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   1984篇
  免费   111篇
  国内免费   54篇
电工技术   146篇
综合类   464篇
化学工业   197篇
金属工艺   22篇
机械仪表   39篇
建筑科学   142篇
矿业工程   90篇
能源动力   123篇
轻工业   299篇
水利工程   56篇
石油天然气   103篇
武器工业   4篇
无线电   46篇
一般工业技术   130篇
冶金工业   117篇
原子能技术   2篇
自动化技术   169篇
  2024年   1篇
  2023年   17篇
  2022年   34篇
  2021年   36篇
  2020年   55篇
  2019年   40篇
  2018年   34篇
  2017年   29篇
  2016年   58篇
  2015年   44篇
  2014年   99篇
  2013年   124篇
  2012年   105篇
  2011年   145篇
  2010年   115篇
  2009年   122篇
  2008年   93篇
  2007年   129篇
  2006年   136篇
  2005年   146篇
  2004年   131篇
  2003年   89篇
  2002年   96篇
  2001年   76篇
  2000年   55篇
  1999年   36篇
  1998年   21篇
  1997年   13篇
  1996年   17篇
  1995年   13篇
  1994年   10篇
  1993年   4篇
  1992年   4篇
  1991年   3篇
  1990年   2篇
  1989年   5篇
  1988年   2篇
  1986年   1篇
  1985年   1篇
  1984年   1篇
  1981年   4篇
  1979年   1篇
  1973年   1篇
  1956年   1篇
排序方式: 共有2149条查询结果,搜索用时 15 毫秒
21.
When the component proportions in mixture experiments are restricted by lower and upper bounds, the input space of a designed experiment space can become an irregular region that can induce multicollinearity problems when estimating the component proportion parameters. Thus, ridge regression provides a beneficial means of stabilizing the coefficient estimates in the fitted model. Previous research has focused on using prediction variance as a metric for determining an appropriate value of the ridge constant, k. We use visualization techniques to illustrate and evaluate ridge regression estimators and the robustness of estimation with respect to the variance and the bias. The addition of bias allows better balancing between the stability of the estimators and minimally changing the estimates. We illustrate the graphical methods with mixture and mixture‐process examples from the literature. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   
22.
王建  窦正道  徐浩 《新疆石油天然气》2020,(1):25-29,I0002,I0003
分析近年来江苏油田侧钻小井眼固井质量,存在固井过程中水泥浆发生漏失导致水泥未返至悬挂器处无法形成密封井筒、油层附近固井质量差导致油水层无法有效分隔等问题,提出从井筒预处理、尾管注水泥设计优化方面提高固井质量。研究了一种井筒预处理液可将地层承压能力提高6 MPa以上,研究的变密度水泥浆体系可防止顶替过程中的漏失。井筒预处理技术在CS20-32A井试验,对漏层深部形成堵塞,采用桥浆+井筒预处理液成功封堵漏层,提高承压能力至固井要求;尾管注水泥设计优化成果在CL30-2A井实验,固井施工顺利,固井质量优质。两口井的成功实例对后续Φ139.7mm套管开窗侧钻小井眼固井质量提高具有一定的指导意义。  相似文献   
23.
ABSTRACT

This study analyzed how information and communication technology (ICT) influences international trade volume, and it undertook a comparative analysis of BRICS countries using panel data from the 2000 to 2016 period. The findings showed that (1) the effect of ICT was more positive on exports than imports, (2) the higher the ICT levels in the value chain were, the less effective they simultaneously were on both exports and imports, (3) the effect of ICT levels on trade increased over time, and (4) ICT improvement levels have more positive effects on trade in labor-intensive countries than on resources-intensives BRICS countries. To improve their export volume, BRICS countries would benefit from increasing their use of fixed-broadband and the internet.  相似文献   
24.
