全文获取类型
收费全文 | 13116篇 |
免费 | 2173篇 |
国内免费 | 1999篇 |
专业分类
化学 | 9947篇 |
晶体学 | 175篇 |
力学 | 721篇 |
综合类 | 122篇 |
数学 | 1829篇 |
物理学 | 4494篇 |
出版年
2024年 | 26篇 |
2023年 | 245篇 |
2022年 | 391篇 |
2021年 | 406篇 |
2020年 | 487篇 |
2019年 | 466篇 |
2018年 | 379篇 |
2017年 | 425篇 |
2016年 | 646篇 |
2015年 | 657篇 |
2014年 | 830篇 |
2013年 | 987篇 |
2012年 | 1195篇 |
2011年 | 1207篇 |
2010年 | 894篇 |
2009年 | 864篇 |
2008年 | 913篇 |
2007年 | 776篇 |
2006年 | 742篇 |
2005年 | 691篇 |
2004年 | 605篇 |
2003年 | 543篇 |
2002年 | 485篇 |
2001年 | 377篇 |
2000年 | 290篇 |
1999年 | 295篇 |
1998年 | 197篇 |
1997年 | 155篇 |
1996年 | 191篇 |
1995年 | 150篇 |
1994年 | 137篇 |
1993年 | 98篇 |
1992年 | 91篇 |
1991年 | 91篇 |
1990年 | 92篇 |
1989年 | 54篇 |
1988年 | 37篇 |
1987年 | 35篇 |
1986年 | 40篇 |
1985年 | 16篇 |
1984年 | 15篇 |
1983年 | 19篇 |
1982年 | 11篇 |
1981年 | 11篇 |
1979年 | 3篇 |
1977年 | 3篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1973年 | 3篇 |
1928年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
921.
Influence of heat treatment of rayon-based activated carbon fibers on the adsorption of formaldehyde 总被引:5,自引:0,他引:5
The influence of heat treatment of rayon-based activated carbon fibers on the adsorption behavior of formaldehyde was studied. Heat treatment in an inert atmosphere of nitrogen for rayon-based activated carbon fibers (ACFs) resulted in a significant increase in the adsorption capacities and prolongation of breakthrough time on removing of formaldehyde. The effect of different heat-treatment conditions on the adsorption characteristics was investigated. The porous structure parameters of the samples under study were investigated using nitrogen adsorption at the low temperature 77.4 K. The pore size distributions of the samples under study were calculated by density functional theory. With the aid of these analyses, the relationship between structure and adsorption properties of rayon-based ACFs for removing formaldehyde was revealed. Improvement of their performance in terms of adsorption selectivity and adsorption rate for formaldehyde were achieved by heat post-treatment in an inert atmosphere of nitrogen. 相似文献
922.
Esterification of carboxylic acids with alcohols is one of the most fundamental and useful transformations in organic synthesis. The most common catalysts are H2SO4 and TsOH. However, H2SO4 or TsOH-catalyzed esterification procedure has some problems such as corrosion, side reactions, difficulty in separation. Hence, recently, various solid acid catalysts such as ion-exchanged resins, molecular sieve, and heteropoly acids etc. have been employed for esterification reaction. However, the s… 相似文献
923.
Electrochemistry behaviors including linear sweep voltammetry and cyclic voltammetry of tertiary cyclic amines with different substituted group were studied. The effect of different substituted group of the nitrogen on the oxidation potential was analyzed. The most suited potential used in α-aminonitrile synthesis through potentiostatic anodic cyanation of cyclic teritary amines was found. The anodic cyanation of N-alkyl-substituted cyclic six-membered amines including N-benzylpiperidine and… 相似文献
924.
925.
926.
927.
采用氩弧熔炼后热处理方法制备了PtBi金属间化合物材料.采用循环伏安法和旋转圆盘电极进行电化学性能测试.通过在0.5 mol•L-1 H2SO4+0.25 mol•L-1 CH3OH溶液中对氧还原的起始电位和电流密度大小比较发现,与光滑铂电极相比,PtBi金属间化合物具有良好的氧还原催化性能和抗甲醇中毒性能.从结构方面分析了PtBi具有抗甲醇中毒性能的原因,认为是PtBi中Pt-Pt的间距大,不利于甲醇的吸附解离. X射线光电子能谱(XPS)结果表明,PtBi材料中Pt的d电子空穴增加,可能是导致PtBi电极表面氧还原电流增大的原因. 相似文献
928.
Two new dicyanamide coordination polymers, {Mn(dmpz)[N(CN)2]2}2 (1) and {Cu(dmpz)[N(CN)2]2}2 (2)(dmpz=3,5-dimethylpyrazole), were synthesized and characterized by single crystal X-ray diffraction analysis and IR spectroscopy. In 1 and 2 the metal ions have two different coordination modes, where one is coordinated to four dicyanamide anions and two monodentate dmpz molecules to form a slightly distorted octahedral geometry, while the other adopts octahedral geometry, surrounded by four nitrile N atoms and two amide N atoms of the dicyanamide anions. Both complexes contain two alternating chains that are parallel to each other. 相似文献
929.
930.
超临界水中聚乙烯油化的研究 总被引:9,自引:2,他引:9
采用125mL间歇式高压釜反应器,在超临界水条件下考察了反应温度、反应时间、水/聚乙烯比和水填充率对聚乙烯降解油化的影响。实验结果表明,聚乙烯在超临界水中迅速降解,油收率可达90%以上;随温度从450℃提高到480℃,油收率从91.4%下降到61.7%,气体收率从1.9%提高到27.7%;在450 ℃反应时间从1 min延长到30 min时,油收率略有下降,油品中C7-11组分所占比例增大一倍。水/聚乙烯比和水填充率的增加在一定程度上对聚乙烯的降解起抑制作用。 相似文献