全文获取类型
收费全文 | 4286篇 |
免费 | 383篇 |
国内免费 | 155篇 |
专业分类
电工技术 | 232篇 |
综合类 | 239篇 |
化学工业 | 786篇 |
金属工艺 | 212篇 |
机械仪表 | 241篇 |
建筑科学 | 314篇 |
矿业工程 | 98篇 |
能源动力 | 128篇 |
轻工业 | 349篇 |
水利工程 | 90篇 |
石油天然气 | 321篇 |
武器工业 | 41篇 |
无线电 | 450篇 |
一般工业技术 | 518篇 |
冶金工业 | 228篇 |
原子能技术 | 78篇 |
自动化技术 | 499篇 |
出版年
2024年 | 17篇 |
2023年 | 77篇 |
2022年 | 142篇 |
2021年 | 221篇 |
2020年 | 176篇 |
2019年 | 123篇 |
2018年 | 158篇 |
2017年 | 152篇 |
2016年 | 169篇 |
2015年 | 213篇 |
2014年 | 217篇 |
2013年 | 259篇 |
2012年 | 317篇 |
2011年 | 314篇 |
2010年 | 258篇 |
2009年 | 240篇 |
2008年 | 203篇 |
2007年 | 179篇 |
2006年 | 179篇 |
2005年 | 153篇 |
2004年 | 125篇 |
2003年 | 108篇 |
2002年 | 85篇 |
2001年 | 77篇 |
2000年 | 83篇 |
1999年 | 91篇 |
1998年 | 79篇 |
1997年 | 67篇 |
1996年 | 62篇 |
1995年 | 60篇 |
1994年 | 43篇 |
1993年 | 29篇 |
1992年 | 22篇 |
1991年 | 24篇 |
1990年 | 13篇 |
1989年 | 12篇 |
1988年 | 9篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1985年 | 7篇 |
1984年 | 9篇 |
1983年 | 6篇 |
1982年 | 7篇 |
1980年 | 9篇 |
1978年 | 8篇 |
1977年 | 5篇 |
1974年 | 2篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有4824条查询结果,搜索用时 148 毫秒
81.
基于MODIS数据分析了2000~2010年祁连山区植被净初级生产力(Net Primary Productivity,NPP)的空间变化特征。结果显示:祁连山区植被NPP并不高,多年平均植被NPP仅为121.95gC/(m2·a),自东向西植被NPP逐渐减少。不同植被类型其NPP具有明显差异,大体上为:常绿阔叶林平原草地常绿针叶林典型草地农田高寒草甸草地荒漠草地落叶针叶林。祁连山区植被NPP变化在区域间也存在差异。植被NPP呈增长趋势的地区主要分布在青海年南山、拉脊山、达坂山和青海湖及其西侧,约占47.30%;乌鞘岭东部及以东的地区(约占1.97%)植被NPP呈减少趋势。降水是祁连山区植被NPP变化的主要因素,气温对植被NPP的影响并不明显,不合理的人类活动可能是造成部分区域植被NPP减少的重要原因。 相似文献
82.
This paper is concerned with the stability and L2‐gain problems for a class of continuous‐time linear switched systems with the existed asynchronous behaviors, where ‘asynchronous’ means that the switching of the controllers to be designed has a lag to the switching of the system modes. Firstly, a new sufficient condition on the asymptotic stability and weighted L2‐gain analysis is obtained by using multiple Lyapunov functions combined with the average dwell time technique. Moreover, a result that is formulated in form of linear matrix inequalities is derived for the problem of asynchronous H ∞ control. Based on the result, the mode‐dependent controllers can be designed. Finally, an illustrative numerical example is presented to show the effectiveness of the obtained results.Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
83.
