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排序方式: 共有206条查询结果,搜索用时 31 毫秒
1.
降雨入渗过程的水-气二相流模型研究 总被引:2,自引:0,他引:2
本文根据多孔介质中水、气的质量守恒定律,结合多相流理论,建立了求解饱和-非饱和渗流的水-气二相流数学模型,并采用积分形式的有限差分法和NewtonRaphson迭代方法进行数值求解,提出了各种边界条件,包括水相、气相和降雨入渗边界的数学处理方法。利用上述模型对土柱试验进行模拟,将计算结果与试验数据比较,验证了模型的正确性;然后对土质边坡降雨入渗过程进行计算,得到孔隙水压力、孔隙气压力和毛细压力的变化过程,其变化规律符合实际,实现了降雨入渗的水-气二相渗流过程,为定量研究空气阻力对入渗水流的影响提供有效途径。 相似文献
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为了减少迭代次数,提高收敛性,在一阶牛顿拉夫逊法基础上对不平衡量ΔP和ΔQ进行修正,采用一阶牛顿法得到的修正量作为预测量,利用节点注入电流方程和电压方程形成不平衡量的校正值,从而得到新的修正方程,沿用传统牛顿法进行迭代计算。从理论上讲该方法具有三阶收敛性。通过对典型IEEE节点实例进行Matlab编程仿真,与传统牛拉法做对比,该方法具有迭代次数少,收敛性好,编程量增加不多的特点。 相似文献
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在大量分布式电源接入中低压配电网的新形势下,三相潮流计算是分析其影响的基本手段。针对现有中压不接地配电网三相潮流研究主要采用人为设置参考中性点/零序电压的方式,导致无法仿真分析中性点/零序电压偏移、不接地网络零序潮流和相-地电压不平衡等情况,提出一种中压不接地配电网三相潮流新算法。首先,提出不接地配电网三相潮流在节点变量和导纳矩阵方面的特殊性。然后,设计基于功率平衡方程和牛拉法,采用导纳矩阵可逆化处理和矩阵替换技术实现约束零序电流为零的不接地配电网三相潮流算法。最后,基于6节点系统和修改的IEEE123算例仿真不接地配网的潮流,结合PSCAD验证所提方法在不同场景下的准确性以及在大电网中的适用性和收敛性,并在地市电网中进行实际应用。算例分析表明,所提算法计算结果准确,具有良好的工程实用性。 相似文献
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Yahya H. Zweiri 《国际自动化与计算杂志》2008,5(2):185-192
Parameter identification is a key requirement in the field of automated control of unmanned excavators (UEs). Furthermore, the UE operates in unstructured, often hazardous environments, and requires a robust parameter identification scheme for field applications. This paper presents the results of a research study on parameter identification for UE. Three identification methods, the Newton-Raphson method, the generalized Newton method, and the least squares method are used and compared for prediction accuracy, robustness to noise and computational speed. The techniques are used to identify the link parameters (mass, inertia, and length) and friction coefficients of the full-scale UE. Using experimental data from a full-scale field UE, the values of link parameters and the friction coefficient are identified. Some of the identified parameters are compared with measured physical values. Furthermore, the joint torques and positions computed by the proposed model using the identified parameters are validated against measured data. The comparison shows that both the Newton-Raphson method and the generalized Newton method are better in terms of prediction accuracy. The Newton-Raphson method is computationally efficient and has potential for real time application, but the generalized Newton method is slightly more robust to measurement noise. The experimental data were obtained in collaboration with QinetiQ Ltd. 相似文献
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Guo-Liang TianMan-Lai Tang Chunling Liu 《Computational statistics & data analysis》2012,56(2):255-265
When the Newton-Raphson algorithm or the Fisher scoring algorithm does not work and the EM-type algorithms are not available, the quadratic lower-bound (QLB) algorithm may be a useful optimization tool. However, like all EM-type algorithms, the QLB algorithm may also suffer from slow convergence which can be viewed as the cost for having the ascent property. This paper proposes a novel ‘shrinkage parameter’ approach to accelerate the QLB algorithm while maintaining its simplicity and stability (i.e., monotonic increase in log-likelihood). The strategy is first to construct a class of quadratic surrogate functions Qr(θ|θ(t)) that induces a class of QLB algorithms indexed by a ‘shrinkage parameter’ r (r∈R) and then to optimize r over R under some criterion of convergence. For three commonly used criteria (i.e., the smallest eigenvalue, the trace and the determinant), we derive a uniformly optimal shrinkage parameter and find an optimal QLB algorithm. Some theoretical justifications are also presented. Next, we generalize the optimal QLB algorithm to problems with penalizing function and then investigate the associated properties of convergence. The optimal QLB algorithm is applied to fit a logistic regression model and a Cox proportional hazards model. Two real datasets are analyzed to illustrate the proposed methods. 相似文献
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《Calphad》2018
Due to the importance of phase diagrams in a wide range of material based industries, additional efforts should be dedicated to their elaboration techniques. The cluster variation method is a promising technique to model the entropy within different plane lattices and is recognized by the materials physics community as a powerful modeling framework. Motivated by the efficiency of genetic algorithms in solving numerous types of optimization problems, our aim in this work is to investigate their performance in minimizing the grand potential in the context of the cluster variation method. A comparison is conducted with respect to numerical iterative techniques namely the Newton-Raphson and natural iteration methods, where many performance criteria are computed and compared. The obtained results allow the ranking of the considered approaches according to their performance measures and suggest a more profound investigation of metaheuristics particularly for complicated cluster structures in the future. 相似文献