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   262517篇
  免费   3220篇
  国内免费   826篇
电工技术   5147篇
综合类   330篇
化学工业   37667篇
金属工艺   10311篇
机械仪表   8554篇
建筑科学   6188篇
矿业工程   1081篇
能源动力   6424篇
轻工业   22979篇
水利工程   2580篇
石油天然气   3932篇
武器工业   68篇
无线电   34828篇
一般工业技术   50389篇
冶金工业   47341篇
原子能技术   5447篇
自动化技术   23297篇
  2021年   2055篇
  2019年   2046篇
  2018年   3487篇
  2017年   3552篇
  2016年   3757篇
  2015年   2333篇
  2014年   4070篇
  2013年   11457篇
  2012年   6604篇
  2011年   8941篇
  2010年   7045篇
  2009年   7919篇
  2008年   8735篇
  2007年   8690篇
  2006年   7876篇
  2005年   7200篇
  2004年   6942篇
  2003年   6784篇
  2002年   6438篇
  2001年   6530篇
  2000年   6222篇
  1999年   6290篇
  1998年   14321篇
  1997年   10348篇
  1996年   8182篇
  1995年   6463篇
  1994年   5754篇
  1993年   5641篇
  1992年   4599篇
  1991年   4237篇
  1990年   4091篇
  1989年   3817篇
  1988年   3653篇
  1987年   3201篇
  1986年   3109篇
  1985年   3650篇
  1984年   3423篇
  1983年   3070篇
  1982年   2897篇
  1981年   2982篇
  1980年   2784篇
  1979年   2700篇
  1978年   2546篇
  1977年   2986篇
  1976年   3602篇
  1975年   2336篇
  1974年   2337篇
  1973年   2351篇
  1972年   1875篇
  1971年   1757篇
排序方式: 共有10000条查询结果,搜索用时 30 毫秒
81.
82.
The operation of a torsional oscillator for detection, of flow-driven textural transitions in, 3He-A is described. The detection technique, tracking the shift of the resonant frequency of the torsional oscillator, allows us to observe textural changes and the presence of vortices in zero magnetic field. It relies on. the anisotropic superfluid density of 3He-A and its change due to reorientation of the Î-texture caused by counterflow.  相似文献   
83.
84.
A newly developed membrane performance enhancer (MPE) was used to prevent membrane fouling in a membrane bioreactor (MBR) process. It transpired that 1,000 mg/l of MPE reduced polysaccharide levels from 41 mg/I to 21 mg/I on average under the experimental condition. Repeated experiments also confirmed that 50-1,000 mg/l of MPE could reduce membrane fouling significantly and increase the intervals between membrane cleanings. Depending on MPE dosages and experimental conditions, trans-membrane pressure (TMP) increase was suppressed for 20-30 days, while baseline TMP surged within a few days. In addition, MPE allowed MBR operation even at 50,000 mg/l of total solid and reduced permeate COD. However, no evidence of toxicity for sludge was found from respiratory works.  相似文献   
85.
The biochemical composition can be seen as a good indicator of both the biodegradability and the methane potential of a given waste. The work presented here is an attempt to elaborate a typology of wastes and to compare it to the anaerobic degradation characteristics. The first data indicate that there is a link between the ligno-cellulosic content of the waste and the biodegradability. When dealing with application to anaerobic digestion processes, having a tool to predict the ability of the waste to be degraded could be of the greatest interest for preventing failures, estimating biogas production, methane content, or for the management of co-digestion processes.  相似文献   
86.
The TELEMAC project brings new methodologies from the Information and Science Technologies field to the world of water treatment. TELEMAC offers an advanced remote management system which adapts to most of the anaerobic wastewater treatment plants that do not benefit from a local expert in wastewater treatment. The TELEMAC system takes advantage of new sensors to better monitor the process dynamics and to run automatic controllers that stabilise the treatment plant, meet the depollution requirements and provide a biogas quality suitable for cogeneration. If the automatic system detects a failure which cannot be solved automatically or locally by a technician, then an expert from the TELEMAC Control Centre is contacted via the internet and manages the problem.  相似文献   
87.
88.
Long-term trends in alpine and prairie snow pack accumulation and melt are affecting streamflow within the Oldman River Basin in southern Alberta, Canada. Unchecked rural and urban development also has contributed to changes in water quality, including enhanced microbial populations and increased waterborne pathogen occurrence. In this study we look at changing environment within the Oldman River Basin and its impact on water quality and quantity. The cumulative effects include a decline in net water supplies, and declining quality resulting in increased risk of disease. Our data indicates that decreases in the rate of flow of water can result in sedimentation of bacterial contaminants within the water column. Water for ecosystems, urban consumption, recreation and distribution through irrigation is often drawn from waterholding facilities such as dams and weirs, and concern must be expressed over the potential for contaminate build-up and disproportionate potential of these structures to pose a risk to human and animal health. With disruption of natural flow rates for water resulting from environmental change such as global warming and/or human intervention, increased attention needs to be paid to use of best management practices to protect source water supplies.  相似文献   
89.
The objective of this note is to propose a method for stabilization of structurally fixed modes in expansions of LTI dynamic systems in the scope of overlapping decentralized control design based on the expansion/contraction framework, enabling successful design for a broader class of problems than considered so far. The method is based on a judicious choice of complementary matrices in the expanded space. Numerical examples are provided to illustrate simplicity and efficiency of the proposed approach.  相似文献   
90.
In this letter, we propose a generalization of the progressive edge-growth (PEG) algorithm with the aim of designing LDPC code graphs with substantially improved approximated cycle extrinsic message degree (ACE) properties. The proposed realization of generalized PEG algorithm outperforms original PEG algorithm and its subsequent modification proposed by Xiao and Banihashemi.  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