全文获取类型
收费全文 | 23258篇 |
免费 | 3595篇 |
国内免费 | 2215篇 |
专业分类
电工技术 | 2776篇 |
综合类 | 2844篇 |
化学工业 | 1199篇 |
金属工艺 | 392篇 |
机械仪表 | 1226篇 |
建筑科学 | 709篇 |
矿业工程 | 306篇 |
能源动力 | 464篇 |
轻工业 | 205篇 |
水利工程 | 322篇 |
石油天然气 | 348篇 |
武器工业 | 466篇 |
无线电 | 5997篇 |
一般工业技术 | 1761篇 |
冶金工业 | 359篇 |
原子能技术 | 134篇 |
自动化技术 | 9560篇 |
出版年
2024年 | 147篇 |
2023年 | 409篇 |
2022年 | 590篇 |
2021年 | 697篇 |
2020年 | 816篇 |
2019年 | 824篇 |
2018年 | 754篇 |
2017年 | 1031篇 |
2016年 | 1103篇 |
2015年 | 1140篇 |
2014年 | 1508篇 |
2013年 | 1810篇 |
2012年 | 1667篇 |
2011年 | 1904篇 |
2010年 | 1417篇 |
2009年 | 1423篇 |
2008年 | 1546篇 |
2007年 | 1682篇 |
2006年 | 1331篇 |
2005年 | 1185篇 |
2004年 | 914篇 |
2003年 | 801篇 |
2002年 | 661篇 |
2001年 | 543篇 |
2000年 | 449篇 |
1999年 | 401篇 |
1998年 | 324篇 |
1997年 | 324篇 |
1996年 | 249篇 |
1995年 | 248篇 |
1994年 | 214篇 |
1993年 | 146篇 |
1992年 | 151篇 |
1991年 | 110篇 |
1990年 | 95篇 |
1989年 | 65篇 |
1988年 | 48篇 |
1987年 | 38篇 |
1986年 | 27篇 |
1985年 | 35篇 |
1984年 | 52篇 |
1983年 | 24篇 |
1982年 | 40篇 |
1981年 | 36篇 |
1980年 | 25篇 |
1979年 | 14篇 |
1978年 | 14篇 |
1977年 | 14篇 |
1957年 | 2篇 |
1951年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
61.
Abstract. Locally stationary processes are non‐stationary stochastic processes the second‐order structure of which varies smoothly over time. In this paper, we develop a method to bootstrap the local periodogram of a locally stationary process. Our method generates pseudo local periodogram ordinates by combining a parametric time and non‐parametric frequency domain bootstrap approach. We first fit locally a time varying autoregressive model so as to capture the essential characteristics of the underlying process. A locally calculated non‐parametric correction in the frequency domain is then used so as to improve upon the locally parametric autoregressive fit. As an application, we investigate theoretically the asymptotic properties of the bootstrap method proposed applied to the class of local spectral means, local ratio statistics and local spectral density estimators. Some simulations demonstrate the ability of our method to give accurate estimates of the quantities of interest in finite sample situations and an application to a real‐life data‐set is presented. 相似文献
62.
Sebastián López Gustavo M. Callicó Félix Tobajas Valentín de Armas José F. López Roberto Sarmiento 《ETRI Journal》2008,30(6):862-864
This letter presents a novel approach for organizing computational resources into groups within H.264/AVC motion estimation architectures, leading to reductions of up to 75% in the equivalent gate count with respect to state‐of‐the‐art designs. 相似文献
63.
In this paper the response of nonlinear systems driven by parametric Poissonian white noise is examined.As is well known, the response sample function or the response statistics of a system driven by external white noise processes is completely defined. Starting from the system driven by external white noise processes, when an invertible nonlinear transformation is applied, the transformed system in the new state variable is driven by a parametric type excitation. So this latter artificial system may be used as a tool to find out the proper solution to solve systems driven by parametric white noises. In fact, solving this new system, being the nonlinear transformation invertible, we must pass from the solution of the artificial system (driven by parametric noise) to that of the original one (driven by external noise, that is known). Moreover, introducing this invertible nonlinear transformation into the Itô’s rule for the original system driven by external input, one can derive the Itô’s rule for systems driven by a parametric type excitation, directly. In this latter case one can see how natural is the presence of the Wong–Zakai correction term or the presence of the hierarchy of correction terms in the case of normal and Poissonian white noise, respectively. Direct transformation on the Fokker–Planck and on the Kolmogorov–Feller equation for the case of parametric input are found. 相似文献
64.
Minglun Gong Author Vitae Author Vitae 《Pattern recognition》2004,37(8):1723-1733
Many computer vision problems can be formulated as optimization problems. Presented in this paper is a new framework based on the quadtree-based genetic algorithm that can be applied to solve many of these problems. The proposed algorithm incorporates the quadtree structure into the conventional genetic algorithm. The solutions of image-related problems are encoded through encoding the corresponding quadtrees, and therefore, the 2D locality within a solution can be preserved. Examples addressed using the proposed framework include image segmentation, stereo vision, and motion estimation. In all cases, encouraging results are obtained. 相似文献
65.
The transit time of the coolant, and thus its velocity, has been measured using the temperature fluctuation at the outlet of a reactor core. An impulse response function estimation is introduced, which substitutes the widely used cross-correlation measurement technique. It is shown in theory and practice that the time delay estimation is improved when using the impulse response function instead of the cross-correlation function in parameter estimation. Extremely low velocities (down to 2 cm/sec) have been measured in a natural circulation regime in a research reactor. 相似文献
66.
光纤荧光传感器衰减寿命的加权对数拟合法 总被引:2,自引:0,他引:2
荧光寿命的检测是荧光光学传感器的核心内容,国际上尝试了多种方法来拟合这种理论上为单指数衰减信号的荧光衰减曲线。这些方法包括非线性函数标准拟合方法。即Levenburg-Marquardt方法,以及Prony方法、FFT方法,对数拟合法等等。为了克服在实际应用中发生的信号退化,需要在测量信号衰减寿命的同时测量信号的初始强度。文章介绍了一种加权的对数拟合法,经计算机仿真及实际数据测试均可以得到和Levenburg-Marquardt方法非常接近的结果,且拟合时间大大缩短,测量稳定性大大提高。仿真测试及具体实验测试结果显示了这种方法的有效性。该方法不仅与Levenburg-Marquardt方法的偏差曲线非常相似,而且实验测得的荧光寿命与Levenburg-Marquardt方法偏差在0.2%以内。 相似文献
67.
68.
69.
Rudolf Habison 《International Journal of Project Management》1985,3(3):178-181
Meeting time and cost objectives in complex projects involves specific problems and risks. An attempt is made to analyse the components of total cost increase of a project caused by time delay. An outline is given as to how these considerations can be used to estimate cost increases in investors' decision situations as well as to ascertain fair contractual penalties and claims for compensation and for the evaluation of justified project acceleration costs. 相似文献
70.