首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   3687篇
  免费   230篇
  国内免费   12篇
电工技术   53篇
综合类   2篇
化学工业   757篇
金属工艺   140篇
机械仪表   188篇
建筑科学   72篇
矿业工程   2篇
能源动力   134篇
轻工业   316篇
水利工程   20篇
石油天然气   8篇
无线电   698篇
一般工业技术   756篇
冶金工业   367篇
原子能技术   28篇
自动化技术   388篇
  2024年   9篇
  2023年   25篇
  2022年   61篇
  2021年   120篇
  2020年   89篇
  2019年   72篇
  2018年   115篇
  2017年   116篇
  2016年   124篇
  2015年   101篇
  2014年   144篇
  2013年   232篇
  2012年   216篇
  2011年   255篇
  2010年   190篇
  2009年   202篇
  2008年   192篇
  2007年   158篇
  2006年   132篇
  2005年   96篇
  2004年   92篇
  2003年   91篇
  2002年   59篇
  2001年   93篇
  2000年   72篇
  1999年   60篇
  1998年   154篇
  1997年   115篇
  1996年   79篇
  1995年   62篇
  1994年   64篇
  1993年   51篇
  1992年   33篇
  1991年   41篇
  1990年   23篇
  1989年   28篇
  1988年   24篇
  1987年   12篇
  1986年   13篇
  1985年   7篇
  1984年   12篇
  1983年   13篇
  1982年   12篇
  1981年   9篇
  1980年   11篇
  1979年   5篇
  1977年   8篇
  1976年   13篇
  1974年   3篇
  1973年   3篇
排序方式: 共有3929条查询结果,搜索用时 0 毫秒
181.
Based on the study of equilibrium adsorption on viscose rayon-based activated carbon fiber (ACF) by gravimetric method, mounting of TiO2 on PAN-based activated carbon cloth (ACC) and their photocatalytic activity as well as adsorption performance for benzene were investigated. The crystallinity of TiO2 and pore structure were characterized by XRD and N2 adsorption. The results show that crystallinity of TiO2 and pore structure could be postulated by heat treatment condition. Both crystallinity of TiO2 and pore structure of hybrid have effects on photocatalytic performance of TiO2-mounted ACC. It would be more attractive and prospective for the combination of TiO2 photocatalytic activity and adsorption ability of porous materials.  相似文献   
182.
In this paper, we propose a new error concealment (EC) method using inter‐layer correlation for scalable video coding. In the proposed method, the auxiliary motion vector (MV) and the auxiliary mode number (MN) of intra prediction are interleaved into the bitstream to recover the corrupted frame. In order to reduce the bit rate, the proposed method encodes the difference between the original and the predicted values of the MV and MN instead of the original values. Experimental results show that the proposed EC outperforms the conventional EC by 2.8 dB to 6.7 dB.  相似文献   
183.
Image-based rendering has been successfully used to display 3-D objects for many applications. A well-known example is the object movie, which is an image-based 3-D object composed of a collection of 2-D images taken from many different viewpoints of a 3-D object. In order to integrate image-based 3-D objects into a chosen scene (e.g., a panorama), one has to meet a hard challenge--to efficiently and effectively remove the background from the foreground object. This problem is referred to as multiview images (MVIs) segmentation. Another task requires MVI segmentation is image-based 3-D reconstruction using multiview images. In this paper, we propose a new method for segmenting MVI, which integrates some useful algorithms, including the well-known graph-cut image segmentation and volumetric graph-cut. The main idea is to incorporate the shape prior into the image segmentation process. The shape prior introduced into every image of the MVI is extracted from the 3-D model reconstructed by using the volumetric graph cuts algorithm. Here, the constraint obtained from the discrete medial axis is adopted to improve the reconstruction algorithm. The proposed MVI segmentation process requires only a small amount of user intervention, which is to select a subset of acceptable segmentations of the MVI after the initial segmentation process. According to our experiments, the proposed method can provide not only good MVI segmentation, but also provide acceptable 3-D reconstructed models for certain less-demanding applications.  相似文献   
184.
185.
