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551.
本文描述一台虚拟式扫描声显微镜及应用技术研究,它的硬件特别简单,仅由一台带有超高速A/D卡和快脉冲收发卡的PC机和机械扫描系统组成,主要的功能均由软件完成,脉冲收发卡仅包括脉冲产生和高频放大器,A/D卡采用PCI总线,采样率1GSPS,数据传输率100MB/s,系统能采集并实时显示频率达百兆的未检波回波信号,采修订本以的信号经软件处理,可在屏幕上实时显示样品的A、B、C型幅度像或相位像,仪器利用信号处理技术提高信号的信噪比;进行特征提取,识别,该仪器在材料识别,电子、光电子器件和焊接质量检测等方面功能较强,具有广阔的开发应用前景。 相似文献
552.
本文提出一个价值函数,作为高速光测装置的评价准则。此函数建立在装置可能获得的信息容量和质量的基础上,例如,数据锐度和装置的多功能性等。 相似文献
553.
A new oscillating capillary viscometer has been developed and used for measuring viscoelastic flow properties of dilute polymer solutions. These flow properties are determined from measurements of the pressure to volume flow relationships for sinusoidal flow in cylindrical glass capillaries. The theory for this measurement procedure is based upon the known theory for oscillatory flow of a viscoelastic fluid in circular tubes and which is presented with a few supplementations in this paper.The oscillatory flow is generated by a piezoelectric driver which is dipped directly into the aqueous solution. The advantage of this driver is that the excitation voltage for the piston is a direct measure of the motion of the piston. Changes in pressure are measured with a sensitive low-pressure quartz tranducer.The viscometer was tested with aqueous glycerol solutions and a gelatin gel. The viscoelastic flow properties of dilute polymer solutions (gelatin, gelatin/color-coupler, polyacrylamide) were then investigated in the frequency range 5 Hz to 150 Hz at very small volume flow amplitudes. The results presented illustrate the suitability of the method. The results are also evaluated with regard to the stabilizing action of slightly viscoelastic gelatinous coating liquids in the high-speed coating process in the manufacture of photographic materials. 相似文献
554.
Some characteristics of the 30- 60 day oscillation in general circulation are investigatedin this paper. In the tropical atmosphere, besides some results consisting with the knownfacts, we still find that the 30- 60 day atmospheric oscillations are very obvious in theequatorial eastern Pacific, and the zonal scale of the vorticity and divergence for the30- 60 day oscillation in the tropics is much smaller than wavenumber 1. There are the strongest 30- 60 day oscillations at the high latitudes in the Northern Hemi-sphere, but weaker at 20°-40°N latitudes. The 30- 60 day oscillations have an obviousbarotropic structure at mid-high latitudes and their zonal scales are smaller than those in thetropics. The 30- 60 day oscillations at the mid-latitudes propagate westwards and fast in thewintertime. At the high latitudes, 30- 60 day oscillations propagate westwards in the win-tertime but eastwards in the summertime. Meridional propagations of the oscillation arerather different in various regions. 相似文献
555.
