全文获取类型
收费全文 | 50866篇 |
免费 | 4753篇 |
国内免费 | 1873篇 |
专业分类
电工技术 | 2208篇 |
技术理论 | 5篇 |
综合类 | 2888篇 |
化学工业 | 11994篇 |
金属工艺 | 1806篇 |
机械仪表 | 1575篇 |
建筑科学 | 2600篇 |
矿业工程 | 402篇 |
能源动力 | 18004篇 |
轻工业 | 1309篇 |
水利工程 | 666篇 |
石油天然气 | 1190篇 |
武器工业 | 250篇 |
无线电 | 2560篇 |
一般工业技术 | 4855篇 |
冶金工业 | 1375篇 |
原子能技术 | 964篇 |
自动化技术 | 2841篇 |
出版年
2024年 | 183篇 |
2023年 | 1535篇 |
2022年 | 2426篇 |
2021年 | 2466篇 |
2020年 | 2417篇 |
2019年 | 2356篇 |
2018年 | 1932篇 |
2017年 | 1880篇 |
2016年 | 1313篇 |
2015年 | 1369篇 |
2014年 | 2945篇 |
2013年 | 3289篇 |
2012年 | 3114篇 |
2011年 | 3674篇 |
2010年 | 2897篇 |
2009年 | 2821篇 |
2008年 | 2548篇 |
2007年 | 2730篇 |
2006年 | 2283篇 |
2005年 | 2064篇 |
2004年 | 1628篇 |
2003年 | 1582篇 |
2002年 | 1292篇 |
2001年 | 1002篇 |
2000年 | 891篇 |
1999年 | 700篇 |
1998年 | 681篇 |
1997年 | 592篇 |
1996年 | 495篇 |
1995年 | 441篇 |
1994年 | 328篇 |
1993年 | 285篇 |
1992年 | 272篇 |
1991年 | 181篇 |
1990年 | 172篇 |
1989年 | 148篇 |
1988年 | 107篇 |
1987年 | 82篇 |
1986年 | 73篇 |
1985年 | 53篇 |
1984年 | 65篇 |
1983年 | 45篇 |
1982年 | 25篇 |
1981年 | 12篇 |
1980年 | 13篇 |
1979年 | 5篇 |
1978年 | 5篇 |
1966年 | 7篇 |
1959年 | 15篇 |
1951年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
991.
A steady and laminar convective flow has been numerically simulated in the fully-developed annular region of a finned double-pipe subjected to the constant heat flux boundary condition imposed at the inner-pipe wall. Finite element method has been employed in this study. Friction factor and Nusselt number have been studied as flow characteristics against variations in the ratio of radii of the inner and the outer pipes, the fin height, the fin half angle and the number of fins. The results show significant enhancement in the heat transfer rate in both the cases when sufficient pumping power is available and when it is not. The minimum and maximum increase in the product of friction factor and Reynolds number relative to the finless geometry is more than one time and more than 40 times respectively while gain in the relative value of Nusselt number lies in the range 1–177. This provides an evidence of more than four times enhancement in the heat transfer coefficient relative to that in the pressure loss as a result of extended fin surfaces. 相似文献
992.
Karim JaballiAuthor Vitae Alain BellaciccoAuthor VitaeJamel LouatiAuthor Vitae Alain RiviereAuthor VitaeMohamed HaddarAuthor Vitae 《Computers in Industry》2011,62(5):541-554
During the production of new part in an industrial environment, it results in a high percentage of scrap if manufacturing planning is not carried out properly. One of the major factors responsible for this phenomenon is tolerance synthesis. In this paper, we deal with tolerance synthesis, and especially tolerance type identified after transfer. An algorithmic Rational method for 3D Manufacturing Tolerancing Synthesis (R3DMTSyn), which is based on the use of the Technologically and Topologically Related Surface (TTRS) rules, is developed. The TTRS concept helps to generate only the necessary manufacturing specification needed to guarantee the respect of the functional specification studied.The manufacturing project is modeled by a graphical representation called the SPIDER GRAPH. With the SPIDER GRAPH, all active surfaces can be detected (machined and positioning surfaces), so it is possible to identify the location of the functional surfaces used in each functional specification. The construction or the determination of the tolerancing torsor, belonging to each active surface, contributes to the selection of the adequate case of associations. A semantic study is already done to identify all possible combinations or associations needed to locate surfaces during each phases.Finally, referring to the developed TTRS_Cars_Process and in every phase, one or more manufacturing specifications are generated until finishing the treatment of all surfaces (surface belonging to the functional condition, or intermediate surfaces). 相似文献
993.
