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   1645712篇
  免费   26665篇
  国内免费   7138篇
电工技术   35546篇
综合类   6613篇
化学工业   279613篇
金属工艺   67045篇
机械仪表   48254篇
建筑科学   49476篇
矿业工程   11964篇
能源动力   50593篇
轻工业   130303篇
水利工程   16939篇
石油天然气   38418篇
武器工业   155篇
无线电   201633篇
一般工业技术   309466篇
冶金工业   221201篇
原子能技术   34738篇
自动化技术   177558篇
  2021年   15747篇
  2020年   12035篇
  2019年   14828篇
  2018年   19368篇
  2017年   19186篇
  2016年   23361篇
  2015年   17820篇
  2014年   28975篇
  2013年   88496篇
  2012年   39776篇
  2011年   55639篇
  2010年   46892篇
  2009年   54282篇
  2008年   50827篇
  2007年   49103篇
  2006年   48127篇
  2005年   43978篇
  2004年   45259篇
  2003年   44742篇
  2002年   43216篇
  2001年   40274篇
  2000年   38218篇
  1999年   38003篇
  1998年   62272篇
  1997年   50000篇
  1996年   42377篇
  1995年   35086篇
  1994年   32363篇
  1993年   31959篇
  1992年   27367篇
  1991年   24692篇
  1990年   24886篇
  1989年   24014篇
  1988年   22528篇
  1987年   20681篇
  1986年   20141篇
  1985年   23543篇
  1984年   23150篇
  1983年   21045篇
  1982年   19790篇
  1981年   19876篇
  1980年   18543篇
  1979年   19042篇
  1978年   18213篇
  1977年   19034篇
  1976年   21670篇
  1975年   16371篇
  1974年   15833篇
  1973年   15954篇
  1972年   13424篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Bone marrow examination revealed a lipid-laden histiocytosis in seven patients undergoing long-term total parenteral nutrition necessitated by extensive short-bowel surgical resection. Clinical abnormalities occurred during this treatment which required bone marrow examination. These included hepatosplenomegaly and peripheral blood cytopenia; the median time to the detection of these abnormalities was 64 months. The most striking change within the bone marrow was the presence of many pigment-laden histiocytes which had the typical morphology of sea-blue histiocytes seen in the so-called idiopathic sea-blue histiocyte syndrome. The occurrence of sea-blue histiocytosis in the bone marrow in association with long-term parenteral nutrition for short-bowel syndrome has not, to our knowledge, been reported previously and should now be considered in the differential diagnosis of bone marrow sea-blue histiocytosis.  相似文献   
992.
993.
本文概述了离子注入过程中污染产生的原因和防止污染的措施,特别强调了对微粒污染和金属污染的防护以满足ULSI加工对离子注入的要求。  相似文献   
994.
This paper discusses the problem of violence and its expression upon mortality due to external causes. A few indicators are offered, which have been worked upon it to emphasise the importance of the theme. In a general way, the study demonstrates violent death has had its magnitude increased along the years, not only throughout Latin America but also in Brazil and in Santa Catarina.  相似文献   
995.
High division of the brachial artery was observed in two cadavers, during routine dissection of upper extremities. In the first case, the brachial artery of the right upper extremity was divided into its two terminal branches immediately after passing between the lateral and medial roots of the median nerve and just below the origin of the profunda brachii artery. The lateral branch was the radial artery, located in the space normally occupied by the brachial artery and the medial one was the ulnar artery. In the second case, the brachial artery was divided into its two terminal branches just below the origin of the profunda brachii artery. Accurate knowledge of the relationships and course of these major arterial conduits and particularly of their variational patterns, is of considerable practical importance in the conduct of reperative surgery in the arm, forearm and hand.  相似文献   
996.
The paper covers a simple idea. If we sample an aperture, we can obtain valid patterns over a limited angular region about the normal to the aperture. The same expression can be used with near-field measurements. I reduced the expression to a nomograph. A nomograph allows one to rapidly test various choices. In the second half of the paper, I answer questions caused by the February column which discussed polarization (Milligan, IEEE Antennas. Propag. Mag., vol.38, no.1, p.56-8, 1996)  相似文献   
997.
The formation of mullite was investigated using microcomposite powders which consist of α-alumina cores and amorphous silica coatings. Differential thermal analysis and X-ray diffraction showed that the mullitization reaction was endothermic. In contrast, mullite forms exothermically in samples prepared by sol-gel processing. The results are shown to be consistent with available thermodynamic data for mullite formation from different alumina and silica phases.  相似文献   
998.
999.
1000.
The objective of this study is to determine the economic and operational impact on energy cost of incorporating large photovoltaic (PV) and wind energy conversion systems (WECS) into the electric utility generation mix. In most cases, PV and WECS power outputs are subtracted from the utility load with the expectation that conventional generation would meet the residual load. This approach is valid for small penetration levels and/or for PV and WECS facilities connected near load centers, However, several constraints such as thermal generation characteristics, fuel supply and delivery, spinning reserve requirements, and hydro availability are not adequately represented in this process. To determine the optimal value of large-scale PV and WECS applications, a new methodology that would take into account the aforementioned constraints as well as a more global penetration is developed. Results indicate that while high hydro availability increases PV penetration levels, high ramping rates can also significantly increase penetration levels  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