全文获取类型
收费全文 | 5226篇 |
免费 | 188篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 69篇 |
综合类 | 5篇 |
化学工业 | 1073篇 |
金属工艺 | 122篇 |
机械仪表 | 76篇 |
建筑科学 | 226篇 |
矿业工程 | 4篇 |
能源动力 | 97篇 |
轻工业 | 544篇 |
水利工程 | 32篇 |
石油天然气 | 7篇 |
武器工业 | 1篇 |
无线电 | 411篇 |
一般工业技术 | 961篇 |
冶金工业 | 1264篇 |
原子能技术 | 61篇 |
自动化技术 | 462篇 |
出版年
2022年 | 45篇 |
2021年 | 71篇 |
2020年 | 49篇 |
2019年 | 52篇 |
2018年 | 78篇 |
2017年 | 75篇 |
2016年 | 100篇 |
2015年 | 102篇 |
2014年 | 117篇 |
2013年 | 169篇 |
2012年 | 169篇 |
2011年 | 197篇 |
2010年 | 186篇 |
2009年 | 156篇 |
2008年 | 194篇 |
2007年 | 161篇 |
2006年 | 174篇 |
2005年 | 126篇 |
2004年 | 122篇 |
2003年 | 141篇 |
2002年 | 118篇 |
2001年 | 134篇 |
2000年 | 117篇 |
1999年 | 131篇 |
1998年 | 372篇 |
1997年 | 262篇 |
1996年 | 182篇 |
1995年 | 102篇 |
1994年 | 101篇 |
1993年 | 102篇 |
1992年 | 64篇 |
1991年 | 50篇 |
1990年 | 65篇 |
1989年 | 59篇 |
1988年 | 38篇 |
1987年 | 46篇 |
1986年 | 51篇 |
1985年 | 39篇 |
1984年 | 43篇 |
1983年 | 43篇 |
1982年 | 46篇 |
1981年 | 41篇 |
1980年 | 41篇 |
1979年 | 47篇 |
1978年 | 41篇 |
1977年 | 84篇 |
1976年 | 102篇 |
1975年 | 37篇 |
1972年 | 27篇 |
1970年 | 27篇 |
排序方式: 共有5415条查询结果,搜索用时 15 毫秒
101.
Why do fish strand? An analysis of ten years of flow reduction monitoring data from the Columbia and Kootenay rivers,Canada
下载免费PDF全文
![点击此处可从《河流研究与利用》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Stranding of fish due to flow reductions has been documented in the near shore of the Columbia and Kootenay Rivers, Canada, and can result in sub‐lethal or lethal effects on fish. Ten years (1999–2009) of monitoring data have been collected at sites below two hydro‐electric dams (Hugh‐L‐Keenleyside and Brilliant Dam) following flow reductions. A generalized linear mixed effects model analysed the probability of a stranding event in relation to environmental and operational variables including the rate of change in the water levels, the duration of shoreline inundation prior to a reduction (wetted history), the river stage, the magnitude of the reduction, distance downstream from the dam, time of day, day of year (season) and whether a site had been physically altered to mitigate stranding. The results demonstrated statistically significant effects on stranding risk from minimum river stage, day of the year and whether a site had been physically re‐contoured. The combination of investigated factors giving the highest probability of stranding was a large magnitude reduction completed in the afternoon in midsummer, at low water levels when the near shore had been inundated for a long period. This research is significant in its approach to assessing years of ecosystem scale monitoring data and using the modelling results to determine ways for these findings to be applied in regulated river management to minimize fish stranding. It also highlighted data gaps that require addressing and provides ecosystem scale results to compare with stranding studies carried out in mesocosms. © 2014 The Authors. River Research and Applications published by John Wiley & Sons Ltd. 相似文献
102.
Bernhard Esslinger Ludger Schmidt Benjamin Strenge Arno Wacker 《Datenschutz und Datensicherheit - DuD》2016,40(5):283-289
E-Mail-Verschlüsselung könnte längst flächendeckend Verwendung finden. Der Beitrag gibt eine Antwort auf die Frage, warum dies nicht der Fall ist–und macht Vorschläge, was getan werden sollte, um dies zu ändern. 相似文献
103.
