全文获取类型
收费全文 | 5343篇 |
免费 | 419篇 |
国内免费 | 5篇 |
专业分类
电工技术 | 66篇 |
综合类 | 7篇 |
化学工业 | 1639篇 |
金属工艺 | 61篇 |
机械仪表 | 105篇 |
建筑科学 | 211篇 |
矿业工程 | 10篇 |
能源动力 | 203篇 |
轻工业 | 709篇 |
水利工程 | 45篇 |
石油天然气 | 7篇 |
无线电 | 348篇 |
一般工业技术 | 1012篇 |
冶金工业 | 378篇 |
原子能技术 | 29篇 |
自动化技术 | 937篇 |
出版年
2024年 | 16篇 |
2023年 | 98篇 |
2022年 | 327篇 |
2021年 | 400篇 |
2020年 | 184篇 |
2019年 | 188篇 |
2018年 | 219篇 |
2017年 | 191篇 |
2016年 | 266篇 |
2015年 | 197篇 |
2014年 | 283篇 |
2013年 | 364篇 |
2012年 | 359篇 |
2011年 | 458篇 |
2010年 | 293篇 |
2009年 | 253篇 |
2008年 | 302篇 |
2007年 | 243篇 |
2006年 | 169篇 |
2005年 | 151篇 |
2004年 | 129篇 |
2003年 | 118篇 |
2002年 | 85篇 |
2001年 | 59篇 |
2000年 | 46篇 |
1999年 | 50篇 |
1998年 | 40篇 |
1997年 | 32篇 |
1996年 | 43篇 |
1995年 | 22篇 |
1994年 | 21篇 |
1993年 | 22篇 |
1992年 | 25篇 |
1991年 | 13篇 |
1990年 | 7篇 |
1989年 | 11篇 |
1988年 | 9篇 |
1987年 | 9篇 |
1986年 | 5篇 |
1985年 | 6篇 |
1984年 | 10篇 |
1983年 | 10篇 |
1982年 | 11篇 |
1981年 | 6篇 |
1980年 | 3篇 |
1979年 | 8篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1967年 | 2篇 |
1948年 | 1篇 |
排序方式: 共有5767条查询结果,搜索用时 31 毫秒
101.
Philip E. Dennison Andrea R. Brunelle Vachel A. Carter 《Remote sensing of environment》2010,114(11):2431-2435
Continuing, severe outbreaks of mountain pine beetle (Dendroctonus ponderosae) across western North America have resulted in widespread mortality of lodgepole pine (Pinus contorta). Multiple studies have used high spatial resolution satellite data to map areas of beetle kill; these studies have largely focused on mapping red canopy cover associated with recent tree mortality and have not examined mapping gray canopy cover that occurs after red needles have dropped. The work presented here examines the use of newly available GeoEye-1 data for mapping both red and gray canopy area in southeastern Wyoming lodgepole pine forest. A 0.5 m spatial resolution, pan-sharpened GeoEye-1 image was used to classify areas of green, red, and gray canopy cover. Reference data were collected at twelve 500 m2 field plots. Shadow-normalized green, red, and gray canopy area from classified GeoEye-1 data closely agreed with field-estimated green, red, and gray canopy area. Mean absolute error in canopy cover for the twelve sample plots was 8.3% for the green class, 5.4% for the red class, and 7.2% for the gray class. When all twelve plots were aggregated, remotely sensed estimates of green, red, and gray cover were within 1.7% of the field-estimated cover. Our results demonstrate that high spatial resolution spaceborne multispectral data are a promising tool for mapping canopy mortality caused by mountain pine beetle outbreaks. 相似文献
102.
103.
The introduction of Internet and Information and communication Technologies (ICT) in offices is a global phenomenon that transformed
white-collar worker job demands. Although there are several studies of e-skills and mental workload for central countries,
there is a lack of similar studies for the Latin American context. An online snowball sampled (n = 352) survey was developed and validated by the authors (internal consistency = 0.7). We characterized ICT worker profiles
from e-skills and these dimensions: attitudes toward, resources usage and technology dependency. Mental Strain was assessed with raw task load index (RTLX) and correlated with the proposed profiles by means of paired
T-tests and Mann–Whitney Tests. The sample was characterized by 7.2% of non visual display terminal users and 92.8% of visual
display terminal, ICT skilled users. Of the latter, 30.7% were ICT practitioners, 30.4% were ICT Users and 27.2% were E-Business
Users. Non VDT users’ mental strain was statistically meaningful smaller than VDT–ICT skilled users’ mental workload. No statistical
differences were found in RTLX results when comparing ICT skilled user profiles. Non VDT users can be identified from ICT
skilled Users by their lower ITC Dependency and minor use of ICT resources. There were no differences in those dimensions
among ICT skilled Profiles. Attitude toward these technologies was a distinct factor for ICT Users in relation to ICT Practitioners
and ITC Business Users. The application of this tool in peripheral and central countries would allow a complete ergonomical
characterization of white-collar workers within the Information Society. 相似文献
104.