《Oil and Energy Trends》2020,45(9):41-45
Values of net oil imports(-)/exports for Austria, Belgium, Denmark, Finland, France, Germany, Italy, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland, the United Kingdom, Japan, Canada, the United States and Australia. Updated on a monthly basis. Number of imports for Belgium, France, Germany, Greece, Republic of Ireland, Italy, Netherlands, Portugal, Spain, Sweden, the United Kingdom, and Other EU-15 (EU-15), Norway, Poland, Switzerland, Turkey, and Other Europe (OECD Europe), Canada, Chile, Mexico, and the United States (OECD Western Hemisphere), and Australia, Japan, Republic of Korea, New Zealand, (OECD Asia-Pacific), and Total OECED. Current data for Austria, Belgium, Finland, France, Germany, Greece, Italy, Netherlands, Portugal, Spain, Sweden, the United Kingdom, Other EU-15 (EU-15), Czech Republic, Hungary, Poland, Slovakia, Turkey, and Other Europe (OECD Europe), Canada, Mexico, and the United States (OECD Western Hemisphere), Australia, Japan, Republic of Korea, and New Zealand (OECD Asia-Pacific). Updated on a monthly basis. Current data for principal importers of natural gas and the amount in which they import from United States, Republic of Korea, United Kingdom, France, Japan, Italy, Germany and Spain (Table 19.1). Current data for principal exporters of natural gas and the amount they export to Canada, Trinidad and Tobago, the United States, Netherlands, Norway, Russia, Turkmenistan, Qatar, Algeria, Nigeria, Indonesia, Malaysia and Australia (Table 19.2). Updated on a monthly basis.  相似文献   
25.
《Oil and Energy Trends》2019,44(3):43-47
Values of net oil imports(-)/exports for Austria, Belgium, Denmark, Finland, France, Germany, Italy, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland, the United Kingdom, Japan, Canada, the United States and Australia. Updated on a monthly basis. Number of imports for Belgium, France, Germany, Greece, Republic of Ireland, Italy, Netherlands, Portugal, Spain, Sweden, the United Kingdom, and Other EU-15 (EU-15), Norway, Poland, Switzerland, Turkey, and Other Europe (OECD Europe), Canada, Chile, Mexico, and the United States (OECD Western Hemisphere), and Australia, Japan, Republic of Korea, New Zealand, (OECD Asia-Pacific), and Total OECED. Current data for Austria, Belgium, Finland, France, Germany, Greece, Italy, Netherlands, Portugal, Spain, Sweden, the United Kingdom, Other EU-15 (EU-15), Czech Republic, Hungary, Poland, Slovakia, Turkey, and Other Europe (OECD Europe), Canada, Mexico, and the United States (OECD Western Hemisphere), Australia, Japan, Republic of Korea, and New Zealand (OECD Asia-Pacific). Updated on a monthly basis. Current data for principal importers of natural gas and the amount in which they import from United States, Republic of Korea, United Kingdom, France, Japan, Italy, Germany and Spain (Table 19.1). Current data for principal exporters of natural gas and the amount they export to Canada, Trinidad and Tobago, the United States, Netherlands, Norway, Russia, Turkmenistan, Qatar, Algeria, Nigeria, Indonesia, Malaysia and Australia (Table 19.2). Updated on a monthly basis.  相似文献   
26.
