全文获取类型
收费全文 | 3340篇 |
免费 | 353篇 |
国内免费 | 964篇 |
专业分类
化学 | 3749篇 |
晶体学 | 42篇 |
力学 | 115篇 |
综合类 | 34篇 |
数学 | 69篇 |
物理学 | 648篇 |
出版年
2024年 | 10篇 |
2023年 | 62篇 |
2022年 | 152篇 |
2021年 | 153篇 |
2020年 | 178篇 |
2019年 | 138篇 |
2018年 | 145篇 |
2017年 | 153篇 |
2016年 | 172篇 |
2015年 | 140篇 |
2014年 | 184篇 |
2013年 | 251篇 |
2012年 | 217篇 |
2011年 | 281篇 |
2010年 | 207篇 |
2009年 | 213篇 |
2008年 | 210篇 |
2007年 | 250篇 |
2006年 | 234篇 |
2005年 | 208篇 |
2004年 | 174篇 |
2003年 | 150篇 |
2002年 | 113篇 |
2001年 | 99篇 |
2000年 | 85篇 |
1999年 | 62篇 |
1998年 | 65篇 |
1997年 | 53篇 |
1996年 | 53篇 |
1995年 | 38篇 |
1994年 | 62篇 |
1993年 | 30篇 |
1992年 | 34篇 |
1991年 | 12篇 |
1990年 | 20篇 |
1989年 | 12篇 |
1988年 | 8篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1979年 | 1篇 |
1978年 | 2篇 |
排序方式: 共有4657条查询结果,搜索用时 0 毫秒
991.
S. Borysiak 《Journal of Thermal Analysis and Calorimetry》2007,88(2):455-462
Composites
made from an isotactic polypropylene matrix and wood (pine or beech) have
been prepared and tested. To improve adhesion between components, the wood
modification was performed by esterification with maleic, propionic, crotonic,
succinic and phthalic anhydrides. The surface of wood fillers was also modified
by chemical treatment with NaOH as well as by extraction process. Non-isothermal
crystallisation of polypropylene in wood composites is studied by DSC, and
the basic parameters of crystallisation are determined. We discovered that
the composites containing chemical treated wood fillers showed the tendency
reduction the nucleation efficiency of polypropylene. The ability of wood
filler to induce nucleation in polypropylene matrix is dependent on the kind
of chemical modification of surface wood 相似文献
992.
G. N. Dalimova 《Chemistry of Natural Compounds》2006,42(1):88-91
The content of reactive groups such as OH, CO, and COOH was increased by modifying hydrolyzed lignin with sulfuric acid and
sodium hydroxide. The increase was confirmed by IR spectral analysis. The sorptive capacity of the resulting hydrolyzed lignin
derivatives was increased sharply by base activation.
__________
Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 70–72, January–February, 2006. 相似文献
993.
In this work, an alkoxide solution route to synthesize Ca phosphates was developed. For the precursors, a CaO2C2H4 solution was prepared by dissolving Ca metal powder into ethylene glycol, and a PO(OH)x(OBut)3–x solution was prepared by dissolving P2O5 inton -butanol under reflux conditions. In order to obtain a mixed solution of the two precursors, acetic acid was used as an additive. The experimental results show that (1) -2CaO · P2O5, -3CaO · P2O5, and hydroxyapatite can be easily synthesized by converting the corresponding mixed solutions to powder products in a hot plate, and calcining the as prepared products at 1100°C; (2) acetic acid behaves as a good agent for controlling the reactions between the two precursors by modifying the CaO2C2H4 species in solution and decreasing the reactivity of the PO(OH)x(OBut)3–x species. 相似文献
994.
A new way to prepare hydrophobic membranes is reported. Polydimethylsiloxane oil (and any other silicone oil molecules) was grafted onto a porous alumina membrane (or any hydroxylated ceramic or glass) by heating, to 180°C, producing a covalently grafted monolayer of silicone oil, chemically and thermally stable, unaffected by organic solvents but susceptible to alkali attack (as is the silicone oil itself). The membrane is totally impermeable to pure water, and organic solvents may be extracted from water mixtures by pervaporation. Very high permeation fluxes were obtained, suggesting possible use of these silicone/ceramic membranes in extraction of volatile organic compounds (VOCs). This simple modification can be applied to macroporous membranes increasing hydrophobicity without pore blocking. 相似文献
995.
996.
非均匀成核法表面包覆氧化铝的尖晶石LiMn2O4研究 总被引:13,自引:0,他引:13
采用高温固相法合成尖晶石LiMn2O4,以非均匀成核方式对其进行包覆氧化铝的表面处理.通过XRD、SEM、粒度分析等技术对表面处理前后的LiMn2O4进行表征,分析了表面处理前后LiMn2O4物理特性的变化,并结合电化学性能测试,研究了表面处理工艺对LiMn2O4电化学容量与循环性能的影响.未经表面处理的LiMn2O4在1 C倍率下初期放电容量为86.5 mA•h•g-1,50次循环充放电后容量衰减26.3%.表面包覆0.5%、1%(w)氧化铝的LiMn2O4在1 C倍率下的初期放电容量分别为96.0、80.1 mA•h•g-1,经过50次循环后,容量分别降低7.0%、5.6%.实验结果表明,表面处理后的LiMn2O4循环性能显著提高,而且随着氧化物含量的增加,循环性能增强,但放电容量降低. 相似文献
997.
998.
PU/MOMMT纳米复合材料的制备与研究 总被引:3,自引:0,他引:3
纳米复合材料由于其纳米尺寸效应,表面效应以及纳米粒子与基体界面间强的相互作用,具有优于相同组分常规复合材料的力学、热学等性能,引起了人们的广泛关注。用纳米材料改性聚合物,制备纳米复合材料是获得高性能高分子复合材料的重要方法。1998年以来,Pinnavaia等首先制备了聚氨酯,蒙脱土(PU/MMT)纳米复合材料,研究了有机蒙脱土在聚醚中的分散性。其后Chen等将聚羟基己内酯/蒙脱土(PCL/MMT)纳米复合材料加入到PCL和二苯基甲烷-4,4'-二异氰酸酯(MDI)合成的预聚体与1,4-丁二醇扩链反应后的溶液中,制备了PU/MMT纳米复合材料。少量PCL/MMT的引入可使复合材料的综合性能大幅提高。 相似文献
999.
Distributions ofn-butane pyrolysis products and activities of catalysts have been analyzed. The catalysts based on magnesium oxide was preparedvia modification with magnesium acetate.n-Butane decomposition is shown to be accelerated due to active surface centers of at least two types. 相似文献
1000.
高强聚乙烯纤维的冷等离子体改进 总被引:8,自引:0,他引:8
高强聚乙烯纤维的冷等离子体改进金士九,倪亦斌,张佐光(中国科学院化学研究所北京100080)(北京航空航天大学北京)关键词 高强聚乙烯纤维,等离子体,表面改性,界面性能由高强聚乙烯纤维制成的复合材料抗高速撞击(抗弹)性能远远优于芳纶纤维,广泛用作各种... 相似文献