全文获取类型
收费全文 | 116484篇 |
免费 | 8350篇 |
国内免费 | 4243篇 |
专业分类
电工技术 | 5808篇 |
综合类 | 4775篇 |
化学工业 | 19507篇 |
金属工艺 | 5375篇 |
机械仪表 | 7012篇 |
建筑科学 | 5687篇 |
矿业工程 | 1679篇 |
能源动力 | 4084篇 |
轻工业 | 8120篇 |
水利工程 | 1549篇 |
石油天然气 | 2509篇 |
武器工业 | 832篇 |
无线电 | 17960篇 |
一般工业技术 | 17909篇 |
冶金工业 | 8409篇 |
原子能技术 | 1426篇 |
自动化技术 | 16436篇 |
出版年
2024年 | 314篇 |
2023年 | 1332篇 |
2022年 | 2424篇 |
2021年 | 3724篇 |
2020年 | 2730篇 |
2019年 | 2469篇 |
2018年 | 2897篇 |
2017年 | 3150篇 |
2016年 | 3373篇 |
2015年 | 3815篇 |
2014年 | 5133篇 |
2013年 | 7509篇 |
2012年 | 7395篇 |
2011年 | 8429篇 |
2010年 | 7231篇 |
2009年 | 7350篇 |
2008年 | 6958篇 |
2007年 | 6274篇 |
2006年 | 5862篇 |
2005年 | 4917篇 |
2004年 | 4119篇 |
2003年 | 3776篇 |
2002年 | 3742篇 |
2001年 | 3142篇 |
2000年 | 2578篇 |
1999年 | 2187篇 |
1998年 | 3018篇 |
1997年 | 2053篇 |
1996年 | 1738篇 |
1995年 | 1371篇 |
1994年 | 1085篇 |
1993年 | 985篇 |
1992年 | 717篇 |
1991年 | 674篇 |
1990年 | 568篇 |
1989年 | 529篇 |
1988年 | 447篇 |
1987年 | 345篇 |
1986年 | 325篇 |
1985年 | 284篇 |
1984年 | 247篇 |
1983年 | 189篇 |
1982年 | 185篇 |
1981年 | 165篇 |
1980年 | 158篇 |
1979年 | 122篇 |
1978年 | 113篇 |
1977年 | 146篇 |
1976年 | 193篇 |
1974年 | 87篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
Young-Wan Choi O-Kyun Kwon El-Hang Lee 《Photonics Technology Letters, IEEE》1993,5(12):1406-1409
The authors report significantly improved performances of a symmetric self-electrooptic-effect device (S-SEED), with high on-off contrast ratio (>30:l) and large optical bistability loop widths (ΔP=44%) at an applied bias of Va=0 V, i.e., with no power supply. The S-SEED is made of extremely shallow quantum wells (ESQWs) in an asymmetric Fabry-Perot (AFP) cavity structure. At Va =5 V ΔP increased by up to 95%, preserving the high contrast ratio. The reflectivity changes at Va=0 and 5 V were about 15% and 30%, respectively. These are believed to be the largest values ever reported for such structures 相似文献
102.
The eigenstructures of common covariance matrices are identified for the general case of M closely spaced signals. It is shown that the largest signal-space eigenvalue is relatively insensitive to signal separation. By contrast, the i th largest eigenvalue is proportional to δω2(i-1) or δω4(i-1), where δω is a measure of signal separation. Therefore, matrix conditioning degrades rapidly as signal separation is reduced. It is also shown that the limiting eigenvectors have remarkably simple structures. The results are very general, and apply to planar far-field direction-finding problems involving almost arbitrary scenarios, and also to time-series analysis of sinusoids, exponentials, and other signals 相似文献
103.
