全文获取类型
收费全文 | 4683篇 |
免费 | 3361篇 |
国内免费 | 871篇 |
专业分类
化学 | 1017篇 |
晶体学 | 110篇 |
力学 | 321篇 |
综合类 | 105篇 |
数学 | 709篇 |
物理学 | 6653篇 |
出版年
2024年 | 65篇 |
2023年 | 126篇 |
2022年 | 156篇 |
2021年 | 168篇 |
2020年 | 128篇 |
2019年 | 171篇 |
2018年 | 142篇 |
2017年 | 155篇 |
2016年 | 218篇 |
2015年 | 228篇 |
2014年 | 551篇 |
2013年 | 378篇 |
2012年 | 415篇 |
2011年 | 443篇 |
2010年 | 456篇 |
2009年 | 526篇 |
2008年 | 578篇 |
2007年 | 464篇 |
2006年 | 436篇 |
2005年 | 425篇 |
2004年 | 402篇 |
2003年 | 314篇 |
2002年 | 241篇 |
2001年 | 240篇 |
2000年 | 163篇 |
1999年 | 170篇 |
1998年 | 161篇 |
1997年 | 155篇 |
1996年 | 136篇 |
1995年 | 112篇 |
1994年 | 92篇 |
1993年 | 77篇 |
1992年 | 99篇 |
1991年 | 90篇 |
1990年 | 63篇 |
1989年 | 58篇 |
1988年 | 34篇 |
1987年 | 32篇 |
1986年 | 8篇 |
1985年 | 14篇 |
1984年 | 9篇 |
1983年 | 8篇 |
1982年 | 8篇 |
排序方式: 共有8915条查询结果,搜索用时 296 毫秒
991.
Improving attosecond pulse reflection by large angle incidence for a periodic multilayer mirror in the extreme ultraviolet region 下载免费PDF全文
The improvement of attosecond pulse reflection by large angle incidence for a periodic multilayer mirror in the extreme ultraviolet region has been discussed. Numerical simulations of both spectral and temporal reflection characteristics of periodic multilayer mirrors under various incident angles have been analyzed and compared. It was found that the periodic multilayer mirror under a larger incidence angle can provide not only higher integrated reflectivity but also a broader reflection band with negligible dispersion, making it possible to obtain better a reflected pulse that has a higher pulse reflection efficiency and shorter pulse duration for attosecond pulse reflection. In addition, by increasing the incident angle, the promotion of attosecond pulse reflection capability has been proven for periodic multilayer mirrors with arbitrary layers. 相似文献
992.
By solving the time-dependent Schro¨dinger equation, the dependence of photoelectron energy spectra on the binding energy of targets, wavelength and the intensity of laser pulse is exhibited and a scaling law of kinetic energy spectra of both the direct and the rescattered photoelectrons is concluded. The scaling law provides a convenient tool to determine the equivalent photoionization process of various atoms or molecules in various laser fields. The verification of the scaling law by independent methods provides incontestable support to the validity of the scaling law. 相似文献
993.
Angular distributions of CH3I fragment ions under the irradiation of a single pulse and trains of ultrashort laser pulses 下载免费PDF全文
The angular distribution of CH3I is investigated experimentally using a single Fourier transform-limited laser pulse and a pulse train, where a 90-fs 800-nm linearly polarized laser field with a moderate intensity of 2.8×1013 W/cm2 is used. The dynamic alignment is demonstrated in a single pulse experiment. Moreover, a pulse train is used to optimize the molecular alignment, and the alignment degree is almost identical to that with the single pulse. The results are analysed by using chirped femtosecond laser pulses, and it demonstrates that the structure of pulse train rather than its effective duration is crucial to the molecular alignment. 相似文献
994.
Density-functional theory study of the effect of pressure on the elastic properties of CaB6 下载免费PDF全文
Under high pressure, the long believed single-phase material CaB6 was latterly discovered to have a new phase tI56. Based on the density-functional theory, the pressure effects on the structural and elastic properties of CaB6 are obtained. The calculated bulk, shear, and Young's moduli of the recently synthesized high pressure phase tI56-CaB6 are larger than those of the low pressure phase. Moreover, the high pressure phase of CaB6 has ductile behaviors, and its ductility increases with the increase of pressure. On the contrary, the calculated results indicate that the low pressure phase of CaB6 is brittle. The calculated Debye temperature indicates that the thermal conductivity of CaB6 is not very good. Furthermore, based on the Christoffel equation, the slowness surface of the acoustic waves is obtained. 相似文献
995.
