全文获取类型
收费全文 | 42171篇 |
免费 | 574篇 |
国内免费 | 788篇 |
专业分类
电工技术 | 724篇 |
综合类 | 52篇 |
化学工业 | 6380篇 |
金属工艺 | 3095篇 |
机械仪表 | 1386篇 |
建筑科学 | 863篇 |
矿业工程 | 151篇 |
能源动力 | 1429篇 |
轻工业 | 2269篇 |
水利工程 | 356篇 |
石油天然气 | 1386篇 |
无线电 | 3978篇 |
一般工业技术 | 10673篇 |
冶金工业 | 7229篇 |
原子能技术 | 788篇 |
自动化技术 | 2774篇 |
出版年
2021年 | 340篇 |
2020年 | 276篇 |
2019年 | 374篇 |
2018年 | 667篇 |
2017年 | 657篇 |
2016年 | 745篇 |
2015年 | 540篇 |
2014年 | 807篇 |
2013年 | 2387篇 |
2012年 | 1405篇 |
2011年 | 1884篇 |
2010年 | 1489篇 |
2009年 | 1781篇 |
2008年 | 1625篇 |
2007年 | 1768篇 |
2006年 | 1401篇 |
2005年 | 1226篇 |
2004年 | 1178篇 |
2003年 | 1080篇 |
2002年 | 1066篇 |
2001年 | 1119篇 |
2000年 | 965篇 |
1999年 | 999篇 |
1998年 | 2116篇 |
1997年 | 1659篇 |
1996年 | 1441篇 |
1995年 | 985篇 |
1994年 | 758篇 |
1993年 | 775篇 |
1992年 | 597篇 |
1991年 | 572篇 |
1990年 | 526篇 |
1989年 | 486篇 |
1988年 | 369篇 |
1987年 | 403篇 |
1986年 | 364篇 |
1985年 | 381篇 |
1984年 | 305篇 |
1983年 | 302篇 |
1982年 | 301篇 |
1981年 | 296篇 |
1980年 | 349篇 |
1979年 | 342篇 |
1978年 | 296篇 |
1977年 | 415篇 |
1976年 | 631篇 |
1975年 | 309篇 |
1974年 | 292篇 |
1973年 | 311篇 |
1972年 | 272篇 |
排序方式: 共有10000条查询结果,搜索用时 21 毫秒
771.
A 17Ni–0.2C martensite steel was rapidly heated below the austenite formation temperature and deformed in compression. Continuous dynamic recrystallization was observed. The behavior is similar to that in a ferrite–pearlite steel but the onset strain is much smaller. Sub-micron ferrite grains were obtained through the dynamic recrystallization. 相似文献
772.
张龙 《水电自动化与大坝监测》2015,(1)
水管式沉降仪是土石坝安全监测的主要仪器之一,水管式沉降仪测量误差主要是由管路系统的结构、传感器稳定性和综合精度等造成。目前,水管式沉降仪在工程现场的实际应用中出现一些问题:水管沉降仪安装复杂,主要表现在控制箱、各组件之间的链接;传感器的测量方式,不是直接测得观测管内的水位高度,需要多次转换;在连接的管路中空气得不到有效排出。本文主要针对以上几种情况对水管沉降仪在实际应用中呈现的问题进行优化改进。 相似文献
773.
We present an algorithm for combining the elements of subsequences of a sequence with an associative operator. The subsequences are given by a sliding window of varying size. Our algorithm is greedy and computes the result with the minimal number of operator applications. 相似文献
774.
This paper mainly focuses on the principle component analysis (PCA) and its applications on vision based computing. The underlying mechanism of PCA given and several significant factors, involved with subspace training are discussed theoretically in detail including principle components energy, residuals assessment, and decomposition computation. The typical extensions, including probabilistic PCA (PPCA), kernel PCA (KPCA), multi-dimensional PCA and robust PCA (RPCA), have been presented with critical analysis on both mechanisms and computations. Combining with the studies on, such as, image compression, visual tracking, image recognition and super-resolution image reconstruction, PCA and its extensions applied to computer vision are critically reviewed and evaluated on the targeted issues in each application as well as the role they played at specific tasks to the characteristics, cost and suitable situations of each PCA based vision processing technique. 相似文献
775.