On the Controllability of Nonlocal Second‐Order Impulsive Neutral Stochastic Integro‐Differential Equations with Infinite Delay 下载免费PDF全文
Diem Dang Huan 《Asian journal of control》2015,17(4):1233-1242
In this paper, we investigate the controllability for a class of nonlocal second‐order impulsive neutral stochastic integro‐differential equations with infinite delay in Hilbert spaces. More precisely, a set of sufficient conditions for the controllability results of nonlocal second‐order impulsive neutral stochastic integro‐differential equations with infinite delay are derived by means of the Banach fixed point theorem combined with theories of a strongly continuous cosine family of bounded linear operators. As an application, an example is provided to illustrate the obtained theory. 相似文献
84.
提出寻迹与搬运机器人的一种智能控制系统设计;该系统主要由单片机、传感器和执行舵机组成;通过分析直行、弯道与取物等工作模式,建立相应的舵机驱动控制;传感器将检测到的路线和工件信号传送给单片机进行处理;按照不同的优先级别,由单片机发出脉冲信号,控制舵机的速度与方向,完成抓取、转运工件的任务;实验结果表明:多路传感器的信息融合能有效识别寻迹路径,确定优先级别的控制;舵机的驱动控制能满足寻迹与搬运的要求;系统设计简单,实用可靠,具有良好的开放性与扩展性. 相似文献
85.
86.
In this paper, we introduce an internet voting protocol which satisfies desired security requirements of electronic voting. In the newly proposed protocol, we allow the adversaries to get more power than in any previous works. They can be coercers or vote buyers outside, and corrupted parties inside our system. These adversaries also have ability to collude with each other to ruin the whole system. Our main contribution is to design an internet voting protocol which is unsusceptible to most of sophisticated attacks. We employ the blind signature technique and the dynamic ballots instead of complex cryptographic techniques to preserve privacy in electronic voting. Moreover, we also aim at the practical system by improving the blind signature scheme and removing physical assumptions which have often been used in the previous works. 相似文献
87.
Web 2.0 has brought a huge amount of user-generated, social media data that contains rich information about people’s opinions and ideas towards various products, services, and ongoing social and political events. Nowadays, many companies start to look into and try to leverage this new type of data to understand their customers in order to make better business strategies and services. As a nation with rapid economic growth in recently years, China has become visible and started to play an important role in the global business and economy. Also, with the large number of Chinese Internet users, a considerable amount of options about Chinese business and market have been expressed in social media sites. Thus, it will be of interest to explore and understand those user-generated contents in Chinese. In this study, we develop an integrated framework to analyze user sentiments from Chinese social media sites by leveraging sentiment analysis techniques. Based on the framework, we conduct experiments on two popular Chinese Web forums, both related to business and marketing. By utilizing Elastic Net together with a rich body of feature representations, we achieve the highest F-measures of 84.4 and 86.7 % for the two data sets, respectively. We also demonstrate the interpretability of Elastic Net by discussing the top-ranked features with positive or negative sentiments. 相似文献
88.
A robust fault‐tolerant attitude control scheme is proposed for a launch vehicle (LV) in the presence of unknown external disturbances, mismodeling dynamics, actuator faults, and actuator's constraints. The input‐output representation is employed to describe the rotational dynamics of LV rendering three independently decoupled second order single‐input‐single‐output (SISO) systems. In the differential algebraic framework, general proportional integral (GPI) observers are used for the estimations of the states and of the generalized disturbances, which include internal perturbations, external disturbances, and unknown actuator failures. In order to avoid the defects of the conventional sliding surface, a new nonlinear integral sliding manifold is introduced for the robust fault‐tolerant sliding mode controller design. The stability of the GPI observer and that of the closed‐loop system are guaranteed by Lyapunov's indirect and direct methods, respectively. The convincing numerical simulation results demonstrate the proposed control scheme is with high attitude tracking performance in the presence of various disturbances, actuator faults, and actuator constraints. 相似文献
89.
90.
科学的风险评估方法对保障信息系统安全至关重要,文中对信息安全风险管理进行了介绍,并且对各种风险评估方法进行了分析和比较. 相似文献