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   159篇
  免费   14篇
  国内免费   11篇
化学   27篇
力学   5篇
综合类   1篇
数学   116篇
物理学   35篇
  2023年   2篇
  2022年   1篇
  2021年   2篇
  2020年   1篇
  2019年   2篇
  2018年   5篇
  2017年   5篇
  2016年   3篇
  2015年   6篇
  2014年   8篇
  2013年   21篇
  2012年   2篇
  2011年   8篇
  2010年   9篇
  2009年   8篇
  2008年   11篇
  2007年   11篇
  2006年   14篇
  2005年   7篇
  2004年   3篇
  2003年   6篇
  2002年   7篇
  2001年   3篇
  2000年   8篇
  1999年   6篇
  1998年   10篇
  1997年   7篇
  1996年   2篇
  1995年   1篇
  1994年   3篇
  1992年   1篇
  1977年   1篇
排序方式: 共有184条查询结果,搜索用时 15 毫秒
171.
虽然整数规划中经典的Lagrange对偶方法是一个有效的方法,但是由于对偶缝隙的原因它经常不能求出原问题的最优解。该文提出一个用于有界整数规划的指数对偶公式。此公式具有渐进强对偶的特性并且可以保证找到原问题的最优解。它的另一个特性是当参数选择的合适时不需要进行实际的对偶搜索。  相似文献   
172.
Wang Y  Liang D  Ying Q  Chu B 《Electrophoresis》2005,26(1):126-136
Quasi-interpenetrating network (IPN) formed by polyacrylamide and poly(N,N-dimethylacrylamide) was designed, synthesized, and tested as a high-performance DNA separation medium by capillary electrophoresis. The performance of quasi-IPN on DNA sequencing was determined by the acrylamide to dimethylacrylamide molar ratio, polyacrylamide molecular weight, and its size distribution. Under optimal operating conditions, quasi-IPN was able to achieve one-color DNA sequencing up to 1000 bases in 39 min, or 1200 bases in 60 min. Its performance was compared with some of the existing commercialized products, such as POP6 from Applied Biosystems and MegaBACE matrix from Amersham Biosciences. By using the ABI 310 Genetic Analyzer, even without optimized base-calling software, quasi-IPN yielded a read length of up to 700 bases of contiguous sequence (50-750 bases) in 35 min with 99.6% accuracy, or 750 bases of contiguous sequence (50-800 bases) in 37 min with 98.0% accuracy.  相似文献   
173.
We analyze quasi-phase-matched (QPM) conversion efficiency of the five possible types of periodic two-dimensional nonlinear structures: Hexagonal, square, rectangular, centered-rectangular, and oblique. The frequency conversion efficiency, as a function of the two-dimensional quasi-phase-matching order, is determined for the general case. Furthermore, it is demonstrated for two basic feasible motifs, a circular motif and a rectangular motif. This enables to determine the optimal motif dimensions for achieving the highest conversion efficiency. We find that a rectangular motif is more efficient than a circular motif for quasi-phase-matched processes that rely on a single reciprocal lattice vector (RLV), and that under optimal choice of motif dimensions, it converges into a one-dimensional periodic structure. In addition, in a few specific cases we found that higher order QPM can be significantly more efficient than lower order QPM.  相似文献   
174.
Stochastic decompositions in the M/M/1 queue with working vacations   总被引:1,自引:0,他引:1  
We demonstrate stochastic decomposition structures of the queue length and waiting time in an M/M/1/WV queue, and obtain the distributions of the additional queue length and additional delay. Furthermore, we discuss the relationship between the stochastic decomposition properties of the working vacation queue and those of the standard M/G/1 queue with general vacations.  相似文献   
175.
The velocity of an incompressible flow in a bounded three‐dimensional domain is represented by its vorticity with the help of an apparently new representation formula. Using this formula we prove a quasi‐Lipschitz estimate for in dependence of the supremum norm of . Our quasi‐Lipschitz bound extends to the case where is represented by any continuous ≠ rot  相似文献   
176.
This paper elaborates a nonlinear fluidic low frequency vibration isolator designed with the characteristics of quasi-zero stiffness (QZS). The existing model of QZS vibration isolator enhances amplitude of vibration and attenuating vibration frequencies. This concern with displacement plays a vital role in the performance and instability of oblique spring setup reduces the isolator performance in horizontal non-nominal loads, in this accordance; this paper associates double acting hydraulic cylinder (fluidic actuators in short) in oblique and helical coil spring. An approximate expression of unique analytical relationship between the stiffness of vertical spring and bulk modulus of the fluid is derived for Quasi – Zero Stiffness Non-Linear Vibration Isolator with Fluidic Actuators (NLVIFA in short) system and the force transmissibility is formulated and damping ratio are discussed for characteristic analysis. Modal analysis carried out and compared with analytical results and an experimental prototype is developed and investigated. The performance of the NLVIFA reduces the external embarrassment more at low frequencies and the series of experimental studies showing that the soft nonlinearity causes limitation in the resonant frequency thereupon the isolation will be enhanced and NLVIFA greatly outperform some other type of nonlinear isolators.  相似文献   
177.
幂环   总被引:6,自引:0,他引:6  
提出幂环概念,使环的提升更趋合理,建立了幂环的结构定理,并得到了某种条件下幂环同商环的关系。  相似文献   
178.
定义了拟有理映照的Fatou集,将有理映照的部分结果推广到拟有理映照,并提出了供进一步研究的问题.  相似文献   
179.
Experimental results are presented on natural convection in a spherical shell of inner and outer radii r 1 = 14 mm and r 2 = 35 mm, with the inner sphere cooled and the outer sphere heated. The fluids filling the shell are two different silicon oils having Prandtl numbers 39 and 233. Both spheres are fixed together and can be rotated. In the studied regime, both Coriolis and centrifugal forces become significant. For sufficiently small Rayleigh numbers the resulting flow pattern is axisymmetric and steady, consisting of a plume descending from the south pole of the inner sphere, and returning in the equatorial regions. For greater Rayleigh numbers the flow becomes non-axisymmetric, with azimuthal modes m = 2 to 4 arising. We map out the critical Rayleigh number for the onset of these different modes, and consider how they vary with increasingly rapid overall rotation. Detailed flow measurements are done by converting a standard 2D particle image velocimetry system into a scanning quasi-3D PIV system.  相似文献   
180.
运用积分变换法推导了超微盘电极上同时受扩散、电化学反应、化学反应伏安法统一理论.对簿层电解池中超微盘电极伏安方程进行了研究,列出了计算所得的典型伏安曲线.  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