On the output characteristics of a semiconductor optical amplifier driven by an ultrafast optical time division multiplexing pulse train 总被引:1,自引:0,他引:1
A comprehensive theoretical analysis of a semiconductor optical amplifier (SOA) that is subject to an ultrafast optical time division multiplexing pulse stream is presented with the help of a simple but efficient model developed for this purpose. The model combines the necessary set of mathematical equations with the appropriate simplifying assumptions to describe in the time domain gain saturation and recovery for the case of multiple incoming pulses. In this manner, analytical expressions can be obtained for the power and chirp profile of the amplified pulses, essentially extending the work that has been performed for a single pulse only. This allows to identify the critical operational parameters and to investigate and evaluate their effect on these two output characteristics. The derived simulation curves are thoroughly studied to specify the limitations imposed on the SOA small signal gain and carrier lifetime as well as on the full-width at half-maximum (FWHM) and energy of the input pulses and, based on a series of logical arguments, to extract useful rules concerning their selection so as to achieve improved performance with respect to the practical applications of all-optical switching and pulse compression. The obtained results indicate that due to the continuous insertion of pulses, the requirements for the SOA small signal gain and the input pulse energy are stringent than those for the case of isolated pulse amplification. The combination of these two parameters determines also the regime in which the amplifier must be biased to operate in order to ensure distortionless pulse amplification and enhanced chirp for efficient pulse compression and it has been found that low saturation is necessary for the former case whilst heavy saturation for the latter. The scopes of the corresponding requirements for the carrier lifetime and the FWHM are also tight but to a less extent and can be simply satisfied with the available photonics technology. These results are in good agreement with the available experimental data essentially proving the validity and robustness of the model. The model can be thus applied to predict the behavior of more complex all-optical circuits of enhanced functionality in which the SOA is the basic functional device. 相似文献
556.
Rail noise prediction models enable consideration of different scenarios for the optimal management of noise prevention and mitigation. This project is aimed at developing an equation that enables computation of LA,max for the Tehran-Karaj commuter train, a type of Diesel-Electric Locomotive. The form of the proposed model is derived from equations for predicting LA,max for a single locomotive pass-by, proposed in the manual prepared by Harris Miller Miller & Hanson Inc. for the US Federal Transit Administration, and in the French rail noise prediction model. The algorithm for predicting LA,max for the Tehran-Karaj commuter train has been developed on the basis of the 50 measurements from 5 locations at distances of 25 m, 35 m, 45 m, 55 m, and 65 m from the centre of the track and at a height of 1.5 m. In the field measurements, the reference distance and the reference vehicle speed have respectively been set equal to 25 m and 80 km per hour. The reference LA,max, length and the speed correction coefficients have been estimated from the field measurements and have been found to be 86.2 dB(A), 11.3, and 18.4 respectively. The fitness test (Kolmogorov-Smirnov) and regression analysis indicate satisfactory results. 相似文献
557.
558.
A detailed study has been conducted on the long-term changes in the diurnal, semi-diurnal and tri-diurnal anisotropies of
cosmic rays in terms of the high/low amplitude anisotropic wave train events (HAE/LAE) during the period 1981–94 using the
neutron monitor data from Deep River Neutron Monitoring Station. In all, 38 HAE and 28 LAE cases have been studied. An inter-comparison
of the first three harmonics during these events has been made so as to understand the basic reason for the occurrence of
these types of events. It has been observed that the phase of diurnal anisotropy shifts towards earlier hours for HAEs and
it shifts towards earlier hour as compared to 18-h direction for LAEs. For semi-diurnal anisotropy, phase remains statistically
the same for both HAE and LAE. In the case of tri-diurnal anisotropy, phase is evenly distributed for both types of events.
The interplanetary magnetic field (IMF) and solar wind plasma (SWP) parameters during these events are also investigated.
It has also been observed that HAE/LAEs are weakly dependent on high-speed solar wind velocity. The two types of solar wind
streams (corotating streams and flare-generated streams) produce significant deviations in cosmic ray intensity during HAE/LAE.
相似文献
559.
采用高速摄影方法在实验水箱中获得了长径比为3.35~6.75的柱形PETN炸药水中爆炸气泡脉动的图像,进而结合真实的爆轰过程和Rayleigh气泡运动方程,研究了气泡的形态演变规律。研究结果表明,柱形装药在水中爆炸时,形成的初始气泡的形状为非球对称形,这种非对称特征随长径比的增加而增大。气泡表面的运动也表现出明显的非球对称特征,气泡表面在装药径向的膨胀运动呈指数衰减,在装药轴向两端的膨胀运动更接近于分段线性衰减。气泡表面的不对称运动与柱形装药水下爆炸的能量输出结构不均有关,与冲击波的有效能量分布规律是相似的。 相似文献
560.