全文获取类型
收费全文 | 7439篇 |
免费 | 623篇 |
国内免费 | 983篇 |
专业分类
化学 | 2142篇 |
晶体学 | 35篇 |
力学 | 590篇 |
综合类 | 76篇 |
数学 | 408篇 |
物理学 | 1734篇 |
无线电 | 4060篇 |
出版年
2024年 | 1篇 |
2023年 | 1篇 |
2022年 | 5篇 |
2021年 | 1篇 |
2020年 | 1篇 |
2018年 | 20篇 |
2017年 | 3篇 |
2016年 | 7篇 |
2015年 | 2篇 |
2014年 | 397篇 |
2013年 | 47篇 |
2012年 | 4篇 |
2011年 | 20篇 |
2010年 | 4篇 |
2009年 | 9篇 |
2008年 | 3篇 |
2007年 | 6篇 |
2006年 | 4篇 |
2005年 | 3篇 |
2004年 | 4篇 |
2003年 | 614篇 |
2002年 | 2525篇 |
2001年 | 2729篇 |
2000年 | 530篇 |
1999年 | 410篇 |
1998年 | 323篇 |
1997年 | 96篇 |
1996年 | 168篇 |
1995年 | 205篇 |
1994年 | 144篇 |
1993年 | 183篇 |
1992年 | 132篇 |
1991年 | 142篇 |
1990年 | 163篇 |
1989年 | 129篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1982年 | 1篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1965年 | 5篇 |
排序方式: 共有9045条查询结果,搜索用时 13 毫秒
991.
Antitumour Acitivty of Chitosan Hydrogen Selenites 总被引:1,自引:0,他引:1
Chitosans reacted with selenious acid to prepare chitosan hydrogen selenites, which were found to be growth-inhibitory against sarcoma 180 solid tumor. The results indicated that the activity also depended on the molecular weight of chitosan supports. 相似文献
992.
微波消解试样催化极谱法测定香茹和黑木耳中痕量锗 总被引:1,自引:0,他引:1
采用双层聚四氟乙烯密闭容器,以HNO3-HClO4为溶解试剂,CaO为外层吸附剂,微波消解香菇及黑木耳试样。在草酸介质中,当有少量高氨酸存在时,锗(Ⅳ)-苏木精-钒(Ⅳ)体系可产生一灵敏的吸附催化波,峰电位在-0.59V(vs.SCE)处。锗浓度在0ng-300ng/25mL范围内与峰电流呈良好的线性关系,检出限为4.5ng/25mL,适宜于香菇和黑木耳中痕量锗的测定。 相似文献
993.
本首先介绍了IDC网络管理安全的有关知识和技术,并结合城域局IDC建设的实践经验,阐述了简单可行的实施方案及其设计与实现,具有较强的可操作性和应用参考性。 相似文献
994.
995.
996.
997.
A self-consistent hybrid Monte Carlo Fluid model is presented to describe the nitrogen dc glow discharge.The movement of fast electrons is simulated by the Monte Carlo method while the dynamics of slow electrons and ions is by fluid equations.The spatial features of the charged species and the corresponding electric field throughout the discharge have been calculated,which include the creation rates of ions and slow electrons,densities of the charged species,the electric field and the potential distribution.These closely related results can give a selfconsistent explanation of the discharge characteristics throughout the space of nitrogen dc glow discharge.The calculated ion density is also compared with the corresponding experimental result. 相似文献
998.
Due to interaction with the vacuum of the radiation field,near-degenerate lower levels in a Λ system have an additional coherence term,the spontaneously generated coherence (SGC) term.For such a system,we investigate the effect of the relative phase between two coherent fields on the inversionless gain in the presence of the SGC.We find that the inversionless gain,which stems from both SGC and dynamically induced coherence,can be modulated by the relative phase. 相似文献
999.
A Pseudospectral Time—Domain Algorithm for Calculating the Band Structure of a Two—Dimensional Photonic Crystal 下载免费PDF全文
A pseudospectral time-domain (PSTD) method is developed for calculating the band structure of a two-dimensional photonic crystal.Maxwell‘s equations are rewritten in terms of period fields by using the Bloch theorem.Instead of spatial finite differences,the fast Fourier transform is used to calculate the spatial derivatives.To reach a similar accuracy,fewer sample points are required in the present PSTD method as compared to the conventional finite-difference time-domain methods.Our numerical simulation shows that the present PSTD method is an efficient and accurate method for calculating the band structure of a photonic crystal. 相似文献
1000.
Isospin effects of the mean field and two-body collision on the fragmentation as well as their dependences on the momentum-dependent interaction at intermediate energy heavy ion collisions are studied by using an isospindependent quantum molecular dynamics model.We find the prominent isospin effects of the multiplicity of the intermediate mass fragments Ninf,where Nimf depends sensitively on the isospin effect of the in-medium nucleonnucleon cross section and weakly on the variation of symmetry potential in the intermediate energy region.The momentum dependence interaction enhances the sensitivity of Nimf on the isospin effect of two-body collision. 相似文献