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   3293篇
  免费   103篇
  国内免费   3篇
电工技术   41篇
综合类   1篇
化学工业   888篇
金属工艺   54篇
机械仪表   53篇
建筑科学   115篇
矿业工程   4篇
能源动力   88篇
轻工业   256篇
水利工程   21篇
石油天然气   12篇
无线电   298篇
一般工业技术   580篇
冶金工业   614篇
原子能技术   20篇
自动化技术   354篇
  2022年   42篇
  2021年   60篇
  2019年   25篇
  2018年   51篇
  2017年   53篇
  2016年   58篇
  2015年   33篇
  2014年   68篇
  2013年   141篇
  2012年   117篇
  2011年   159篇
  2010年   117篇
  2009年   124篇
  2008年   150篇
  2007年   138篇
  2006年   117篇
  2005年   109篇
  2004年   84篇
  2003年   96篇
  2002年   99篇
  2001年   71篇
  2000年   59篇
  1999年   72篇
  1998年   153篇
  1997年   113篇
  1996年   95篇
  1995年   77篇
  1994年   54篇
  1993年   53篇
  1992年   42篇
  1991年   44篇
  1990年   56篇
  1989年   38篇
  1988年   47篇
  1987年   40篇
  1986年   41篇
  1985年   49篇
  1984年   38篇
  1983年   27篇
  1982年   33篇
  1981年   26篇
  1980年   23篇
  1979年   38篇
  1978年   24篇
  1977年   34篇
  1976年   39篇
  1975年   23篇
  1974年   18篇
  1973年   20篇
  1971年   18篇
排序方式: 共有3399条查询结果,搜索用时 389 毫秒
1.
2.
The authors reanalyzed assessment center (AC) multitrait-multimethod (MTMM) matrices containing correlations among postexercise dimension ratings (PEDRs) reported by F. Lievens and J. M. Conway (2001). Unlike F. Lievens and J. M. Conway, who used a correlated dimension-correlated uniqueness model, we used a different set of confirmatory-factor-analysis-based models (1-dimension-correlated Exercise and 1-dimension-correlated uniqueness models) to estimate dimension and exercise variance components in AC PEDRs. Results of reanalyses suggest that, consistent with previous narrative reviews, exercise variance components dominate over dimension variance components after all. Implications for AC construct validity and possible redirections of research on the validity of ACs are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
3.
Abstract— A Fourier series approach is proposed to calculate stress intensity factors using weight functions for semi-elliptical surface cracks in flat plates subjected to two-dimensional stress distributions. The weight functions were derived from reference stress intensity factors obtained by three-dimensional finite element analyses. The close form weight functions derived are suitable for the calculation of stress intensity factors for semi-elliptical surface cracks in flat plates under two-dimensional stress distributions with the crack aspect ratio in the range of 0.1 ≤ a/c ≤ 1 and relative depth in the range of 0 ≤ a/t ≤ 0.8. Solutions were verified using several two-dimensional non-linear stress distributions; the maximum difference being 6%.  相似文献   
4.
The extinction coefficient ? at 2.9 μm for OH in fluoride glasses is measured by determining the amount of HF evolved during heating of the glass under steam and the corresponding intensity of the OH absorption band. This coefficient is respectively equal to 31 litre mole?1 cm?1 for BTYbZ glass (15 BaF2 - 29 ThF4 - 28 YbF3 - 28 ZnF2) and 19.5 litre mole?1 cm?1 for BALLA glass (34 BaF2 - 57 ZrF4 - 4 AlF3 - 5 LaF3).  相似文献   
5.
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   
6.
An assessment of the Fe-C-Si system   总被引:1,自引:0,他引:1  
  相似文献   
7.
Reaction of metallic fluorides: WF6 TaF5, NbF5 and TiF4 with C60/C70 extract was performed at appropriate temperatures. M0F5 and BF3 fluorides do not react. Chemical formulas based on mass uptake show MFn/C60 ratios up to 2.00. Compounds were analysed by means of X-ray diffraction, FT-IR and NMR spectroscopies. The presence of neutral fluorides and associated anionic species is put forward and it is shown that MFn compounds do not act as fluorination agents. Electrical conductivity measurements are also presented.  相似文献   
8.
Data transmission networks and systems are often subject to perturbations due to the fact that (low level) data signals are surrounded by perturbing electromagnetic fields. This paper presents and analyses information perturbing mechanisms. The authors examine data streams transmitted by an elementary system which represents the basis of any electronic device. We show the influence of technological families of cmos circuits and present a test method and bench to investigate the sensitivity of devices under test by means of statistical parameters.  相似文献   
9.
A 1% Pd catalyst (38% dispersion) was prepared by impregnating a γ-alumina with palladium acetylacetonate dissolved in acetone. The behaviour of this catalyst in oxidation and steam reforming (SR) of propane was investigated. Temperature-programmed reactions of C3H8 with O2 or with O2 + H2O were carried out with different stoichiometric ratios S(S =[O2]/5[C3H8]). The conversion profiles of C3H8 for the reaction carried out in substoichiometry of O2 (S < 1) showed two discrete domains of conversion: oxidation at temperatures below 350°C and SR at temperatures above 350°C. The presence of steam in the inlet gases is not necessary for SR to occur: there is sufficient water produced in the oxidation to form H2 and carbon oxides by this reaction. Contrary to what was observed with Pt, an apparent deactivation between 310 and 385°C could be observed with Pd in oxidation. This is due to a reduction of PdOx into Pd0, which is much less active than the oxide in propane oxidation. Steam added to the reactants inhibits oxidation while it prevents the reduction of PdOx into Pd0. Compared to Pt and to Rh, Pd has a higher thermal resistance: no deactivation occurred after treatment up to 700°C and limited deactivation after treatment up to 900°C, provided that the catalyst is maintained in an oxygen-rich atmosphere during the cooling.  相似文献   
10.
The performance of Nd3+-doped fibre amplifiers is limited by strong excited-state absorption (ESA) of the signal, and, even for fluorozirconate glasses, ESA prevents the important region below 1320 nm from being used. To quantify this limitation and explore alternative host materials, ESA and stimulated-emission cross sections have been measured for a representative group of glass compositions. These parameters have been used in an accurate fiber-amplifier model to provide the first quantitative comparisons of performance for Nd3+ -doped glasses in the 1300-nm band as a function of host  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