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31.
针对接地网圆钢杆腐蚀检测问题,本文进行了接地网圆钢杆高频纵向超声导波无损检测方法研究。首先对埋地环境下圆钢杆中纵向导波传播特性进行理论研究,分析了不同模态导波的群速度和衰减频散特性。研究发现,高阶纵向模态导波在衰减最小和群速度最大对应的频率处,在圆钢杆中传播能力强,是适合进行地埋圆钢杆导波检测试验的频率范围。在此基础上,进行了埋地圆钢杆高频纵向超声导波无损检测试验研究。结果发现,利用优选的检测参数可以很好地实现埋地圆钢杆中腐蚀缺陷检测。研究工作为接地网运行状态评价提供了很好的技术支撑。 相似文献
32.
玉米种子萌发期抗旱性评价是节水农业研究中的难点和热点问题之一,生物延迟发光分析技术的应用有可能解决这一问题。采用生物延迟发光评价方法研究了玉米种子萌发期的抗旱性能力,探讨了在渗透势-0.1 MPa和-0.3 MPa的PEG-6000溶液中萌发的玉米品种万瑞168号和堰单8号延迟发光的变化规律。结果表明,万瑞168号和堰单8号玉米品种的延迟发光积分强度都随着萌发进程逐渐升高,-0.1 MPa和-0.3 MPa的PEG-6000溶液形成的干旱胁迫对两个玉米品种延迟发光积分强度的升高有不同的抑制作用,胁迫强度越大,两个品种延迟发光积分强度的差异就越大。研究还发现,在干旱胁迫下萌发的万瑞168号和堰单8号玉米延迟发光相对变化率RDL与种子萌发抗旱指数和储藏物质转运率的变化是一致的,依据干旱胁迫下种子萌发过程中延迟发光积分强度相对变化率RDL的大小可以评价玉米种子萌发期抗旱性的强弱。 相似文献
33.
边缘提取是DSPI无损检测缺陷自动识别的基础。根据人类视觉识别的特点,提出以Curvelet多尺度几何分析为基础进行缺陷图像的边缘提取,为了对DSPI检测过程中因光照不足等原因产生的伪缺陷进行分辨,基于矢量积定义了图像的方向离散度,并与Curvelet多尺度分析方法相结合,在橡胶复合材料DSPI无损检测中进行应用。 相似文献
34.
A novel nondestructive testing (NDT) method is reported in which temporal evolution of the speckles in speckle interferometry
is used to measure large object deformations. The basic principle of the method is that continuous object movement introduces
fluctuations in the phase of the speckle and is recorded as intensity modulation. Acquiring a large number of frames of the
object motion, the phase data for the whole object deformation are then retrieved by the Fourier transformation technique.
The method is capable of measuring more than 100 μm in-plane and out-of-plane deformation with speckle interferometry and
more than 500 μm for speckle shearing interferometry. The authors discuss the NDT results obtained with the three methods
and make some relative comparisons of each. 相似文献
35.
A laser ultrasonic method for nondestructive evaluation of the structure of composite materials is proposed. Specimens of graphite-epoxy composites with compaction-type defects and air cavities are investigated. The method is based on the laser thermooptical generation of wide-band acoustic pulses - optoacoustic (OA) signals - in the material investigated. The acoustic pulses backscattered by structural ingomogeneities and defects are registered by a wide-band piezotransducer, which makes it possible to detect acoustic pulses in the frequency range from 0.1 to 30 MHz. Since the generation and detection of acoustic pulses takes place on the front surface of the specimen, this method allows us to carry out nondestructive evaluation with one-sided access to the object under study. The spectral and correlation analyses of backscattered OA signals are used for mathematical processing of the experimental data. The method developed makes it possible to determine the type of defects and the depth of their location. 相似文献
36.
文章主要介绍了强磁场的发展状况和最近取得的一些进展,包括45T稳态磁场、60T长脉冲磁场、80T非破坏性脉冲磁场和百特斯拉级磁场,同时文章也介绍了强磁场的发展趋势和各磁场实验室的强磁场发展计划. 相似文献
37.
Scanning patterns of a modified AC magnetic bridge are established through the use of finite-width flaws. From these patterns,
the widths and depths of surface flaws can be determined. The technique was also applied fatigue cracks. 相似文献
38.
Nondestructive methods, in particular the measurement of elastic waves, have become increasingly important in determining the microstructure of many materials in recent years. One of these methods is observing the attenuation of ultrasonic waves of known amplitude and direction, e.g., in granular metals. The waves are exponentially attenuated with distance with a frequency-dependent attenuation fractor. The attenuation factor can be decomposed into two parts: absorption and scattering. Experimentally, the absorption part varies linearly with frequency, while the scattering part has a noninteger power law behavior, the exponent of which is related to the strength of the material. Theoretically, at long wavelengths the exponent is 4 (Rayleigh scattering) while for grain-sized wavelengths it is 2 (diffusive scattering). We relate the attenuation factor to the forward scattering amplitude which is related to the frequency dependence of the scatterers and their cross sections. We attribute the noninteger attenuation exponent to a fractal distribution of grain shapes and sizes.Supported by the Defense Advanced Research Projects Agency. 相似文献
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