全文获取类型
收费全文 | 6399篇 |
免费 | 962篇 |
国内免费 | 750篇 |
专业分类
化学 | 4435篇 |
晶体学 | 74篇 |
力学 | 413篇 |
综合类 | 68篇 |
数学 | 742篇 |
物理学 | 2379篇 |
出版年
2024年 | 16篇 |
2023年 | 122篇 |
2022年 | 183篇 |
2021年 | 208篇 |
2020年 | 265篇 |
2019年 | 199篇 |
2018年 | 197篇 |
2017年 | 188篇 |
2016年 | 281篇 |
2015年 | 283篇 |
2014年 | 371篇 |
2013年 | 410篇 |
2012年 | 528篇 |
2011年 | 570篇 |
2010年 | 429篇 |
2009年 | 396篇 |
2008年 | 389篇 |
2007年 | 383篇 |
2006年 | 366篇 |
2005年 | 321篇 |
2004年 | 236篇 |
2003年 | 164篇 |
2002年 | 186篇 |
2001年 | 137篇 |
2000年 | 128篇 |
1999年 | 154篇 |
1998年 | 140篇 |
1997年 | 123篇 |
1996年 | 129篇 |
1995年 | 79篇 |
1994年 | 90篇 |
1993年 | 66篇 |
1992年 | 67篇 |
1991年 | 66篇 |
1990年 | 39篇 |
1989年 | 56篇 |
1988年 | 42篇 |
1987年 | 38篇 |
1986年 | 15篇 |
1985年 | 15篇 |
1984年 | 9篇 |
1983年 | 9篇 |
1982年 | 4篇 |
1981年 | 8篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1959年 | 1篇 |
1957年 | 2篇 |
排序方式: 共有8111条查询结果,搜索用时 15 毫秒
51.
The energy exchange between the pumping laser and FIR signal in the optically pumped FIR laser (OPFIRL) system was studied. The iteration method has been used to calculate the power density of the pumping and FIR signals at any point along the optical axis of the sample tube. It was found that the power density of the FIR signal did not always increase along the length of the laser tube. There was a maximum FIR power density at the appropriate point in the sample tube. If the distance of maximum power point from the entrance of the OPFIRL tube was taken as the length of sample tube Zopt, the maximum FIR laser output should be obtained. This was the optimum length of OPFIRL tube. The value of Zopt was closely related to the parameter of OPFIRL such as the pumping power density, the pumping detuning and the frequency of the FIR laser. The energy-exchange and the maximum output of the fir laser were calculated under the ideal condition. 相似文献
52.
半导体激光泵浦预激光锁模调Q固体激光器研究 总被引:1,自引:0,他引:1
报道半导体激光侧面泵浦预激光锁模调Q的Nd:YAG固体板条激光器,预激光锁模调Q的激光脉冲宽度为36ps,调Q包纤各心的锁模单脉冲能量超过7μJ,相应的峰值功率达200kW。 相似文献
53.
本文报道热丝化学气相沉积法(HFCVD)生长金钢石薄膜的喇曼散射结果。选取多种峰型,对金钢石薄膜喇曼谱(110-1800cm-1)采用最小二乘法进行非线性拟合,得到最佳拟合模型,其计算得到的拟合曲线怀实验谱图符合得较好。该模型揭示,石墨D峰(1355cm-1)是金刚石薄膜喇曼谱中不可缺少的一个组份,并且结合石墨D峰和金刚石喇曼的空间相关线型,可以解释金刚石喇曼区特殊峰形的物理机制,拟合参量的进一步 相似文献
54.
For structural parameters with uncertainties, interval mathematics can, in the case where the probabilistic distribution density
of uncertain variables is unavailable, deal with the influence of uncertainties in structural parameters on the response of
structures. In order to evaluate the region containing natural frequencies of structures with interval parameters, the interval
parameter perturbation method is presented in this paper. The advantage of the present method is its computational efficiency
in evaluating the region containing natural frequencies. A numerical example is used to illustrate the efficiency of the method
proposed.
The project is supported by National Youth Natural Science Foundation of China and National Outstanding Youth Science Foundation
of China. 相似文献
55.
56.
57.
58.
59.
The type-II phase-matched third-harmonic light generation in a -BaB2O4 crystal is studied experimentally. A passively mode-locked Nd: phosphate glass laser is used as a pump source. At a pump pulse peak intensity ofI
10=5×1010W/cm2 a third-harmonic conversion efficiency of a percent is obtained. A theoretical discussion of phase-matched third-harmonic generation in crystals of the symmetry group of -BaB2O4 (trigonal class 3) is given. The effective nonlinear susceptibility eff for type-II phase-matching is determined.On leave from the Shanghai Institute of Optics and Fine Mechanics, Academia Sinica, Shanghai, P.R. China 相似文献
60.
The electronic structures of the laser crystal MgF2:V2+ were obtained with the spinpolarized MS-X
method. The calculated value of 10Dq and the energies of the lowest doublet states were given for the first time. The relations between the laser properties and the electronic structures were discussed. 相似文献