首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   270篇
  免费   14篇
  国内免费   11篇
化学   120篇
晶体学   1篇
力学   4篇
数学   55篇
物理学   115篇
  2023年   3篇
  2021年   2篇
  2018年   3篇
  2017年   6篇
  2016年   8篇
  2015年   3篇
  2014年   5篇
  2013年   21篇
  2012年   17篇
  2011年   15篇
  2010年   9篇
  2009年   5篇
  2008年   14篇
  2007年   15篇
  2006年   21篇
  2005年   13篇
  2004年   19篇
  2003年   10篇
  2002年   2篇
  2001年   7篇
  2000年   4篇
  1999年   8篇
  1998年   5篇
  1997年   6篇
  1996年   6篇
  1995年   4篇
  1994年   7篇
  1993年   8篇
  1992年   4篇
  1991年   3篇
  1990年   6篇
  1989年   3篇
  1988年   5篇
  1987年   2篇
  1986年   5篇
  1985年   3篇
  1984年   3篇
  1983年   3篇
  1981年   1篇
  1980年   2篇
  1979年   1篇
  1977年   5篇
  1974年   1篇
  1973年   1篇
  1970年   1篇
排序方式: 共有295条查询结果,搜索用时 46 毫秒
31.
Twin-image elimination in the context of optical scanning holography has recently been proposed. The proposed technique involves simultaneously acquiring sine and cosine Fresnel holograms. A complex hologram is then formed by complex addition of the holograms, and twin-image rejection is predicted by computer simulations. An experimental verification of the technique by optical acquisition of the two holograms and subsequent reconstruction of the complex hologram digitally is reported. Three-dimensional image reconstruction without twin-image noise is demonstrated.  相似文献   
32.
The internal space of a N = 4 supersymmetric model with Wess–Zumino term has a connection with totally skew-symmetric torsion and holonomy in SP(n). We study the mathematical background of this type of connection. In particular, we relate it to classical Hermitian geometry, construct homogeneous as well as inhomogeneous examples, characterize it in terms of holomorphic data, develop its potential theory and reduction theory. Received: 1 October 1999 / Accepted: 30 January 2000  相似文献   
33.
The temporal course of masking and the auditory filter shape   总被引:1,自引:0,他引:1  
Recent experiments have shown that frequency selectivity measured in tone-on-tone simultaneous masking improves with increasing delay of a brief signal relative to the onset of a longer duration gated masker. To determine whether a similar improvement occurs for a notched-noise masker, threshold was measured for a 20-ms signal presented at the beginning, the temporal center, or the end of the 400-ms masker (simultaneous masking), or immediately following the masker (forward masking). The notch width was varied systematically and the notch was placed both symmetrically and asymmetrically about the 1-kHz signal frequency. Growth-of-masking functions were determined for each temporal condition, for a noise masker without a spectral notch. These functions were used to express the thresholds from the notched-noise experiment in terms of the level of a flat-spectrum noise which would produce the same threshold. In simultaneous masking the auditory filter shapes derived from the transformed data did not change significantly with signal delay, suggesting that the selectivity of the auditory filter does not develop over time. In forward masking the auditory filter shapes were sharper than those for simultaneous masking, particularly on the high-frequency side, which was attributed to suppression.  相似文献   
34.
In this paper, we formulate two classes of problems, the colored range query problems and the colored point enclosure query problems to model multi-dimensional range and point enclosure queries in the presence of categorical information. Many of these problems are difficult to solve using traditional data structural techniques. Based on a new framework of combining sketching techniques and traditional data structures, we obtain two sets of results in solving the problems approximately and efficiently. In addition, the framework can be employed to attack other related problems by finding the appropriate summary structures.  相似文献   
35.
We characterize linear maps between different rectangular matrix spaces preserving Ky Fan norms.

  相似文献   

36.
37.
The work uses the data in the TTS mode of BATSE to analyze the time lags and pulse widths of GRB960113 and GRB960722 in high as well as low energy bands. The results show that their time lags increase monotonously. This phenomenon can reasonably be interpreted with the model of internal shock waves of γ-ray bursts (GRB). Perhaps we obtain the direct observational evidence for the fireball model of GRBs for the first time.  相似文献   
38.
Feng S  Luo X  Du S  Poon AW 《Optics letters》2011,36(7):1278-1280
We report the demonstration of electro-optical tunable time delay and advance using a silicon feedback-microring resonator integrated with p-i-n diodes. By controlling the feedback and round-trip phase shifts through the carrier-injection-based free-carrier dispersion effect, we obtain a large dynamic time tuning range (-88 ps to 110 ps) upon dc bias voltage change in the range of few tens of millivolts at a given resonance wavelength. We also demonstrate tunable time delay and advance at different resonance wavelengths within 0.76 nm wavelength range.  相似文献   
39.
Kruger BA  Poon JK 《Optics letters》2011,36(11):2155-2157
Waveguides at interfaces with a linearly graded permittivity between a metal and a dielectric are studied. Analytic expressions for the dispersion relations, modes, losses, and cutoff wavelengths are derived and agree well with simulations. The gradation results in anomalous dispersion, a reduction in the energy velocity, and increased field confinement in the metal-dielectric transition region. These effects lead to increased propagation losses, which are sensitive to the spatial extent of the interface gradation.  相似文献   
40.
The dynamics of liquid-vapor phase-change in the nanosecond time-scale induced by pulsed-laser heating of a liquid on a solid sample is studied by means of optical reflectance and scattering measurements, and the piezoelectric detection technique. The liquids studied include water, ethanol, methanol, IsoproPropyl Alcohol (IPA), and mixtures of water and IPA. The threshold fluence for nucleation is determined with high accuracy using the optical and acoustic signals. Heat diffusion calculations performed for the threshold fluences indicate that the liquids are sufficiently superheated before nucleation sets on. The transient optical reflectance signal is analyzed by an effective-medium theory to provide bubble-growth kinetics, so that the bubble-growth velocity for the test liquids could be estimated. In addition, it is observed that, following the thermally induced nucleation, repetitive acoustic cavitation at the surface of the solid sample occurs, with a time interval related to the speed of sound in the liquid.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号