2·3H2O with H2L and imidazole. Their structures were fully characterized by elemental analysis, FT-IR, molar conductivity and UV-Vis methods. The analytical data suggest that the metal, H2L and imidazole ratios in the Schiff base complex are 1:1:1. Single crystal diffraction was also used to better understand the molecular structure of the Cu(II) complex. The results of physico-chemical analyses of the Schiff base complex reveal the coordination geometry around the central atom is square planar. The H2L ligand (NNO donor) is coordinated to the metal center as a tridentate bionegatively agent. Another position of the square planar geometry is occupied by the imidazole ligand. Furthermore, computational studies of the new complex were performed by carrying out DFT calculations. Geometry optimization and natural band analysis of the complex is discussed in further detail. 相似文献
106.
In present work, the ionic liquid, 1‐butyl‐3‐methylimidazolium bis (trifluoromethylsulfonyl) imide was incorporated in the carbon paste electrode as the binder (IL‐CPE). O‐anisidine (OA) monomer is electropolymerized in the presence of an aqueous acidic solution onto IL‐CPE (POA/IL‐CPE). The as‐prepared substrate is used as a porous matrix for dispersion of Ni(II) ions by immersing the modified electrode in a nickel(II) nitrite solution. The modified electrodes are characterized by scanning electron microscopy (SEM) and electrochemical methods. The POA/IL‐CPE was applied successfully to highly efficient (current density of 18.2 mA cm?2) electrocatalytic oxidation of formaldehyde in alkaline medium. Finally, the rate constant for chemical reaction between formaldehyde and redox sites of the electrode was calculated. 相似文献
107.
Mohammad Ghaffarzadeh Mohammad Bolourtchian Zohreh Hassanzadeh Fard Mohammad Reza Halvagar Farshid Mohsenzadeh 《合成通讯》2013,43(14):1973-1981
One‐step microwave‐assisted synthesis of phenylacetylenes 2a–j from the corresponding ketones 1a–j in the presence of a new reagent, PCl5–pyridine, is described. The reaction is carried out under a simple operational and experimental procedure, avoiding the use of the complicated and harsh multistep reaction. 相似文献
108.
Mohammad Ali Zolfigol Maryam Kiany-borazjani Majid M. Sadeghi Hamid Reza Memarian Iraj Mohammadpoor-baltork 《合成通讯》2013,43(16):2945-2950
A combination of NaHSO4.H2O and NaNO2 in the presence of wet SiO2 was used as an effective oxidizing agent for the oxidation of dihydropyridines to their corresponding pyridine derivatives at room temperature with excellent yields. 相似文献
109.
Shahnaz Rostamizadeh Ali Mohammad Amani Reza Aryan Hamid Reza Ghaieni Nasrin Shadjou 《合成通讯》2013,43(20):3567-3576
A simple, inexpensive, and efficient one-pot synthesis of 2,3-dihydroquinazoline-4(1H)-one derivatives under solvent-free conditions using a catalytic amount of iodine with excellent product yields is reported. This methodology provides easy, quantitative access to various 2,3-dihydroquinazoline-4(1H)-one derivatives, using commercially available iodine as a catalyst. 相似文献
110.
A series of three-component reactions has been carried out using HClO4-SiO2 as a versatile heterogeneous catalyst. A series of new and novel N-protected 1-aminoalkyl-2-naphthol derivatives have been prepared under thermal solvent-free reaction conditions. In all cases, the reaction conditions were very simple and high-yielding. 相似文献