全文获取类型
收费全文 | 468篇 |
免费 | 71篇 |
国内免费 | 217篇 |
专业分类
化学 | 447篇 |
晶体学 | 10篇 |
力学 | 7篇 |
综合类 | 6篇 |
数学 | 3篇 |
物理学 | 138篇 |
综合类 | 145篇 |
出版年
2023年 | 2篇 |
2022年 | 7篇 |
2021年 | 9篇 |
2020年 | 14篇 |
2019年 | 22篇 |
2018年 | 13篇 |
2017年 | 24篇 |
2016年 | 39篇 |
2015年 | 28篇 |
2014年 | 34篇 |
2013年 | 43篇 |
2012年 | 50篇 |
2011年 | 51篇 |
2010年 | 46篇 |
2009年 | 43篇 |
2008年 | 43篇 |
2007年 | 55篇 |
2006年 | 37篇 |
2005年 | 32篇 |
2004年 | 27篇 |
2003年 | 15篇 |
2002年 | 27篇 |
2001年 | 20篇 |
2000年 | 9篇 |
1999年 | 7篇 |
1998年 | 13篇 |
1997年 | 10篇 |
1996年 | 5篇 |
1995年 | 7篇 |
1994年 | 4篇 |
1993年 | 3篇 |
1992年 | 8篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 3篇 |
1986年 | 2篇 |
1984年 | 1篇 |
排序方式: 共有756条查询结果,搜索用时 31 毫秒
51.
Xin Hou Dongge Huang Xiaomin Chen Zheguo Zhang Kangde Yao 《Journal of polymer science. Part A, Polymer chemistry》2008,46(5):1674-1682
A novel route to synthesize crosslinked porous polyvinylamine (PVAm) microspheres from acrylonitrile (AN) was developed. In the first step, crosslinked porous polyacrylonitrile (PAN) spheres were prepared by copolymerization of AN and divinylbenzene (DVB). Then they were hydrolyzed to form polyacrylamide (PAM) spheres. And lastly, the porous PVAm spheres were successfully obtained via Hofmann degradation of PAM spheres. Scanning electron microscope (SEM) indicated that these PVAm microspheres have rough surfaces and porous interior structure. The pore size, the amino content, and the content of equilibrium water were also investigated. The pore size of these PVAm microspheres increased with the hydrolytic process. The contents of equilibrium water was changed from 49.6 to 96.5% depending on the different crosslinking degrees, and the amino contents were varied between 9.60 and 15.30 mmol/g depending on the different molar ratio of n(NaClO)/n(NaOH). © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1674–1682, 2008 相似文献
52.
Introduction As a competitive substitute of lead-containedsolder,ACAs appear a promising future due totheir numerous advantages,such as low-tempera-ture compatible assembly,higher packaging densi-ty,environmental friendliness,low-stress on thesubstrates.T… 相似文献
53.
A quantitative and fast method of dissolution of refractory thoria (ThO2) was developed for the determination of thorium (Th) in a given sample. The dissolution of sintered ThO2 powder, microspheres and pellets using 88% phosphoric acid was investigated. The conditions of quantitative dissolution of ThO2 microspheres were optimized by conventional heating in autoclave and also by microwave heating. 100 mg of sintered ThO2 microspheres were dissolved in 8 g of phosphoric acid in an autoclave, and heating at 170 °C for 3 h, in comparison to 5 g of phosphoric acid by microwave heating (375 W) at 220 °C for 1 h. Dissolution studies on the powder form of sintered ThO2 were also performed. 1 g of sintered ThO2 powder could be dissolved in 6.5 g of phosphoric acid in autoclave heating at 170 °C for 1 h. Strong complexing of (PO4)3− with Th4+ may be the influencing factor for quantitative dissolution of ThO2. 相似文献
54.