Mischa Schmidt Jan Seedorf Stefano Napolitano Rosario G. Garroppo Andrea Cavaliere Thilo Ewald Armin Jahanpanah Zbigniew Kopertowski Marcin Pilarski Pawel Grochocki 《Peer-to-Peer Networking and Applications》2013,6(2):134-154
Application Layer Traffic Optimization (ALTO) has recently gained attention in the research and standardisation community as a way for a network operator to guide the peer selection process of distributed applications by providing network layer topology information. In particular P2P applications are expected to gain from ALTO, due to the many connections peers form among each other, often without taking network layer topology information into account. In this paper, we present results of an extensive intra-ISP trial with an ALTO-enhanced P2P filesharing software. In summary, our results show that—depending on the concrete setting and on the distribution of upload capacity in the network—ALTO enables an ISP to save operational costs significantly while not degrading application layer performance noticeably. In addition, based on our experience we are able to give advice to operators on how to save costs with ALTO while not sacrificing application layer performance at all. 相似文献
104.
Information-centric networking (ICN) raises data objects to first class routable entities in the network and changes the Internet paradigm from host-centric connectivity to data-oriented delivery. However, current approaches to content routing heavily rely on data-driven protocol events and thereby introduce a strong coupling of the control to the data plane in the underlying routing infrastructure. In this paper, threats to the stability and security of the content distribution system are analyzed in theory, simulations, and practical experiments. We derive relations between state resources and the performance of routers, and demonstrate how this coupling can be misused in practice. We further show how state-based forwarding tends to degrade by decorrelating resources. We identify intrinsic attack vectors present in current content-centric routing, as well as possibilities and limitations to mitigate them. Our overall findings suggest that major architectural refinements are required prior to global ICN deployment in the real world. 相似文献
105.
Degradation of the lower chlorinated ethenes is crucial to the application of natural attenuation or in situ bioremediation on chlorinated ethene contaminated sites. Recently, within mixtures of several chloroethenes as they can occur in contaminated groundwater inhibiting effects on aerobic chloroethene degradation have been shown. The current study demonstrated that metabolic vinyl chloride (VC) degradation by an enrichment culture originating from groundwater was not affected by an equimolar concentration (50 μM) of cis-1,2-dichloroethene (cDCE). Only cDCE concentrations at a ratio of 2.4:1 (initial cDCE to VC concentration) caused minor inhibition of VC degradation. Furthermore, the degradation of VC was not affected by the presence of trans-1,2-dichloroethene (tDCE), 1,1-dichloroethene (1,1-DCE), trichloroethene (TCE), and tetrachloroethene (PCE) in equimolar concentrations (50 μM). Only cDCE and tDCE were cometabolically degraded in small amounts. The VC-degrading culture demonstrated a broad pH tolerance from 5 to 9 with an optimum between 6 and 7. Results also showed that the culture could degrade VC concentrations up to 1,800 μM (110 mg/L). 相似文献
106.
Validation of GOES and MODIS active fire detection products using ASTER and ETM+ data 总被引:2,自引:0,他引:2
Wilfrid Schroeder Elaine Prins Louis Giglio Ivan Csiszar Christopher Schmidt Jeffrey Morisette Douglas Morton 《Remote sensing of environment》2008,112(5):2711-2726
In this study we implemented a comprehensive analysis to validate the MODIS and GOES satellite active fire detection products (MOD14 and WFABBA, respectively) and characterize their major sources of omission and commission errors which have important implications for a large community of fire data users. Our analyses were primarily based on the use of 30 m resolution ASTER and ETM+ imagery as our validation data. We found that at the 50% true positive detection probability mark, WFABBA requires four times more active fire area than is necessary for MOD14 to achieve the same probability of detection, despite the 16× factor separating the nominal spatial resolutions of the two products. Approximately 75% and 95% of all fires sampled were omitted by the MOD14 and WFABBA instantaneous products, respectively; whereas an omission error of 38% was obtained for WFABBA when considering the 30-minute interval of the GOES data. Commission errors for MOD14 and WFABBA were found to be similar and highly dependent on the vegetation conditions of the areas imaged, with the larger commission errors (approximately 35%) estimated over regions of active deforestation. Nonetheless, the vast majority (> 80%) of the commission errors were indeed associated with recent burning activity where scars could be visually confirmed in the higher resolution data. Differences in thermal dynamics of vegetated and non-vegetated areas were found to produce a reduction of approximately 50% in the commission errors estimated towards the hours of maximum fire activity (i.e., early-afternoon hours) which coincided with the MODIS/Aqua overpass. Lastly, we demonstrate the potential use of temporal metrics applied to the mid-infrared bands of MODIS and GOES data to reduce the commission errors found with the validation analyses. 相似文献
107.