Franco Cicirelli Angelo Furfaro Andrea Giordano Libero Nigro 《Simulation Modelling Practice and Theory》2011,19(1):283-300
RePast is a popular agent toolkit with proven capabilities to fulfil the modelling challenges of large multi-agent systems (MASs). The toolkit, though, is normally used on a standalone workstation and therefore its practical use can be constrained (in space and time) by the limited available computing resources. This paper proposes an original approach – HLA_ACTOR_REPAST – aimed to distributing RePast models for high-performance simulation of complex scalable models. Novel in HLA_ACTOR_REPAST is an exploitation of a lean actor infrastructure implemented in Java. Actors bring to RePast agents such features as migration, location-transparent naming, efficient communications, and a control-centric framework. Actors can be orchestrated by an in-the-large custom control structure which is in charge of ensuring the necessary message causality constraints. Distribution and time management concerns depend on the IEEE standard HLA middleware. The paper first discusses details of the software engineering process underlying the development of HLA_ACTOR_REPAST. The mapping techniques, assisted by Java text annotations and aspect-oriented programming, try to minimize “code intrusions” in the original model and favour model transparency. The paper then furnishes some experimental data which witness the good performance results achieved by applying HLA_ACTOR_REPAST to a distributed version of a classic MAS benchmark model. 相似文献
105.
Combinatorial testing is as an effective testing technique to reveal failures in a given system, based on input combinations
coverage and combinatorial optimization. Combinatorial testing of strength
t (t ≥ 2) requires that each t-wise tuple of values of the different system input parameters is covered by at least one test case. Combinatorial test suite generation
algorithms aim at producing a test suite covering all the required tuples in a small (possibly minimal) number of test cases,
in order to reduce the cost of testing. The most used combinatorial technique is the pairwise testing (t = 2) which requires coverage of all pairs of input values. Constrained combinatorial testing takes also into account constraints
over the system parameters, for instance forbidden tuples of inputs, modeling invalid or not realizable input values combinations. In this paper a new approach to combinatorial
testing, tightly integrated with formal logic, is presented. In this approach, test predicates are used to formalize combinatorial
testing as a logical problem, and an external formal logic tool is applied to solve it. Constraints over the input domain
are expressed as logical predicates too, and effectively handled by the same tool. Moreover, inclusion or exclusion of select
tuples is supported, allowing the user to customize the test suite layout. The proposed approach is supported by a prototype
tool implementation and results of experimental assessment are also presented. 相似文献
106.
107.
Distributed moving object database servers offer a feasible solution to the scalability problems of centralized database systems. In these potentially large-scale systems, querying about the time-varying location of specific moving objects can be particularly expensive in terms of running time. This work proposes a meta-index based strategy that can significantly speed up the processing of these queries. The meta-index acts as an entry point for spatio-temporal queries and quickly drives the search process to the database servers that contain solutions. It also enables very fast approximated solutions to queries such as top-k and spatio-temporal range queries. 相似文献
108.
Roberto Marzotto Paul Zoratti Daniele Bagni Andrea Colombari Vittorio Murino 《Computer Vision and Image Understanding》2010,114(11):1164-1179
This paper presents an algorithm for roadway path extraction and tracking and its implementation in a Field Programmable Gate Array (FPGA) device. The implementation is particularly suitable for use as a core component of a Lane Departure Warning (LDW) system, which requires high-performance digital image processing as well as low-cost semiconductor devices, appropriate for the high volume production of the automotive market. The FPGA technology proved to be a proper platform to meet these two contrasting requirements. The proposed algorithm is specifically designed to be completely embedded in FPGA hardware to process wide VGA resolution video sequences at 30 frames per second. The main contributions of this work lie in (i) the proper selection, customization and integration of the main functions for road extraction and tracking to cope with the addressed application, and (ii) the subsequent FPGA hardware implementation as a modular architecture of specialized blocks. Experiments on real road scenario video sequences running on the FPGA device illustrate the good performance of the proposed system prototype and its ability to adapt to varying common roadway conditions, without the need for a per-installation calibration procedure. 相似文献
109.
Electronic documents used in the framework of the goods delivery industry—i.e. electronic bills of lading (e-BOLs)—are the enablers of any payment, and therefore exposed to frauds. As of today, e-BOLs are handled by special private companies, which provide paperless trading services through their trade chains. This paper contributes a zero-knowledge open solution to the problem of designing secure electronic bills of lading, in the framework of a shipper-carrier-buyer transmission model. The suggested solution is a cryptographic protocol based on digital signatures and blind merchandise counts—that is, counts that do not reveal any information about actually counted quantities. The model is designed to mitigate a number of security threats and assumes the existence of both a trusted third party and a bank in charge of payment procedures. The paper discusses the drawbacks of the existing proprietary solutions and shows how the suggested open protocol addresses them. 相似文献
110.
Paolo Casoli Andrea Vacca Gian L. Berta 《Simulation Modelling Practice and Theory》2010,18(2):125-138
This paper describes a numerical procedure for the prediction of the homogenizing performance of high pressure homogenizing valves used in diary plants. The method is based on a strict interaction between a complex CFD code and a simple homogenizing simulation code developed by the authors. This latter implements a mathematical model for the evaluation of droplets break-up, that needs an accurate evaluation of few significant fluid dynamic parameters in the whole fluid dynamic domain inside the valve. Due to the relevant pressure gradients within the flow and to the possibility of cavitation, particular attention has been paid in defining the fluid model, the mesh and the parameters required for CFD simulations. Notwithstanding the quite simple model of the homogenizing process, comparatively with the complexity of phenomena involved, the first results obtained are in general agreement with the experimental data available. These results point out the potential of the procedure proposed as a starting point for further implementation of more complex effects. 相似文献