全文获取类型
收费全文 | 2958篇 |
免费 | 258篇 |
国内免费 | 199篇 |
专业分类
电工技术 | 111篇 |
综合类 | 130篇 |
化学工业 | 202篇 |
金属工艺 | 96篇 |
机械仪表 | 311篇 |
建筑科学 | 87篇 |
矿业工程 | 47篇 |
能源动力 | 89篇 |
轻工业 | 50篇 |
水利工程 | 15篇 |
石油天然气 | 25篇 |
武器工业 | 27篇 |
无线电 | 514篇 |
一般工业技术 | 279篇 |
冶金工业 | 36篇 |
原子能技术 | 34篇 |
自动化技术 | 1362篇 |
出版年
2024年 | 4篇 |
2023年 | 29篇 |
2022年 | 45篇 |
2021年 | 55篇 |
2020年 | 52篇 |
2019年 | 56篇 |
2018年 | 89篇 |
2017年 | 93篇 |
2016年 | 101篇 |
2015年 | 122篇 |
2014年 | 194篇 |
2013年 | 220篇 |
2012年 | 205篇 |
2011年 | 233篇 |
2010年 | 198篇 |
2009年 | 201篇 |
2008年 | 202篇 |
2007年 | 212篇 |
2006年 | 194篇 |
2005年 | 152篇 |
2004年 | 116篇 |
2003年 | 116篇 |
2002年 | 89篇 |
2001年 | 51篇 |
2000年 | 44篇 |
1999年 | 57篇 |
1998年 | 49篇 |
1997年 | 36篇 |
1996年 | 25篇 |
1995年 | 34篇 |
1994年 | 28篇 |
1993年 | 17篇 |
1992年 | 17篇 |
1991年 | 10篇 |
1990年 | 15篇 |
1989年 | 7篇 |
1988年 | 7篇 |
1987年 | 6篇 |
1986年 | 10篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1977年 | 3篇 |
1976年 | 1篇 |
1973年 | 1篇 |
1972年 | 2篇 |
排序方式: 共有3415条查询结果,搜索用时 15 毫秒
1.
Steganography is the science of hiding secret message in an appropriate digital multimedia in such a way that the existence of the embedded message should be invisible to anyone apart from the sender or the intended recipient. This paper presents an irreversible scheme for hiding a secret image in the cover image that is able to improve both the visual quality and the security of the stego-image while still providing a large embedding capacity. This is achieved by a hybrid steganography scheme incorporates Noise Visibility Function (NVF) and an optimal chaotic based encryption scheme. In the embedding process, first to reduce the image distortion and to increase the embedding capacity, the payload of each region of the cover image is determined dynamically according to NVF. NVF analyzes the local image properties to identify the complex areas where more secret bits should be embedded. This ensures to maintain a high visual quality of the stego-image as well as a large embedding capacity. Second, the security of the secret image is brought about by an optimal chaotic based encryption scheme to transform the secret image into an encrypted image. Third, the optimal chaotic based encryption scheme is achieved by using a hybrid optimization of Particle Swarm Optimization (PSO) and Genetic Algorithm (GA) which is allowing us to find an optimal secret key. The optimal secret key is able to encrypt the secret image so as the rate of changes after embedding process be decreased which results in increasing the quality of the stego-image. In the extracting process, the secret image can be extracted from the stego-image losslessly without referring to the original cover image. The experimental results confirm that the proposed scheme not only has the ability to achieve a good trade-off between the payload and the stego-image quality, but also can resist against the statistics and image processing attacks. 相似文献
2.
Namyong Kim 《ETRI Journal》2006,28(2):155-161
In this paper, we introduce an escalator (ESC) algorithm based on the least squares (LS) criterion. The proposed algorithm is relatively insensitive to the eigenvalue spread ratio (ESR) of an input signal and has a faster convergence speed than the conventional ESC algorithms. This algorithm exploits the fast adaptation ability of least squares methods and the orthogonalization property of the ESC structure. From the simulation results, the proposed algorithm shows superior convergence performance. 相似文献
3.