In this paper, we present efficient VLSI architectures for full-search block-matching motion estimation (BMME) algorithm. Given a search range, we partition it into sub-search arrays called tiles. By fully exploiting data dependency within a tile, efficient VLSI architectures can be obtained. Using the proposed VLSI architectures, all the block-matchings in a tile can be processed in parallel. All the tiles within a search range can be processed serially or concurrently depending on various requirements. With the consideration of processing speed, hardware cost, and I/O bandwidth, the optimal tile size for a specific video application is analyzed. By partitioning a search range into tiles with appropriate size, flexible VLSI designs with different throughput can be obtained. In this way, cost effective VLSI designs for a wide range of video applications, from H.261 to HDTV, can be achieved. 相似文献
104.
105.
Kwang Soo Lee In Soo Park & Dong Sun Lee 《International Journal of Food Science & Technology》1996,31(1):7-13
The aim of this study was to design a modified atmosphere package for a mixed vegetable salad consisting of 75 g of cut carrot, 55 g of cut cucumber, 20 g of sliced garlic and 50 g of whole green pepper. Respiration data of all the components were combined with film permeability data to predict package atmospheres and design optimal packages for experimental testing for improved shelf-life of the produce. The optimal package avoided minimum O2 and maximum CO2 tolerance limits, and chilling injury temperatures for any component. A pouch form package made of 27 mm low density polyethylene developed a modified atmosphere of 2.0–2.1% O2 and 5.5–5.7% CO2 , which was beneficial for all components and provided better quality retention than other test packages. 相似文献
106.
J. Lee R. T. Haftka O. H. Griffin Jr. L. T. Watson M. D. Sensmeier 《Structural and Multidisciplinary Optimization》1994,8(2-3):93-100
The present study proposes a detection technique for delaminations in a laminated beam. The proposed technique optimizes the spatial distribution of harmonic excitation so as to magnify the difference in response between the delaminated and intact beam. The technique is evaluated by numerical simulation of two-layered aluminum beams. Effects of measurement and geometric noise are included in the analysis. A finite element model for a delaminated composite, based on a layer-wise laminated plate theory is used in conjunction with a step function to simulate delaminations 相似文献
107.
A neural network-based power system stabilizer (neuro-PSS) is designed for a generator connected to a multi-machine power system utilizing the nonlinear power flow dynamics. The use of power flow dynamics provides a PSS for a wide range of operation with reduced size neural networks. The neuro-PSS consists of two neural networks: neuro-identifier and neuro-controller. The low-frequency oscillation is modeled by the neuro-identifier using the power flow dynamics, then a generalized backpropagation-through-time (GBTT) algorithm is developed to train the neuro-controller. The simulation results show that the neuro-PSS designed in this paper performs well with good damping in a wide operation range compared with the conventional PSS 相似文献
108.
109.
钢管内径光电检测装置 总被引:3,自引:0,他引:3
介绍了一种检测细长钢管内径的光电检测装置。该装置利用线阵CCD作传感器,采用8031单片机作为主控制。 相似文献
110.
It is essential to automate the scanning path generation process to effectively implement the micro-stereolithography. However, a scanning path that is generated based only on a 3D CAD model introduces dimensional inaccuracies. In micro-stereolithography, the photopolymer solidification is affected by fabrication conditions, such as the optical properties (laser power, laser scanning speed, laser scanning pitch focusing condition, etc.) and material properties of the photopolymer. Thus, the photopolymer solidification phenomena must be considered when generating a laser scanning path. In this paper, a scanning path generation algorithm that uses 3D CAD data and considers the photopolymer solidification phenomena is proposed to improve the dimensional accuracy in micro-stereolithography. Multi-line photopolymer solidification experiments were performed for various laser scanning conditions to examine the photopolymer solidification phenomena. From these experiments, linear relations between the solidification length (width) and scanning length (width) were acquired and stored in a database. Subsequently, these data were utilized to compensate the scanning path of the laser beam. In addition, experiments for determining the layer thickness in the z-direction were performed and these results were also used in the scanning path generation algorithm.This research was supported by the Highly Advanced National Project (http://www.most.go.kr), which performs some of the National R&D Program, and sponsored by the Korean Ministry of Science and Technology under the contract project code M10214000116-02B1500-02010. 相似文献