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   1466篇
  免费   40篇
电工技术   112篇
综合类   5篇
化学工业   306篇
金属工艺   29篇
机械仪表   39篇
建筑科学   34篇
能源动力   93篇
轻工业   70篇
水利工程   3篇
无线电   148篇
一般工业技术   302篇
冶金工业   161篇
原子能技术   37篇
自动化技术   167篇
  2022年   16篇
  2021年   21篇
  2020年   10篇
  2019年   20篇
  2018年   18篇
  2017年   13篇
  2016年   29篇
  2015年   21篇
  2014年   46篇
  2013年   82篇
  2012年   58篇
  2011年   61篇
  2010年   67篇
  2009年   60篇
  2008年   70篇
  2007年   66篇
  2006年   55篇
  2005年   63篇
  2004年   45篇
  2003年   44篇
  2002年   39篇
  2001年   34篇
  2000年   23篇
  1999年   30篇
  1998年   62篇
  1997年   59篇
  1996年   48篇
  1995年   30篇
  1994年   28篇
  1993年   37篇
  1992年   14篇
  1991年   25篇
  1990年   15篇
  1989年   20篇
  1988年   11篇
  1987年   9篇
  1986年   21篇
  1985年   23篇
  1984年   9篇
  1983年   11篇
  1982年   12篇
  1981年   12篇
  1980年   10篇
  1979年   8篇
  1978年   10篇
  1977年   8篇
  1976年   12篇
  1974年   4篇
  1973年   3篇
  1972年   3篇
排序方式: 共有1506条查询结果,搜索用时 15 毫秒
141.
Energy service business, or energy service company (ESCO), is expanding among industrial users as a means of energy saving. The ESCO business normally tends to become a long-term operation. During the operation, fluctuations of fuel and electricity costs significantly impact on the stability of the profit from ESCO business. Therefore, it is essential to reduce the risk of fuel and electricity cost fluctuations. Generally, a transaction called “financial derivative” is used as a measure of hedging against the fuel price fluctuation. In the case of ESCO business, it is necessary to manage the risk of both electricity and fuel price fluctuations because the variation in electricity price strongly affects the profit from ESCO as that in fuel price does.  相似文献   
142.
This paper is about measurements, analyses and evaluation of residential PV systems in the Japanese Monitoring Program, on which JQA was subsidized by NEDO (New Energy Development and Industrial Technology Organization) that is currently proceeding [NSS R&D] from FY1997 to FY 2000.The aim of this investigation refers, through the data evaluation and analyses, to obtain knowledge required for optimizing design of PV systems, such as system performance, characteristics and regional dependency under practical operation and to develop the system evaluation technology on the design parameter method.  相似文献   
143.
Linear energy transfer (LET) is an average quantity, which cannot display the stochastics of the interactions of radiation tracks in the target volume. For this reason, microdosimetry distributions have been defined to overcome the LET shortcomings. In this paper, model calculations of frequency distributions for energy depositions in nanometre size targets, diameters 1-100 nm, and for a 1 μm diameter wall-less TEPC, for electrons, protons, alpha particles and carbon ions are reported. Frequency distributions for energy depositions in small-size targets with dimensions similar to those of biological molecules are useful for modelling and calculations of DNA damage. Monte Carlo track structure codes KURBUC and PITS99 were used to generate tracks of primary electrons 10 eV to 1 MeV, and ions 1 keV μm(-1) to 300 MeV μm(-1) energies. Distribution of absolute frequencies of energy depositions in volumes with diameters of 1-100 nm randomly positioned in unit density water irradiated with 1 Gy of the given radiation was obtained. Data are presented for frequency of energy depositions and microdosimetry quantities including mean lineal energy, dose mean lineal energy, frequency mean specific energy and dose mean specific energy. The modelling and calculations presented in this work are useful for characterisation of the quality of radiation beam in biophysical studies and in radiation therapy.  相似文献   
144.
