全文获取类型
收费全文 | 2569篇 |
免费 | 170篇 |
国内免费 | 140篇 |
专业分类
化学 | 1683篇 |
晶体学 | 6篇 |
力学 | 155篇 |
综合类 | 19篇 |
数学 | 479篇 |
物理学 | 537篇 |
出版年
2024年 | 11篇 |
2023年 | 91篇 |
2022年 | 163篇 |
2021年 | 118篇 |
2020年 | 124篇 |
2019年 | 126篇 |
2018年 | 117篇 |
2017年 | 153篇 |
2016年 | 114篇 |
2015年 | 85篇 |
2014年 | 179篇 |
2013年 | 205篇 |
2012年 | 118篇 |
2011年 | 163篇 |
2010年 | 121篇 |
2009年 | 142篇 |
2008年 | 113篇 |
2007年 | 135篇 |
2006年 | 96篇 |
2005年 | 74篇 |
2004年 | 93篇 |
2003年 | 53篇 |
2002年 | 53篇 |
2001年 | 36篇 |
2000年 | 26篇 |
1999年 | 36篇 |
1998年 | 29篇 |
1997年 | 23篇 |
1996年 | 14篇 |
1995年 | 9篇 |
1994年 | 6篇 |
1993年 | 12篇 |
1992年 | 4篇 |
1991年 | 2篇 |
1990年 | 10篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1987年 | 4篇 |
1986年 | 2篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1975年 | 1篇 |
1972年 | 1篇 |
1969年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有2879条查询结果,搜索用时 15 毫秒
71.
72.
《印度化学会志》2021,98(10):100150
The traditional methods of synthesis of biguanide drugs generally result in the formation of high levels of waste. In this study, we have developed a simple and green route for the synthesis of olanexidine, the novel antimicrobial compound developed by Otsuka Pharmaceutical Factory Inc. This molecule has been clinically explored in Japan for pre-operative skin preparations. The proposed synthesis scheme is beneficial as it has obviated the use of harmful sodium dicyanamide and has employed the readily available dicyandiamide to facilitate cyanoguanidylation of 3,4-dichlorobenzylamine into 3,4-dichlorobenzylbiguanide. This intermediate was further condensed with 1-bromooctane, using tetrabutyl ammonium bromide as the phase transfer catalyst, in a biphasic solvent system comprising of water and ethyl acetate. The developed method resulted in an overall yield of 76% of olanexidine. 相似文献
73.
《印度化学会志》2021,98(7):100099
An effective and eco-friendly technique were designated for quick alcohol oxidation by glycine functionalised imidazolium ionic liquids in presence of FeCl3 at ambient-temperature. No over the primary alcohols oxidation to carbonyl compounds was observed in presence of this FeCl3/[Gmim]Cl. These benefits of the catalyst resulted mainly from the circumstance with alcohols-H2O2, and the Fe3+ was coordinated by the immobilized IL to permitted both reactants to access the active sites of the catalyst effectively. The catalyst recycled nine times without loss of activity. 相似文献
74.
《印度化学会志》2021,98(6):100081
Various metal-containing ionic liquids were used as catalysts for Friedel-Crafts reactions. The reaction of R-X with benzene in the presence of M-IL (M = Fe, Zn, Cd, Cu) along with 1-glycyl-3-methylimidazolium chloride ([Gmim] Cl) ionic liquid, leads to the development of several key intermediates. Among them, metal-iron showed higher catalytic activity without organic solvents. This technique features high yield, a simple product isolation, ILs reusability and reduced waste discharge, thus rendering this catalytic system both effective and natural friendly. 相似文献
75.
M. N. Hafiza A. N. A. Bashirah N. Y. Bakar 《International Journal of Polymer Analysis and Characterization》2014,19(2):151-158
This present work discusses dual-blend green polymer electrolyte (GPE)–based natural polymers, composed of carboxyl methylcellulose (CMC) and chitosan (CS), created by introducing various compositions of ammonium bromide (NH4Br) as a dopant in the system. These GPEs were successfully prepared by the solution casting technique and characterized using electrical impedance spectroscopy (EIS). From EIS measurement, the highest room-temperature conductivity is 1.21 × 10?5 Scm?1 for the sample containing 20 wt.% of NH4Br. Plot of the temperature dependence of the GPEs revealed that the system obeys the Arrhenius rule and was thermally assisted. Besides that, dielectric studies were also conducted and the data were analyzed using complex permittivity, ?*, and complex electrical modulus, M*, to determine the sample with the highest conductivity value. Thus, this study confirmed non-Debye behavior in the sample. 相似文献
76.
