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   3882篇
  免费   234篇
  国内免费   13篇
电工技术   53篇
综合类   2篇
化学工业   749篇
金属工艺   141篇
机械仪表   189篇
建筑科学   69篇
矿业工程   2篇
能源动力   134篇
轻工业   307篇
水利工程   20篇
石油天然气   9篇
无线电   693篇
一般工业技术   741篇
冶金工业   606篇
原子能技术   28篇
自动化技术   386篇
  2024年   9篇
  2023年   25篇
  2022年   59篇
  2021年   119篇
  2020年   88篇
  2019年   67篇
  2018年   116篇
  2017年   116篇
  2016年   123篇
  2015年   100篇
  2014年   143篇
  2013年   233篇
  2012年   215篇
  2011年   253篇
  2010年   189篇
  2009年   194篇
  2008年   189篇
  2007年   156篇
  2006年   133篇
  2005年   95篇
  2004年   93篇
  2003年   91篇
  2002年   57篇
  2001年   94篇
  2000年   73篇
  1999年   65篇
  1998年   228篇
  1997年   159篇
  1996年   110篇
  1995年   81篇
  1994年   80篇
  1993年   64篇
  1992年   36篇
  1991年   42篇
  1990年   28篇
  1989年   33篇
  1988年   24篇
  1987年   12篇
  1986年   15篇
  1985年   7篇
  1984年   12篇
  1983年   13篇
  1982年   13篇
  1981年   11篇
  1980年   13篇
  1979年   6篇
  1977年   9篇
  1976年   17篇
  1974年   3篇
  1973年   3篇
排序方式: 共有4129条查询结果,搜索用时 31 毫秒
21.
22.
Acyl-CoA:cholesterol acyltransferase (ACAT) is the enzyme largely responsible for intracellular cholesterol esterification. A systemic inhibitor of ACAT is believed to be able to slow or even reverse the atherosclerotic process. Towards that goal, a series of cyclic sulfides, derived from the hetero-Diels-Alder reaction of thioaldehydes with 1,3-dienes, and bearing carboxamide substituents, were prepared and evaluated for in vitro (in several tissues and species) and ex vivo ACAT inhibition. Minor changes in subsequent structure were found to have a significant effect in optimization of the biological activity of this series of compounds.  相似文献   
23.
This study focuses on how to assess the optimal environmental investment decisions under economic and ecological uncertainty, and establishes the continuous time model using the real option approach to optimize environmental pollution policy. Unlike traditional cost benefit analysis, this work extends the model of [Pindyck, R.S., 2002. Optimal timing problems in environmental economics. Journal of Economic Dynamics and Control 26(9–10), 1677–1697], and attempts to identify the storage threshold of pollution stocks and the optimal timing for implementing environmental pollution decisions.  相似文献   
24.
以不同PAN系炭纤维布制备燃料电池气体扩散层之研究   总被引:1,自引:1,他引:0  
采用石墨化PAN系炭纤维布制备了高分子电解质燃料电池气体扩散层。通过电学实验、X-ray绕射与元素分析考察了所制气体扩散层的性能。结果表明:随热处理温度的升高,气体扩散层的电阻率降低,L2增加,d(x)2减小。高温处理后的炭纤维布作为高分子电解质燃料电池气体扩散层显示了较高的电池效能。  相似文献   
25.
We report the successful growth of Ga-polar GaN epilayers on O-polar ZnO templates pre-deposited on c-sapphire. Prior to GaN growth, NH3 is exposed onto the ZnO template. The polarity of the GaN layers is confirmed by etching of the surface and by conversion beam electron diffraction (CBED), while the O-polar ZnO is confirmed by CBED. It is suggested that the NH3 pre-exposure helps form a Zn3N2 layer, which possesses inversion symmetry and inverts the crystal from anion polar to cation polar.  相似文献   
26.
Dynamic RSVP protocol   总被引:5,自引:0,他引:5  
RSVP is a resource reservation setup protocol that can be used by a host to request specific QoS for multicast multimedia flows on the Internet. Multiprotocol label switching (MPLS) architecture also needs RSVP. The fact that the resolutions of the display system used in different receiver nodes might have different, multi-resolution characteristics is supported in the MPEG-4 standard, and the EZW compression algorithm can cease decoding at any point in the bitstream. However, RSVP does not provide a more flexible mechanism. In this article we propose an extension of RSVP to provide the needed mechanism, coined dynamic RSVP (DRSVP), to dynamically adjust reserved resources on nodes without much effort. It provides different video resolutions to different receiver nodes with different needed reserved resources. Therefore, it does not waste precious Internet resources to transmit unnecessary multimedia packets.  相似文献   
27.
A reinjection experiment has been conducted in an attempt to sustain reservoir pressure and steam production and to extract remaining heat energy in the superheated reservoir in the Matsukawa vapor-dominated geothermal field. This experiment was undertaken because the increase in superheat of produced steam and the decline of steam production are the current major issues for stable operation of the power plant. Almost all the reinjected fluid into well MR 1 was recovered from well M5, and the steam production of well M5 has increased by approximately 67%.  相似文献   
28.
29.
From April 1990 to December 1993, 140 patients were recruited to a randomized study to evaluate transcatheter hepatic arterial chemoembolization (TACE) as an adjuvant therapy for primary liver carcinoma after hepatectomy. This study investigated the principle, techniques and results of TACE. The results showed that the intrahepatic recurrence rate was 48.9% in the patients who underwent radical resection only, but only 21.3% in the patients who also underwent TACE 3-4 weeks after hepatectomy (P < 0.01). The 1-, 2-, 3-, and 4-year survival rates were 72.3%, 52.7%, 35.1%, and 35.1% respectively for the patients who underwent radical resection only, and were 97.9%, 85.5%, 69.5%, and 56.9% for the patients who also underwent TACE 3-4 weeks after radical resection (P < 0.001). The 1-, 2-, 3-, and 4-year survival rates were 38.9%, 0%, 0%, and 0% for the patients who underwent palliative resection only, and were 68.3%, 32.3%, 21.5%, and 21.5% respectively for the patients undergoing TACE 3-4 weeks after palliative hepatectomy (P < 0.001).  相似文献   
30.
It has been found that the subthreshold currents of fully depleted silicon-on-insulator (SOI) MOSFETs show a transient behavior under certain front-gate and back-gate voltage conditions. The cause of this anomaly is explained, and applications for the phenomenon are pointed out. Particularly, a simple way to measure the silicon film thickness is suggested  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