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   271796篇
  免费   3628篇
  国内免费   871篇
电工技术   5252篇
综合类   353篇
化学工业   39315篇
金属工艺   10465篇
机械仪表   8693篇
建筑科学   6890篇
矿业工程   1120篇
能源动力   6714篇
轻工业   23732篇
水利工程   2699篇
石油天然气   3957篇
武器工业   69篇
无线电   35544篇
一般工业技术   52175篇
冶金工业   48812篇
原子能技术   5473篇
自动化技术   25032篇
  2021年   2238篇
  2019年   2206篇
  2018年   3699篇
  2017年   3730篇
  2016年   4024篇
  2015年   2548篇
  2014年   4400篇
  2013年   12042篇
  2012年   7145篇
  2011年   9663篇
  2010年   7593篇
  2009年   8419篇
  2008年   9348篇
  2007年   9261篇
  2006年   8344篇
  2005年   7648篇
  2004年   7320篇
  2003年   7081篇
  2002年   6800篇
  2001年   6729篇
  2000年   6409篇
  1999年   6460篇
  1998年   14451篇
  1997年   10463篇
  1996年   8264篇
  1995年   6620篇
  1994年   5872篇
  1993年   5754篇
  1992年   4696篇
  1991年   4275篇
  1990年   4167篇
  1989年   3891篇
  1988年   3724篇
  1987年   3274篇
  1986年   3145篇
  1985年   3730篇
  1984年   3499篇
  1983年   3110篇
  1982年   2908篇
  1981年   3012篇
  1980年   2800篇
  1979年   2699篇
  1978年   2536篇
  1977年   2971篇
  1976年   3589篇
  1975年   2337篇
  1974年   2337篇
  1973年   2336篇
  1972年   1864篇
  1971年   1755篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
We analyze the non-Fermi liquid behavior in the proximity of the quantum phase transition induced by the strong polarization of the electrons due to local magnetic moments in Ni x Pd1-x alloys. We use the renormalization group approach introduced by Hertz–Mi11is–Moriya (HMM) to estimate the temperature dependence of the electrical resistivity for the case of three dimensional itinerant ferromagnets. We study two different cases, namely, the clean and disordered ferromagnets, and argue that at the present time more experimental data are needed to decide if the HMM theory can accurately describe the physical properties in Ni x Pd1-x alloys.  相似文献   
82.
83.
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   
84.
85.
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   
86.
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   
87.
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   
88.
89.
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   
90.
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   
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