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   199977篇
  免费   902篇
  国内免费   199篇
电工技术   3227篇
综合类   78篇
化学工业   32319篇
金属工艺   12071篇
机械仪表   8105篇
建筑科学   3368篇
矿业工程   3010篇
能源动力   3121篇
轻工业   7867篇
水利工程   3290篇
石油天然气   10359篇
武器工业   22篇
无线电   16174篇
一般工业技术   50194篇
冶金工业   25849篇
原子能技术   8884篇
自动化技术   13140篇
  2021年   2220篇
  2019年   2288篇
  2018年   4353篇
  2017年   4549篇
  2016年   4801篇
  2015年   2470篇
  2014年   4291篇
  2013年   8071篇
  2012年   5870篇
  2011年   7042篇
  2010年   5809篇
  2009年   6490篇
  2008年   6552篇
  2007年   6306篇
  2006年   5078篇
  2005年   4421篇
  2004年   4386篇
  2003年   4180篇
  2002年   4083篇
  2001年   3994篇
  2000年   3950篇
  1999年   3438篇
  1998年   5798篇
  1997年   4623篇
  1996年   3535篇
  1995年   2940篇
  1994年   2711篇
  1993年   2889篇
  1992年   2555篇
  1991年   2712篇
  1990年   2774篇
  1989年   2666篇
  1988年   2583篇
  1987年   2538篇
  1986年   2507篇
  1985年   2583篇
  1984年   2653篇
  1983年   2528篇
  1982年   2431篇
  1981年   2456篇
  1980年   2469篇
  1979年   2614篇
  1978年   2765篇
  1977年   2777篇
  1976年   3106篇
  1975年   2589篇
  1974年   2639篇
  1973年   2674篇
  1972年   2386篇
  1971年   2192篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Rapid 3D positioning and modeling in construction can be used to more effectively plan, visualize, and communicate operations before execution. It can also help to optimize equipment operations, significantly improve safety, and enhance a remote operator's spatial perception of the workspace. A new framework for rapid local area sensing and 3D modeling for better planning and control of construction equipment operation is described and demonstrated. By combining human-assisted graphical workspace modeling with pre-stored Computer-Aided Design (CAD) models and simple sensors (such as single-axis laser rangefinders and remote video cameras), modeling time can be significantly reduced while potentially increasing modeling accuracy.  相似文献   
42.
It has long been stated that the pressure distribution around a circular cylinder at high values of Reynolds number can be reproduced at lower values of Reynolds number by a suitable roughening of the surface of the cylinder. This paper shows that this is indeed possible and explains the problems.  相似文献   
43.
Finite element modelling of plate girders with web openings   总被引:1,自引:0,他引:1  
This paper is concerned with a finite element model to predict the behaviour and ultimate load of plate girders with web openings. The finite element package is used to model the plate girders with web openings. Accuracy of the model is assessed by applying it to plate girders tested earlier by other researchers. Comparison of analytical results with the available experimental results for yielding patterns, ultimate load values and load–deflection relationships show good agreement between the finite element and experimental results thus validating the accuracy of the proposed model. The proposed finite element method was extended to carry out a parametric study. The study covered parameters such as web slenderness and flange stiffness.  相似文献   
44.
In this paper experiments are described in a bio-disc pilot plant. A new method has been developed for a reproducible measurement of the thickness of the waterfilm on the rotating discs. The results were used to calculate the oxygen transfer coefficient into water (KL). The values of KL, calculated in this way, appeared to be considerably higher than experimental KL-values, which is mainly due to the fact that the water layer on the rotating disc is outdistanced by the disc. This effect has not been taken into account in the literature so far.  相似文献   
45.
Weak base phenol formaldehyde anion exchange resins were found to have an excellent capacity for removing the anionic organic species benzenesulfonate (BS), p-toluenesulfonate (PTS) and dodecylbenzenesulfonate (DBS) from pH 2 and 4 solutions. The capacity for DBS was generally greater than that of activated carbon and significantly greater than that of a polystyrene-divinylbenzene resin with no ion exchange functional groups. The maximum capacity of the weak base resins appeared to be limited by the exchange capacity of the resin. The mechanism of removal was strongly indicated as being either ion exchange at the amine functional groups in the acid form, or uptake of a proton by the amine groups in the free base form with the organic anion as the associated counter ion. Increasing concentrations of Cl decreased the amount of organic anion that could be sorbed.The swelling of one of the resins, Duolite A-7, also had a marked effect on its sorption capacity. The pores of the acid chloride or acid organic anion form of the resin were apparently larger than those of the free base form; thus, as conversion of the resin to the acid form took place, a greater amount of uptake was observed. The effect of swelling on the capacity of Duolite S-37 was much less, apparently owing to its larger pore structure, but its capacity for DBS at low pH was lower than that for A-7 because of its lower nitrogen content. Also, BS and DBS were easily removed from the weak base resins by washing them with NaOH. Four bed volumes of 1 m NaOH gave essentially complete regeneration of BS saturated A-7.  相似文献   
46.
issues of origin of water on the planet Earth and hypotheses of hydrosphere genesis have been dealt with. The article underscores interrelationship between the quality of drinking water and the level of evolution of human intellect. Substantiated is the principled insufficiency of assessing the drinking water using only chemical and microbiological methods of control. The research showed the necessity of introducing new standards for drinking water taking into consideration its safety at the cytogenetic level. The article has analyzed problems of obtaining high quality drinking water and methods of its decontamination. For the first time we demonstrated that chlorinated tap water is the medium habitat of hazardous for humans of nonculturable, but viable pathogenic forms of microflora.  相似文献   
47.
48.
Heavy metals in maternal and cord blood   总被引:8,自引:0,他引:8  
Heavy metal concentrations have been determined in maternal and cord blood samples collected from mothers in the age group 20-25 years with full-term neonates (37-40 weeks). The concentrations of Pb, Cd, Cu and Zn were found to be low in cord blood as compared to mother's blood and the ratio between cord blood and maternal blood for the respective elements was found to be approximately 0.80, 0.86, 0.47 and 0.40. On the other hand, the concentrations of Fe and Mg in the mother's blood were found to be lower than those in the cord blood. Prenatal exposure to lead in Mumbai, though low (5.1 microg/dl), is approximately 2-3 times higher than that observed in Canada or Italy. A strong correlation (r = 0.79) between the maternal and cord blood lead levels has been observed during the present study.  相似文献   
49.
Bulletin of Engineering Geology and the Environment - Information about distribution of elastic wave propagation velocities Vp, Vs in the subsurface zone of a soil mass can be obtained rapidly and...  相似文献   
50.
This paper gives the results of a series of experiments and how they shed light on problems of electrical fires. Experimental glowing connections were made by allowing wires to make poor contact with another object in series in a circuit. Note: The information in this paper was presented in the course “Electrical fires” at the University of Wisconsin—Extension, Madison, Wisconsin, April 1982.  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