全文获取类型
收费全文 | 28952篇 |
免费 | 3558篇 |
国内免费 | 2883篇 |
专业分类
电工技术 | 2959篇 |
综合类 | 4446篇 |
化学工业 | 1846篇 |
金属工艺 | 756篇 |
机械仪表 | 1765篇 |
建筑科学 | 1626篇 |
矿业工程 | 655篇 |
能源动力 | 680篇 |
轻工业 | 1511篇 |
水利工程 | 892篇 |
石油天然气 | 795篇 |
武器工业 | 381篇 |
无线电 | 3309篇 |
一般工业技术 | 3037篇 |
冶金工业 | 562篇 |
原子能技术 | 268篇 |
自动化技术 | 9905篇 |
出版年
2024年 | 104篇 |
2023年 | 377篇 |
2022年 | 705篇 |
2021年 | 799篇 |
2020年 | 933篇 |
2019年 | 936篇 |
2018年 | 835篇 |
2017年 | 1139篇 |
2016年 | 1193篇 |
2015年 | 1210篇 |
2014年 | 1734篇 |
2013年 | 2313篇 |
2012年 | 2129篇 |
2011年 | 2285篇 |
2010年 | 1783篇 |
2009年 | 1849篇 |
2008年 | 1792篇 |
2007年 | 2051篇 |
2006年 | 1663篇 |
2005年 | 1458篇 |
2004年 | 1248篇 |
2003年 | 1046篇 |
2002年 | 910篇 |
2001年 | 769篇 |
2000年 | 649篇 |
1999年 | 544篇 |
1998年 | 436篇 |
1997年 | 428篇 |
1996年 | 341篇 |
1995年 | 288篇 |
1994年 | 251篇 |
1993年 | 203篇 |
1992年 | 173篇 |
1991年 | 160篇 |
1990年 | 142篇 |
1989年 | 99篇 |
1988年 | 68篇 |
1987年 | 49篇 |
1986年 | 38篇 |
1985年 | 25篇 |
1984年 | 43篇 |
1983年 | 40篇 |
1982年 | 30篇 |
1981年 | 28篇 |
1980年 | 23篇 |
1979年 | 10篇 |
1978年 | 12篇 |
1977年 | 14篇 |
1975年 | 4篇 |
1959年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
Let us consider n data measurements of a univariate process that have been altered by random errors. We assume that an underlying model function has a substantially smaller number of turning points than the observed ones. We propose algorithms that make least the sum of the moduli of the errors by requiring k monotonic sections, alternately increasing and decreasing, in the sequence of the smoothed values. The main difficulty in this calculation is that the optimal positions of the joins of the monotonic sections have to be found automatically among so many combinations that it is impossible to test each one separately. Moreover, the calculation seems to be very intractable to general optimization techniques because O(nk ) local minima can occur. It is shown that dynamic programming can be used for separating the data into optimal disjoint sections of adjacent data, where each section requires a single L1 monotonic calculation. This procedure is highly efficient, requiring at most O(kn2 ) computer operations and O(n) best L1 monotonic calculations to subranges of data for a global minimum. 相似文献
92.
With the growing size and complexity of power systems, system analysis—such as transients calculation—takes much time. Hence, fast calculation methods are required. Although parallel processing is a hopeful method, there have been difficulties in the parallel solution of linear equations which appear in power-flow calculations by the Newton-Raphson method. This paper aims at the fast calculation of the power-flow problem by means of parallel processing. In order to improve the suitability to the parallel solution of the differential equation in transients calculation, we assume the use of a direct-mapping parallel processing machine to map directly the network of a power system onto a network of processors. Under this assumption, we propose a new parallel-processing-oriented method in which the linear equation is solved by linear iterations between nodes with Aitken acceleration. We simulate the method on three model power systems and compare this Parallel Iterative Method (PIN) with a Parallel Direct Method (PDM) which uses the banded matrix according to the number of operations required. As a result, we can expect that PIM may solve linear equations faster than PDM with m processors, although the PIM might be inferior to the PDM with m × m processors, where m denotes the half-band width of the banded matrix. 相似文献
93.