Mohammed Farid 《Chemical engineering science》2003,58(13):2985-2993
A model was developed to predict the change in droplet mass and temperature when it is exposed to hot air, as in spray drying of droplets containing solids. The droplet was assumed first to undergo sensible rapid heating with no mass change. Then the droplet experiences some shrinkage, with no temperature change but rapid mass losses, followed by a period of crust formation with a significant change in droplet mass and temperature and finally a short period of sensible heating of the dried particle. The model, unlike previous models, accounts for shrinkage and for the temperature distribution in the droplet. It provided a good prediction for the change in droplet temperature and mass for some of the experimental measurements available in the literatures. 相似文献
4.
M. Liess R. Hua K. Elsenaar 《The International Journal of Advanced Manufacturing Technology》2002,20(1):58-62
Cables to moving parts on a linear actuator in production machines, such as pick-and-place machines, are a source of unreliability
owing to the possible breaking of a cable. They further reduce the positioning precision of the actuator owing to additional
forces. Slotted waveguide systems for rail vehicles based on 2.4 GHz transmission frequency are well known, but transmitters/receivers
and waveguides are bulky. The paper reports on the reduction in size of the equipment, adapted to 5.8 GHz using a commercial
off-the-shelf RadioLan communication module. Further, the efficient termination of the wave-guide and a new way to reduce
standing-wave effects is also discussed. 相似文献
5.
二维多孔数控钻床加工路径的生成及优化 总被引:7,自引:0,他引:7
印刷电路板 PCB的加工是二维多孔数控钻的典型。实践表明加工同一零件不同的走刀路径其长度相差极大。为提高生产率 ,应使刀具的走刀路径尽量短 ,这其实是大型的 TSP问题。本文提出了几种路径的生成方法 ,分析了各自的适用场合。并用实例验证所提出的路径生成方法可极大地提高实际钻孔的加工效率。 相似文献
6.
7.
历史中心区复兴中的地域性问题与对策 总被引:2,自引:0,他引:2
本文以上海思南路47~48街坊改造为例,探讨城市形态更新与居民外迁问题,并期待相关地域性社会对策的出现。 相似文献
8.
In this paper, a robust control system is first proposed which is suitable for the control of a class of nonlinear systems. A parallel connection of a relay to a proportional integral derivative (PID) controller collectively forms the robust controller. The relay ensures robust control by providing a high feedback gain, but it also induces a control chattering phenomenon. Instead of viewing chattering as an undesirable yet inevitable feature, the chattering signals are used as natural excitation signals for identifying an equivalent PID controller using the recursive least squares algorithm. No other explicit input signal is required. Analysis is provided on the stability properties of the control scheme. Simulation results for the level control of fluid in a spherical tank using the scheme are presented. 相似文献
9.
The elastodynamic response of a rectangular Mindlin plate subjected to a distributed moving mass is investigated. The set of governing characteristic partial differential equations that include the effects of shear deformation and rotary inertia is expressed in its dimensionless form. A finite difference algorithm is employed to transform the differential equations into a set of linear algebraic equations. Simply supported edge conditions were used as an illustrative example. The analysis is also valid for other edge conditions. It is found that the maximum shearing forces, bending and twisting moments occur almost the same time. Also, the values of the maximum deflections are higher for Mindlin plates than for non-Mindlin plates. 相似文献
10.
圆筒形铸件缩松缩孔的产生原因及解决方法 总被引:1,自引:0,他引:1
针对圆筒形铸铁辊体冒口端面产生的缩松、缩孔缺陷,进行了举例说明、系统分析,找到了缺陷产生的原因及影响因素。通过解决措施的应用与实施,有效地克服了圆筒形辊体铸件冒口端面产生的缩松、缩孔缺陷,同时应用到其它大型圆筒形铸件中,都得到了良好效果。 相似文献