The behaviors of lead zirconate titanate (PZT) deposited as the dielectric for high-voltage devices are investigated experimentally and theoretically. The devices demonstrate not only high breakdown voltages above 350 V, but also excellent memory behaviors. A drain current-gate voltage (ID-VG) memory window of about 2.2 V is obtained at the sweep voltages of ±10 V for the 350-V laterally diffused metal oxide semiconductor (LDMOS). The retention time of about 270 s is recorded for the LDMOS through a controlled ID-VG measurement. The LDMOS with memory behaviors has potential to be applied in future power conversion circuits to boost the performance of the energy conversion system. 相似文献
996.
A new silicon-on-insulator(SOI)power lateral MOSFET with a dual vertical field plate(VFP)in the oxide trench is proposed.The dual VFP modulates the distribution of the electric field in the drift region,which enhances the internal field of the drift region and increases the drift doping concentration of the drift region,resulting in remarkable improvements in breakdown voltage(BV)and specific on-resistance(Ron,sp).The mechanism of the VFP is analyzed and the characteristics of BV and Ron,spare discussed.It is shown that the BV of the proposed device increases from 389 V of the conventional device to 589 V,and the Ron,sp decreases from 366 m·cm2to 110 m·cm2. 相似文献
997.
The photoluminescence (PL) characteristics of hybrid β-FeSi2/Si and pure β-FeSi2 films fabricated by pulsed laser deposition at 20 K are investigated. The intensity of the 1.54-μm PL from the former is enhanced, but the enhancement vanishes when the excitation wavelength is larger than the widened band gap of Si nanocrystal. Time-resolved PL decay measurements reveal that the lifetime of the photo-excited carriers in the hybrid β-FeSi2/Si film is longer than that in the pure β-FeSi2 film, providing evidence that the PL enhancement results from the resonant charge transfer from nanocrystalline Si to β-FeSi2. 相似文献
998.
Imprints of molecular orbitals using photoelectron angular distribution by strong laser pulses of circular polarization 下载免费PDF全文
We theoretically investigate the strong-field ionization of H+2 molecules in four different electronic states by calculating photoelectron angular distributions in circularly polarized fields. We find that the structure of photoelectron angular distribution depends on the molecular orbital as well as the energy of the photoelectron. The location of main lobes changes with the symmetric property of the molecular orbital. Generally, for molecules with bonding electronic states, the photoelectron's angular distribution shows a rotation of π/2 with respect to the molecular axis, while for molecules with antibonding electronic states, no rotation occurs. We use an interference scenario to interpret these phenomena. We also find that, due to the interference effect, a new pair of jets appears in the waist of the main lobes, and the main lobes or jets of the photoelectron's angular distribution are split into two parts if the photoelectron energy is sufficiently high. 相似文献
999.
We theoretically investigate the propagation of few-cycle laser pulses in resonant two-level dense media with a sub- wavelength structure, which is described by the full Maxwell-Bloch equations without the frame of slowly varying envelope and rotating wave approximations. The input pulses can be shaped into shorter ones with a single or less than one optical cycle. The effect of the parameters of the subwavelength structure and laser pulses is studied. Our study shows that the media with a subwavelength structure can significantly shape the few-cycle pulses into a subcycle pulse, even for the case of chirp pulses as input fields. This suggests that such subwavelength structures have potential application in the shaping of few-cycle laser pulses. 相似文献
1000.
Bipolar resistive switching is studied in BiFe0.95Zn0.05O3 films prepared by pulsed laser deposition on (001) SrTiO3 substrate, with LaNiO3 as the bottom electrode, and Pt as the top electrode. Multiple steps of resistance change are ob- served in the resistive switching process with a slow voltage sweep, indicating the formation/rupture of multiple conductive filaments. A resistive ratio of the high resistance state (HRS) to the low resistance state (LRS) of over three orders of mag- nitude is observed. Furthermore, the conduction mechanism is confirmed to be space-charge-limited conduction with the Schottky emission at the interface with the top Pt electrodes in the HRS, and Ohmic in the LRS. Impedance spectroscopy demonstrates a conductive ferroelectric/interfacial dielectric 2-layer structure, and the formation/rupture of the conductive filaments mainly occurs at the interfacial dielectric layer close to the top Pt electrodes. 相似文献