全文获取类型
收费全文 | 4949篇 |
免费 | 2745篇 |
国内免费 | 1543篇 |
专业分类
化学 | 729篇 |
晶体学 | 176篇 |
力学 | 645篇 |
综合类 | 209篇 |
数学 | 1868篇 |
物理学 | 5610篇 |
出版年
2024年 | 80篇 |
2023年 | 178篇 |
2022年 | 210篇 |
2021年 | 220篇 |
2020年 | 145篇 |
2019年 | 161篇 |
2018年 | 162篇 |
2017年 | 201篇 |
2016年 | 243篇 |
2015年 | 236篇 |
2014年 | 490篇 |
2013年 | 322篇 |
2012年 | 322篇 |
2011年 | 383篇 |
2010年 | 388篇 |
2009年 | 356篇 |
2008年 | 504篇 |
2007年 | 389篇 |
2006年 | 370篇 |
2005年 | 377篇 |
2004年 | 359篇 |
2003年 | 371篇 |
2002年 | 314篇 |
2001年 | 258篇 |
2000年 | 251篇 |
1999年 | 203篇 |
1998年 | 191篇 |
1997年 | 173篇 |
1996年 | 186篇 |
1995年 | 175篇 |
1994年 | 168篇 |
1993年 | 146篇 |
1992年 | 135篇 |
1991年 | 154篇 |
1990年 | 119篇 |
1989年 | 111篇 |
1988年 | 31篇 |
1987年 | 36篇 |
1986年 | 32篇 |
1985年 | 24篇 |
1984年 | 14篇 |
1983年 | 26篇 |
1982年 | 23篇 |
排序方式: 共有9237条查询结果,搜索用时 31 毫秒
81.
激光二极管端面抽运的棒状Yb:YAG激光器 总被引:5,自引:1,他引:4
分析了影响激光二极管抽运Yb:YAG激光器调Q效率的参量,推导了激光二极管端面脉冲抽运Yb:YAG晶体的速率方程,解出了双程抽运情况下的净抽运量子产率。利用数值计算方法,模拟了净抽运量子产率与晶体长度,抽运光脉冲宽度等关系,得出晶体长度的优化可以提高Yb:YAG激光器输出效率。计算了词Q Yb:YAG激光器的最大增益、最大储能,分析了放大自发辐射对于Yb:YAG能量存储的影响。同时给出了激光二极管端面抽运调Q Yb:YAG优化设计方法。这些分析和计算为实际器件的研制提供参考。 相似文献
82.
83.
PANYondong QIANMenglu XUWeijiang M.OURAK 《声学学报:英文版》2004,23(1):11-16
A residual-stress profile along the thickness of an aluminum alloy sheet is determined by laser-ultrasonic technique. Surface acoustic waves are generated by a Nd:YAG pulse laser and detected by a Heterodyne interferometer on a lateral free surface of the sheet. The distribution of residual stress is determined by measuring the relative variation of the wavevelocities at different location of the sample along its thickness. This technique is validated by three different residual stress profiles obtained experimentally. 相似文献
84.
Based on the Dyson-Schwinger equations (DSEs) in the ‘rainbow‘ approximation, we investigate the quark virtuality in the vacuum state and quantum-chromodynamics (QCD) vacuum condensates. In particular, we calculate the local quark vacuum condensate and quark-gluon mixed condensates, and then the virtuality of quark. The calculated quark virtualities are λu,d^2 0.7 GeV^2 for u, d quarks, and λs^2=1.6 GeV^2 for s quark. Our theoretical predictions are consistent with empirical values used in QCD sum rules, and also fit to lattice QCD predictions. 相似文献
85.
86.
87.
The evolution of shower parton distributions in a jet is investigated in the framework of a quark recombination model. The distributions are parameterized and the Q^2 dependence of the parameters is given by polynomials of In Q^2 for a wide range of Q^2 相似文献
88.
本文介绍了一种能工作于特浅水域的高分辨地层剖面仪。首先分析了国际现有产品存在的技术问题,然后阐述GPY中所采用的声学和信号处理上的新技术,最后介绍它的主要技术特点及应用效果。 相似文献
89.
Raman spectra of ceramic Sr2Bi4Ti5O18 (SBTi5) are reported to consist of four different Raman bands. Temperature-dependent spectra reveal the relationship between the lattice vibration and the material's structure. There appears a relatively large change in structure of the material at about 273K, The anharmonic potential of the material has a great influence on its phonon mode full width at half maximum (FWHM), which can be expressed by a function of temperature. Theoretical fittings of the FWHMs for the two modes at around 312 cm^-1 and 464cm^-1 indicate that the latter phonon mode is more anharmonic than the former one. 相似文献
90.
We study some classes of functions satisfying the assumptions similar to but weaker than those for the classical B2 function classes used in the research of quasi-linear parabolic equations as well as the ones used in the research of degenerate parabolic equations including porous medium equationsl.Comsequently,we prove that a function in such a class is continuous.As an application,we obtain the estimate for the continuous modulus of the solutions of a few degenerate parabolic equations in divergence form,including the anisotropic porous equations. 相似文献