全文获取类型
收费全文 | 1466篇 |
免费 | 81篇 |
国内免费 | 233篇 |
专业分类
化学 | 1394篇 |
晶体学 | 11篇 |
力学 | 130篇 |
综合类 | 11篇 |
数学 | 10篇 |
物理学 | 224篇 |
出版年
2024年 | 1篇 |
2023年 | 8篇 |
2022年 | 16篇 |
2021年 | 36篇 |
2020年 | 74篇 |
2019年 | 46篇 |
2018年 | 29篇 |
2017年 | 94篇 |
2016年 | 81篇 |
2015年 | 74篇 |
2014年 | 62篇 |
2013年 | 189篇 |
2012年 | 73篇 |
2011年 | 59篇 |
2010年 | 56篇 |
2009年 | 65篇 |
2008年 | 63篇 |
2007年 | 76篇 |
2006年 | 71篇 |
2005年 | 68篇 |
2004年 | 84篇 |
2003年 | 60篇 |
2002年 | 85篇 |
2001年 | 39篇 |
2000年 | 31篇 |
1999年 | 25篇 |
1998年 | 20篇 |
1997年 | 23篇 |
1996年 | 23篇 |
1995年 | 27篇 |
1994年 | 21篇 |
1993年 | 24篇 |
1992年 | 15篇 |
1991年 | 15篇 |
1990年 | 7篇 |
1989年 | 11篇 |
1988年 | 11篇 |
1987年 | 3篇 |
1986年 | 4篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 4篇 |
1979年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有1780条查询结果,搜索用时 72 毫秒
81.
82.
A gauche-gauche interaction is proposed as a powerful controlling factor for the stereochemistry in the intramolecular nitrile oxide cycloaddition reaction derived from N-protected 3-(N-allylamino)propionaldehyde and 2-(N-homoallylamino)acetaldehyde oximes. High levels of stereoselectivity (76% de to perfect) were obtained from the reaction involving nitrile oxides with substituents at the adjacent carbon atom to the tether nitrogen. 相似文献
83.
New double negative and positive temperature coefficients of conductive EPDM rubber TiC ceramic composites 总被引:1,自引:0,他引:1
Farid El-Tantawy 《European Polymer Journal》2002,38(3):567-577
In this paper, we have successfully prepared ethylene-propylene-diene monomer (EPDM)/TiC composites as thermistors, with new double negative and positive temperature coefficients of conductivity (NTCC/PTCC). EPDM composites loaded with 50 phr HAF carbon black and different concentrations of TiC were prepared. This study focuses on the effect of TiC content on the vulcanization process, the network structure and the electrical and thermal properties of EPDM/TiC composites. The effect of TiC on the network structure was evaluated e.g. the curing process, the characteristic time constant during vulcanization, the volume fraction of rubber, gel fraction, interparticle distance between conductive particles, the extent of TiC reinforcement in the rubber matrix and molecular weight between cross-linking through experimental and affine-phantom models. The effects of TiC content on the percolation theory, electrical conductivity, conducting mechanism of conductivity, conducting hysteresis and I-V characteristics were also studied, as well as its TiC on the (NTCC/PTCC), thermoelectric power, dielectric constant and thermal conductivity. Stability and reproducibility of the thermal cycles for heating element applications was tested. Specific heat and the amount of heat transfer by radiation and convection as a function of TiC content was calculated using both the calorimetric technique and a theoretical model. It was proved that TiC improves the network structure, electrical and thermal properties of EPDM composites for practical applications. 相似文献
84.
Aldoximes are readily dehydrated to nitriles with Raney nickel in refluxing 2-propanol. 相似文献
85.
86.
Precipitation temperature-total polymer concentration diagrams for toluene solutions of two styrene-acrylonitrile copolymers different in chemical composition and their mixtures were determined and then triangular phase diagrams of this system were constructed from these diagrams. It is speculated from the triangular phase diagrams and experimentally shown that the copolymer may be effectively fractionated by chemical composition in this system. 相似文献
87.
Bound rubber formation was investigated in detail by applying various extraction temperatures (at room temperature, 90°C, and 180°C) and novel treatment methods (ammonia bubbling and sonication). Bound rubbers could be divided into three major components of core shell, primary layer including tightly primary layer and occluded rubber, and secondary layer including connecting filament. Bound rubber content of the core shell was measured by four successive procedures of extraction at room temperature, ammonia bubbling, extraction at 180°C and sonication. Bound rubber content of the tightly primary layer was measured by three successive procedures of extraction at 90°C, ammonia bubbling and sonication. Bound rubber content of the primary layer was measured by two successive procedures of extraction at 90°C and sonication. 相似文献
88.
89.
90.
以十八烷/聚(苯乙烯-甲基丙烯酸甲酯)(P(St-MMA))微胶囊为相变材料,硅橡胶作为载体,制备了十八烷/P(St-MMA)/硅橡胶复合材料。研究了微胶囊的加入方式及加入量,硅橡胶包覆方法。通过红外光谱(IR)和扫描电镜(SEM)研究复合材料的结构和形貌。通过力学性能测试如拉伸强度、扯断伸长率,确定最佳的加工方法。通过热重分析法(TG)、差示扫描量热法(DSC)和储热性能对复合材料的热性能进行研究。结果表明,十八烷制成微胶囊加入到硅橡胶中,且微胶囊加入量是2份时,十八烷/P(St-MMA)微胶囊/硅橡胶的热稳定性热稳定性及力学性能较好。室温硅橡胶包覆微胶囊掺混固化法制备的复合材料的力学性能优于直接共混后热固化法和混炼涂抹后热固化法。十八烷/P(MMA-St)/硅橡胶复合材料的焓值为67.6J/g,储能效果好。 相似文献