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   13223篇
  免费   499篇
  国内免费   48篇
电工技术   139篇
综合类   23篇
化学工业   2514篇
金属工艺   237篇
机械仪表   232篇
建筑科学   865篇
矿业工程   47篇
能源动力   351篇
轻工业   1028篇
水利工程   161篇
石油天然气   52篇
武器工业   1篇
无线电   896篇
一般工业技术   2382篇
冶金工业   2571篇
原子能技术   58篇
自动化技术   2213篇
  2023年   70篇
  2022年   141篇
  2021年   233篇
  2020年   168篇
  2019年   185篇
  2018年   263篇
  2017年   217篇
  2016年   327篇
  2015年   252篇
  2014年   402篇
  2013年   839篇
  2012年   665篇
  2011年   903篇
  2010年   691篇
  2009年   640篇
  2008年   757篇
  2007年   749篇
  2006年   614篇
  2005年   582篇
  2004年   502篇
  2003年   396篇
  2002年   472篇
  2001年   287篇
  2000年   275篇
  1999年   236篇
  1998年   245篇
  1997年   219篇
  1996年   183篇
  1995年   230篇
  1994年   189篇
  1993年   196篇
  1992年   162篇
  1991年   78篇
  1990年   138篇
  1989年   122篇
  1988年   112篇
  1987年   116篇
  1986年   84篇
  1985年   138篇
  1984年   128篇
  1983年   82篇
  1982年   67篇
  1981年   64篇
  1980年   45篇
  1979年   53篇
  1978年   42篇
  1977年   27篇
  1976年   35篇
  1974年   25篇
  1973年   22篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
72.
The aim of the study was to screen any possible synergistic effect available with combination of plant oils and boron compounds to decrease boron leaching and improve thermal degradation of wood by means of dual treatment. In order to reduce the leachability of boron compounds, sapwood of beech and Scots pine samples were treated with oils to create a hydrophobic layer on the wood cells that may prevent water uptake. Increase (%) of boron retained in double-treated samples after leaching was approximately 20% compared to boron-treated samples without oil. The most promising results on boron leaching obtained in the case of using waste and sunflower oil. Thermogravimetric residues were increased by the higher loading of boron compounds in double-treated samples. Spectra of FTIR-Photoacoustic spectrometer showed some deformation of lignin and cellulose followed by degradation of hemicelluloses of treated wood samples due to heat effect at 160 °C.  相似文献   
73.
This study evaluated the significance of different process parameters (press temperature, closing time, holding time, moisture content and compression ratio) on solid wood surface densification and its effect on the density profile generated in Scots pine sapwood. Changes in the microstructure of the wood were also evaluated microscopically. The results showed that with a shorter closing time, densification occurred closer to the sample surface than with an extended closing time. At a compression temperature of 150 °C, the vertical density profile exhibited a sharp peak in density that was close to the wood surface. A higher temperature of 200 °C resulted in a slightly broader density peak that was less intense and further from the surface. A holding time of 10 min resulted in the wood compressing to a slightly greater extent than when using a holding time of 1 min. Higher moisture content led to more extensive deformation. The results indicate that surface modification by densification is a viable method of enhancing wood properties.  相似文献   
74.
It is demonstrated that for an isolated Mode I planar crack embedded in an infinite body, the stress intensity factor along the crack front is a function independent of the elastic constants.  相似文献   
75.
The corrosion behavior of pure Mg,AZ31,and AZ91D were evaluated in various in vitro and in vivo environments to investigate the potential application of these metals as biodegradable implant materials.DC polarization tests and immersion tests were performed in different simulated body solutions,such as distilled(DI) water,simulated body fluid(SBF) and phosphate buffered solution(PBS).Mg/Mg alloys were also implanted in different places in a mouse for in vivo weight loss and biocompatibility investigations.The in vivo subcutis bio-corrosion rate was lower than the corrosion rate for all of the in vitro simulated corrosive environments.The Mg/Mg alloys were biocompatible based on histology results for the liver,heart,kidney,skin and lung of the mouse during the two months implantation.Optical microscopy and scanning electron microscopy were carried out to investigate the morphology and topography of Mg/Mg alloys after immersion testing and implantation to understand the corrosion mechanisms.  相似文献   
76.