Aniruddha Gokhale Jaiganesh Balasubramanian Gan Deng Jeffrey Parsons Douglas C. Schmidt 《Science of Computer Programming》2008,73(1):39-58
Distributed real-time and embedded (DRE) systems have become critical in domains such as avionics (e.g., flight mission computers), telecommunications (e.g., wireless phone services), tele-medicine (e.g., robotic surgery), and defense applications (e.g., total ship computing environments). These types of system are increasingly interconnected via wireless and wireline networks to form systems of systems. A challenging requirement for these DRE systems involves supporting a diverse set of quality of service (QoS) properties, such as predictable latency/jitter, throughput guarantees, scalability, 24x7 availability, dependability, and security that must be satisfied simultaneously in real-time. Although increasing portions of DRE systems are based on QoS-enabled commercial-off-the-shelf (COTS) hardware and software components, the complexity of managing long lifecycles (often ∼15-30 years) remains a key challenge for DRE developers and system integrators. For example, substantial time and effort is spent retrofitting DRE applications when the underlying COTS technology infrastructure changes.This paper provides two contributions that help improve the development, validation, and integration of DRE systems throughout their lifecycles. First, we illustrate the challenges in creating and deploying QoS-enabled component middleware-based DRE applications and describe our approach to resolving these challenges based on a new software paradigm called Model Driven Middleware (MDM), which combines model-based software development techniques with QoS-enabled component middleware to address key challenges faced by developers of DRE systems — particularly composition, integration, and assured QoS for end-to-end operations. Second, we describe the structure and functionality of CoSMIC (Component Synthesis using Model Integrated Computing), which is an MDM toolsuite that addresses key DRE application and middleware lifecycle challenges, including partitioning the components to use distributed resources effectively, validating software configurations, assuring multiple simultaneous QoS properties in real-time, and safeguarding against rapidly changing technology. 相似文献
108.
Nishanth Shankaran Xenofon D. Koutsoukos Douglas C. Schmidt Yuan Xue Chenyang Lu 《Real-Time Systems》2008,39(1-3):237-282
Real-time and embedded systems have traditionally been designed for closed environments where operating conditions, input workloads, and resource availability are known a priori, and are subject to little or no change at runtime. There is increasing demand, however, for adaptive capabilities in distributed real-time and embedded (DRE) systems that execute in open environments where system operational conditions, input workload, and resource availability cannot be characterized accurately a priori. A challenging problem faced by researchers and developers of such systems is devising effective adaptive resource management strategies that can meet end-to-end quality of service (QoS) requirements of applications. To address key resource management challenges of open DRE systems, this paper presents the Hierarchical Distributed Resource-management Architecture (HiDRA), which provides adaptive resource management using control techniques that adapt to workload fluctuations and resource availability for both bandwidth and processor utilization simultaneously. This paper presents three contributions to research in adaptive resource management for DRE systems. First, we describe the structure and functionality of HiDRA. Second, we present an analytical model of HiDRA that formalizes its control-theoretic behavior and presents analytical assurance of system performance. Third, we evaluate the performance of HiDRA via experiments on a representative DRE system that performs real-time distributed target tracking. Our analytical and empirical results indicate that HiDRA yields predictable, stable, and efficient system performance, even in the face of changing workload and resource availability. 相似文献
109.
Anders A. Larsen Martin Bendsøe Jesper Hattel Henrik Schmidt 《Structural and Multidisciplinary Optimization》2009,38(3):289-299
The aim of this paper is to optimize a thermal model of a friction stir welding process by finding optimal welding parameters.
The optimization is performed using space mapping and manifold mapping techniques in which a coarse model is used along with
the fine model to be optimized. Different coarse models are applied and the results and computation time are compared to gradient
based optimization using the full model. It is found that the use of space and manifold mapping reduces the computational
cost significantly due to the fact that fewer function evaluations and no fine model gradient information is required. 相似文献
110.
A Langmuir monolayer trough that is equipped for simultaneous microrheology and standard rheology measurements has been constructed. The central elements are the trough itself with a full range of optical tools accessing the air-water interface from below the trough and a portable knife-edge torsion pendulum that can access the interface from above. The ability to simultaneously measure the mechanical response of Langmuir monolayers on very different length scales is an important step for our understanding of the mechanical response of two-dimensional viscoelastic networks. 相似文献