全文获取类型
收费全文 | 49378篇 |
免费 | 2756篇 |
国内免费 | 155篇 |
专业分类
电工技术 | 709篇 |
综合类 | 65篇 |
化学工业 | 10594篇 |
金属工艺 | 2136篇 |
机械仪表 | 3241篇 |
建筑科学 | 1099篇 |
矿业工程 | 25篇 |
能源动力 | 2112篇 |
轻工业 | 3887篇 |
水利工程 | 271篇 |
石油天然气 | 88篇 |
武器工业 | 2篇 |
无线电 | 7834篇 |
一般工业技术 | 10662篇 |
冶金工业 | 3881篇 |
原子能技术 | 658篇 |
自动化技术 | 5025篇 |
出版年
2024年 | 50篇 |
2023年 | 570篇 |
2022年 | 870篇 |
2021年 | 1484篇 |
2020年 | 1069篇 |
2019年 | 1176篇 |
2018年 | 1429篇 |
2017年 | 1411篇 |
2016年 | 1750篇 |
2015年 | 1294篇 |
2014年 | 2089篇 |
2013年 | 3006篇 |
2012年 | 3265篇 |
2011年 | 3890篇 |
2010年 | 2814篇 |
2009年 | 2921篇 |
2008年 | 2811篇 |
2007年 | 2185篇 |
2006年 | 2031篇 |
2005年 | 1723篇 |
2004年 | 1571篇 |
2003年 | 1513篇 |
2002年 | 1329篇 |
2001年 | 1134篇 |
2000年 | 996篇 |
1999年 | 928篇 |
1998年 | 1557篇 |
1997年 | 991篇 |
1996年 | 803篇 |
1995年 | 557篇 |
1994年 | 461篇 |
1993年 | 406篇 |
1992年 | 290篇 |
1991年 | 274篇 |
1990年 | 258篇 |
1989年 | 241篇 |
1988年 | 205篇 |
1987年 | 168篇 |
1986年 | 119篇 |
1985年 | 115篇 |
1984年 | 92篇 |
1983年 | 63篇 |
1982年 | 38篇 |
1981年 | 39篇 |
1980年 | 30篇 |
1979年 | 31篇 |
1978年 | 30篇 |
1977年 | 38篇 |
1976年 | 61篇 |
1973年 | 20篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
Use of a dark object concept and support vector machines to automate forest cover change analysis 总被引:5,自引:0,他引:5
Chengquan Huang Kuan Song Sunghee Kim Paul Davis Jeffrey G. Masek 《Remote sensing of environment》2008,112(3):970-985
An automated method was developed for mapping forest cover change using satellite remote sensing data sets. This multi-temporal classification method consists of a training data automation (TDA) procedure and uses the advanced support vector machines (SVM) algorithm. The TDA procedure automatically generates training data using input satellite images and existing land cover products. The derived high quality training data allow the SVM to produce reliable forest cover change products. This approach was tested in 19 study areas selected from major forest biomes across the globe. In each area a forest cover change map was produced using a pair of Landsat images acquired around 1990 and 2000. High resolution IKONOS images and independently developed reference data sets were available for evaluating the derived change products in 7 of those areas. The overall accuracy values were over 90% for 5 areas, and were 89.4% and 89.6% for the remaining two areas. The user's and producer's accuracies of the forest loss class were over 80% for all 7 study areas, demonstrating that this method is especially effective for mapping major disturbances with low commission errors. IKONOS images were also available in the remaining 12 study areas but they were either located in non-forest areas or in forest areas that did not experience forest cover change between 1990 and 2000. For those areas the IKONOS images were used to assist visual interpretation of the Landsat images in assessing the derived change products. This visual assessment revealed that for most of those areas the derived change products likely were as reliable as those in the 7 areas where accuracy assessment was conducted. The results also suggest that images acquired during leaf-off seasons should not be used in forest cover change analysis in areas where deciduous forests exist. Being highly automatic and with demonstrated capability to produce reliable change products, the TDA-SVM method should be especially useful for quantifying forest cover change over large areas. 相似文献
982.
The influence of wall charge distribution on the time lag of address discharge in an AC plasma display panel is investigated using two different reset waveforms: one (typical reset) induces both face and surface discharges and the other (TR reset) induces face discharges only. The measured formative time lag and statistical time lag of address discharge for TR were 21–31 ns and 31–74 ns shorter than the one for the typical reset, respectively. The TR reset resulted in much less increase of statistical time lag than the typical reset when the reset-to-address time interval was increased, and 70 ns smaller deviation of the statistical time lag among different color cells. Calculations show that the TR reset forms a much smoother wall charge profile, which is less susceptible to cell parameter variations, than the typical reset. The observed differences in the time lags of address discharge between different scan lines and color cells are strongly correlated to the differences of the wall charge profile, indicating that a smooth wall charge profile formed by the reset using face discharges only reduces the time lag of address discharge and minimizes the susceptibility of address discharge to cell parameter variation. 相似文献
983.
Jae Hoon Kong Seung Pil Jeong Sunhong Lee Gwang Il Kim 《Computer Aided Geometric Design》2008,25(4-5):214-229
We introduce a new method of solving C1 Hermite interpolation problems, which makes it possible to use a wider range of PH curves with potentially better shapes. By characterizing PH curves by roots of their hodographs in the complex representation, we introduce PH curves of type K(t−c)2n+1+d. Next, we introduce a speed reparametrization. Finally, we show that, for C1 Hermite data, we can use PH curves of type K(t−c)2n+1+d or strongly regular PH quintics satisfying the G1 reduction of C1 data, and use these curves to solve the original C1 Hermite interpolation problem. 相似文献
984.