A current premium vehicle is implemented with a variety of information, entertainment, and communication functions, which are generally referred as an infotainment system. During vehicle development, testing of the infotainment system at an overall level is conventionally carried out manually by an expert who can observe at a customer level. This approach has significant limitations with regard to test coverage and effectiveness due to the complexity of the system functions and human’s capability. Hence, it is highly demanded by car manufacturers for an automated infotainment testing system, which replicates a human expert encompassing relevant sensory modalities relating to control (i.e., touch) and observation (i.e., sight and sound) of the system under test. This paper describes the design, development, and evaluation of such a system that consists of simulation of vehicle network, vision-based inspection, automated navigation of features, random cranking waveform generation, sound detection, and test automation. The system developed is able to: stimulate a vehicle system across a wide variety of initialisation conditions, exercise each function, check for system responses, and record failure situations for post-testing analysis.  相似文献   
77.
Those living in deprived areas may have a greater reliance on the neighbourhood as a setting for social activity. However, the reduced quality of deprived neighbourhoods may make attachment in such places less likely. Other factors, like high turnover and social mix, may also act to reduce an individual’s attachment in these neighbourhoods. Using qualitative methods, this study examines both emotional and functional attachment to deprived neighbourhoods, specifically considering the impact of high turnover and of social mix. Social mix is broadly defined, including but not limited to ethnic and tenure mix. Many respondents reported strong emotional attachments to their communities, with the presence of strong social networks and a sense of security the most important contributing factors. Functional attachments and attachments to the physical environment were weak or absent. High turnover in deprived areas was found to reduce place attachment by undermining social networks, lowering social interaction, and eroding trust and feelings of security. There was little evidence that social mix in any dimension reduced attachment significantly. However, high residential turnover and a rapidly changing (ethnic) mix in one area had led to increased anxieties and reduced attachments. The research shows that rather than systemic factors being dominant, place attachment in deprived areas is very context dependent (e.g. in terms of where the neighbourhood is located in relation to others). For an individual, also experiential, historical and personal factors are strong determinants of attachment.  相似文献   
78.
79.
Transdermal drug delivery (TDD) systems with feedback control have attracted extensive research and clinical interest owing to their unique advantages of convenience, self‐administration, and safety. Here, a self‐powered wearable iontophoretic TDD system that can be driven and regulated by the energy harvested from biomechanical motions is proposed for closed‐loop motion detection and therapy. A wearable triboelectric nanogenerator (TENG) is used as the motion sensor and energy harvester that can convert biomechanical motions into electricity for iontophoresis without stored‐energy power sources, while a hydrogel‐based soft patch with side‐by‐side electrodes is designed to enable noninvasive iontophoretic TDD. Proof‐of‐concept experiments on pig skin with dyes as model drugs successfully demonstrate the feasibility of the proposed system. This work not only extends the application of TENG in the biomedical field, but may also provide a cost‐effective solution for noninvasive, electrically assisted TDD with closed‐loop sensing and treatment.  相似文献   
80.
In this work, a nanohybrid material based on a freestanding polymeric liquid crystal network capable of postmodification via cation exchange to tune birefringence is proposed. The smectic liquid crystal films can be infiltrated with a variety of cations, thereby changing the refractive indices (ne and no) and the effective birefringence (Δn) of the nanohybrid material, with reversible cation infiltration occurring within minutes. Birefringence could be tuned between values of 0.06 and 0.19, depending on the cation infiltrated into the network. Upon infiltration, a decrease in the smectic layer spacing is found with layer contraction independent of the induced change in birefringence. Potential applications are in the field of specialty optical devices, such as flexible, retunable reflective filters.  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