全文获取类型
收费全文 | 324篇 |
免费 | 181篇 |
国内免费 | 165篇 |
专业分类
化学 | 212篇 |
晶体学 | 11篇 |
力学 | 21篇 |
综合类 | 45篇 |
数学 | 70篇 |
物理学 | 311篇 |
出版年
2024年 | 7篇 |
2023年 | 33篇 |
2022年 | 38篇 |
2021年 | 34篇 |
2020年 | 32篇 |
2019年 | 26篇 |
2018年 | 40篇 |
2017年 | 31篇 |
2016年 | 33篇 |
2015年 | 24篇 |
2014年 | 35篇 |
2013年 | 33篇 |
2012年 | 20篇 |
2011年 | 21篇 |
2010年 | 19篇 |
2009年 | 23篇 |
2008年 | 31篇 |
2007年 | 27篇 |
2006年 | 26篇 |
2005年 | 15篇 |
2004年 | 21篇 |
2003年 | 11篇 |
2002年 | 13篇 |
2001年 | 5篇 |
2000年 | 14篇 |
1999年 | 11篇 |
1998年 | 5篇 |
1997年 | 7篇 |
1996年 | 2篇 |
1995年 | 8篇 |
1994年 | 3篇 |
1993年 | 4篇 |
1991年 | 1篇 |
1990年 | 6篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1984年 | 1篇 |
1983年 | 1篇 |
排序方式: 共有670条查询结果,搜索用时 15 毫秒
91.
92.
AlGaInAs/InP coupled-circular microlasers with radius of 10- and 2-μm width middle bus waveguide are fabricated by photolithography and inductively coupled plasma etching techniques. Room-temperature continuous-wave single-mode operation is realized with an output power of 0.17 mW and a side-mode suppression ratio of 23 dB at 45 mA. A longitudinal mode interval of 11 nm is obtained from the lasing spectra, and mode Q factor of 6.2×10 3 is estimated from 3-dB width of a minor peak near the threshold current. The mode characteristics are simulated by finite-difference time-domain technique for coupled- circular resonators. The results show that, in addition to the coupled modes, high-radial-order whispering gallery modes with travelling wave behaviors can also have high Q factors in the coupled-circular resonators with a middle bus waveguide. 相似文献
93.
在多处理机系统中,处理机之间的连接关系和任务对通讯需要的匹配程度是影响系统性能的重要因素,不同任务的需要往往是大相径庭的.因此,多处理机系统的可重构能力是提高它的效率和性能价格比的一个重要关键.本文提出了一个基于三维MESH网连接的可重构计算机系统RCS,它属于并行MIMD计算机系统,在处理机之间提供了灵活的连接机制,能够有效地实现各种计算结构的重构,并且能够实现处理机级和进程级的容错. 相似文献
94.
张穗萌 《原子与分子物理学报》2004,21(Z1):154-156
在前期工作的基础上,当初通道使用具有有效电荷库仑波时,完成了电子入射离化氦原子三重微分截面的理论推导.计算表明初通道库仑场对较低入射能量情况下,(e,2e)过程的三重微分截面有较大影响. 相似文献
95.
中高能电子入射单电离He原子过程中屏蔽效应的理论研究 总被引:1,自引:1,他引:0
这篇文章用3C和DS3C模型,在不同几何条件下研究了中高能电子入射单电离He原子的三重微分截面(TDCS),将计算结果与早期的测量和最新的绝对测量结果进行了比较;分析了有效电荷对三重微分截面影响.研究表明:在中高入射能下,截面的角分布由binary峰和recoil峰组成,末态电子与电子之间的排斥作用对峰的大小有显著贡献.更进一步,修正后的binary峰的幅值对入射电子能量E_0和散射电子偏角θ_1的变化比较敏感. 相似文献
96.
A novel slotted helix slow-wave structure (SWS) is proposed to develop a high power, wide-bandwidth, and high reliability millimeter-wave traveling-wave tube (TWT). This novel structure, which has higher heat capacity than a conven- tional helix SWS, evolves from conventional helix SWS with three parallel rows of rectangular slots made in the outside of the helix tape. In this paper, the electromagnetic characteristics and the beam-wave interaction of this novel structure operating in the Ka-band are investigated. From our calculations, when the designed beam voltage and beam current are set to be 18.45 kV and 0.2 A, respectively, this novel circuit can produce over 700-W average output power in a frequency range from 27.5 GHz to 32.5 GHz, and the corresponding conversion efficiency values vary from 19% to 21.3%, and the maximum output power is 787 W at 30 GHz. 相似文献
97.
A prototype laser ion source that could demonstrate the possibility of producing intense pulsed high charge state ion beams has been established with a commercial Nd:YAG laser (Emax=3 J,1064 nm,8-10 ns) to produce laser plasma for the research of Laser Ion Source (LIS). At the laser ion source test bench,high purity (99.998%) aluminum and lead targets have been tested for laser plasma experiment. An Electrostatic Ion Analyzer (EIA) and Electron Multiply Tube (EMT) detector were used to analyze the charge state and energy distribution of the ions produced by the laser ion source. The maximum charge states of Al12+ and Pb7+ were achieved. The results will be presented and discussed in this paper. 相似文献
98.
We study the response function of the neutron wall for 300 MeV neutrons with GEANT4 simulations. The methods to find the correct neutron incident position and time are discussed, and the neutron emission angle and energy are reconstructed and compared with the simulation. 相似文献
99.
介绍了一种全新的基于飞秒激光局域场加强效应的纳米加工技术,通过使用了微焦级别脉宽为130 fs、波长800 nm的飞秒激光照射于原子力显微镜的探针针尖,利用其局域场加强效应在金薄膜表面加工出各种纳米图形。对加工参数对加工线宽的影响中,我们发现了随着加工能量的减小和加工速度的不断增大将导致加工线宽不断减小,最终达到了极限线宽(~10 nm)。这项技术可以广泛的应用与各种材料的加工中,尤其适合各种金属薄膜的加工,特别是结合了现有的自动化控制系统更是可以加工出任意复杂的二维纳米图形。 相似文献
100.
L-Shell X-Ray Yields and Production Cross Sections of Zr and Mo Bombarded by Slow Highly Charged Ar16+ Ions 下载免费PDF全文
The L-shell x-ray yields of Zr and Mo bombarded by slow Ar16+ ions are measured. The energy of the Ar^16+ ions ranges from about 150 keV to 350 keV. The L-shell x-ray production cross sections of Zr and Mo are extracted from these yields data. The explanation of these experimental results is in the framework of the adiabatic direct- ionization and the binding energy modified BEA approximation. We consider, in the slow asymmetric collisions such as Ar and Mo/Zr, the transient united atoms (UA) are formed during the ion-surface interaction and the direct-ionization is the main mechanism for the inner-shell vacancy production. Generally, the theoretical results are in good agreement with the experimental data. 相似文献