In this paper we present a new practical camera characterization technique to improve color accuracy in high dynamic range (HDR) imaging. Camera characterization refers to the process of mapping device‐dependent signals, such as digital camera RAW images, into a well‐defined color space. This is a well‐understood process for low dynamic range (LDR) imaging and is part of most digital cameras — usually mapping from the raw camera signal to the sRGB or Adobe RGB color space. This paper presents an efficient and accurate characterization method for high dynamic range imaging that extends previous methods originally designed for LDR imaging. We demonstrate that our characterization method is very accurate even in unknown illumination conditions, effectively turning a digital camera into a measurement device that measures physically accurate radiance values — both in terms of luminance and color — rivaling more expensive measurement instruments. 相似文献
985.
One of the benefits of software product line approach is to improve time-to-market. The changes in market needs cause software requirements to be flexible in product lines. Whenever software requirements are changed, software architecture should be evolved to correspond with them. Therefore, domain architecture should be designed based on domain requirements. It is essential that there is traceability between requirements and architecture, and that the structure of architecture is derived from quality requirements. The purpose of this paper is to provide a framework for modeling domain architecture based on domain requirements within product lines. In particular, we focus on the traceable relationship between requirements and architectural structures. Our framework consists of processes, methods, and a supporting tool. It uses four basic concepts, namely, goal based domain requirements analysis, Analytical Hierarchy Process, Matrix technique, and architecture styles. Our approach is illustrated using HIS (Home Integration System) product line. Finally, industrial examples are used to validate DRAMA. 相似文献
986.
We perform continuous collision detection (CCD) for articulated bodies where motion is governed by an adaptive dynamics simulation.
Our algorithm is based on a novel hierarchical set of transforms that represent the kinematics of an articulated body recursively,
as described by an assembly tree. The performance of our CCD algorithm significantly improves as the number of active degrees
of freedom in the simulation decreases. 相似文献
987.
A direction finder is a military weapon that is used to find locations of targets that emit radio frequencies. Multiple direction finders are used in a direction finder system for finding locations of targets in an area of interest. We present a two-stage heuristic algorithm for disposing direction finders in a direction finder system for the objective of maximizing the accuracy of estimation of the location of a target that is assumed to be located in the area of interest. In the suggested heuristic algorithm, a simulation-based method is used for estimating the probability of coverage, the probability that a target is in a given region (of a given size) surrounding the estimated location of the target, and another simulation-based method and a local search method are used to determine locations of direction finders that result in the maximum probability of coverage. Performance of the suggested algorithm is evaluated through computational experiments and results show that the algorithm gives a good disposition plan in a reasonable amount of computation time. 相似文献
988.
This paper presents a computer-aided measurement plan (CAMP) for an impeller on a coordinate measurement machine (CMM) with a rotating/tilting probe. The blade surfaces of a machined impeller were measured exactly to secure the machining tolerance and surface finish of the impeller. CMM with a rotating and tilting probe is commonly used for this measurement. However, it is not easy to evaluate all the points on the impeller surfaces due to the time-consuming nature of the CMM measurement. In addition, many points cannot be easily accessed by the CMM probe due to the interference between the probe and the impeller blades. Furthermore, the inherent complexity of the existing teaching operation of a probe using a joystick suggests the necessity of developing a new method for the measurement planning of an impeller. Thus, this paper proposes a CAMP for effectively gauging the inspection points based on the ruled line information of the impeller blade surfaces. The proposed plan partitions the surfaces into several measurement regions based on the ruled lines of a blade surface and the approach vectors of the probe. Finally, a case example for an impeller is presented to demonstrate the effectiveness of the proposed strategy. 相似文献
989.
Although there have been a number of studies of the determinant factors of Electronic Data Interchange (EDI) implementation, most studies were carried out in the United States or Europe. The purpose of this study is to identify the determinant factors which affect implementation of EDI systems by Korean companies. Decentralization, EDI standards, technical compatibility, technical support by EDI vendors, education and training and participation of trading partners positively affect the extent of EDI usage. Formalization, technical compatibility, user involvement and participation of trading partners affect EDI integration with internal applications. Top management support and the participation of trading partners promote the extent of EDI operations. This study provides evidence of the effect of important determinant factors such as participation of trading partners and technical compatibility replicating previous EDI studies conducted in that US and Europe. For policy makers ad EDI developers, this study provides insights as to appropriate measures and incentives system designed to encourage EDI and B2B implementation. 相似文献
990.
Detailed Real-Time Urban 3D Reconstruction from Video 总被引:2,自引:0,他引:2
M. Pollefeys D. Nistér J.-M. Frahm A. Akbarzadeh P. Mordohai B. Clipp C. Engels D. Gallup S.-J. Kim P. Merrell C. Salmi S. Sinha B. Talton L. Wang Q. Yang H. Stewénius R. Yang G. Welch H. Towles 《International Journal of Computer Vision》2008,78(2-3):143-167
The paper presents a system for automatic, geo-registered, real-time 3D reconstruction from video of urban scenes. The system
collects video streams, as well as GPS and inertia measurements in order to place the reconstructed models in geo-registered
coordinates. It is designed using current state of the art real-time modules for all processing steps. It employs commodity
graphics hardware and standard CPU’s to achieve real-time performance. We present the main considerations in designing the
system and the steps of the processing pipeline. Our system extends existing algorithms to meet the robustness and variability
necessary to operate out of the lab. To account for the large dynamic range of outdoor videos the processing pipeline estimates
global camera gain changes in the feature tracking stage and efficiently compensates for these in stereo estimation without
impacting the real-time performance. The required accuracy for many applications is achieved with a two-step stereo reconstruction
process exploiting the redundancy across frames. We show results on real video sequences comprising hundreds of thousands
of frames. 相似文献