全文获取类型
收费全文 | 21604篇 |
免费 | 1550篇 |
国内免费 | 4405篇 |
专业分类
化学 | 7146篇 |
晶体学 | 178篇 |
力学 | 523篇 |
综合类 | 298篇 |
数学 | 1581篇 |
物理学 | 2799篇 |
综合类 | 15034篇 |
出版年
2024年 | 135篇 |
2023年 | 483篇 |
2022年 | 575篇 |
2021年 | 682篇 |
2020年 | 529篇 |
2019年 | 495篇 |
2018年 | 304篇 |
2017年 | 459篇 |
2016年 | 530篇 |
2015年 | 659篇 |
2014年 | 1264篇 |
2013年 | 1070篇 |
2012年 | 1294篇 |
2011年 | 1348篇 |
2010年 | 1287篇 |
2009年 | 1323篇 |
2008年 | 1536篇 |
2007年 | 1377篇 |
2006年 | 1240篇 |
2005年 | 1167篇 |
2004年 | 1010篇 |
2003年 | 1004篇 |
2002年 | 840篇 |
2001年 | 963篇 |
2000年 | 754篇 |
1999年 | 686篇 |
1998年 | 632篇 |
1997年 | 567篇 |
1996年 | 528篇 |
1995年 | 527篇 |
1994年 | 445篇 |
1993年 | 351篇 |
1992年 | 347篇 |
1991年 | 314篇 |
1990年 | 257篇 |
1989年 | 295篇 |
1988年 | 112篇 |
1987年 | 78篇 |
1986年 | 38篇 |
1985年 | 17篇 |
1984年 | 9篇 |
1983年 | 8篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1963年 | 1篇 |
1959年 | 1篇 |
1958年 | 1篇 |
1957年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
211.
212.
213.
214.
本文总结了最近改良 Sharpless 烯丙醇不对称环氧化试剂[Ti(OiPr)_4,酒石酸酯]的几种方法,通过在试剂中加入几种催化剂,改变试剂组成或相对含量,优化了反应条件,扩大了试剂的使用范围。 相似文献
215.
216.
In the 21st century, hydrogen energy is a novel energy source. Its use is expected to mitigate the problems of environmental pollution and global warming caused by the excessive use of conventional fossil fuels. The hydrogen evolution reaction (HER) for water splitting has attracted considerable attention because of its environmental friendliness. To improve electrocatalyst performance and reduce operation cost, carbon-based metal hybrid materials exhibiting high efficiency and catalytic activity have been developed. Among them, carbon dots (CDs) have garnered significant research attention and have been widely applied in biosensing, bioimaging, and energy conversion/storage because of their facile synthesis, biocompatibility, tunable photoluminescence, excellent stability, and good electronic properties. CDs are widely used as carriers in the construction of electrocatalysts prepared from carbon-based metal hybrid materials. At present, it is believed that CDs exhibit excellent confinement effects, which can effectively inhibit the growth and agglomeration of metal nanoparticles, thereby preparing well-distributed carbon-based metal hybrid materials with a uniform and controllable size. However, the formation process of the small-molecule raw materials of CDs has not been elucidated. In this study, CDs and small-molecule raw materials from synthetic CDs were used as precursors to prepare nitrogen-doped CD-supported ruthenium nanoparticle (Ru@CDs) and small-molecule-supported ruthenium nanoparticle (Ru@Molecule) hybrid materials, respectively. The interaction between the small molecules and Ru in the process of CD formation and the effect on HER performance were explored. Moreover, we prepared different carriers such as metal organic frameworks(MOF), carbon nanotubes (CNTs), and graphene (GO)-supported ruthenium nanoparticle hybrid materials. Among them, Ru@CDs exhibited controllable size and excellent dispersibility and exhibited outstanding HER activity and good stability. Ru@CDs were found to require a low overpotential of 22 mV to reach a current density of 10 mA·cm−2. Moreover, we observed the presence of an intermediate state between the molecules and CDs and demonstrated that the intermediate state exhibits no confinement effect. Furthermore, we found that with increasing calcination temperature, the intermediate state gradually changes to CDs. The unique spatial confinement between CDs and metal ions is key to the formation of monodisperse Ru nanoparticles. Our results confirmed that Ru@CDs serve as excellent HER catalyst supports. This work not only reveals the effect of the unique spatial confinement of CDs on the supported metals and their promoting effect on electrocatalytic activity but also provides guides the future development of CD-based metal hybrid electrocatalysts. 相似文献
217.
218.
219.
密胺树脂/硼酸锌双层包覆微胶囊化红磷的制备及其在阻燃聚烯烃中的应用 总被引:3,自引:0,他引:3
描述了采用密胺树脂和硼酸锌连续双层包覆微胶囊化红磷(MRP)的最新制备方法。采用红外光谱、电子能谱和透射电镜等分析手段对其进行了表征,并证实红磷已被完全包覆。实验数据表明:经包覆的MRP的热稳定性获得了明显改善,吸水率和磷化氢的发生量均大大减少。MRP作为阻燃助剂应用于聚烯烃阻燃材料表现出了良好的阻燃效果。实时红外和热失重测量以及扫描电镜观察表明:其阻燃机制是红磷受热时与树脂反应促进了含磷膨胀炭层的形成,从而提高了材料的热稳定性,碳层起到了隔氧、隔热作用,而且主要在凝聚相中发挥其阻燃作用。 相似文献
220.