钢铁企业价格预测决策模型体系研究 总被引:1,自引:0,他引:1
通过对钢铁企业现行价格管理体系的分析 ,建立了钢铁企业价格预测决策模型体系。充分利用大量的定性、定量信息 ,并把趋势预测和因果预测技术相结合 ,采用组合预测模型对价格进行预测 ,最后对预测出来的多方案进行模糊综合评价 ,给出推荐方案顺序。实际应用表明 ,模型体系是有效的。 相似文献
94.
The present paper demonstrates the applicability of population based search optimization method, namely, Differential Evolution
(DE) to a case study of Mahi Bajaj Sagar Project (MBSP), India. Ten different strategies of DE are employed to assess the
ability of DE for solving higher dimensional problems as an alternative methodology for irrigation planning. The parameters
considered in DE are population size, crossover constant and weighting factor. Linear Programming (LP) is utilized as a comparative
approach to assess the ability of DE. Comparison of results of LP and the 10 DE strategies for the given parameters indicated
that both the results are comparable even for high dimensional problems. Extensive sensitivity analysis studies, performed
for 3,600 combinations of above parameters for the 10 DE strategies suggested that DE/rand-to-best/1/bin strategy is the best
strategy giving maximum benefits taking minimum CPU time. It is concluded that DE can be utilized for efficient planning of
any irrigation system with suitable modifications. 相似文献
95.
本文提出了一种宽线性共轭梯度算法,分析了算法在均值意义下的收敛性,并给出了算法稳定条件。仿真表明,新算法应用于码分多址系统多址干扰抑制时的性能优于Yin(2003)及Schober(2004)所提出的算法。 相似文献
96.
97.
M. M. Rashid 《International journal for numerical methods in engineering》2002,55(4):431-450
A computational procedure for remapping material state information from one finite element mesh to another is described. The procedure is useful in connection with evolving meshes for inelastic problems, as for example occur in the context of fracture simulation and adaptive mesh refinement. The proposed method is based on weak enforcement of equality between corresponding fields on the two meshes, where piecewise‐constant fields on both meshes are generalized from the quadrature‐point values. The essential algorithmic problem is that of calculating the volume partition of an arbitrary convex region with respect to a covering set of disjoint convex regions. Instead of geometrically resolving the associated intersections, the problem is herein approximated by a constrained optimization problem, which may be readily and efficiently solved computationally. This formulation is a main contribution of the paper. Computational examples are given that illustrate the effectiveness of the proposed procedure. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
98.
基于二阶矩阵微分方程的机械振动系统线性二次型调节器设计 总被引:1,自引:0,他引:1
本文讨论机械振动系统线性二次型状态调节器(LQR)问题,直接针对系统二阶运动微分方程,性能指标为一个依赖于二阶导数的泛函。由欧拉-拉格朗日方程得出一个系统矩阵增广的二阶线性微分方程,指出该方程稳定的特征对就是最优控制振动系统闭环特征对,并给出求解最优控制状态反馈矩阵的方法,另外,由本文方法还可得出基于速度和加速度反馈的最优控制反馈矩阵。这里不涉及求解代数矩阵Riccati方程。 相似文献
99.
打括隧道监控量测结果的一元非线性回归分析 总被引:2,自引:0,他引:2
针对黄织铁路工程打括隧道923延米V级围岩土质地段,根据施工中的地质动态对打括隧道初期支护中监控量测结果进行一元非性线回归分析,以制定科学施工方案和确定合理支护参数,保证工程质量和作业的安全性。 相似文献
100.
P. I. Stetsyuk 《Cybernetics and Systems Analysis》2006,42(1):54-64
New quadratic models are proposed to improve the upper-bound estimates in the maximum weighted cut problem. They are found
by two original methods for deriving redundant quadratic constraints. A well-known linear model is shown to follow from the
models proposed. Recommendations on how to develop its strengthened analogs are given.
This study is partially sponsored from the grant UM2-2574-KV-03 (CRDF Cooperative Grants Program).
__________
Translated from Kibernetika i Sistemnyi Analiz, No. 1, pp. 63—75, January–February 2006. 相似文献