全文获取类型
收费全文 | 5811篇 |
免费 | 627篇 |
国内免费 | 456篇 |
专业分类
化学 | 4234篇 |
晶体学 | 54篇 |
力学 | 297篇 |
综合类 | 36篇 |
数学 | 653篇 |
物理学 | 1620篇 |
出版年
2024年 | 19篇 |
2023年 | 75篇 |
2022年 | 181篇 |
2021年 | 219篇 |
2020年 | 195篇 |
2019年 | 211篇 |
2018年 | 182篇 |
2017年 | 161篇 |
2016年 | 286篇 |
2015年 | 219篇 |
2014年 | 272篇 |
2013年 | 441篇 |
2012年 | 406篇 |
2011年 | 432篇 |
2010年 | 311篇 |
2009年 | 285篇 |
2008年 | 322篇 |
2007年 | 301篇 |
2006年 | 299篇 |
2005年 | 222篇 |
2004年 | 202篇 |
2003年 | 174篇 |
2002年 | 201篇 |
2001年 | 142篇 |
2000年 | 115篇 |
1999年 | 120篇 |
1998年 | 110篇 |
1997年 | 91篇 |
1996年 | 57篇 |
1995年 | 75篇 |
1994年 | 69篇 |
1993年 | 61篇 |
1992年 | 56篇 |
1991年 | 36篇 |
1990年 | 37篇 |
1989年 | 20篇 |
1988年 | 21篇 |
1987年 | 18篇 |
1986年 | 31篇 |
1985年 | 34篇 |
1984年 | 26篇 |
1983年 | 23篇 |
1982年 | 20篇 |
1981年 | 16篇 |
1980年 | 12篇 |
1979年 | 14篇 |
1978年 | 11篇 |
1975年 | 8篇 |
1974年 | 8篇 |
1973年 | 9篇 |
排序方式: 共有6894条查询结果,搜索用时 15 毫秒
71.
Cr^4+:YAG的可饱和吸收特性与被动Q开关性能研究 总被引:16,自引:6,他引:16
运用速率方程计算了Cr^4+:YAG晶体的可饱和吸收特性参数,包括初始吸收系数,饱和吸收系数,饱和光强和损耗调制度,用Cr^4+:YAG对脉冲和连续Nd:YAG激光器进行了被动调Q,在脉冲Nd:YAG激光器上得到了8ns的调Q激光脉冲,在连续Nd:YAG激光器的调Q中得到了间隔和幅度抖动小于5%的输出脉冲充列。 相似文献
72.
73.
74.
从速率方程出发对双区共腔(common-cavitytwosection简称CCTS)光双稳激光器进行了精确的理论分析与计算,并对其稳态特性进行了实验研究和测试,得出了定量和定性的分析结果,同时还首次发现当激光输出高态出又出现了一次光双稳和开关效应。经研究确认是量子阱探测器的自电光效应,并提出一种可集成双逻辑功能显示的新型网络模型器件。 相似文献
75.
76.
In this study the geometry optimization of monomeric and dimeric forms (D1, D2, and D3) of hydantoin molecule were done using DFT method employing 6?C31++G(d, p) basis set. Harmonic and anharmonic wavenumbers and infrared intensities were computed at the same theory level. Experimental IR spectrum was recorded in the region 400?C4000 cm?1. It has also been characterized by 1H and 13C NMR spectrum. The hydrogen bond (HB) interaction of hydantoin was analyzed via dimers of hydantoin. Detailed vibrational wavenumber shifts and all vibrational mode analyses were reported. Total energy distributions (TED, %) calculations were done to characterize the fundamentals. 相似文献
77.
Study of sawtooth oscillations on the HT-7 tokamak using 2D tomography of soft x-ray signal 总被引:1,自引:0,他引:1 下载免费PDF全文
It is the first time so far as we know that two arrays of multi-channel soft x-ray detectors are used to generate twodimensional (2D) images of sawtooth oscillation on the HT-7 tokamak using the Fourier-Bessel harmonic reconstruction method, and using the singular value decomposition to analyse the data from soft x-ray cameras. By these two arrays, 2D image reconstruction of soft x-ray emissivity can be obtained without assumption of plasma rigid rotation. Tomographic reconstruction of the m=1 mode structure is obtained during the precursor oscillation of the sawtooth crash. The crescent-shaped mode structure appearing on the contour map of the soft x-ray emissivity is consistent with the quasiinterchange mode. The characteristics of the m=1/n=1 mode structure observed in the soft x-ray tomography are as follows: the magnetic surface is made up of the crescent-shaped “hot core” and the circular “cold bubble”. The structure of the magnetic surface rotates in the direction of the electron diamagnetic drift and the rotation frequency is the oscillation frequency of soft x-ray signals. 相似文献
78.
The line-integrated optical measurement of impurity radiation profiles for the study of light impurity transport is performed in the HT-7 tokamak. The carbon impurity line emissivity is obtained by Abel inversion. The radial transport behaviours of carbon impurities at different central line averaged electron densities ne are investigated in ohmic discharges. The diffusion coefficient Dk(r), the convection velocity Wk(r) and the total flux of the impurity ions Fk decrease with the increase of ne, which shows a reduction in the impurity particle transport at higher electron densities. 相似文献
79.
研究了多壁碳纳米管(MWNTs)薄膜的湿敏特性,实验所用的多壁碳纳米管是用热灯丝化学气相沉积法(CVD)合成的.分别对未修饰和修饰的多壁碳纳米管膜温度和湿度特性进行研究后发现,修饰的多壁碳纳米管对温度和湿度非常敏感,且对湿度的响应时间和恢复时间短,重复性好.而未修饰的多壁碳纳米管对温度和湿度不太敏感.对修饰多壁碳纳米管的湿敏特性进行了理论分析,给出了其理论表示式.
关键词:
多壁碳纳米管
化学修饰
湿敏特性
物理吸附 相似文献
80.
Kyung Sam Park Soung Hie Kim Wan Chul Yoon 《The Journal of the Operational Research Society》1996,47(11):1415-1420
This paper is concerned with the use of incomplete information about utilities and weights in multiattribute decisionmaking. Because of time pressure and/or lack of knowledge, a decision maker may only be able to provide incomplete information which might be expressed as a set of linear inequalities. If the decision maker's information on both weights and utilities is imprecisely identified, then the model for establishing pairwise dominance becomes a non-linear program. A method for obtaining non-dominated alternatives without solving the non-linear program is proposed using a simple weighted-additive function. 相似文献