全文获取类型
收费全文 | 26081篇 |
免费 | 3185篇 |
国内免费 | 2091篇 |
专业分类
电工技术 | 3193篇 |
技术理论 | 1篇 |
综合类 | 3086篇 |
化学工业 | 2088篇 |
金属工艺 | 1496篇 |
机械仪表 | 2697篇 |
建筑科学 | 1804篇 |
矿业工程 | 1293篇 |
能源动力 | 807篇 |
轻工业 | 1030篇 |
水利工程 | 947篇 |
石油天然气 | 2048篇 |
武器工业 | 521篇 |
无线电 | 2341篇 |
一般工业技术 | 2493篇 |
冶金工业 | 800篇 |
原子能技术 | 286篇 |
自动化技术 | 4426篇 |
出版年
2024年 | 119篇 |
2023年 | 307篇 |
2022年 | 662篇 |
2021年 | 725篇 |
2020年 | 830篇 |
2019年 | 687篇 |
2018年 | 644篇 |
2017年 | 881篇 |
2016年 | 993篇 |
2015年 | 1033篇 |
2014年 | 1491篇 |
2013年 | 1532篇 |
2012年 | 1792篇 |
2011年 | 1915篇 |
2010年 | 1521篇 |
2009年 | 1611篇 |
2008年 | 1534篇 |
2007年 | 1926篇 |
2006年 | 1731篇 |
2005年 | 1461篇 |
2004年 | 1244篇 |
2003年 | 1062篇 |
2002年 | 889篇 |
2001年 | 735篇 |
2000年 | 677篇 |
1999年 | 547篇 |
1998年 | 423篇 |
1997年 | 405篇 |
1996年 | 334篇 |
1995年 | 325篇 |
1994年 | 282篇 |
1993年 | 172篇 |
1992年 | 185篇 |
1991年 | 151篇 |
1990年 | 123篇 |
1989年 | 87篇 |
1988年 | 65篇 |
1987年 | 36篇 |
1986年 | 30篇 |
1985年 | 14篇 |
1984年 | 34篇 |
1983年 | 18篇 |
1982年 | 22篇 |
1981年 | 27篇 |
1980年 | 19篇 |
1979年 | 19篇 |
1978年 | 14篇 |
1977年 | 12篇 |
1959年 | 5篇 |
1951年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
In this paper, the problem of robust matrix root‐clustering is addressed. The studied matrices are subject to both polytopic and unstructured uncertainties. An original point is the large choice of clustering regions enabled by the proposed approach since these regions can be unions of possibly disjoint and non‐symmetric subregions of the complex plane. The precise purpose is, considering a specified polytope, to determine the greatest robustness bound on the unstructured uncertainty such that robust matrix root‐clustering is ensured. To reduce conservatism in the derivation of the bound, the reasoning relies on a framework based upon parameter‐dependent Lyapunov functions. The bound value is computed by solving an ?? ?? ? problem. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
992.
L Jarlan P MazzegaE Mougin F LavenuG Marty P.L FrisonP Hiernaux 《Remote sensing of environment》2003,87(1):72-84
The West African Sahel rainfall regime is known for its spatio-temporal variability at different scales which has a strong impact on vegetation development. This study presents results of the combined use of a simple water balance model, a radiative transfer model and ERS scatterometer data to produce map of vegetation biomass and thus vegetation cover at a spatial resolution of 25 km. The backscattering coefficient measured by spaceborne wind scatterometers over Sahel shows a marked seasonality linked to the drastic changes of both soil and vegetation dielectric properties associated to the alternating dry and wet seasons. For lack of a direct observation, METEOSAT rainfall estimates are used to calculate temporal series of soil moisture with the help of a water balance model. This a priori information is used as input of the radiative transfer model that simulates the interaction between the radar wave and the surface components (soil and vegetation). Then, an inversion algorithm is applied to retrieve vegetation aerial mass from the ERS scatterometer data. Because of the nonlinear feature of the inverse problem to be solved, the inversion is performed using a global stochastic nonlinear inversion method. A good agreement is obtained between the inverse solutions and independent field measurements with mean and standard deviation of −54 and 130 kg of dry matter by hectare (kg DM/ha), respectively. The algorithm is then applied to a 350,000 km2 area including the Malian Gourma and Seno region and a Sahelian part of Burkina Faso during two contrasted seasons (1999 and 2000). At the considered resolution, the obtained herbaceous mass maps show a global qualitative consistency (r2=0.71) with NDVI images acquired by the VEGETATION instrument. 相似文献
993.
电气参数交流采样技术 总被引:6,自引:1,他引:6
分析了半波付里叶算法(Half-cycle Fournier Arithmetic)在电气参数测量装置中应用的基本原理,指出了影响该算法测量精度的各种因素,并结合80C196KC单片机交流采样测量系统,从算法、测频、采样步长划分、采样同步、单片机A/D转换、抗干扰以及参数计算等角度提出了相应的改进措施,从而提高了电气参数的测量精度,增强了半波付里叶算法在电气参数测量中的实用性。 相似文献
994.
995.
996.
基于脉冲响应的输出误差模型的辨识 总被引:7,自引:0,他引:7
基于系统脉冲响应参数, 利用相关分析方法, 提出了一种辨识输出误差模型参数的方法. 该方法是利用有限脉冲响应模型逼近输出误差模型, 通过依次递增脉冲响应参数的数目N来提高逼近精度. 理论分析表明, 只要N足够大, 模型的辨识精度可以满足实际要求. 提出的辨识方法可以在假设阶次N =1的条件下, 依次递增计算N较大时的脉冲响应参数和目标函数值, 从而根据脉冲响应确定系统的参数. 仿真试验说明提出的方法估计输出误差模型的参数是有效的. 相似文献
997.
研究了一类分布参数系统在有限维输出反馈下的指数能稳性,用构造有限维观测输出反馈控制器的方法,得到这一类系统反馈指数能稳的充分条件. 相似文献
998.
This paper presents a homotopy-based algorithm for the recovery of depth cues in the spatial domain. The algorithm specifically deals with defocus blur and spatial shifts, that is 2D motion, stereo disparities and/or zooming disparities. These cues are estimated from two images of the same scene acquired by a camera evolving in time and/or space. We show that they can be simultaneously computed by resolving a system of equations using a homotopy method. The proposed algorithm is tested using synthetic and real images. The results confirm that the use of a homotopy method leads to a dense and accurate estimation of depth cues. This approach has been integrated into an application for relief estimation from remotely sensed images. 相似文献
999.
This paper considers the design of feedback controllers for linear, time-invariant, spatially distributed systems in an approach which generalises the H∞-framework and in particular the H∞ loop-shaping method. To this end, we introduce a class of spatially distributed system models called finite dimensional, distributed, linear, time-invariant systems. Sensors and actuators are considered to be part of the controller, rather than part of the plant, and thus the controller we wish to design is itself a spatially distributed system. Optimising over placements and shapes of the sensor and actuator spatial distribution functions is an integrated part of the controller design procedure. As an illustrative design example, we present the feedback stabilisation of an electrostatically destabilised, electrically conducting membrane. 相似文献
1000.
Oracle数据库性能优化策略 总被引:1,自引:0,他引:1
Orack数据库应用系统性能优化是一个周而复始的系统工程。本文论述了Orack数据库管理系统的一些基本工作原理,并分析了一些影响应用性能的可能因素,同时结合实际给出了一些可行的调整数据库应用性能的策略与方法。 相似文献