全文获取类型
收费全文 | 1081篇 |
免费 | 60篇 |
专业分类
电工技术 | 13篇 |
综合类 | 1篇 |
化学工业 | 269篇 |
金属工艺 | 3篇 |
机械仪表 | 12篇 |
建筑科学 | 33篇 |
矿业工程 | 2篇 |
能源动力 | 39篇 |
轻工业 | 81篇 |
水利工程 | 11篇 |
石油天然气 | 4篇 |
无线电 | 175篇 |
一般工业技术 | 131篇 |
冶金工业 | 28篇 |
原子能技术 | 4篇 |
自动化技术 | 335篇 |
出版年
2024年 | 2篇 |
2023年 | 14篇 |
2022年 | 36篇 |
2021年 | 48篇 |
2020年 | 41篇 |
2019年 | 41篇 |
2018年 | 36篇 |
2017年 | 45篇 |
2016年 | 40篇 |
2015年 | 33篇 |
2014年 | 56篇 |
2013年 | 88篇 |
2012年 | 68篇 |
2011年 | 81篇 |
2010年 | 54篇 |
2009年 | 79篇 |
2008年 | 67篇 |
2007年 | 69篇 |
2006年 | 35篇 |
2005年 | 23篇 |
2004年 | 26篇 |
2003年 | 18篇 |
2002年 | 17篇 |
2001年 | 6篇 |
2000年 | 6篇 |
1999年 | 5篇 |
1998年 | 8篇 |
1997年 | 6篇 |
1996年 | 5篇 |
1995年 | 3篇 |
1994年 | 9篇 |
1993年 | 5篇 |
1992年 | 5篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1989年 | 7篇 |
1988年 | 7篇 |
1987年 | 7篇 |
1986年 | 4篇 |
1985年 | 8篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1973年 | 1篇 |
排序方式: 共有1141条查询结果,搜索用时 31 毫秒
81.
82.
Moderate levels of reactive oxygen species (ROS) have been implicated as second messengers in a number of biochemical pathways, and in animal cells have been associated with the activation of the heat shock response (HSR). Here, using an intracellular probe, we demonstrate that differential accumulation of ROS in the yeast Saccharomyces cerevisiae is strongly associated with differential induction of an HS reporter gene over a range of heat shock temperatures. There was a good correlation between cellular ROS levels and the levels of HS-induced reporter gene expression between 37 degrees C and 44 degrees C, both reaching maximal values at 41 degrees C. Furthermore, the addition of 150 microM H2O2 to the yeast cells during heat treatment resulted in a 3 degrees C decrease in the temperature required for maximal induction of the HS expression vector--an increased HS sensitivity that corresponded to a concomitant increase in ROS levels at these lower HS temperatures. Conversely, cells treated with 10 mM of the antioxidant ascorbic acid required a temperature that was 2 degrees C above that required in untreated controls for maximal induction of the HS expression vector. This decreased HS sensitivity corresponded to a decrease in ROS levels at these higher HS temperatures. Finally, cell viability assays reveal that intrinsic thermotolerance remains high in control cells despite concomitant decreases in HS-reporter gene expression and ROS accumulation between 41 degrees C and 44 degrees C. We conclude that the sensitivity of the yeast HSR is strongly associated with ROS accumulation, and suggest that ROS-mediated signalling ensures cooperation between the HS and the antioxidant responses. 相似文献
83.
Determining correspondence in 3-D MR brain images using attribute vectors as morphological signatures of voxels 总被引:3,自引:0,他引:3
Finding point correspondence in anatomical images is a key step in shape analysis and deformable registration. This paper proposes an automatic correspondence detection algorithm for intramodality MR brain images of different subjects using wavelet-based attribute vectors (WAVs) defined on every image voxel. The attribute vector (AV) is extracted from the wavelet subimages and reflects the image structure in a large neighborhood around the respective voxel in a multiscale fashion. It plays the role of a morphological signature for each voxel, and our goal is, therefore, to make it distinctive of the respective voxel. Correspondence is then determined from similarities of AVs. By incorporating the prior knowledge of the spatial relationship among voxels, the ability of the proposed algorithm to find anatomical correspondence is further improved. Experiments with MR images of human brains show that the algorithm performs similarly to experts, even for complex cortical structures. 相似文献
84.
