全文获取类型
收费全文 | 9402篇 |
免费 | 1395篇 |
国内免费 | 1153篇 |
专业分类
化学 | 6839篇 |
晶体学 | 84篇 |
力学 | 583篇 |
综合类 | 81篇 |
数学 | 964篇 |
物理学 | 3399篇 |
出版年
2024年 | 32篇 |
2023年 | 174篇 |
2022年 | 286篇 |
2021年 | 311篇 |
2020年 | 322篇 |
2019年 | 322篇 |
2018年 | 245篇 |
2017年 | 241篇 |
2016年 | 406篇 |
2015年 | 356篇 |
2014年 | 538篇 |
2013年 | 630篇 |
2012年 | 765篇 |
2011年 | 814篇 |
2010年 | 559篇 |
2009年 | 544篇 |
2008年 | 642篇 |
2007年 | 541篇 |
2006年 | 463篇 |
2005年 | 483篇 |
2004年 | 349篇 |
2003年 | 327篇 |
2002年 | 347篇 |
2001年 | 287篇 |
2000年 | 244篇 |
1999年 | 211篇 |
1998年 | 191篇 |
1997年 | 165篇 |
1996年 | 164篇 |
1995年 | 124篇 |
1994年 | 146篇 |
1993年 | 102篇 |
1992年 | 117篇 |
1991年 | 98篇 |
1990年 | 75篇 |
1989年 | 77篇 |
1988年 | 43篇 |
1987年 | 26篇 |
1986年 | 37篇 |
1985年 | 26篇 |
1984年 | 16篇 |
1983年 | 18篇 |
1982年 | 13篇 |
1981年 | 8篇 |
1980年 | 8篇 |
1978年 | 8篇 |
1977年 | 7篇 |
1976年 | 7篇 |
1975年 | 5篇 |
1974年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
ELECTRON TRANSPORT BEHAVIOURS IN THE NITROGEN DIRECT CURRENT GLOW DISCHARGE 总被引:9,自引:0,他引:9 下载免费PDF全文
A Monte Carlo simulation is presented to describe the electron transport behaviours in the nitrogen direct current glow discharge. The energy and angular distributions of the electrons at different positions of the cathode dark space are calculated; their energy and density distribution features throughout the entire discharge are discussed. The influence of molecular vibrational excitation, typical for electron-molecule collisions, has been studied and the elementary process of active species generation has been illustrated. The simulated results reveal that, in the cathode dark space, the high-energy electrons are mainly forward scattering and behave as a high-energy ‘electron beam'. The sharp increase of the number of secondary electrons plays an important role in producing active species at the interface between the cathode dark space and the negative glow region. The vibrational excitation enhances the energy loss of electrons in the negative glow region. 相似文献
93.
本文介绍一台采用双潘宁型多电荷重离子源的200kV重离子加速器,简述它在GaP光探测器的研制、聚合物材料和金属材料的离子注入改性等方面的研究与应用。 相似文献
94.
Qiang Wu Shenyuan Fu Jin Han Pingan Song 《Journal of Macromolecular Science: Physics》2013,52(11):1591-1602
The nonisothermal crystallization behavior of polypropylene (PP) and PP-fullerene (C60) nanocomposites was studied by differential scanning calorimetry (DSC). The kinetic models based on the Jeziorny, Ozawa, and Mo methods were used to analyze the nonisothermal crystallization process. The onset crystallization temperature (Tc), half-time for the crystallization (t1/2), kinetic parameter (F(T)) by the Mo method and activation energy (ΔE) estimated by the Kissinger method showed that C60 accelerates the crystallization of PP, implying a nucleating role of C60. Furthermore, due to the reduced viscosity of PP by adding 5% C60, the parameters of crystallization kinetics for the PP-5%C60 nanocomposites changed remarkably relative to that of neat PP and when lower contents of C60 were added to PP. 相似文献
95.
