全文获取类型
收费全文 | 10088篇 |
免费 | 4693篇 |
国内免费 | 1659篇 |
专业分类
化学 | 1503篇 |
晶体学 | 410篇 |
力学 | 511篇 |
综合类 | 62篇 |
数学 | 85篇 |
物理学 | 13869篇 |
出版年
2024年 | 81篇 |
2023年 | 275篇 |
2022年 | 318篇 |
2021年 | 353篇 |
2020年 | 246篇 |
2019年 | 273篇 |
2018年 | 230篇 |
2017年 | 334篇 |
2016年 | 341篇 |
2015年 | 493篇 |
2014年 | 899篇 |
2013年 | 622篇 |
2012年 | 659篇 |
2011年 | 877篇 |
2010年 | 675篇 |
2009年 | 773篇 |
2008年 | 959篇 |
2007年 | 745篇 |
2006年 | 787篇 |
2005年 | 627篇 |
2004年 | 679篇 |
2003年 | 517篇 |
2002年 | 515篇 |
2001年 | 437篇 |
2000年 | 456篇 |
1999年 | 380篇 |
1998年 | 369篇 |
1997年 | 409篇 |
1996年 | 335篇 |
1995年 | 340篇 |
1994年 | 278篇 |
1993年 | 250篇 |
1992年 | 230篇 |
1991年 | 196篇 |
1990年 | 209篇 |
1989年 | 156篇 |
1988年 | 52篇 |
1987年 | 41篇 |
1986年 | 8篇 |
1985年 | 11篇 |
1984年 | 1篇 |
1983年 | 3篇 |
1982年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
蓝宝石具有超强硬度及耐腐蚀、耐高温、在紫外-红外波段具有良好的透光性等优点,在军工业以及医疗器械方面具有广泛的应用前景.然而这些优点又对蓝宝石的机械加工或化学腐蚀加工带来困难.飞秒激光脉冲具有热损伤小、加工分辨率高、材料选择广等特点,被广泛应用于固体材料改性和高精度三维微纳器件加工.本文提出了利用飞秒激光多光子吸收特性在蓝宝石表面实现超越光学衍射极限的精细加工.利用聚焦后的波长为343 nm的飞秒激光,配合高精密三维压电位移台,实现激光焦点和蓝宝石晶体的相对三维移动,在蓝宝石晶体衬底上进行精确扫描,得到了线宽约61 nm的纳米线,纳米线间的最小间距达到142 nm左右.利用等离子体模型解释了加工得到的纳米条纹的产生原因,研究了激光功率、扫描速度对加工分辨率的影响.最终本工作实现了超越光学衍射极限的加工精度,为实现利用飞秒激光对高硬度材料的微纳结构制备提供了参考. 相似文献
992.
Generation and Modulation of Phase Difference of Output Intensities in a Feedback Nd:YAG Laser with an Extracavity Waveplate Rotated 总被引:1,自引:0,他引:1 下载免费PDF全文
External anisotropic feedback effects on the phase difference behaviour of output intensities in a microchip Nd:YAG laser are presented. By rotating a quarter wave plate placed in the external cavity, the angle between laser initial polarization direction and o-axis of the wave plate is tuned from -45°to 45°, which results in variable extra-cavity birefringence along two orthogonal detection directions. With only one optical path and one wave plate, laser intensities of the two orthogonal directions, both modulated by the external cavity length, are output with a tunable phase difference, which can be continuously changed from zero to twice as large as that of the waveplate. Experimental results as well as a theoretical analysis based on Fabry-Perot cavity equivalent model and the refractive index ellipsoid, are presented. The potential applications of this phenomenon are also discussed. 相似文献
993.
用ZnO陶瓷靶,采用脉冲激光沉积(PLD)技术在c-Al2O3衬底上制备了ZnO薄膜。通过不同温度下光致发光(PL)光谱的测量,对样品的紫外发光机理进行研究。 在较低温度(10 K)下的PL光谱中,观测到一个位于3.354 eV处的束缚激子(D0X)发射,随着温度的升高(~50 K),在D0X的高能侧观测到了自由激子的发射峰。在10 K温度下,3.309 eV处出现了一个较强的发光带A,此发光带强度随着温度升高先增大然后减小,并且一直延续到室温。重点讨论了此发光带的起源,并认为A带可归属于自由电子-受主之间的复合发射。 相似文献
994.
Polarization self-modulation effect in a free oscillated Nd:YAG laser is investigated after a quarter wave plate is introduced independently in the two positions of the cavity. As described in the previous experiments, the intensity components in the orthogonal directions are modulated with a period of the round-trip time or twice. Different pulse shapes reveal that the seed field from the spontaneous emission is not uniform and seems to be stochastic for each pulse. 相似文献
995.
996.
研究了Er∶Yb∶YCa4O(BO3)3(简称Er∶Yb∶YCOB)的多晶制备和单晶生长,用提拉法生长出光学质量优良的Er∶Yb∶YCOB单晶,测量了其吸收光谱和荧光光谱,分析了其能级和泵浦原理,并进行了以激光二极管为抽运源的激光试验,实现了Er∶Yb∶YCOB晶体的在1.55μm附近110mW的激光输出,且斜效率达18.9;. 相似文献
998.
Laser-phase determination methods and transfer equations for direct temporal structure measure- ments of atto- and femtosecond XUV pulses 下载免费PDF全文
In this paper the laser-phase determination methods and transfer equations are
presented to directly reconstruct the detailed temporal structures
of ultra-short extreme ultraviolet (xuv) pulses from the measured
photoelectron energy spectra (PES). Each transfer equation
includes one of PID
(proportional-integral-differential) terms of PES. The
intensity and instantaneous frequency of attosecond xuv can be
retrieved from the integral term of PES. The
intensity profiles of narrow bandwidth atto- and femtosecond xuvs
can be rebuilt from the proportional and
differential terms of PES respectively. The
methods and equations may be used to improve time resolutions in
measuring ultrashort pulses. 相似文献
999.
以中国散裂中子源CSNS的直线加速器控制网为例,对其数据处理方法进行研究,采用平面与高程二维平差以及三维定向平差两种方式对准直控制网进行处理分析。同时,为了使准直数据处理更加简易便利,提出利用激光跟踪仪的测量软件SA实现三维定向平差的方法。通过不同软件及不同数据处理方法的对比,验证准直控制网数据处理的正确性,最终200 m长直线控制网点位精度优于0.2 mm,这为准直控制网的数据处理提供了指导。 相似文献
1000.
Dynamics of cooperative emissions in a cascade three-level molecular system driven by an ultrashort laser pulse 下载免费PDF全文
This paper investigates the dynamics of cooperative emissions in a cascade three-level system driven by an ultra, short laser pulse by solving numerically the full-wave Maxwell-Bloch equations. The 4, 4'-bis(dimethylamino) stilbene molecule is used as the model molecule because of its strong two-photon absorption property. The two-colour cooperative emissions are studied as functions of molecular number density and dephasing rate of the dipole coherence. The propagation effects on the evolution of the cooperative radiations are also taken into account. The cooperative radiations are enhanced for large number density of the molecule, while the fast dephasing of the dipole coherence reduces the intensity of the cooperative radiations and delays the emission times or even inhibits the formation of the emissions. The delay time of the radiation decreases with the increase of the molecular number density and the propagation distance. 相似文献