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   50000篇
  免费   2828篇
  国内免费   156篇
电工技术   717篇
综合类   68篇
化学工业   10601篇
金属工艺   2163篇
机械仪表   3323篇
建筑科学   1115篇
矿业工程   25篇
能源动力   2170篇
轻工业   3950篇
水利工程   272篇
石油天然气   88篇
武器工业   2篇
无线电   7991篇
一般工业技术   10819篇
冶金工业   3901篇
原子能技术   665篇
自动化技术   5114篇
  2024年   24篇
  2023年   545篇
  2022年   686篇
  2021年   1505篇
  2020年   1085篇
  2019年   1197篇
  2018年   1453篇
  2017年   1435篇
  2016年   1789篇
  2015年   1335篇
  2014年   2140篇
  2013年   3078篇
  2012年   3336篇
  2011年   3965篇
  2010年   2860篇
  2009年   2972篇
  2008年   2855篇
  2007年   2224篇
  2006年   2063篇
  2005年   1753篇
  2004年   1597篇
  2003年   1540篇
  2002年   1364篇
  2001年   1151篇
  2000年   1015篇
  1999年   945篇
  1998年   1573篇
  1997年   1006篇
  1996年   821篇
  1995年   567篇
  1994年   469篇
  1993年   408篇
  1992年   295篇
  1991年   275篇
  1990年   261篇
  1989年   244篇
  1988年   205篇
  1987年   169篇
  1986年   123篇
  1985年   118篇
  1984年   93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   40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 140 毫秒
991.
The purpose of this study was to investigate the effect of wheelchair-based rehabilitation on the physical functions, health perception, and blood lipids according to the length of time since the stroke. Wheelchair-based rehabilitation progressed for 60 min per session, five times per week for 6 weeks. Physical functions, health perception (SF-36), and blood lipids were measured before and after rehabilitation. Physical fitness for physical function such as agility, grip strength, lower-body muscular endurance, flexibility, and posture control significantly improved after 6 weeks of rehabilitation. Health perception improved significantly with physical and mental health according to time since the stroke occurred. Overall, 6 weeks of wheelchair-based rehabilitation had a positive effect on the physical function and health perception regardless of stroke duration. Wheelchair-based rehabilitation had a more positive effect on the physical functions and health perception on the patients who suffered their stroke most recently. We suggested that wheelchair-based rehabilitation is necessary even through wheelchair based for chronic stroke patients, and it was useful their improved of quality of life.  相似文献   
992.
A position and direction is a fundamental information for U-Business as an anywhere service. A mobile device camera image can increase an accuracy of the positioning, and a range image provides significant information in an occlusion scene. U-Business service queries the information with the range image for a precision position or a target object. We present a method for smoothing heavy noisy surfaces acquired by mobile 3D imaging devices to obtain the stable curvature. The smoothing is performed in a way that finds centers of probability distributions, which maximizes the likelihood of observed points with smooth constraints. The smooth constraints are derived from the unit tangent vector equality. This provides a way of obtaining smooth surfaces and stable curvatures. We achieve the smoothing by solving the regularized linear system. The unit tangent vector equality involves consideration of geometric symmetry, and it minimizes the variation of differential values that are a factor of curvatures. The proposed algorithm has two apparent advantages. The first thing is that the surfaces in a scene with various signals-to-noise ratio are smoothed, and then they can earn suitable curvatures. The second is that the proposed method works on heavy noisy surfaces, for example, a stereo camera image. Experiments on range images demonstrate that the proposed method yields the smooth surfaces from the input with various signals-to-noise ratio and the stable curvatures obtained from the smooth surfaces.  相似文献   
993.
