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   313268篇
  免费   3765篇
  国内免费   740篇
电工技术   6222篇
综合类   565篇
化学工业   47317篇
金属工艺   10542篇
机械仪表   8961篇
建筑科学   7937篇
矿业工程   929篇
能源动力   8637篇
轻工业   31176篇
水利工程   2649篇
石油天然气   4116篇
武器工业   8篇
无线电   39884篇
一般工业技术   59338篇
冶金工业   56988篇
原子能技术   5696篇
自动化技术   26808篇
  2021年   2319篇
  2019年   2173篇
  2018年   3698篇
  2017年   3518篇
  2016年   3632篇
  2015年   2582篇
  2014年   4508篇
  2013年   14365篇
  2012年   7442篇
  2011年   10222篇
  2010年   8010篇
  2009年   9228篇
  2008年   9690篇
  2007年   9668篇
  2006年   8579篇
  2005年   7947篇
  2004年   7808篇
  2003年   7557篇
  2002年   7397篇
  2001年   7602篇
  2000年   7266篇
  1999年   7575篇
  1998年   17704篇
  1997年   12868篇
  1996年   10126篇
  1995年   7908篇
  1994年   7222篇
  1993年   6931篇
  1992年   5334篇
  1991年   5120篇
  1990年   4972篇
  1989年   4844篇
  1988年   4747篇
  1987年   3951篇
  1986年   4067篇
  1985年   4769篇
  1984年   4327篇
  1983年   4072篇
  1982年   3658篇
  1981年   3816篇
  1980年   3510篇
  1979年   3492篇
  1978年   3303篇
  1977年   3854篇
  1976年   4910篇
  1975年   2845篇
  1974年   2740篇
  1973年   2745篇
  1972年   2297篇
  1971年   2017篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Russian Journal of Non-Ferrous Metals - Experimental studies have been carried out with theoretical calculations of wave synthesis in the Ni–Al–Cu system using a mathematical model....  相似文献   
82.
83.
The focus of this research was the development of a model to address the problem of reassigning summer construction workers to winter snow and ice removal teams in an efficient and cost-effective manner. The model is a multi-objective integer program that can generate the complete and precise trade-off curve between the objectives of minimizing total distance that the reassigned workforce must travel from their respective homes to one of many site locations, and minimizing the maximum distance that any one worker must travel. System constraints include demand requirements for workers at each site and the limited availability of state-owned vehicles that may be issued to workers assigned to remote sites. Details of the model structure and solution procedure are presented together with the results of an actual application.  相似文献   
84.
85.
86.
87.
Male Wistar rats received a combination of 25 ppm PbCl2 and 5 ppm CdCl2 in drinking water at different developmental stages. Pb and Cd levels of incisors, molars, epiphyses, diaphyses and kidney cortex were recorded by atomic absorption spectrophotometry. The results confirmed that Pb has an affinity for hard tissue and especially to teeth, but it also accumulated in soft tissues under the above conditions. In addition, the results indicated none or only a moderate placental or mammary barrier for Pb, and suggested a high absorption of lead from the intestine of sucklings. The results also confirmed that kidney cortex is a primary target for Cd, and indicated that Cd has crossed the placental and mammary barriers to some degree. The positive significant correlation between Cd levels in molars and kidney cortex suggested that rodent molars indicate a degree of Cd absorption, whereas incisors do not. It is supposed that rodent molars are comparable to human deciduous teeth. It is thus confirmed that human deciduous teeth indicate previous lead exposure. It is further inferred that they also can be used as indicators of previous Cd‐exposures.  相似文献   
88.
89.
The development of an enormous culture gap, in which no individuals of advanced societies possess even a billionth of the non‐genetic information possessed by their entire society, has threatened a global collapse of civilisation. Critical parts of that gap must be rapidly bridged so that problems such as climate disruption, toxification of the Earth, loss of biodiversity and ecosystem services, and the decay of the epidemiological environment can be satisfactorily attacked. The essential need is to alter human behaviour to put society on a route to sustainability; one cheering development is a growing interest in the Millennium Assessment of Human Behaviour (MAHB), whose goal is to do just that.  相似文献   
90.
Processing municipal and industrial wastes on land and particularly near inhabited centra has met with increased opposition. An apparent remedy to the problem is the establishment of such facilities offshore, hence various projects to build them on artificial islands. The paper examines a concrete proposal to locate such an island offshore from the Belgian Coast. Oceanographic and environmental aspects of the site are discussed, construction methods reviewed, erosion and corrosion effects looked at. The possibility of utilizing ocean power to provide the necessary operation energy is likewise considered.  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