全文获取类型
收费全文 | 15154篇 |
免费 | 4941篇 |
国内免费 | 1071篇 |
专业分类
化学 | 3225篇 |
晶体学 | 236篇 |
力学 | 741篇 |
综合类 | 87篇 |
数学 | 266篇 |
物理学 | 16611篇 |
出版年
2024年 | 19篇 |
2023年 | 90篇 |
2022年 | 241篇 |
2021年 | 294篇 |
2020年 | 313篇 |
2019年 | 237篇 |
2018年 | 290篇 |
2017年 | 451篇 |
2016年 | 553篇 |
2015年 | 435篇 |
2014年 | 843篇 |
2013年 | 1384篇 |
2012年 | 987篇 |
2011年 | 1280篇 |
2010年 | 884篇 |
2009年 | 1051篇 |
2008年 | 1178篇 |
2007年 | 1240篇 |
2006年 | 1117篇 |
2005年 | 930篇 |
2004年 | 888篇 |
2003年 | 753篇 |
2002年 | 799篇 |
2001年 | 614篇 |
2000年 | 644篇 |
1999年 | 558篇 |
1998年 | 492篇 |
1997年 | 403篇 |
1996年 | 366篇 |
1995年 | 305篇 |
1994年 | 260篇 |
1993年 | 252篇 |
1992年 | 228篇 |
1991年 | 169篇 |
1990年 | 139篇 |
1989年 | 105篇 |
1988年 | 67篇 |
1987年 | 76篇 |
1986年 | 47篇 |
1985年 | 35篇 |
1984年 | 35篇 |
1983年 | 16篇 |
1982年 | 25篇 |
1981年 | 20篇 |
1980年 | 13篇 |
1979年 | 6篇 |
1977年 | 5篇 |
1976年 | 3篇 |
1974年 | 3篇 |
1973年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Dynamical analysis,circuit realization,and application in pseudorandom number generators of a fractional-order laser chaotic system 下载免费PDF全文
Chenguang Ma 《中国物理 B》2021,30(12):120504-120504
A new five-dimensional fractional-order laser chaotic system (FOLCS) is constructed by incorporating complex variables and fractional calculus into a Lorentz-Haken-type laser system. Dynamical behavior of the system, circuit realization and application in pseudorandom number generators are studied. Many types of multi-stable states are discovered in the system. Interestingly, there are two types of state transition phenomena in the system, one is the chaotic state degenerates to a periodical state, and the other is the intermittent chaotic oscillation. In addition, the complexity of the system when two parameters change simultaneously is measured by the spectral entropy algorithm. Moreover, a digital circuit is design and the chaotic oscillation behaviors of the system are verified on this circuit. Finally, a pseudo-random sequence generator is designed using the FOLCS, and the statistical characteristics of the generated pseudo-random sequence are tested with the NIST-800-22. This study enriches the research on the dynamics and applications of FOLCS. 相似文献
2.
Pattern transition and regulation in a subthalamopallidal network under electromagnetic effect 下载免费PDF全文
Although the significant roles of magnetic induction and electromagnetic radiation in the neural system have been widely studied, their influence on Parkinson's disease (PD) has yet to be well explored. By virtue of the magnetic flux variable, this paper studies the transition of firing patterns induced by magnetic induction and the regulation effect of external magnetic radiation on the firing activities of the subthalamopallidal network in basal ganglia. We find: (i) The network reproduces five typical waveforms corresponding to the severity of symptoms: weak cluster, episodic, continuous cluster, episodic, and continuous wave. (ii) Magnetic induction is a double-edged sword for the treatment of PD. Although the increase of magnetic coefficient may lead the physiological firing activity to transfer to pathological firing activity, it also can regulate the pathological intensity firing activity with excessive β-band power transferring to the physiological firing pattern with weak β-band power. (iii) External magnetic radiation could inhibit continuous tremulous firing and β-band power of subthalamic nucleus (STN), which means the severity of symptoms weakened. Especially, the bi-parameter plane of the regulation region shows that a short pulse period of magnetic radiation and a medium level of pulse percentage can well regulate pathological oscillation. This work helps to understand the firing activity of the subthalamopallidal network under electromagnetic effect. It may also provide insights into the mechanisms behind the electromagnetic therapy of PD-related firing activity. 相似文献
3.