Environmental ecological modeling (EEM), which unifies models simulating transport of chemicals and exposure of humans to chemicals, was used to simulate long-term trends of female adult human blood lead levels (BLLs) and historical exposure to the atmospheric lead in four East Asian countries: Japan, Korea, China, and Vietnam. Anthropogenic lead emissions to the atmosphere in Vietnam were estimated from energy statistics to be 1931 t yr(-1). Calculated BLLs generally agreed with those observed in samples collected in these countries as the error factors were less than 2. The model results revealed that BLLs decreased significantly in Tokyo (by 58%) and Seoul (by 45%) in recent decades and confirmed the effects of efforts to reduce environmental lead in Japan and Korea. The model results also revealed that BLLs in Beijing did not decrease in this decade as much as in Tokyo and Seoul, despite the phasing out of leaded gasoline, and that the contribution from the atmospheric component was increasing (43% in 2009). Finally, we applied EEM to simulate BLLs of children in Hanoi. The probability of children having BLLs greater than 50 μg L(-1) was 7.5%, which was greater than those observed in developed countries.  相似文献   
145.
146.
This paper presents the comparison of a three dimensional Computational Fluid Dynamics (CFD) analysis with empirical performance data of a 0.6 m impulse turbine with fixed guide vanes used for wave energy power conversion. Pro-Engineer, Gambit and Fluent 6 were used to create a 3-D model of the turbine. A hybrid meshing scheme was used with hexahedral cells in the near blade region and tetrahedral and pyramid cells in the rest of the domain. The turbine has a hub-to-tip ratio of 0.6 and results were obtained over a wide range of flow coefficients. The model yielded a maximum efficiency of approximately 54% as compared to a maximum efficiency of around 49% from experiment. A degree of insight into flow behaviour, not possible with experiment, was obtained.  相似文献   
147.
Reaction sintering behavior of cBN, which is accompanied by the transformation from hBN to cBN in the presence of 30 wt% diamond seed grains, was investigated under high pressure conditions (6.0–7.5 GPa, 1400–1700°C, 0–30 min) using volatile catalysts such as NH4NO3, NH4Cl, and NH2NH2. Fully dense sintered compacts having a Vickers microhardness of more than 5000 kg/mm2 were prepared with no residual catalytic solid components. The activation energy for the conversion from hBN to cBN was 200–230 kJ/mol. Adsorbed N2, H2, and/or NH x components which were formed by decomposition of these catalysts during high pressure and temperature treatments, would have a favorable kinetic effect on cBN formation from hBN and its simultaneous sintering.  相似文献   
148.
Three newly found vibrational levels at energies Te(v) = 45127.88(3), 51900.40(4), and 52604.95(3) cm-1 allow the first application of resonance-enhanced multiphoton ionization for detecting the SO radical in its low-energy singlet states, a1Delta and b1Sigma+. The analysis of the spectra is based on the observation of 10 rotationally resolved bands starting from a1Delta v = 0, 6 ellipsis 11 and b1Sigma+ v = 8, covering a typical range of J = 5 ellipsis 40 or 50. Population of these SO singlet states has been achieved by two-photon dissociation of SO2 in a molecular beam environment, applying wavelengths in the 248 to 291 nm range. This paper presents an analysis of the rotational, vibrational, and electronic properties of the new levels. Reviewing earlier works on the singlet states of SO, a revised term energy scheme is provided which connects the singlet and triplet systems of the molecule. Copyright 1998 Academic Press.  相似文献   
149.
New inhibitors have been designed for cdc2 kinase based on a multiple pseudosubstrate structure. The new inhibitors have three different structural components: 3,4-bis(indol-3-yl)maleimide, Ac-Cys-(Ser)-Pro-Lys-Lys-NHMe, and ethyloxy group between the two components. Inhibitory activities toward cdc2 and other protein kinases were investigated, and the compound (21) with Ac-Cys-Pro-Lys-Lys-NHMe connected with the triethylene glycol spacer exhibited the most potent inhibition with relatively high selectivity.  相似文献   
150.
Thermophoretic sampling (TS) of the aerosol was conducted to manifest the formation of hollow and solid alumina particles in spray flames. The collected particles were investigated by transmission electron microscopy. Hollow particles with a thin shell (e.g., 10 nm) were formed from the aluminum nitrate precursor emulsion at less than 4-cm flame height. Hollow particles maintained their shapes in the flame using air as dispersion/oxidant gas, whereas hollow-to-solid restructuring of the particles took place in the flame using oxygen. With oxygen, nanoparticles were formed in the gas phase from the aluminum butoxide/2-propanol precursor solution only, whereas gas-phase reaction was hindered, forming large particles from the aluminum nitrate/2-propanol precursor solution.  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