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   112497篇
  免费   11705篇
  国内免费   5810篇
电工技术   13566篇
技术理论   5篇
综合类   7950篇
化学工业   18290篇
金属工艺   3241篇
机械仪表   4253篇
建筑科学   12245篇
矿业工程   7229篇
能源动力   7554篇
轻工业   6074篇
水利工程   2072篇
石油天然气   20203篇
武器工业   743篇
无线电   5228篇
一般工业技术   7105篇
冶金工业   5167篇
原子能技术   1535篇
自动化技术   7552篇
  2024年   455篇
  2023年   1558篇
  2022年   3059篇
  2021年   3937篇
  2020年   4279篇
  2019年   3584篇
  2018年   3301篇
  2017年   3689篇
  2016年   4326篇
  2015年   4355篇
  2014年   7146篇
  2013年   7221篇
  2012年   8448篇
  2011年   8751篇
  2010年   6126篇
  2009年   6332篇
  2008年   5606篇
  2007年   6705篇
  2006年   6714篇
  2005年   5503篇
  2004年   4767篇
  2003年   4125篇
  2002年   3489篇
  2001年   3014篇
  2000年   2628篇
  1999年   2110篇
  1998年   1665篇
  1997年   1360篇
  1996年   1082篇
  1995年   940篇
  1994年   837篇
  1993年   578篇
  1992年   467篇
  1991年   389篇
  1990年   331篇
  1989年   294篇
  1988年   160篇
  1987年   118篇
  1986年   100篇
  1985年   88篇
  1984年   70篇
  1983年   47篇
  1982年   47篇
  1981年   68篇
  1980年   50篇
  1979年   14篇
  1977年   9篇
  1976年   7篇
  1959年   10篇
  1951年   25篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
采用X射线衍射分析技术,研究了脉冲化学镀非晶态Ni-P合金的原子分布和函数,得出其短程有序原子集团的尺度为0.754nm,约为熔体激冷法获得的非晶态Ni-P合金短程有序畴的1/2。并利用脉冲化学沉积非晶态合金的微机制择这一结果进行了解释。  相似文献   
42.
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   
43.
含聚二甲基硅氧烷的聚醚聚氨酯膜透气性及表面性质研究   总被引:2,自引:0,他引:2  
以聚二甲基硅氧烷(PDMS)/聚四氢呋喃(PTMO)为软段,4,4'-二环己基甲烷二异氰酸酯(HMDI)为硬段(丁二醇BD为扩链剂)制成的多相嵌段共聚物作为基质材料,进行了气体(O2和N2)透过性试验,同时对膜材料进行了ESCA表面分析。结果表明,共聚物膜的透气性能取决于材料中连续相组分,随着软段中PDMS含量的改变而变化。当PDMS含量较高时,共聚物膜显示出PDMS均聚物的特性,具有较高的气体秀  相似文献   
44.
Z. Jiang  Q. Chen  A. Moser 《Indoor air》1992,2(3):168-179
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   
45.
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   
46.
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   
47.
在导弹近炸引信起爆延时具有随机性基础上,本文建立了一种用延时及其数学特征表示的评定引战配合效率的简便方法,并对有关应用问题进行了讨论。  相似文献   
48.
This paper highlights the possibility of inverse gas chromatography for the surface characterization of common fillers (CaCO3, talc, SiO2,) for paints and coatings. Divided solids are described, on the one hand, by the dispersive component of their surface energy and, on the other, by a specific parameter indicating their acid-base interaction potential. The role of the surface morphology at a molecular level is also examined. It is demonstrated that steric effects play an important role in the adsorption of probes on lamellar solids like talc. The consequences of surface treatments as well as examples of practical applications are also reported.  相似文献   
49.
50.
张杰  熊玮 《世界建筑》2004,(11):90-95
本文通过量化分析探索了清代皇家园林规划设计的控制规律及相关理论。  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