全文获取类型
收费全文 | 18079篇 |
免费 | 3143篇 |
国内免费 | 2422篇 |
专业分类
化学 | 12968篇 |
晶体学 | 203篇 |
力学 | 1285篇 |
综合类 | 162篇 |
数学 | 1845篇 |
物理学 | 7181篇 |
出版年
2024年 | 62篇 |
2023年 | 387篇 |
2022年 | 644篇 |
2021年 | 668篇 |
2020年 | 761篇 |
2019年 | 678篇 |
2018年 | 594篇 |
2017年 | 531篇 |
2016年 | 823篇 |
2015年 | 829篇 |
2014年 | 1015篇 |
2013年 | 1238篇 |
2012年 | 1631篇 |
2011年 | 1662篇 |
2010年 | 1101篇 |
2009年 | 1026篇 |
2008年 | 1192篇 |
2007年 | 1033篇 |
2006年 | 1063篇 |
2005年 | 872篇 |
2004年 | 687篇 |
2003年 | 570篇 |
2002年 | 568篇 |
2001年 | 470篇 |
2000年 | 395篇 |
1999年 | 455篇 |
1998年 | 318篇 |
1997年 | 298篇 |
1996年 | 341篇 |
1995年 | 286篇 |
1994年 | 272篇 |
1993年 | 202篇 |
1992年 | 191篇 |
1991年 | 155篇 |
1990年 | 133篇 |
1989年 | 112篇 |
1988年 | 107篇 |
1987年 | 66篇 |
1986年 | 60篇 |
1985年 | 43篇 |
1984年 | 31篇 |
1983年 | 26篇 |
1982年 | 13篇 |
1981年 | 18篇 |
1980年 | 7篇 |
1979年 | 2篇 |
1966年 | 1篇 |
1957年 | 5篇 |
1936年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
142.
Guangyun Zheng Jiemin Jiang Yuping Wu Renxi Zhang Huiqi Hou 《Plasma Chemistry and Plasma Processing》2003,23(1):59-68
Non-equilibrium plasma, which was engendered by dielectric barrier discharge (DBD) was used to analyze the mutual conversion between CO2 and CO. The results showed that the conversion ratio of CO increased monotonously with the increasing voltage. But CO2 was not so. Its conversion ratio reached maximum when the voltage was 3600 V in Ar system. It also showed that the existence of water molecules was more advanageous for the conversion of CO to CO2 in Air system than in oxygen system, and the conversion ratio could reach 75.8% when the relative humidity was 100%. We also discussed the energy yield and energy efficiency, and the result was that high voltage and high concentration of reactant was disadvantageous for energy utilization. 相似文献
143.
The synthesis of formic acid from carbon dioxide and hydrogen using a silica immobilized ruthenium catalyst as precursor has been studied in different reaction conditions. The results revealed that the TOF (turn over frequency) of HCOOH achieved 1481.5 h^-1 on immobilized ruthenium catalyst near the critical pressure point of CO2 with H2 pressure of 4.0 MPa, reaction temperature of 80℃ and PPh3/Ru molar ratio of 6:1. The reaction activity of immobilized catalyst was higher than that of homogeneous catalyst, and the immobilized catalyst also offered the practical advantages such as easy separation and reuse. 相似文献
145.
镀金层识别及其厚度测定的X—荧光强度比值法 总被引:3,自引:0,他引:3
利用Au原子在X射线激发下所发射的Lβ线和M线的强度比值识别样品是镀金还是K金,同时利用这个比值测定镀金层的厚度,镀金层厚度的测定范围为0~4μm,测定值与标定值的相对误差小于15%。 相似文献
146.
This paper reports the first example of diruthenium phosphonate with kagomé structure, namely, [NH3(CH2)4NH3][Ru2(hedpH(0.5))2].2H2O (hedp = 1-hydroxyethylidenediphosphonate). The compound contains kagomé layers that are linked by very strong hydrogen bonds into a nanoscale kagomé structure. Ferromagnetic interactions are mediated between the paramagnetic diruthenium units. 相似文献
147.
微分倒数示波计时电位法的研究—定量测试及滴定分析 总被引:3,自引:0,他引:3
首次利用微分倒数示波图定量测试微量金属离子并滴定分析药物,结果满意。 相似文献
148.
Direct band gap copper indium chalcogenides are of great technological importance in part because of their high photovoltaic conversion efficiency. Covalent superlattices constructed from copper indium chalcogenide clusters are of particular interest because they may combine open framework architecture with semiconducting properties. Here two photoluminescent covalent superlattices built from core-shell type copper indium sulfide supertetrahedral clusters are reported. Each cluster consists of 35 metal cations and is so far the largest known supertetrahedral cluster with a metal-to-metal distance of 1.6 nm. In addition, this is the first example of supertetrahedral clusters in heterometallic copper indium chalcogenides. The preparation of these large clusters has narrowed down the size gap between colloidal nanoclusters and small supertetrahedral clusters and revealed new possibilities in the construction of nanoporous semiconducting superlattices with tunable pore size. Through the combination of metal ions with different oxidation states to provide both overall and local charge neutrality, an effective approach has been demonstrated in the rational synthesis of chalcogenide open framework materials with large and unprecedented supertetrahedral clusters. 相似文献
149.
150.