Shadpour Mallakpour Fariba Derakhshan 《International Journal of Polymer Analysis and Characterization》2014,19(8):750-764
In this study, the goal was the preparation, characterization, and surface morphology of poly(amide-imide)/TiO2-citric acid nanocomposites (PAI/TiO2-CA NCs). Owing to the high surface energy and tendency for agglomeration, the surface of TiO2 nanoparticles was modified with citric acid. Then poly(amide-imide) was synthesized by direct polycondensation reaction of N,N′-(pyromellitoyl)-bis-L-leucine diacid with 4,4′-diaminodiphenylmethane by triphenyl phosphite and tetra-n-butylammonium bromide as a green medium. The attained polymer and modified TiO2 nanoparticles were used to prepare PAI/TiO2-CA NCs through ultrasonic irradiation. The resulting PAI/TiO2-CA NC was characterized with FT-IR spectroscopy, X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, and thermogravimetric analysis. 相似文献
77.
《Journal of Saudi Chemical Society》2014,18(5):502-506
A one-pot, three-component condensation reaction of 2-aminobenzothiazole, 2-naphthol and appropriate aldehydes catalyzed by heteropolyacid (HPA) in an aqueous medium afforded the Mannich adduct 2′-aminobenzothiazolomethylnaphthols at 45 °C under ultrasound irradiation. This method provides several advantages such as simple work-up procedure, short reaction time and high yields. 相似文献
78.
The improvement of miscibility between toughened Polyamide-6 (PA6) and Styrene-Butadiene Rubber (SBR) was carried out using grafted Glycidyl Methacrylate (SBR-g-GMA). At first, the compatibilizers were prepared using different comonomers, Styrene, and N-vinyl pyrrolidone. Central composited design (CCD) was distinctly applied to study the influence of Glycidyl Methacrylate (GMA) content and comonomer/GMA on the process of compatibilizer preparation. Four models were developed for Gel content and Degree of grafting for both comonomers using Design-expert software. The models were used to calculate the optimum operating conditions and according to the Flory-Huggins parameter and obtained results, SBR-co-NVP-g-GMA was chosen as an effective compatibilizer. Afterward, another CCD was employed to scrutinize the effect of various amounts and grafting degree of compatibilizer on morphology and mechanical properties of PA6/SBR. The Interparticle distance and polydispersity were studied using a Scanning electron microscope (SEM) and also the Izod impact test inspected in order to evaluate the mechanical properties. Finally, modulus and impact strength were optimized to minimize the former and maximize the latter. Also, the most practical terms in the fitted model are statistically specified using F-value. The root causes for the improvement of blend properties were attributed to a chemical reaction between epoxy groups in SBR-g-GMA and both the carboxylic and amine groups in PA6. Impact strength (539.8 J/m) and modulus (2017.2 N/mm2) of the optimum blend indicate an excellent agreement with the amounts predicted by the models. 相似文献
79.
21世纪"绿色"化学已成为世界各国社会经济发展中的研究与开发战略方向.纤维素是自然界中储量最丰富的天然高分子,是重要的可再生资源以及未来的主要工业原料.然而由于纤维素存在着大量的分子内以及分子间氢键,其结构致密,难以溶解或熔融进一步加工.本文简要介绍了近几年来关于直接使用物理溶剂方法(非衍生化)对纤维素材料开发利用的新进展,主要包括以下4个方面:(1)纤维素在"绿色"溶剂-碱/尿素以及离子液体体系中的溶解和再生;(2)纳米纤维素的制备以及组装;(3)木材纳米技术的开发及利用;(4)细菌纤维素基材料等,旨在推进"绿色"技术实现纤维素资源的研究开发及利用. 相似文献
80.
《Journal of Saudi Chemical Society》2020,24(8):636-641
A catalyst-free and solvent-free synthetic route for convenient one-pot synthesizing pyrano[2,3-d] pyrimidine scaffolds through Knoevenagel-Michael cyclocondensation is reported using visible light irradiation as a green promoter at room temperature based on green chemistry principles. Completing the reactions takes thoroughly less time while obtaining the products in outstanding yields. This green method includes the application of non-hazardous reaction circumstances, direct work-up without column chromatographic separation, catalyst-free, solvent-free, cost effective, simple synthesis, one-pot procedure, and high atom-economy. 相似文献