There are many methods of healing wounds. Among these, light therapy is reported to be beneficial, as beams assist the human body in treating, sterilizing, and regenerating cells. Both Laser and LED irradiation with specific wavelengths induce proliferation of fibroblasts depending on the wound area or wavelength and are effective in wound healing. This study used 8-week-old 250–300 g Male Sprague–Dawley Rats (ILAR Code: NTacSam:SD). The experiment was carried out for the non-irradiation group and the Red–Green–Blue LEDs irradiation groups (n of each group = 5). The experiment animals were relieved for 24 h after wounds had been excised and then the Red–Green–Blue LEDs irradiation groups were given irradiation therapy over 9 days 1 h per day. Immunohistochemical staining was conducted for cytokeratin in order to precisely measure the defect size. Also, Masson’s trichrome staining was conducted for comparison of collagen between the Red–Green–Blue LEDs irradiation groups and the non-irradiation group. Animals treated with Blue LEDs irradiation (p < 0.05), Green LEDs irradiation (p < 0.05), and Red LEDs irradiation (N.S.) healed at a faster rate than non-irradiated group. The LEDs irradiated groups also had more collagen, according to Masson’s trichrome staining for collagen analysis. The Red–Green–Blue LEDs irradiation had a beneficial effect on wound healing and could probably replace low power laser treatment.  相似文献   
994.
In a load balancing algorithm [O. Lee, M. Anshel, I. Chung, Design of an efficient load balancing algorithm on distributed networks by employing symmetric balanced incomplete block design, IEE Proceedings - Communications 151 (6) (2004) 535-538] based on the SBIBD (Symmetric Balanced Incomplete Block Design), each node receives global workload information by only two round message exchange with traffic overhead, where v is the number of nodes. It is very efficient and works well only when v=p2+p+1 is used for a prime number p. In this paper, we generated a special incidence structure using the SBIBD and then propose a new load balancing algorithm, which executes well for an arbitrary number of nodes. To accomplish this, we add a number of links to nodes in order for each node to receive more than 80% of the workload information by two round message exchange. For performance of our algorithm, we carried out an experiment for the number of nodes, w, which was up to 5000. Traffic overhead is less than in a round and standard deviation of traffic overhead shows that each node has a mostly well-balanced amount of traffic.  相似文献   
995.
An accurate and rapid method is required to retrieve the overwhelming majority of digital images. To date, image retrieval methods include content-based retrieval and keyword-based retrieval, the former utilizing visual features such as color and brightness, and the latter utilizing keywords that describe the image. However, the effectiveness of these methods in providing the exact images the user wants has been under scrutiny. Hence, many researchers have been working on relevance feedback, a process in which responses from the user are given as feedback during the retrieval session in order to define a user’s need and provide an improved result. Methods that employ relevance feedback, however, do have drawbacks because several pieces of feedback are necessary to produce an appropriate result, and the feedback information cannot be reused. In this paper, a novel retrieval model is proposed, which annotates an image with keywords and modifies the confidence level of the keywords in response to the user’s feedback. In the proposed model, not only the images that have been given feedback, but also other images with visual features similar to the features used to distinguish the positive images are subjected to confidence modification. This allows for modification of a large number of images with relatively little feedback, ultimately leading to faster and more accurate retrieval results. An experiment was performed to verify the effectiveness of the proposed model, and the result demonstrated a rapid increase in recall and precision using the same amount of feedback.  相似文献   
996.
Color segmentation takes a great attention because color is an effective and robust visual cue for characterizing an object from the others. However, color segmentation suffers from color variations incurred by irregular illumination changes. We propose a reliable color modeling approach in hue–saturation–intensity (HSI) color space while considering intensity information by adopting the B-spline curve fitting to make a mathematical model for statistical characteristics of a color with respect to intensity. It is based on the fact that color distribution of a single-colored object is not invariant with respect to brightness variations even in the HS (hue–saturation) plane. The statistical characteristics contain the mean and standard deviation of hue and saturation with respect to intensity. They are mathematically expressed as four bar graphs. In order to fit the bar graphs to continuous curves, we use B-spline curve fitting procedure. From several experimental results, we verify that the proposed algorithm is successfully applied to color segmentation under various illumination conditions.  相似文献   
997.
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   
998.
M.J. Jeon  J.W. Seo  S.Y. Soh  S.H. Kim  J.G. Han  B.K. Kang   《Displays》2008,29(3):195-201
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   
999.
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(tc)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(tc)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   
1000.
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   
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