In the densely-populated urban areas, pedestrian flows often cross each other and congestion is caused. The congestion makes us feel uncomfortable and sometimes leads to pedestrian accidents. To reduce the congestion or the risk of accidents, it is required to control the swarm behavior of pedestrian flows. This paper proposes modeling and controlling method of the crossing pedestrian flows. In the social/urban engineering, it is well known that the swarm behavior with a diagonal stripe pattern emerges in the crossing area of the flows. This is a self-organized phenomenon caused by the local collision avoidance effect of the pedestrians. To control the macroscopic behavior of the flows, we utilize this self-organized phenomenon. Firstly, we propose the continuum model of the crossing pedestrian flows. In the continuum model, the dynamic change of the congestion in the diagonal stripe pattern is simulated as the density. Secondly, the novel control method to improve average flow velocity is proposed based on the model. The proposed method utilizes the dynamic interaction between the diagonal stripe pattern and guides, who are moving in the flows. The authors derive the control algorithm through an analysis on the temporal and spatial frequencies of the crossing flows. The validity is verified with simulations using the continuum model. Moreover, we apply the proposed method to the particle model, assuming the actual pedestrians.  相似文献   
186.
Recently, there are many situations where the quality of a process is characterized by a relationship of functional data (or profiles) such as time series and image data. Such data have been used for detecting out-of-process and quality improvement in many engineering applications such as semiconductor manufacturing, automobile manufacturing, and nano-machining systems. The functional data contain high dimensionality, high feature correlation, non-stationality, and large amount of noise. Due to such characteristics, most classic statistical process control (SPC) may not perform on-line monitoring satisfactorily on functional data. In addition, local shift monitoring with functional data is more significant than the detection of global shifting patterns. In this paper, wavelet-based exponentially weighted moving average (EWMA) test statistic with adaptive thresholding method, which extracts several significant coefficients from original functional data in the wavelet domain and monitors out-of-control events, is proposed. Instead of monitoring global shifting, the local shifting in functional data is of major significance in our study. Throughout this study, we use a spectroscopy in monitoring of plasma etching process from semiconductor manufacturing to illustrate the implementation of the proposed approach. Experiment studies show that the proposed approach quickly detects smaller local shifts compared with the well-known methods.  相似文献   
187.
This study was aimed to investigate the influence of solvent (water and ethanol in concentration: 50%, 70% and 96%) and extraction temperature (25–80) °C on polyphenols extraction of grape seed (Vitis vinifera L. cv. “Frankovka”) cultivated in Eastern Croatia. The best results were reached using 50% ethanol at 80 °C. The most abundant individual polyphenolic compound was catechin which makes the average of 45.11% of the total phenolic content followed by epicatechin (34.45%), procyanidin B2 (12.90%), gallic acid (5.34%), gallocatechin (1.58%), epicatechin gallate (1.01%). The antioxidant activity of extracts was determined by DPPH‐method and it was highly dependent on extraction solvent and temperature. The total extractable proanthocyanidins content of extract had the highest positive correlation (r = 0.994) with antioxidant activity, which indicated that these compounds might be the most important antioxidant in examined grape seed extracts. Relationship between phenolic content and colour of extracts was observed.  相似文献   
188.
This paper investigates performance, power, and energy efficiency of several CMOS master-slave D-flip-flops (DFF's). To improve performance and energy efficiency, a push-pull DFF and a push-pull isolation DFF are proposed. Among the five DFF's compared, the proposed push-pull isolation circuit is found to be the fastest with the best energy efficiency. Effects of using a double-pass-transistor logic (DPL) circuit and tri-state push-pull driver are also studied. Last, metastability characteristics of the five DFP's are also analyzed  相似文献   
189.
The hybrid ring coupler was designed and fabricated on a GaAs substrate using surface micromachining techniques, which adopted dielectric-supported air-gapped microstrip line (DAML) structure. The fabrication process of DAML is compatible with the standard monolithic microwave integrated circuit (MMIC) techniques, and the hybrid ring coupler can be simply integrated into a plane-structural MMIC. The fabricated hybrid ring coupler shows wideband characteristics of the coupling loss of 3.57 /spl plusmn/ 0.22dB and the transmission loss of 3.80 /spl plusmn/ 0.08dB across the measured frequency range of 85 to 105GHz. The isolation characteristics and output phase differences are -34dB and 180/spl plusmn/1/spl deg/, at 94GHz, respectively.  相似文献   
190.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号