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   235篇
  免费   7篇
电工技术   2篇
化学工业   45篇
金属工艺   2篇
机械仪表   6篇
建筑科学   7篇
能源动力   6篇
轻工业   36篇
水利工程   1篇
石油天然气   1篇
无线电   17篇
一般工业技术   38篇
冶金工业   31篇
原子能技术   1篇
自动化技术   49篇
  2022年   8篇
  2021年   7篇
  2020年   6篇
  2019年   5篇
  2018年   5篇
  2017年   9篇
  2016年   7篇
  2015年   6篇
  2014年   6篇
  2013年   13篇
  2012年   22篇
  2011年   17篇
  2010年   15篇
  2009年   11篇
  2008年   10篇
  2007年   12篇
  2006年   6篇
  2005年   6篇
  2004年   5篇
  2003年   4篇
  2002年   3篇
  2001年   4篇
  2000年   3篇
  1999年   3篇
  1998年   8篇
  1997年   5篇
  1996年   9篇
  1995年   6篇
  1994年   2篇
  1993年   3篇
  1991年   1篇
  1990年   1篇
  1989年   1篇
  1987年   2篇
  1983年   1篇
  1980年   1篇
  1979年   1篇
  1977年   1篇
  1976年   1篇
  1969年   1篇
  1968年   2篇
  1967年   2篇
  1966年   1篇
排序方式: 共有242条查询结果,搜索用时 218 毫秒
11.
A bottom-up method for creating a hierarchy of entity-relationship diagrams (HERD) from a given, flat ER diagram (ERD) is proposed. The hierarchy consists of simple and interrelated diagrams—ER structures—with external relationships to other structures. The HERD-tree diagram, which provides the most general view of the conceptual schema, is located at the top of the hierarchy. The method is based on packaging operations, which group entities and relationships according to certain criteria. These operations are applied in several steps on a given (presumably large-scale) ERD. We describe the new constructs, which are added to the ER model to enable the creation of HERD, and a bottom-up method for creating HERD. We also evaluate HERD from the point of view of user comprehension and preference, based on an experimental comparison to flat ERDs.
Peretz ShovalEmail:
  相似文献   
12.
The performance of Advanced Spaceborne Thermal Emission Reflection Radiometer (ASTER) thermal infrared (TIR) data product algorithms was evaluated for low spectral contrast surfaces (such as vegetation and water) in a test site close to Valencia, Spain. Concurrent ground measurements of surface temperature, emissivity, and atmospheric radiosonde profiles were collected at the test site, which is a thermally homogeneous area of rice crops with nearly full vegetation cover in summer. Using the ground data and the local radiosonde profiles, at-sensor radiances were simulated for the ASTER TIR channels and compared with L1B data (calibrated at-sensor radiances) showing discrepancies up to 3% in radiance for channel 10 at 8.3 μm (equivalently, 2.5 °C in temperature or 7% in emissivity), whereas channel 13 (10.7 μm) yielded a closer agreement (maximum difference of 0.5% in radiance or 0.4 °C in temperature). We also tested the ASTER standard products of land surface temperature (LST) and spectral emissivity generated with the Temperature-Emissivity Separation (TES) algorithm with standard atmospheric correction from both global data assimilation system profiles and climatology profiles. These products showed anomalous emissivity spectra with lower emissivity values and larger spectral contrast (or maximum-minimum emissivity difference, MMD) than expected, and as a result, overestimated LSTs. In this work, a scene-based procedure is proposed to obtain more accurate MMD estimates for low spectral contrast materials (vegetation and water) and therefore a better retrieval of LST and emissivity with the TES algorithm. The method uses various gray-bodies or near gray-bodies with known emissivities and assumes that the calibration and atmospheric correction performed with local radiosonde data are accurate for channel 13. Taking the channel 13 temperature (atmospherically and emissivity corrected) as the true LST, the radiances for the other channels were simulated and used to derive linear relationships between ASTER digital numbers and at-ground radiances for each channel. The TES algorithm was applied to the adjusted radiances and the resulting products showed a closer agreement with the ground measurements (differences lower than 1% in channel 13 emissivities and within ± 0.3 °C in temperature for rice and sea pixels).  相似文献   
13.
14.
In this work, the different computational paradigms used in Artificial Intelligence (AI) and Autonomous Robotics are revised in the context of the reactive and situated paradigm. In particular, a Neural Computational paradigm based on perceptual association maps is revised. We explore the Singer hypothesis about the evidence of the same neural mechanism known from retinotopic projections. Finally, the implications of this computational paradigm with maps in the context of the definition, design, building and evaluation of neuroprosthesis are discussed.  相似文献   
15.