Xiaofan Zhang 《中国物理 B》2022,31(11):114209-114209
We theoretically investigate the yield enhancement of elliptical high harmonics in the interaction of molecules with bicircular laser pulses by solving the time-dependent Schrödinger equation. It is shown that by adjusting the relative intensity ratio of the two bicircular field components in specific ranges the yield of the molecular high harmonics for the plateau and cutoff regions can be respectively enhanced. To analyze this enhancement phenomenon, we calculate the weights of the electron classical trajectories. Additionally, we also study the ellipticity distribution of harmonics for different intensity ratios. We find that these enhanced harmonics are elliptically polarized, which we mainly attribute to the recombination dipole moment of the major weighted trajectories. These enhanced elliptical extreme ultraviolet and soft x-ray radiations may serve as essential tools for exploring the ultrafast dynamics in magnetic materials and chiral media. 相似文献
4.
The possibility of realizing SASE Free Election Laser in x-ray waveband with EM-wave wiggler is studied in this paper. SASE effect including saturation length, saturation power and nonlinear process is explored through a 3-D simulation code. A utilization of seed light from laser plasma x-ray is also analyzed, which demonstrates the feature of shortening the interaction length for saturation. The results show that sizeable output power of x-ray laser would be generated with a middle energy electron beam. 相似文献
5.
W. L. Liang B. K. A. Ngoi L. E. N. Lim K. Venkatakrishnan C. W. Hee 《Optics & Laser Technology》2003,35(4):285-290
In this paper, integration of interference phenomenon into femtosecond laser micromachining was reported as the femtosecond laser pulses were reshaped spatially to perform ablation. The generation of circular interference pattern was demonstrated by overlapping infrared femtosecond laser pulses. The interference pattern was subsequently focused on a copper substrate to ablate microstructures of concentric circular rings. The present technique is expected to open up new applications in the areas of rapid fabrication of micro-Fresnel lenses, hybrid microlenses and lens arrays. 相似文献
6.
双掺(Tm3+,Tb3+)LiYF4激光器1.5 μm波长激光阈值分析 总被引:1,自引:0,他引:1
由速率方程推出了双掺(Tm^3 ,Tb^3 )离子准四能级系统的激光阈值解析式,讨论了Tm^3 和Tb^3 离子之间的相互作用。分析了1.5μm波长附近的激光阈值和Tm^3 、Tb^3 离子的掺杂原子数分数及晶体长度的关系。结果表明,对于对应Tm^3 离子^3H4→^3F4跃迁的约1.5μm波长的激光,激活离子Tm^3 的掺杂原子数分数过大时,交叉弛豫作用将使系统阈值迅速增加。Tb^3 离子的加入,一方面能抽空激光下能级,起到降低阈值的作用;另一方面亦减少了激光上能级的寿命,使阈值升高。故Tb^3 离子有最佳掺杂原子数分数。对于Tm原子数分数为y=0.01的Tm:LiYF4晶体,Tb^3 离子的最佳掺杂原子数分数为0.002左右,同时表明,激光阈值与晶体长度有关。最佳晶体长度与Tm^3 、Tb^3 离子的掺杂原子数分数以及晶体的衍射损耗和吸收损耗有关。 相似文献
7.
用波导产生倍频波时,如果倍频波进入辐射模区,仍然有相匹配问题。契伦可夫辐射式倍频不是自动地实现相匹配的。相匹配要求导波基波模式场,倍频传输场(自由波),倍频触发场,以及经多次反射透射后的辐射场的迭加形成的总辐射场处于同步的相匹配状态。根据这个相匹配的分析,提出波导契伦可夫相匹配的特有的方法,那就是对波导的模色散进行设计,并指出非对称波导的特有优点,是改变一个边界上的反射相变,即选择不同色散的线性材料作包层,由此可得到相匹配的高效契伦可夫倍频辐射。 相似文献
8.
9.
10.
The dependence of the beam propagation factor (M
2 parameter) with the absorbed pump power in the case of monolithic microchip laser under face-cooled configuration is extensively
studied. Our investigations show that the M
2 parameter is related to the absorbed pump power through two parameters (α and β) whose values depend on the laser material properties and laser configuration. We have shown that one parameter arises due
to the oscillation of higher order modes in the microchip cavity and the other parameter accounts for the spherical aberration
associated with the thermal lens induced by the pump beam. Such dependency of M
2 parameter with the absorbed pump power is experimentally verified for a face-cooled monolithic microchip laser based on Nd3+ -doped GdVO4 crystal and the values of α and β parameters were estimated from the experimentally measured data points. 相似文献