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991.
Large eddy simulation of cross-flow through a staggered tube bundle at subcritical Reynolds number 总被引:1,自引:0,他引:1
The Large Eddy Simulation (LES) technique is used to study the vortex shedding characteristics inside a staggered tube array consisting of six rows with intermediate spacings (SL/D×ST/D=1.6×3.6) at the subcritical Reynolds number of 8600 (based on the gap velocity). The filtered equations are discretised using the finite volume method in an unstructured, collocated grid arrangement with second-order accurate methods in space and time. The predictions of mean velocities and Reynolds stresses are in very good agreement with detailed LDA measurements performed in 17 stations along the depth of the array. The sizes of the recirculation zones behind the cylinders in the first and third row also compare favourably with available correlations. Two distinct and independent shedding frequencies are detected behind the first two rows, but the high-frequency component vanishes in the downstream rows. The corresponding Strouhal numbers agree well with measurements available in the literature for similar tube spacings. The lift coefficient as well as instantaneous flow patterns of the whole array are also examined. 相似文献
992.
993.
空腔流动存在剪切层运动、涡脱落与破裂,以及激波与激波、激波与剪切层、激波与膨胀波和激波/涡/剪切层相互干扰等现象,流动非常复杂,特别是高马赫数(M>2)时,剪切层和激波更强,激波与激波干扰更严重,对数值格式的要求更高,既需要格式耗散小,对分离涡等有很高的模拟精度,又需要格式在激波附近具有较大的耗散,可以很好地捕捉激波,防止非物理解的出现。Roe和HLLC等近似Riemann解格式在高马赫数强激波处可能会出现红玉现象,而HLLE++格式大大改善了这种缺陷,在捕捉高超声速激波时避免了红玉现象的发生,同时还保持在光滑区域的低数值耗散特性。本文在结构网格下HLLE++格式的基础上,通过改进激波探测的求解,建立了基于非结构混合网格的HLLE++计算方法,通过无粘斜坡算例,验证了HLLE++格式模拟高马赫数流动的能力,并应用于高马赫数空腔流动的数值模拟,开展了网格和湍流模型影响研究,验证了方法模拟高马赫数空腔流动的可靠性和有效性。 相似文献
994.
未来的电网将会是一个高度自动化、智能化的电网,如此一个庞大、复杂的系统从发电、输电一直到变、配、用电的过程时刻都会生成海量的电能信息及设备运行状态数据,这就需要一个强有力的信息处理平台作为支撑,且这个平台应具有对海量数据的可靠存储、准确分析、实时同步更新及共享的功能,尤其是音视频等异构数据的分析与处理.云计算技术在大数据处理中具有得天独厚的优势,本文将云计算技术引入到未来智能电网的信息处理平台的建设中,针对未来智能电网信息处理平台的各项功能需求,对比目前电网信息处理平台的诸多瓶颈进行深层次的探讨,证明了将云计算技术应用到未来智能电网信息处理平台中的可行性。 相似文献
995.
996.
S. M. H. Karimian 《国际流体数值方法杂志》2011,65(8):969-988
In this article, a detailed study on the effects of different modelings of cell‐face velocities on pressure–velocity coupling, accuracy and convergence rate of the solution has been conducted. Discussions are focused on the collocated scheme of Schneider and Karimian (Computational Mechanics 1994; 14 : 1–16) in the context of a control‐volume finite‐element Method. In this scheme, variables at the control volume surface are evaluated based on the physics of their governing equations, and the fully coupled system obtained is solved using a direct sparse solver. A special test problem has been defined to check the pressure–velocity coupling for all of the formulations. Other test cases, including Taylor problem, inviscid converging–diverging nozzle and the lid‐driven cavity, have been conducted for different Reynolds numbers, mesh sizes and time steps to investigate the accuracy and the performance of the formulations. Finally, a reliable and efficient scheme for the evaluation of cell‐face velocities is proposed, which can be easily extended to three dimensions. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
997.
998.
999.
Michael Gnewuch Ren Lindloh Reinhold Schneider Anand Srivastav 《Journal of Complexity》2007,23(4-6):828
We construct simple algorithms for high-dimensional numerical integration of function classes with moderate smoothness. These classes consist of square-integrable functions over the d-dimensional unit cube whose coefficients with respect to certain multiwavelet expansions decay rapidly. Such a class contains discontinuous functions on the one hand and, for the right choice of parameters, the quite natural d-fold tensor product of a Sobolev space Hs[0,1] on the other hand.The algorithms are based on one-dimensional quadrature rules appropriate for the integration of the particular wavelets under consideration and on Smolyak's construction. We provide upper bounds for the worst-case error of our cubature rule in terms of the number of function calls. We additionally prove lower bounds showing that our method is optimal in dimension d=1 and almost optimal (up to logarithmic factors) in higher dimensions. We perform numerical tests which allow the comparison with other cubature methods. 相似文献
1000.
We study exact algorithms for the MAX-CUT problem. Introducing a new technique, we present an algorithmic scheme that computes a maximum cut in graphs with bounded maximum degree. Our algorithm runs in time O*(2(1-(2/Δ))n). We also describe a MAX-CUT algorithm for general graphs. Its time complexity is O*(2mn/(m+n)). Both algorithms use polynomial space. 相似文献