Throughout adulthood and old age, levels of well-being appear to remain relatively stable. However, evidence is emerging that late in life well-being declines considerably. Using long-term longitudinal data of deceased participants in national samples from Germany, the United Kingdom, and the United States, we examined how long this period lasts. In all 3 nations and across the adult age range, well-being was relatively stable over age but declined rapidly with impending death. Articulating notions of terminal decline associated with impending death, we identified prototypical transition points in each study between 3 and 5 years prior to death, after which normative rates of decline steepened by a factor of 3 or more. The findings suggest that mortality-related mechanisms drive late-life changes in well-being and highlight the need for further refinement of psychological concepts about how and when late-life declines in psychosocial functioning prototypically begin. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
16.
Meeting the mental health needs of Veterans returning from recent deployment requires the coordinated effort of partnerships across Department of Defense (DoD), Department of Veterans Affairs (VA), and state and local communities. Although the proportion of Veterans of Iraq and Afghanistan who have accessed VA health care has grown, the majority of these new combat Veterans have yet to present for VA care. The stigma associated with reporting a deployment-related mental health problem may be one factor in this, but access to treatment may also be an important concern among the one third of American Veterans who live in rural or highly rural areas. As these Veterans are more likely to present to a primary care, faith-based or mental health provider in their own community, partnerships between community providers, DoD, and VA are of critical importance in ensuring appropriate care, regardless of treatment setting. In an effort to improve services and access to services, especially to rural Veterans, an educational public health initiative was created to educate community providers about military culture, deployment-related mental health issues, VA resources, and evidence-based treatments. We describe the development, dissemination and evaluation of this initiative, as well as lessons learned for future similar endeavors. (PsycINFO Database Record (c) 2011 APA, all rights reserved)  相似文献   
17.
Paediatric reference intervals for blood concentrations of certain nutrients are often based on either adult data or are derived from small samples of young children. Biochemical data were obtained from 467 randomly selected, healthy preschool children aged 9-62 months in Sydney, Australia. Data were obtained for plasma vitamins A, E and beta-carotene and for serum zinc, retinol-binding protein and prealbumin. Reference intervals based on the 2.5 and 97.5 centiles for age groups 9-23, 24-35, 36-47, 48-62 months and for the total group (9-62 months) were calculated. The 2.5-97.5 centiles for the whole group were: vitamin A, 0.7-1.8 mumol/l (20.05-51.56 micrograms/dl); vitamin E, 8-30 mumol/l (0.34-1.29 mg/dl); beta-carotene, 0.1-1.1 mumol/l (5.4-59.0 micrograms/dl); zinc, 9-19 mumol/l (58.8-124.2 micrograms/dl); retinol-binding protein, 14-36 mg/l; prealbumin, 104-264 mg/l. The reference intervals reported are consistent with the findings of a number of smaller studies and are likely to be an accurate reflection of the true intervals for healthy preschool children in western developed countries.  相似文献   
18.
A technique to suppress higher harmonics in side-coupled ring bandpass filters is proposed and demonstrated. The proposed technique basically consists of optimising the ring shape and the excitation stage of the complete filter structure in order to mitigate the excitation of the resonant modes that generate the second-harmonic filter resonances. A harmonic suppression ratio for the second harmonic greater than 25 dB in a flat bandpass filter centred at 2.5 GHz is experimentally demonstrated.  相似文献   
19.
A 71-year-old man was admitted due to brain infarction. An abnormal floating mass was found in the right atrium by echocardiography. The mass was assumed to be a thrombus. The patient was failed to be in danger of pulmonary embolism, so it was decided to remove surgically. The thrombus was removed under cardiopulmonary bypass including the atrial wall where it was attached, because it was difficult to rule out the possibility of cardiac tumor macroscopically. The tumor showed pathological findings of thrombus. Postoperative course was uneventful.  相似文献   
20.
Growth and activity of lactic acid bacteria is crucial for the production and quality of grape wines but studying their metabolism is difficult in wines or complex laboratory media because of the undefined substrate pools. This work presents a new chemically defined medium that meets the fastidious nutritional requirements of wine lactic acid bacteria and yields rapid and strong growth. The new medium is composed of 44 constituents and a precise protocol is provided for its preparation. Maximum specific growth rates and growth yields of the wine strains studied were comparable to those obtained in common laboratory media, and the new medium allows for various modifications, such as changing the medium pH to the wine range, addition of L-malic acid or utilization of different carbon sources while maintaining growth of wine lactic acid bacteria. The medium was successfully tested with 22 wine strains of the genera Oenococcus, Lactobacillus and Pediococcus. It is suggested that this chemically defined medium be considered for the investigation of the nutritional requirements and metabolism of wine lactic acid bacteria.  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