Lina Yao Quan Z. Sheng Anne H. H. Ngu Byron J. Gao Xue Li Sen Wang 《World Wide Web》2016,19(6):1125-1149
Automatic annotation is an essential technique for effectively handling and organizing Web objects (e.g., Web pages), which have experienced an unprecedented growth over the last few years. Automatic annotation is usually formulated as a multi-label classification problem. Unfortunately, labeled data are often time-consuming and expensive to obtain. Web data also accommodate much richer feature space. This calls for new semi-supervised approaches that are less demanding on labeled data to be effective in classification. In this paper, we propose a graph-based semi-supervised learning approach that leverages random walks and ? 1 sparse reconstruction on a mixed object-label graph with both attribute and structure information for effective multi-label classification. The mixed graph contains an object-affinity subgraph, a label-correlation subgraph, and object-label edges with adaptive weight assignments indicating the assignment relationships. The object-affinity subgraph is constructed using ? 1 sparse graph reconstruction with extracted structural meta-text, while the label-correlation subgraph captures pairwise correlations among labels via linear combination of their co-occurrence similarity and kernel-based similarity. A random walk with adaptive weight assignment is then performed on the constructed mixed graph to infer probabilistic assignment relationships between labels and objects. Extensive experiments on real Yahoo! Web datasets demonstrate the effectiveness of our approach. 相似文献
776.
Logan Molyneux Krishnan Vasudevan Homero Gil de Zúñiga 《Journal of Computer-Mediated Communication》2015,20(4):381-399
Recent research suggests that social interactions in video games may lead to the development of community bonding and prosocial attitudes. Building on this line of research, a national survey of U.S. adults finds that gamers who develop ties with a community of fellow gamers possess gaming social capital, a new gaming‐related community construct that is shown to be a positive antecedent in predicting both face‐to‐face social capital and civic participation. 相似文献
777.
An Experimental Study on Three General Interface Layout Designs for Chemical Process Plants 下载免费PDF全文
The human‐machine interface design is not a new problem; however, existing knowledge appears to be focused either on interface conceptual design, which determines what information at what time needs to be displayed, or on interface detailed design, which determines the form of display elements. This article presents a study on interface layout design. Three interface layout designs were proposed based on the proximity compatibility priniciple, which were on the same interface conceptual design. In particular, the first interface layout design is with the highest degree of proximity cognition and the second and third with a reduced degree of proximity cognition. They are called sophisticated, semisophisticated, and nonsophisticated interfaces, respectively. An experiment with a simple process plant was conducted to understand user behaviors on the three interfaces. It is noted that in order to provide an unbiased comparative evaluation of these interfaces the same application problem and similar look‐and‐feel forms of interfaces were designed. In the experiment, three general classes of tasks were considered, namely, normal control operation, fault detection (or monitoring), and fault diagnosis. Two categories of measures were used: the performance measure and the subjective measure. The major results obtained from the experiment are 1) the nonsophisticated interface is the best for fault detections in terms of performance measure; besides, this interface has the lowest mental workload for fault detection; 2) the sophisticated interface is the best for normal operation in terms of performance measure; 3) there appears no significant difference for fault diagnosis in terms of performance measures for all these three interfaces; 4) for normal operation and fault diagnosis, the mental workloads for the three interfaces have no significant difference. Overall, the experiment suggests that the nonsophisticated interface be used in practice with additional two reasons: 1) most of time in the chemical process plant today is the fault detection or operation monitoring task, and 2) it is relatively easier for the nonsophisticated interface to adapt to changes in the chemical process plant design, which are common in today's manufacturing environments. 相似文献
778.
On ADRC for non-minimum phase systems: canonical form selection and stability conditions 总被引:1,自引:0,他引:1
Active disturbance rejection control (ADRC), as proposed by Prof. Jingqing Han, reduces first the plant dynamics to its canonical form, normally in the form of cascade integrators, for which the standard controller can be employed to meet the design specifications. This paper concerns with the selection of the canonical form for non-minimum phase systems. In particular, it
is shown that, by employing the well known controllable canonical form, the uncertainties of such systems can be divided into two terms in the state space model, one in the control channel and the other in the output channel. The necessary and sufficient condition is obtained for the stability of the closed-loop system with the proposed canonical form and ADRC. Also, by showing
the necessity of the detectability of the extended system as well as certain information of the systemˉs “zeros”, we present the fundamental guidelines of design ADRC for non-minimum phase uncertain systems. 相似文献
779.
With the rapid deployments of the active disturbance rejection control (ADRC) as a bonafide industrial technology in the background, this paper summarizes some recent results in the analysis of linear ADRC and offers explanations in the frequency response language with which practicing engineers are familiar. Critical to this endeavor is the concept of bandwidth, which has been used in a more general sense. It is this concept that can serve as the link between the otherwise opaque state space formulation of the ADRC and the command design considerations and concerns shared by practicing engineers. The remarkable characteristics of a simple linear ADRC was first shown in the frequency domain, followed by the corresponding analysis in time
domain, where the relationship between the tracking error and the ADRC bandwidth is established. It is shown that such insight is only possible by using the method of solving linear differential equations, instead of the more traditional techniques such as the Lyapunov methods, which tend to be more conservative and difficult to grasp by engineers. The insight obtained from such
analysis is further demonstrated in the simulation validation. 相似文献
780.