全文获取类型
收费全文 | 1166篇 |
免费 | 301篇 |
国内免费 | 570篇 |
专业分类
化学 | 890篇 |
晶体学 | 56篇 |
力学 | 144篇 |
综合类 | 47篇 |
数学 | 219篇 |
物理学 | 681篇 |
出版年
2024年 | 2篇 |
2023年 | 11篇 |
2022年 | 43篇 |
2021年 | 41篇 |
2020年 | 41篇 |
2019年 | 29篇 |
2018年 | 34篇 |
2017年 | 58篇 |
2016年 | 37篇 |
2015年 | 79篇 |
2014年 | 68篇 |
2013年 | 102篇 |
2012年 | 99篇 |
2011年 | 124篇 |
2010年 | 131篇 |
2009年 | 107篇 |
2008年 | 166篇 |
2007年 | 106篇 |
2006年 | 126篇 |
2005年 | 120篇 |
2004年 | 70篇 |
2003年 | 62篇 |
2002年 | 60篇 |
2001年 | 62篇 |
2000年 | 71篇 |
1999年 | 36篇 |
1998年 | 24篇 |
1997年 | 9篇 |
1996年 | 19篇 |
1995年 | 16篇 |
1994年 | 8篇 |
1993年 | 10篇 |
1992年 | 10篇 |
1991年 | 4篇 |
1990年 | 6篇 |
1989年 | 3篇 |
1988年 | 7篇 |
1987年 | 9篇 |
1986年 | 5篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1981年 | 4篇 |
1979年 | 3篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1974年 | 1篇 |
排序方式: 共有2037条查询结果,搜索用时 31 毫秒
911.
岳嵘 《数学的实践与认识》2012,42(19)
非奇H-矩阵在数值分析和矩阵理论的研究中非常重要,但实际判定一个非奇异H-矩阵却非常困难.给出一类非奇异H-矩阵新的判定条件,改进了近期的相关结果,并用数值例子说明了结果判定范围的更广泛性. 相似文献
912.
913.
采用两种不同的溶剂热路径合成出了不同形貌和尺寸的CdS纳米晶, 一种是以无水乙二胺(en) 为溶剂, CdCl2·2.5H2O和硫脲(H2NCSH2N) 为镉源和硫源, 在不同反应温度(160 ℃-220 ℃ 下制备出了CdS纳米晶, 讨论温度对CdS纳米晶生长的影响; 另一种是以en为溶剂, 将在160 ℃下合成的产物在200 ℃下原位再结晶生长2-8 h, 分析原位生长时间对CdS纳米晶生长的影响. 通过X射线衍射(XRD)、 扫描电子电镜(SEM) 和透射电子电镜(TEM) 等表征产物的物相、 形貌和微结构, 分析可知: 两种路线合成的产物均为六方相CdS; 当温度为160 ℃时, 产物形貌为纳米颗粒状, 当温度高于160 ℃时, 产物为CdS纳米棒状; 同时, 在200 ℃下原位再结晶生长不同时间后发现产物形貌由纳米颗粒转变为纳米棒, 通过场发射扫描电镜(HRTEM) 分析可知: 纳米棒是由零维纳米颗粒自组装而成. 最后, 讨论了影响产物CdS纳米晶形貌转变的因素和纳米棒的生长机理. 相似文献
914.
Generation of broadly tunable picosecond mid-infrared laser and sensitive detection of a mid-infrared signal by parametric frequency up-conversion in MgO:LiNbO3 optical parametric amplifiers
下载免费PDF全文
![点击此处可从《中国物理 B》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Picosecond optical parametric generation and amplification in the near-infrared region within 1.361-1.656 μm and the mid-infrared region within 2.976-4.875 μm is constructed on the basis of bulk MgO:LiNbO 3 crystals pumped at 1.064 μm.The maximum pulse energy reaches 1.3 mJ at 1.464 μm and 0.47 mJ at 3.894 μm,corresponding to a pumpto-idler photon conversion efficiency of 25%.By seeding the hard-to-measure mid-infrared radiation as the idler in the optical parametric amplification and measuring the amplified and frequency up-converted signal in the near-infrared or even visible region,one can measure very week mid-infrared radiation with ordinary detectors,which are insensitive to mid-infrared radiation,with a very high gain.A maximum gain factor of about 7 脳 10 7 is achieved at the mid-infrared wavelength of 3.374 μm and the corresponding energy detection limit is as low as about 390 aJ per pulse. 相似文献
915.
Generation of broadly tunable picosecond mid-infrared laser and sensitive detection of a mid-infrared signal by parametric frequency up-conversion in MgO:LiNbO<sub>3</sub> optical parametric amplifiers
下载免费PDF全文
![点击此处可从《中国物理 B》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Picosecond optical parametric generation and amplification in the near-infrared region within 1.361-1.656 μm and the mid-infrared region within 2.976-4.875 μm is constructed on the basis of bulk MgO:LiNbO 3 crystals pumped at 1.064 μm.The maximum pulse energy reaches 1.3 mJ at 1.464 μm and 0.47 mJ at 3.894 μm,corresponding to a pumpto-idler photon conversion efficiency of 25%.By seeding the hard-to-measure mid-infrared radiation as the idler in the optical parametric amplification and measuring the amplified and frequency up-converted signal in the near-infrared or even visible region,one can measure very week mid-infrared radiation with ordinary detectors,which are insensitive to mid-infrared radiation,with a very high gain.A maximum gain factor of about 7 × 10 7 is achieved at the mid-infrared wavelength of 3.374 μm and the corresponding energy detection limit is as low as about 390 aJ per pulse. 相似文献
916.
917.
To monitor the beam profile at the end of the linac non-destructively, a wire scanner as a new diagnostic instrument was designed, manufactured and installed in 2007. Since then, several measurements have been carried out using this device. This paper describes the whole system of the wire scanner and the testing results. 相似文献
918.
We study the dynamic behavior of marginal metallic glass-forming liquids Al-Ni-M (M=La, Pr, Nd) in terms of liquid fragility in high and low temperature regions. The liquids are extremely fragile above the liquidus temperature T liq, but become rather strong near the glass transition temperature Tg. The strength of the transition is inversely correlated with the fragility index at Tg. This relation is discussed in terms of potential energy landscape. 相似文献
919.
Bending Loss Calculation of a Dielectric-Loaded Surface Plasmon Polariton Waveguide Structure
下载免费PDF全文
![点击此处可从《中国物理快报》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Based on full 3D finite element method simulations, the transmission of a dielectric-loaded surface plasmon polariton waveguide (DLSPPW) based 1/4 circle is calculated for a 90° bend model and a 270° bend model, respectively. It is found that the 270° bend model gives almost pure bending loss while the 90° bend model contains additional coupling loss. The models are applied to deduce the loss and unloaded quality factor of DLSPPW based waveguide ring resonators (WRRs) and the results of the 270° bend model agree well with direct simulating results of the WRRs. Thus the 270° bend model gives a fast and simple way to calculate bending loss and it is helpful for WRR design because no wavelength scan is needed. 相似文献
920.
采用Czochralski 法生长出光学质量的BaWO4:Tm3+单晶,利用X粉末衍射实验确定了不同掺杂浓度晶体的晶胞参数.测定了晶体的室温吸收光谱,应用Juud-Ofelt理论,拟合了光谱的3个强度参数,其值分别为Ω2=404×10-20cm2,Ω4=0509×10-20cm2,Ω关键词:
4:Tm3+单晶')" href="#">BaWO4:Tm3+单晶
吸收谱
光谱参数
上转换发光 相似文献