制备了近纳米级的聚苯乙烯-丙烯酸丁酯(PS-PBA)复合微球粒子,并在40Hz~110×106Hz的宽频范围测量了该粒子分散在9种电解质中时的介电弛豫谱,发现了与PS微球粒子分散系不同的特异介电弛豫:低频弛豫对反离子种类具有敏感性而高频弛豫则与电解质种类几乎无关;根据Shilov-Dukhin模型和M-W-O模型分别分析了高、低频率的弛豫机制,并通过对介电谱的Cole-Cole拟合获得了各体系的介电参数.进一步利用Hanai方法由介电参数计算获得了所有体系的相参数;详细分析了体系的内部参数受PS-PBA微球自身结构以及电解质种类影响的原因;讨论了离子扩散系数对介电参数的影响,从而得出了低、高频的弛豫特征时间分别由同离子的扩散系数和反离子的扩散系数所决定之结论.最后,结合Grosse宽频介电理论计算了粒子表面的以及双电层的主要电参数,并分析了电解质种类差异对这些电参数的影响. 相似文献
55.
56.
将酰氯化的羧基金属卟啉 (MP) 与表面含羟基的苯乙烯-甲基丙烯酸羟基乙酯共聚物微球 (P(St-co-HEMA)) 进行酯化反应, 制备了共聚物微球固载的金属卟啉催化剂 (P(St-co-HEMA)MP). 采用扫描电镜、紫外-可见光谱、红外光谱和热重等手段对微球进行了表征, 并考察了它在“金属卟啉?抗坏血酸?分子氧”体系中催化环己烷羟化反应性能. 结果表明, 共聚物微球固载的金属卟啉比非固载的金属卟啉具有更高的催化活性, 催化剂重复使用 4 次, 仍保持较高催化活性. 各共聚物微球固载的金属卟啉催化活性顺序为 P(St-co-HEMA)FeP > P(St-co-HEMA)MnP > P(St-co-HEMA)CoP. 相似文献
57.
In order to obtain a targeting drug carrier system, magnetic polylactic acid (PLA) microspheres loading curcumin were synthesized by the classical oil-in-water emulsion solvent-evaporation method. In the Fourier transform infrared spectra of microspheres, the present functional groups of PLA were all kept invariably. The morphology and size distribution of magnetic microspheres were observed with scanning electron microscopy and dynamic light scattering, respectively. The results showed that the microspheres were regularly spherical and the surface was smooth with a diameter of 0.55-0.75 μm. Magnetic Fe3O4 was loaded in PLA microspheres and the content of magnetic particles was 12 wt% through thermogravimetric analysis. The magnetic property of prepared microspheres was measured by vibrating sample magnetometer. The results showed that the magnetic microspheres exhibited typical superparamagnetic behavior and the saturated magnetization was 14.38 emu/g. Through analysis of differential scanning calorimetry, the curcumin was in an amorphous state in the magnetic microspheres. The drug loading, encapsulation efficiency and releasing properties of curcumin in vitro were also investigated by ultraviolet-visible spectrum analysis. The results showed that the drug loading and encapsulation efficiency were 8.0% and 24.2%, respectively. And curcumin was obviously slowly released because the cumulative release percentage of magnetic microspheres in the phosphate buffer (pH=7.4) solution was only 49.01% in 72 h, and the basic release of curcumin finished in 120 h. 相似文献
58.
喷雾法制备固定化酶载体--磁性聚丙烯腈微球 总被引:7,自引:0,他引:7
介绍了一种制备磁性聚丙烯腈微球的方法。将纳米磁粉均匀分散于聚丙烯腈的N,N-二甲基甲酰胺溶液中,用喷协和法制备了具有超顺磁性的聚丙烯腈微球,并对微球制备过程中的影响因素进行了综合考察。得到了粒度分布在1.0μm-1.5μm、磁含量约为15%的磁性聚丙烯腈微球,其最佳制备条件为:以N,N-二甲基甲酰胺为溶剂,CPAN=1g/L,T=180℃,n=30000r/min,V=2mL/s,Cmagnetic fluid=2g/L。 相似文献
59.
分别以分散蓝和分散红两种染料为模板分子,3种硅烷偶联剂为功能单体,二氧化硅微球为载体,应用自组织法,制备了两种染料分子印迹的微球形聚硅氧烷。采用分光光度法,研究了分子印迹聚硅氧烷对各自模板分子的吸附性能及选择性识别性能。结果表明,与非印迹聚硅氧烷相比,染料分子印迹的聚硅氧烷对其模板分子具有较高的吸附能力,分子印迹聚硅氧烷的吸附速率也被讨论。 相似文献
60.