基于FPGA的高速自适应滤波器的实现 总被引:2,自引:0,他引:2
在LMS算法进行变步长处理的基础上,结合驰豫超前流水线技术和时序重构技术提出了创新结构和改进算法,在FPGA的仿真综合环境中设计实现了该高速自适应滤波器,并且在AlteraDE2-70开发板上进行了板级测试。 相似文献
994.
大方位失准角传递对准非线性模型研究 总被引:5,自引:0,他引:5
针对惯导系统大方位失准角传递对准的非线性误差方程不准确问题,同时考虑杆臂效应和挠曲变形两种主要误差因素来建立挠曲变形和杆臂效应加速度一体化误差模型,从而完善惯导系统大方位失准角传递对准非线性模型.针对非线性滤波的稳定性和快速性问题,采用比例修正无味卡尔曼(UKF)滤波模型估计姿态失准角,并采用速度匹配算法对模型的正确性和滤波的有效性进行仿真验证.结果表明,该模型在大方位失准角传递对准时可以满足对准精度和时间的要求. 相似文献
995.
996.
Characterisation of a desktop LCD projector 总被引:3,自引:0,他引:3
A typical desktop LCD projector was characterised. Having determined the optimum settings of the brightness and contrast controls, measurements were made with a spectroradiometer to establish the additivity of the primaries, inter-channel dependence, colour gamut, tone scale, contrast, spatial non-uniformity, temporal stability and viewing angle variation. Four mathematical models were compared for their accuracy in predicting the colours generated by the display for arbitrary signal inputs. A new model was developed for the S-shaped electro-optical transfer function of the LCD device, and was extended to predict the anomalous colour tracking of the primaries. 相似文献
997.
目前在网络环境下进行多媒体教学,网络速度是一个严重的瓶颈问题。在分析瓶颈产生的基础上,作者提出了一个新的文件传输协议──NFTP(Narrowband File Transfer Protocol窄带文件传输协议),利用广播数据包方法解决多媒体教学中的速度问题,并设计了一组协议原语,用于协议的描述。 相似文献
998.
999.
When multimedia information is transported over a packet-switched network, the quality of presentation can be degraded due
to network delay variation or jitter. This paper presents a dejittering scheme that can be used in the transport of MPEG-4
and MPEG-2 video to absorb any introduced network jitter, thus preserving the presentation quality of transported media streams.
The dejittering scheme is based on the statistical approximation of delay variation in the arrival times of video packets
carrying encoded clock reference values and a filtering and re-stamping mechanism. In addition, a brief overview of the MPEG-4
system is presented. 相似文献
1000.
This paper describes the geometry of imaged curves in two and three views. Multi-view relationships are developed for lines, conics and non-algebraic curves. The new relationships focus on determining the plane of the curve in a projective reconstruction, and in particular using the homography induced by this plane for transfer from one image to another. It is shown that given the fundamental matrix between two views, and images of the curve in each view, then the plane of a conic may be determined up to a two fold ambiguity, but local curvature of a curve uniquely determines the plane. It is then shown that given the trifocal tensor between three views, this plane defines a homography map which may be used to transfer a conic or the curvature from two views to a third. Simple expressions are developed for the plane and homography in each case.A set of algorithms are then described for automatically matching individual line segments and curves between images. The algorithms use both photometric information and the multiple view geometric relationships. For image pairs the homography facilitates the computation of a neighbourhood cross-correlation based matching score for putative line/curve correspondences. For image triplets cross-correlation matching scores are used in conjunction with line/curve transfer based on the trifocal geometry to disambiguate matches. Algorithms are developed for both short and wide baselines. The algorithms are robust to deficiencies in the segment extraction and partial occlusion.Experimental results are given for image pairs and triplets, for varying motions between views, and for different scene types. The methods are applicable to line/curve matching in stereo and trinocular rigs, and as a starting point for line/curve matching through monocular image sequences. 相似文献