全文获取类型
收费全文 | 19996篇 |
免费 | 3047篇 |
国内免费 | 1913篇 |
专业分类
电工技术 | 2282篇 |
综合类 | 2373篇 |
化学工业 | 1101篇 |
金属工艺 | 138篇 |
机械仪表 | 998篇 |
建筑科学 | 570篇 |
矿业工程 | 243篇 |
能源动力 | 367篇 |
轻工业 | 188篇 |
水利工程 | 263篇 |
石油天然气 | 287篇 |
武器工业 | 440篇 |
无线电 | 5724篇 |
一般工业技术 | 1535篇 |
冶金工业 | 246篇 |
原子能技术 | 114篇 |
自动化技术 | 8087篇 |
出版年
2024年 | 159篇 |
2023年 | 370篇 |
2022年 | 557篇 |
2021年 | 642篇 |
2020年 | 713篇 |
2019年 | 698篇 |
2018年 | 652篇 |
2017年 | 897篇 |
2016年 | 936篇 |
2015年 | 951篇 |
2014年 | 1311篇 |
2013年 | 1522篇 |
2012年 | 1407篇 |
2011年 | 1640篇 |
2010年 | 1219篇 |
2009年 | 1231篇 |
2008年 | 1332篇 |
2007年 | 1461篇 |
2006年 | 1099篇 |
2005年 | 994篇 |
2004年 | 759篇 |
2003年 | 672篇 |
2002年 | 561篇 |
2001年 | 456篇 |
2000年 | 359篇 |
1999年 | 344篇 |
1998年 | 275篇 |
1997年 | 275篇 |
1996年 | 213篇 |
1995年 | 215篇 |
1994年 | 176篇 |
1993年 | 122篇 |
1992年 | 136篇 |
1991年 | 94篇 |
1990年 | 89篇 |
1989年 | 60篇 |
1988年 | 44篇 |
1987年 | 35篇 |
1986年 | 23篇 |
1985年 | 33篇 |
1984年 | 49篇 |
1983年 | 21篇 |
1982年 | 38篇 |
1981年 | 35篇 |
1980年 | 23篇 |
1979年 | 14篇 |
1978年 | 13篇 |
1977年 | 14篇 |
1959年 | 3篇 |
1951年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Hong Jeong Jeong‐Ho Park 《International Journal of Adaptive Control and Signal Processing》2002,16(1):1-23
Tracking targets of interest is one of the major research areas in radar surveillance systems. We formulate the problem as incomplete data estimation and apply EM to the MAP estimate. The resulting filter has a recursive structure analogous to the Kalman filter. The advantage is that the measurement‐update deals with multiple measurements in parallel and the parameter‐update estimates the system parameters on the fly. Experiments tracking separate targets in parallel show that tracking maintenance ratio of the proposed system is better than that of NNF and RMS position error is smaller than that of PDAF. Also, the system parameters are correctly obtained even from incorrect initial values. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
42.
43.
QifengShu JiayunZhang 《北京科技大学学报(英文版)》2005,12(3):221-224
Based on recently published experimental data, the Riboud model was modified for viscosity estimation of the slags containing calcium fluoride. The estimated values were in good agreement with measured data. Reasonable estimation can be achieved using the modified Riboud model for mould fluxes and ESR (eletro slag remelting) slags. Especially for ESR slags, the modified Riboud model can provide much more precise values than the original Riboud model. 相似文献
44.
45.
Toshihiko Hoshide Junpei Fujita 《Journal of Materials Engineering and Performance》2008,17(5):627-632
Strength of ground ceramics may be affected by residual stress as well as surface flaws induced by grinding. Strength prediction
for ground ceramics is convenient for mechanical design of ceramic components. In this article, a numerical procedure based
on fracture mechanics was proposed to estimate strength distribution of ground ceramics by considering grinding-induced residual
stress. Bending strength and residual stress of ground ceramics were measured for three grinding-conditions. By comparison
of simulated results with experimental ones, it was revealed that strength characteristics in experiments were well simulated
by using the proposed procedure. 相似文献
46.
Morten
rregaard Nielsen 《时间序列分析杂志》2005,26(2):279-304
Abstract. We consider semiparametric estimation in time‐series regression in the presence of long‐range dependence in both the errors and the stochastic regressors. A central limit theorem is established for a class of semiparametric frequency domain‐weighted least squares estimates, which includes both narrow‐band ordinary least squares and narrow‐band generalized least squares as special cases. The estimates are semiparametric in the sense that focus is on the neighbourhood of the origin, and only periodogram ordinates in a degenerating band around the origin are used. This setting differs from earlier studies on time‐series regression with long‐range dependence, where a fully parametric approach has been employed. The generalized least squares estimate is infeasible when the degree of long‐range dependence is unknown and must be estimated in an initial step. In that case, we show that a feasible estimate which has the same asymptotic properties as the infeasible estimate, exists. By Monte Carlo simulation, we evaluate the finite‐sample performance of the generalized least squares estimate and the feasible estimate. 相似文献
47.
H. Luo 《Microsystem Technologies》2006,12(4):324-329
This paper focuses on tracking, reconstruction and motion estimation of a well-defined MEMS optical switch from a microscopic
view. For out-of-view reconstruction, a homography capable of transforming feature points and feature lines between a microscopic
image and a CAD model of the switch is implemented. The homography between two sequential microscopic images is decomposed
and factorized for motion estimation. Optical flow has also been explored to provide rough estimations of rotation centre
and angle. The paper also illustrates motion parameter optimization principles to deal with uncertainty inherent in micro
world. After non-linear optimization, estimation accuracy for rotation angle and rotation centre can reach 0.06° and pixel
level, respectively. 相似文献
48.
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
49.
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
50.
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