《Oil and Energy Trends》2019,44(6):41-45
Values of net oil imports(-)/exports for Austria, Belgium, Denmark, Finland, France, Germany, Italy, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland, the United Kingdom, Japan, Canada, the United States and Australia. Updated on a monthly basis. Number of imports for Belgium, France, Germany, Greece, Republic of Ireland, Italy, Netherlands, Portugal, Spain, Sweden, the United Kingdom, and Other EU-15 (EU-15), Norway, Poland, Switzerland, Turkey, and Other Europe (OECD Europe), Canada, Chile, Mexico, and the United States (OECD Western Hemisphere), and Australia, Japan, Republic of Korea, New Zealand, (OECD Asia-Pacific), and Total OECED. Current data for Austria, Belgium, Finland, France, Germany, Greece, Italy, Netherlands, Portugal, Spain, Sweden, the United Kingdom, Other EU-15 (EU-15), Czech Republic, Hungary, Poland, Slovakia, Turkey, and Other Europe (OECD Europe), Canada, Mexico, and the United States (OECD Western Hemisphere), Australia, Japan, Republic of Korea, and New Zealand (OECD Asia-Pacific). Updated on a monthly basis. Current data for principal importers of natural gas and the amount in which they import from United States, Republic of Korea, United Kingdom, France, Japan, Italy, Germany and Spain (Table 19.1). Current data for principal exporters of natural gas and the amount they export to Canada, Trinidad and Tobago, the United States, Netherlands, Norway, Russia, Turkmenistan, Qatar, Algeria, Nigeria, Indonesia, Malaysia and Australia (Table 19.2). Updated on a monthly basis.  相似文献   
27.
《Oil and Energy Trends》2019,44(5):49-53
Values of net oil imports(-)/exports for Austria, Belgium, Denmark, Finland, France, Germany, Italy, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland, the United Kingdom, Japan, Canada, the United States and Australia. Updated on a monthly basis. Number of imports for Belgium, France, Germany, Greece, Republic of Ireland, Italy, Netherlands, Portugal, Spain, Sweden, the United Kingdom, and Other EU-15 (EU-15), Norway, Poland, Switzerland, Turkey, and Other Europe (OECD Europe), Canada, Chile, Mexico, and the United States (OECD Western Hemisphere), and Australia, Japan, Republic of Korea, New Zealand, (OECD Asia-Pacific), and Total OECED. Current data for Austria, Belgium, Finland, France, Germany, Greece, Italy, Netherlands, Portugal, Spain, Sweden, the United Kingdom, Other EU-15 (EU-15), Czech Republic, Hungary, Poland, Slovakia, Turkey, and Other Europe (OECD Europe), Canada, Mexico, and the United States (OECD Western Hemisphere), Australia, Japan, Republic of Korea, and New Zealand (OECD Asia-Pacific). Updated on a monthly basis. Current data for principal importers of natural gas and the amount in which they import from United States, Republic of Korea, United Kingdom, France, Japan, Italy, Germany and Spain (Table 19.1). Current data for principal exporters of natural gas and the amount they export to Canada, Trinidad and Tobago, the United States, Netherlands, Norway, Russia, Turkmenistan, Qatar, Algeria, Nigeria, Indonesia, Malaysia and Australia (Table 19.2). Updated on a monthly basis.  相似文献   
28.
企业工会是我们党领导的基层群众组织。从煤矿企业工会的角度,对怎样切实提高其服务职工、管理职工的水平与能力进行了探讨。  相似文献   
29.
Abstract

CORDIC is a rotation based computation kernel algorithm which has been found to be very attractive for problems which require intensive, frequent evaluations of elementary functions. This paper addresses the implementation issues in the design of a VLSI CORDIC processor for digital signal processing and numerical linear algebra computations. The first part of this paper will discuss various design considerations for practical CORDIC algorithms. In particular, we have established criteria for the selection of nearly optimal shift sequences which are crucial to the performance of the CORDIC computation. The various design considerations of a CORDIC processor are discussed. Finally, the architecture of a prototype CORDIC processor data path chip is described.  相似文献   
30.
随着世界经济一体化的加快,对外进出口贸易在一国经济中发挥越来越重要的作用。进出口贸易影响因素较多,波动性大,一般方法难以准确预测。针对该问题,采用基于PSO优化的GMDH网络预测出口贸易总额,该方法首先根据输入数据特点自适应构造GMDH网络,然后用PSO算法优化GMDH网络权值,最终得到较为精确的预测器。通过仿真结果表明,该方法能够较为准确的预测中国年度进出口贸易总额。  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