全文获取类型
收费全文 | 2482篇 |
免费 | 264篇 |
国内免费 | 368篇 |
专业分类
化学 | 2344篇 |
晶体学 | 193篇 |
力学 | 46篇 |
综合类 | 4篇 |
数学 | 11篇 |
物理学 | 516篇 |
出版年
2024年 | 1篇 |
2023年 | 21篇 |
2022年 | 31篇 |
2021年 | 56篇 |
2020年 | 77篇 |
2019年 | 55篇 |
2018年 | 35篇 |
2017年 | 71篇 |
2016年 | 109篇 |
2015年 | 100篇 |
2014年 | 93篇 |
2013年 | 256篇 |
2012年 | 94篇 |
2011年 | 111篇 |
2010年 | 129篇 |
2009年 | 124篇 |
2008年 | 144篇 |
2007年 | 161篇 |
2006年 | 174篇 |
2005年 | 169篇 |
2004年 | 155篇 |
2003年 | 130篇 |
2002年 | 114篇 |
2001年 | 76篇 |
2000年 | 86篇 |
1999年 | 88篇 |
1998年 | 73篇 |
1997年 | 52篇 |
1996年 | 70篇 |
1995年 | 60篇 |
1994年 | 46篇 |
1993年 | 48篇 |
1992年 | 30篇 |
1991年 | 17篇 |
1990年 | 17篇 |
1989年 | 7篇 |
1988年 | 5篇 |
1987年 | 3篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 8篇 |
1983年 | 1篇 |
1982年 | 4篇 |
1981年 | 4篇 |
排序方式: 共有3114条查询结果,搜索用时 15 毫秒
61.
Effect of multi-walled carbon nanotubes on non-isothermal crystallization kinetics of polyamide 6 总被引:2,自引:0,他引:2
The non-isothermal crystallization behaviors of multi-walled carbon nanotubes (MWNTs)/polyamide 6 (PA6) composites were investigated by differential scanning calorimetry (DSC). Three methods, namely, Avrami, Ozawa and Mo, were carried out to analyze the non-isothermal crystallization data. The results showed that the MWNTs in PA6 acted as effective nucleation agents. However the crystallization rate of composites obtained was lower than that of the neat PA6. It is indicated that the presence of MWNTs influenced the mechanism of nucleation and the growth of PA6 crystallites. 相似文献
62.
63.
64.
Amorphous poly(ethylene terephthalate) was annealed at temperatures around the glass transition temperature and then heated up in differential scanning calorimeter at 20 °C min−1. It was found that the annealing favored the subsequent cold crystallization and this effect became stronger with increasing annealing temperature. The experimental results were explained by considering the structural change during the annealing. 相似文献
65.
G. Vigier J. Tatibouet A. Benatmane R. Vassoille 《Colloid and polymer science》1992,270(12):1182-1187
Crystallization of poly(ethylene terephthalate) from the amorphous state has been studied in the temperature range 90°–120°C to characterize the amorphous phase when crystalline microstructure is developing. Small-angle x-ray scattering, scanning electron microscopy, and density measurements were used to investigate the morphology of semi-crystalline materials. Differential scanning calorimetry and dynamical mechanical spectroscopy experiments were carried out on amorphous, partially crystallized and crystallized specimens and, when structural relaxation is allowed (thermal treatments close to but below glass transition temperature), strong evidence is obtained for the existence of two different amorphous phases with different mobilities. 相似文献
66.
采用差示扫描量热法(DSC)、X射线衍射(XRD)和透射电镜(TEM)研究了Y对Nd-Fe-Al-Ni非晶合金热稳定性和晶化行为的影响。结果表明,淬火态的Nd60Fe20Al10Ni10-xYx(x=0,2)合金基本为非晶组织同时还含有少量的淬态相,Y的加入抑制了淬态相的析出。加入Y后,非晶合金的晶化开始温度和晶化峰值温度都向高温方向移动,证明其热稳定性提高。Y的加入改变了合金的晶化方式和最终晶化产物,使非晶基体中析出的晶化相更加弥散圆整细小。并且Y具有在化学上钝化氧杂质的作用,从而抑制了氧的有害作用。利用Kissinger方程获得了Nd60Fe20Al10Ni8Y2非晶合金的晶化开始和晶化峰值激活能分别为1.21和1.16 eV。 相似文献
67.
用化学还原法制备了NiB、NiB/Al2O3和NiBSm/Al2O3三种催化剂,它们都呈非晶结构.用等离子耦合发射光谱仪(ICP)对催化剂组分进行了分析,采用差示扫描量热法(DSC)对三种催化剂进行了热稳定性分析.结果表明,载体的引入使非晶态NiB合金的体相组成中B的含量降低.将非晶态NiB合金负载到γ-Al2O3上,可以明显改善非晶态合金的热稳定性,少量Sm可以进一步提高晶化温度.晶化激活能数据亦表明了载体和Sm对非晶结构具有良好的稳定作用.载体和Sm可能通过不同的作用提高了非晶态合金的热稳定性. 相似文献
68.
为了探索生物基乙二醇中的1,2-丁二醇(1,2-BDO)作为共聚单体对生物基聚对苯二甲酸乙二醇酯(PET)的结晶行为和力学性能的影响。 本文合成了生物基PET均聚物和不同1,2-BDO共聚单元摩尔分数的系列生物基PET共聚物(共聚单体摩尔分数分别为2.0%、2.7%和5.6%),并采用傅里叶变换红外光谱仪(FTIR)、差示扫描量热仪(DSC)和力学测试等技术手段研究了其结晶行为和力学性能。 结果表明,随着1,2-BDO共聚单元摩尔分数的增加,PET共聚物的熔融温度、结晶速率及结晶度均明显降低,表明1,2-BDO共聚单体的引入破坏了PET分子链的规整性,阻碍了PET链段的结晶。 PET材料的拉伸强度随着1,2-BDO共聚单元摩尔分数的增加而降低,而弯曲强度和弯曲模量略有升高。 相似文献
69.
The melting process of constrained nylon 6 fibers has been studied to estimate the true melting point of its original crystals.
The melting peak became simpler in shape and shifted to higher temperature with increasing fiber-axis restricting force. When
heating rate, β, was increased, the temperature where the melting curve initially departs from its baseline, Tsm, decreased
steeply in the range of 45 to 60°C min-1, and increased linearly with increasing β above 60°C min-1. By linear extrapolation of Tsm to 0°C min-1, the temperature of ca 190°C was obtained for the melting temperature of the original nylon 6 crystals. This seems to correspond
to the zero-entropy-production melting of the most imperfect crystallites of the nylon 6 fabric.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
70.
Jakubus P. Adamski A. Kurzawa M. Sojka Z. 《Journal of Thermal Analysis and Calorimetry》2003,72(1):299-310
The structure and surface properties of ZrO2 strongly depend on its preparation. In the present work the impact of prolonged aging at basic conditions (pH = 9, T = 100°C, t = 48 h), on the phase composition and textural properties, obtained by calcination of the precipitate, was investigated using
several techniques conjointly (DTA/TG, DSC, XRD, porosimetry). The thermal effects accompanying the ZrO2·xH2O gel formation, the coalescence of the particles and crystallization were evaluated and discussed in terms of the structural
differences between the aged and non-aged samples.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献