全文获取类型
收费全文 | 61963篇 |
免费 | 8903篇 |
国内免费 | 4870篇 |
专业分类
电工技术 | 10956篇 |
技术理论 | 3篇 |
综合类 | 7040篇 |
化学工业 | 2618篇 |
金属工艺 | 1400篇 |
机械仪表 | 4529篇 |
建筑科学 | 3113篇 |
矿业工程 | 1524篇 |
能源动力 | 1572篇 |
轻工业 | 987篇 |
水利工程 | 1185篇 |
石油天然气 | 1605篇 |
武器工业 | 939篇 |
无线电 | 15323篇 |
一般工业技术 | 5348篇 |
冶金工业 | 1538篇 |
原子能技术 | 491篇 |
自动化技术 | 15565篇 |
出版年
2024年 | 343篇 |
2023年 | 915篇 |
2022年 | 1491篇 |
2021年 | 1796篇 |
2020年 | 2034篇 |
2019年 | 1800篇 |
2018年 | 1763篇 |
2017年 | 2352篇 |
2016年 | 2613篇 |
2015年 | 2923篇 |
2014年 | 4100篇 |
2013年 | 4227篇 |
2012年 | 4872篇 |
2011年 | 5229篇 |
2010年 | 4090篇 |
2009年 | 3957篇 |
2008年 | 4004篇 |
2007年 | 4690篇 |
2006年 | 3841篇 |
2005年 | 3237篇 |
2004年 | 2546篇 |
2003年 | 2216篇 |
2002年 | 1892篇 |
2001年 | 1557篇 |
2000年 | 1255篇 |
1999年 | 1106篇 |
1998年 | 814篇 |
1997年 | 714篇 |
1996年 | 585篇 |
1995年 | 537篇 |
1994年 | 448篇 |
1993年 | 320篇 |
1992年 | 287篇 |
1991年 | 220篇 |
1990年 | 179篇 |
1989年 | 128篇 |
1988年 | 99篇 |
1987年 | 82篇 |
1986年 | 54篇 |
1985年 | 59篇 |
1984年 | 77篇 |
1983年 | 36篇 |
1982年 | 57篇 |
1981年 | 45篇 |
1980年 | 34篇 |
1979年 | 24篇 |
1978年 | 14篇 |
1977年 | 16篇 |
1975年 | 6篇 |
1959年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
研究了多径信道下OFDM系统的一种新的载波频率跟踪算法,这种算法以判决反馈和接收端的时域信号重构为基础。推导了估计结果的精确解,比较了使用原估计结果和新的估计结果进行频偏补偿时系统跟踪性能的不同。通过对算法的仔细分析,发现除了通常的加性噪声外,信道估计误差、子载波数目和子载波的调制方式也影响频偏的估计结果和跟踪范围,而且子载波的数目和调制方式是决定性的因素。这种频率跟踪方法的优点是即使在很低的信噪比下仍然能获得高的跟踪精度,且实现相对简单。 相似文献
112.
The discrimination problem for two normal populations with the same covariance matrix when additional information on the population is available is considered. A study of the robustness properties against training sample contamination of classification rules that incorporate this additional information is performed. These rules have received recently attention where their total misclassification probability (TMP) is proved to be lower than Fisher's linear discriminant rule. The results of a simulation study on the TMP which compares the behaviour of the new rules against Fisher's rule and some of its robustified versions under different types of contamination are presented. These results show that the rules that incorporate the additional information not only have lower TMP, but they also prevent against some types of contamination. In order to achieve prevention from all types of contamination a robustifed version of these rules is recommended. 相似文献
113.
煤矿局部通风的设计与应用技术 总被引:3,自引:0,他引:3
分析了现有煤矿局部通风工程中普遍存在的问题,采用符合矿井实际的设计和施工技术,就能在使用过程中获得显著效果,可大大减少漏风,提高有效风量,满足安全生产的需要,从而解决长距离独头掘进通风的难题。 相似文献
114.
Previous work by Li et al. in the area of axial vibrations of bellows dealt with fixed end conditions. However, it is seen on several occasions that bellow ends are welded to a small pipe spool that has a lumped mass such as a valve or an instrument. Hence, the present paper aims at finding out the effect of elastically restrained ends on the axial natural frequencies. The analysis considers finite stiffness axial restraints on the bellows, i.e. solving the set of equations with non-homogeneous boundary conditions. Two bellow specimens are considered for comparison having the same dimensions as taken by Li in his analysis. The transcendental frequency equation deduced is accurate as the first, second and third mode frequencies computed are in close agreement to the ones obtained by Li. 相似文献
115.
GPS RTK(Real Time Kinematic)技术的快速定位功能为其应用创造了良好的条件,但其定位精度验后估计的欠缺又使其应用受到一定的限制。本文针对此问题进行了研究,给出了GPS RTK测量成果的精度估计方法,并对GPS RTK测量技术用于控制测量的可行性进行了探讨,导出了相应的测量限差,为CPS RTK测量技术用于控制测量提供了理论依据和技术规定。 相似文献
116.
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
117.
J. L. Barron R. E. Mercer X. Chen P. Joe 《International journal of imaging systems and technology》2005,15(3):189-198
We present local least squares and regularization frameworks for computing 3D velocity (3D optical flow) from 3D radial velocity measured by a Doppler radar. We demonstrate the performance of our algorithms quantitatively on synthetic radial velocity data and qualitatively on real radial velocity data, obtained from the Doppler radar at Kurnell Radar station, Botany Bay, New South Wales, Australia. Radial velocity can be used to predict the future positions of storms in sequences of Doppler radar datasets.© 2005 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 15, 189–198, 2005 相似文献
118.
旋转导向钻井偏心稳定器横向振动研究 总被引:4,自引:1,他引:3
旋转导向钻井偏心稳定器横向振动研究是国家863“可控(闭环)三维轨迹钻井技术”课题研究的部分内容。选取偏心稳定器的心轴作为研究对象,以偏心稳定器心轴连续梁系统的横向振动模型受力分析为基础,根据课题研究中所设计的心轴结构形式,建立了与实际情况较为接近的三铰支点的连续梁系统横向振动方程;并分析了偏心稳定器横向振动对钻井工具和钻具系统的影响,为合理进行心轴设计以及偏心稳定器样机在现场的正确使用和钻井参数的合理选择,提供了科学的理论依据和实用的计算方法。计算实例表明,当钻压范围选择在80~250kN时,215.9mm井眼钻进中的确存在19~20、61~63、162~163r/min前三阶横向共振转速区间,因此在选择钻井参数时应通过钻压与转速的配合,尽可能避开横向共振转速,以保证下部钻具组合系统及作业安全。 相似文献
119.
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
120.
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