A general form of perfectly matched layers for three-dimensional problems of acoustic scattering in lossless and lossy fluid media 总被引:2,自引:0,他引:2
Katsibas TK Antonopoulos CS 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2004,51(8):964-972
The concept of perfectly matched layer (PML) has been proven very effective in absorbing electromagnetic waves in lossless media. An extension of this method and a complete three-dimensional (3-D) scheme properly suited for finite-difference, time-domain (FDTD) modeling of acoustic propagation and scattering in unbounded problems are presented in this paper. This generalized PML is constructed in such a way that it performs significant absorption of traveling waves in acoustics for both lossless and lossy media. Theoretically, no reflections occur when propagating waves encounter the lossy medium-PML interface, no matter what the angle of incidence is, introducing at the same time the possibility for further wave attenuation via the stretched coordinates idea. Numerical results support the suggested PML theory as well as reveal the proper modifications, which lead to the achievement of the optimum absorbing-boundary condition. 相似文献
85.
Rigorous comparison of parabolically tapered and conventional multimode-interference-based 3-dB power splitters in InGaAsP/InP waveguides 总被引:1,自引:0,他引:1
Design issues such as optical transmission, interference mechanisms, the splitting ratio, the polarization dependence, and the fabrication tolerances of a compact parabolically tapered multimode-interference (MMI)-based 3-dB power splitter on an InP-based deeply etched ridge waveguide, by use of the finite-element-based beam-propagation method, are presented. The benefits and drawbacks of the use of the tapered structure, in comparison with an untapered MMI-based 3-dB splitter, have also been investigated. 相似文献
86.
Context-based caching and routing for P2P web service discovery 总被引:1,自引:0,他引:1
Christos Doulkeridis Vassilis Zafeiris Kjetil N⊘rvåg Michalis Vazirgiannis Emmanouel A. Giakoumakis 《Distributed and Parallel Databases》2007,21(1):59-84
In modern heterogeneous environments, such as mobile, pervasive and ad-hoc networks, architectures based on web services
offer an attractive solution for effective communication and inter-operation. In such dynamic and rapidly evolving environments,
efficient web service discovery is an important task. Usually this task is based on the input/output parameters or other functional
attributes, however this does not guarantee the validity or successful utilization of retrieved web services. Instead, non-functional
attributes, such as device power features, computational resources and connectivity status, that characterize the context
of both service providers and consumers play an important role to the quality and usability of discovery results. In this
paper we introduce context-awareness in web service discovery, enabling the provision of the most appropriate services at
the right location and time. We focus on context-based caching and routing for improving web service discovery in a mobile
peer-to-peer environment. We conducted a thorough experimental study, using our prototype implementation based on the JXTA
framework, while simulations are employed for testing the scalability of the approach. We illustrate the advantages that this
approach offers, both by evaluating the context-based cache performance and by comparing the efficiency of location-based
routing to broadcast-based approaches.
Recommended by: Zakaria Maamar 相似文献
87.
A distribution-free tabular CUSUM chart for autocorrelated data 总被引:1,自引:0,他引:1
Seong-Hee Kim Christos Alexopoulos Kwok-Leung Tsui James R. Wilson 《IIE Transactions》2007,39(3):317-330
A distribution-free tabular CUSUM chart called DFTC is designed to detect shifts in the mean of an autocorrelated process. The chart's Average Run Length (ARL) is approximated by generalizing Siegmund's ARL approximation for the conventional tabular CUSUM chart based on independent and identically distributed normal observations. Control limits for DFTC are computed from the generalized ARL approximation. Also discussed are the choice of reference value and the use of batch means to handle highly correlated processes. The performance of DFTC compared favorably with that of other distribution-free procedures in stationary test processes having various types of autocorrelation functions as well as normal or nonnormal marginals. 相似文献
88.
Security of mobile ad hoc networks (MANET) has become a more sophisticated problem than security in other networks, due to the open nature and the lack of infrastructure of such networks. In this paper, the security challenges in intrusion detection and authentication are identified and the different types of attacks are discussed. We propose a two-phase detection procedure of nodes that are not authorized for specific services and nodes that have been compromised during their operation in MANET. The detection framework is enabled with the main operations of ad hoc networking, which are found at the link and network layers. The proposed framework is based on zero knowledge techniques, which are presented through proofs. 相似文献
89.
A new algorithm for fast mode decision in the H264 video coding standard is presented in this paper. The algorithm exploits
temporal information and adaptive thresholding and can provide significant computational savings with similar or even better
Rate Distortion performance as compared to accepted standard contributions and other techniques found in the literature. 相似文献
90.
Multipath routing in ad hoc networks increases the resiliency against security attacks of collaborating malicious nodes, by maximizing the number of nodes that an adversary must compromise in order to take control of the communication. In this paper, we identify several attacks that render multipath routing protocols vulnerable to collaborating malicious nodes. We propose an on-demand multipath routing protocol, the secure multipath routing protocol (SecMR), and we analyze its security properties. Finally, through simulations, we evaluate the performance of the SecMR protocol in comparison with existing secure multipath routing protocols. 相似文献