Tianyu Sun Jianyong Ma Xiaoyong Fu Jianpeng Wang Yunxia Jin Jianda Shao Zhengxiu Fan 《中国光学快报(英文版)》2010,(5):447-448
<正>A guided-mode resonance(GMR) filter with the same material(Ta_2O_5) for both the grating layer and the waveguide layer is designed and fabricated.This simple structure is easy to fabricate and can avoid the defects at the grating/waveguide interface using different materials.The spectral response measured with a Lambda 900 spectrophotometer under normal incidence for TE waves exhibits a peak reflectance exceeding 80%at the wavelength of 1040 nm with a full-width half-maximum(FWHM) linewidth of 23 nm.We evaluate the deviations of the fabricated structure from the designed parameters. 相似文献
96.
直接由标量基本微元(点源)和矢量基本微元(电流元等)的对称性和两个基本假设讨论基本微元产生的场矢量的性质。 相似文献
97.
The surface modification of multi-walled carbon nanotubes (MWCNTs) by O2 plasma was carried out in this study. In order to achieve a relatively homogeneous treatment of MWCNTs powder, a rotating barrel fixed between the two discharge electrodes was used. The effect of plasma treatment parameters, such as power, time, and positions of samples (inside and outside the barrel), on the morphology and structure of MWCNTs surface was systematically analyzed by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The results showed that the direct discharge (outside the barrel) could result in not only a quick grafting of polar functional groups but also an easy damage of MWCNTs after longer time, particularly under intensive power. It was found that the surface of MWCNTs powder might be changed in three steps—expansion (loosed structure formed), peel off and oxidization with increasing of treatment time during the irradiation. In this way, a complete purification of MWCNTs powder could be finished within 30 min via plasma treatment. Our work suggested that plasma treatment could be a simple and nonpolluting method for a large scale purification of MWCNTs. 相似文献
98.
A photonic approach for microwave/millimeter-wave (MMW) frequency measurement is proposed and demonstrated based on stimulated
Brillouin scattering (SBS) of a 20-km standard single mode fiber (SSMF). After the MMW signal is modulated to a laser source
with two sidebands using optical carrier suppression (OCS) modulation, its frequency can be easily measured by monitoring
the SBS-induced amplification with a power meter. Due to the 1-pm resolution of a tunable pump laser source, a frequency measurement
range of 1–40 GHz is demonstrated in our experiment with a frequency resolution of 125 MHz. We believe the frequency measurement
range can be further extended to satisfy photonic radar front-end processing application. 相似文献
99.
We design a Nd:YAG module with symmetrical LD side-pumped structure in a periodical arrangement between circular LD arrays and holders. This novel design has great potential to be used in compact and miniature laser systems. Design optimization and simulation on thermal effects have been performed. An experiment has also been carried out. The experiment results indicate the all-solid-state laser with the-Nd:YAG module can stably operate in the range of 10–30 Hz with no controlling temperature by TE cooler. The laser beam had a divergence angle less than 3.8 mrad and a maximum output pulse of 174 mJ has been obtained at the pump current of 50 A and working frequency of 23 Hz, corresponding to optical-optical conversion efficiency of 40.2%. 相似文献
100.
Experimental study has been performed on nanosecond (ns) laser ablation of silicon at 1064 nm, through which a so-called “multi-pulse enhancement effect” has been revealed, which has been rarely reported in literature. The major features of this effect are: (1) for multi-pulse laser ablation at the same spatial location, the ablation efficiency increases as the pulse number increases and the pulse-to-pulse temporal distance decreases; (2) for multi-pulse ablation performed sequentially at a group of locations, the ablation quality and efficiency starting from the second location can be significantly enhanced if the distance between adjacent locations is sufficiently small. Further study is needed to confirm and understand the underlying physical mechanism for the multi-pulse enhancement effect, which can be utilized to significantly improve the quality and efficiency of laser silicon micromachining using the low-cost and low-energy-consumption infrared ns lasers. This may decrease the cost and energy consumption of many relevant areas, such as the solar cell industry. 相似文献