全文获取类型
收费全文 | 50900篇 |
免费 | 6572篇 |
国内免费 | 3320篇 |
专业分类
电工技术 | 11936篇 |
技术理论 | 1篇 |
综合类 | 5089篇 |
化学工业 | 5853篇 |
金属工艺 | 1551篇 |
机械仪表 | 2541篇 |
建筑科学 | 3948篇 |
矿业工程 | 1898篇 |
能源动力 | 2024篇 |
轻工业 | 1708篇 |
水利工程 | 2069篇 |
石油天然气 | 2915篇 |
武器工业 | 515篇 |
无线电 | 4599篇 |
一般工业技术 | 4007篇 |
冶金工业 | 2266篇 |
原子能技术 | 927篇 |
自动化技术 | 6945篇 |
出版年
2024年 | 264篇 |
2023年 | 727篇 |
2022年 | 1426篇 |
2021年 | 1793篇 |
2020年 | 2014篇 |
2019年 | 1648篇 |
2018年 | 1575篇 |
2017年 | 1962篇 |
2016年 | 1987篇 |
2015年 | 2137篇 |
2014年 | 3307篇 |
2013年 | 3438篇 |
2012年 | 3713篇 |
2011年 | 3859篇 |
2010年 | 2793篇 |
2009年 | 2976篇 |
2008年 | 2853篇 |
2007年 | 3275篇 |
2006年 | 2998篇 |
2005年 | 2537篇 |
2004年 | 2217篇 |
2003年 | 1941篇 |
2002年 | 1624篇 |
2001年 | 1330篇 |
2000年 | 1159篇 |
1999年 | 947篇 |
1998年 | 749篇 |
1997年 | 590篇 |
1996年 | 516篇 |
1995年 | 449篇 |
1994年 | 433篇 |
1993年 | 309篇 |
1992年 | 236篇 |
1991年 | 201篇 |
1990年 | 163篇 |
1989年 | 150篇 |
1988年 | 111篇 |
1987年 | 79篇 |
1986年 | 55篇 |
1985年 | 55篇 |
1984年 | 40篇 |
1983年 | 31篇 |
1982年 | 35篇 |
1981年 | 12篇 |
1980年 | 17篇 |
1979年 | 11篇 |
1977年 | 6篇 |
1976年 | 5篇 |
1959年 | 8篇 |
1951年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
聚碳硅烷的分子量分布与可纺性研究 总被引:6,自引:1,他引:5
阐述了聚碳烷的合成及其分子量分布,讨论了高低分子含量对聚碳硅烷熔点及可纺性的影响,而且提出了分子量分布的控制标准与方法。 相似文献
102.
In order to cumpare the peformance of different supply diffuers of ventilation air, the airflow passern, temperature stratifiation and contaminant dispersion in a furnitured office ventilated by three kinds of air diffuer were numerically investigated. The air diffuers studied in this paper are a quarter-cylinder displacement diffuer on the floor and mixing diffuers (linear and vortex diffuers) on the ceiling. The heat sources in the of-fice are considered to be 50% convective and 50% radiative. The k-? two-equatwn model of turbulence is employed to predict the turbulent diffusion. The results show that the displacement diffuser provides a rather uniform flow field with low velocify in most areas, and the vertical temperature difference from floor to ceiling is as high as 6 K. With the linear diffuser, the air velociry is high, and the temperature is uniform both horizontally and vertically. The air velocity generated by the vortex diffuser is moderate. The distributions of the temperature and the contaminant are rather uniform. 相似文献
103.
泥浆制备中工艺改造的研究 总被引:1,自引:0,他引:1
根据室条件下粉磨试验结果,发现球磨过程中筛上料变化存在的突变范围,提出两次加料一次加水可改变泥浆颗粒分布,并找出适宜的加料种类与时间。另外给予测粒度分布提供了宝贵的试验基础数据。 相似文献
104.
The causes of lightning outage are subdivided into direct lightning strokes and induced lightning strokes, which are identified by the characteristics of the lightning overvoltage. In the past, lightning protection devices were directed mainly toward the latter, and attention has been focused on the installation of lightning protection devices, ground wires, and reinforcement of insulators. However, lightning outages continue to occur. Thus it is extremely important to clarify the fault characteristics of lightning surges and to study the effectiveness of various lightning protection devices by considering both direct lightning stroke and induced lightning stroke in order to prevent lightning outage in the future. In this research, the electromagnetic transients program (EMTP) has been applied to the direct lightning stroke, and the induced lightning outage analysis program for multiple conductor systems has been applied to the induced lightning stroke to study the effectiveness of lightning protection devices provided by combination of various lightning protection devices. The most effective lightning protection schemes are analyzed and evaluated based on verification tests on the full scale models as well as economic considerations. 相似文献
105.
Motoharu Fujigaki In Hong Yang Yoshiharu Morimoto Eung Kyo Han 《NDT & E International》1996,29(4):197-203
There is no good method to measure the shape and the strain distributions of a structure changing with time. We have previously proposed the Fourier transform grid method (FTGM) to measure the three-dimensional shape and surface strain distributions of stationary objects by analysing the two-dimensional grating images recorded with two cameras. In the stereoscopic method, it is very important to determine the accurate geometric parameters of the camera system. In this paper, the positions and the directions of cameras are accurately determined using the FTGM applied to images of a reference object on which a two-dimensional grating is drawn. Applications for analysing shape and strain distributions of vibrating rubber plates and a moving human skin are shown. 相似文献
106.
107.
Osama Y. Abudayyeh 《Advances in Engineering Software》1993,16(3):187-193
Effective management of construction projects depends on good access to and control of data, especially data pertaining to cost and schedule control functions. However, the proper design and development of automated mechanisms have not had the facility to acquire and store quality data in a timely manner. The purpose of this paper, then, is to discuss a prototype, automated data acquisition system that was developed to support an integrated project management system. The data acquisition system is composed of an integrated set of electronic forms used in conjunction with a bar coding data-entry tool. 相似文献
108.
109.
The purpose of this work is to characterize the sky relative radiance and luminance distributions from the analysis of sky images acquired using a monochromatic CCD wide angle lens camera. The proposed methodology is based on the reduction of the number of the gray levels from the original image, in order to sharpen the different regions of the sky hemisphere, resulting in low level gray scale maps. In these maps each gray level is related to an intensity level and each pixel is associated to a sky direction. An experimental system that is able to simultaneously supply images from the sky and solar irradiance data was developed using a commercial CCD camera. The sky relative radiance and luminance distributions for different sky conditions were also determined. The resultant maps agree with observations of the main characteristics of sky radiance and luminance distributions. 相似文献
110.
通过对TN S系统接地方式中重复接地的探讨 ,介绍了重复接地对N线和PE线的不同作用 ,明确了TN S系统接地方式中重复接地的设计和施工方法。 相似文献