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   309950篇
  免费   3774篇
  国内免费   722篇
电工技术   6229篇
综合类   566篇
化学工业   46769篇
金属工艺   10335篇
机械仪表   8826篇
建筑科学   7905篇
矿业工程   863篇
能源动力   8569篇
轻工业   31132篇
水利工程   2538篇
石油天然气   3672篇
武器工业   9篇
无线电   39705篇
一般工业技术   58479篇
冶金工业   56669篇
原子能技术   5464篇
自动化技术   26716篇
  2021年   2276篇
  2019年   2141篇
  2018年   3607篇
  2017年   3450篇
  2016年   3539篇
  2015年   2541篇
  2014年   4439篇
  2013年   14274篇
  2012年   7366篇
  2011年   10119篇
  2010年   7904篇
  2009年   9137篇
  2008年   9601篇
  2007年   9587篇
  2006年   8508篇
  2005年   7894篇
  2004年   7815篇
  2003年   7507篇
  2002年   7342篇
  2001年   7545篇
  2000年   7206篇
  1999年   7548篇
  1998年   17667篇
  1997年   12838篇
  1996年   10099篇
  1995年   7872篇
  1994年   7206篇
  1993年   6905篇
  1992年   5286篇
  1991年   5066篇
  1990年   4934篇
  1989年   4783篇
  1988年   4673篇
  1987年   3887篇
  1986年   4008篇
  1985年   4718篇
  1984年   4275篇
  1983年   4021篇
  1982年   3601篇
  1981年   3762篇
  1980年   3457篇
  1979年   3419篇
  1978年   3225篇
  1977年   3814篇
  1976年   4849篇
  1975年   2781篇
  1974年   2660篇
  1973年   2675篇
  1972年   2216篇
  1971年   1963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