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   1399篇
  免费   18篇
  国内免费   2篇
电工技术   11篇
化学工业   277篇
金属工艺   55篇
机械仪表   36篇
建筑科学   109篇
矿业工程   2篇
能源动力   67篇
轻工业   197篇
水利工程   5篇
石油天然气   5篇
无线电   67篇
一般工业技术   282篇
冶金工业   72篇
原子能技术   20篇
自动化技术   214篇
  2024年   5篇
  2023年   7篇
  2022年   16篇
  2021年   28篇
  2020年   24篇
  2019年   21篇
  2018年   17篇
  2017年   33篇
  2016年   30篇
  2015年   30篇
  2014年   39篇
  2013年   81篇
  2012年   59篇
  2011年   98篇
  2010年   60篇
  2009年   78篇
  2008年   88篇
  2007年   83篇
  2006年   56篇
  2005年   54篇
  2004年   51篇
  2003年   43篇
  2002年   45篇
  2001年   28篇
  2000年   20篇
  1999年   15篇
  1998年   32篇
  1997年   26篇
  1996年   21篇
  1995年   15篇
  1994年   13篇
  1993年   13篇
  1992年   9篇
  1991年   11篇
  1990年   13篇
  1989年   12篇
  1988年   15篇
  1987年   13篇
  1986年   14篇
  1985年   11篇
  1984年   10篇
  1983年   12篇
  1982年   7篇
  1981年   7篇
  1980年   8篇
  1979年   8篇
  1978年   7篇
  1976年   8篇
  1974年   7篇
  1972年   4篇
排序方式: 共有1419条查询结果,搜索用时 15 毫秒
21.
An assessment system that combines digital information on soil types, climates, slopes and crops with simulated values of nitrate leaching and erosion within a geographical information system was developed. The system was used for assessing risks of nitrate leaching and erosion on the regional as well as national scale, having municipalities as the level of aggregation. In Denmark the system has been used for assessing risks of erosion at a catchment scale.  相似文献   
22.
23.
24.
    
The amyloid-like fibril is a biomolecular nanowire template of very high stability. Here we describe the coordination of a conjugated polyelectrolyte, poly(thiophene acetic acid) (PTAA), to bovine insulin fibrils with widths of <10 nm and lengths of up to more than 10 microm. Fibrils complexed with PTAA are aligned on surfaces through molecular combing and transfer printing. Single-molecule spectroscopy techniques are applied to chart spectral variation in the emission of these wires. When these results are combined with analysis of the polarization of the emitted light, we can conclude that the polymer chains are preferentially aligned along the fibrillar axis.  相似文献   
25.
26.
    
A case–control study was conducted on 204 drivers fatally injured in road traffic accidents in south-eastern Norway during the period 2003–2008. Cases from single vehicle accidents (N = 68) were assessed separately. As controls, 10 540 drivers selected in a roadside survey in the same geographical area during 2005–2006 were used. Blood samples were collected from the cases and oral fluid (saliva) samples from the controls. Samples were analysed for alcohol, amphetamines, cannabis, cocaine, opioid analgesics, hypnotics, sedatives and a muscle relaxant; altogether 22 psychoactive substances. Equivalent cutoff concentrations for blood and oral fluid were used. The risk for fatal injury in a road traffic accident was estimated using logistic regression adjusting for gender, age, season of the year, and time of the week. The odds for involvement in fatal road traffic accidents for different substances or combination of substances were in increasing order: single drug < multiple drugs < alcohol only < alcohol + drugs. For single substance use: medicinal drug or THC < amphetamine/methamphetamine < alcohol. For most substances, higher ORs were found when studying drivers involved in single vehicle accidents than for those involved in multiple vehicle accidents, but confidence intervals were wider.  相似文献   
27.
    
Olsson E  Gren P  Sjödahl M 《Applied optics》2011,50(17):2551-2558
Light absorbing objects embedded in silicone have been imaged using photoacoustic digital holography. The photoacoustic waves were generated using a pulsed Nd:YAG laser, λ=1064 nm, and pulse length=12 ns. When the waves reached the silicone surface, they were measured optically along a line using a scanning laser vibrometer. The acoustic waves were then digitally reconstructed using a holographic algorithm. The laser vibrometer is proven to be sensitive enough to measure the surface velocity due to photoacoustic waves generated from laser pulses with a fluence allowed for human tissue. It is also shown that combining digital holographic reconstructions for different acoustic wavelengths provides images with suppressed noise and improved depth resolution. The objects are imaged at a depth of 16.5 mm with a depth resolution of 0.5 mm.  相似文献   
28.
    
A very simple time of flight mass spectrometer has been used to measure mass spectra for the negative ions of organic compounds in the mass range up to 3000 u. Desorbed ions were obtained by applying a constant negative voltage to a flat metallic surface, coated with a few micrograms of organic material. We show that electrons and negative ions are emitted simultaneously from the same point on the surface. Mass spectra obtained by this technique are compared to mass spectra for the same compounds, obtained with 252Cf fission fragment ionization.  相似文献   
29.
Achieving economic competitiveness as compared to LWRs and other Generation IV (Gen-IV) reactors is one of the major requirements to attract large-scale investment in commercial sodium cooled fast reactor (SFR) power plants. Advances in R&D for advanced SFR fuel and structural materials provide key long-term opportunities to improve SFR economics. In addition, other new opportunities are emerging to further improve SFR economics. This paper provides an overview on potential ideas from the perspective of thermal hydraulics to improve SFR economics. These include: (1) a new hybrid loop-pool reactor design to further optimize economics, safety, and reliability of SFRs with more flexibility, (2) a multiple-reheat and intercooling helium Brayton cycle to improve plant thermal efficiency and to reduce safety related overnight and operation costs, and (3) modern multi-physics thermal analysis methods to reduce analysis uncertainties and associated requirements for over-conservatism in reactor design. This paper reviews advances in all three areas and their potential beneficial impacts on SFR economics.  相似文献   
30.
A detailed investigation of the relationship between the parameters of the spray process and the in-flight properties of the particles was carried out using a multivariate statistical approach. A full factorial designed experiment concerning the spray process was performed, the spray gun parameters’ current, argon flow rate, hydrogen flow rate, and powder feed rate being selected to control the process. The particle properties, viz. velocity, temperature, and diameter, were determined using an optical measurement system, DPV 2000. In addition, the standard deviations of, and the correlations between, the measured particle properties were analyzed. The results showed current to have the strongest impact on particle velocity and particle temperature and argon flow rate to be the only parameter with an inverse effect on velocity and temperature.  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