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   1026466篇
  免费   13932篇
  国内免费   2518篇
电工技术   18866篇
综合类   920篇
化学工业   150570篇
金属工艺   41872篇
机械仪表   31688篇
建筑科学   24167篇
矿业工程   6092篇
能源动力   26440篇
轻工业   81483篇
水利工程   11346篇
石油天然气   20065篇
武器工业   70篇
无线电   115362篇
一般工业技术   203887篇
冶金工业   196763篇
原子能技术   21618篇
自动化技术   91707篇
  2021年   8799篇
  2020年   6613篇
  2019年   8414篇
  2018年   17346篇
  2017年   17359篇
  2016年   16980篇
  2015年   10227篇
  2014年   16811篇
  2013年   45768篇
  2012年   27197篇
  2011年   39350篇
  2010年   31993篇
  2009年   34965篇
  2008年   35853篇
  2007年   36372篇
  2006年   28707篇
  2005年   27521篇
  2004年   26148篇
  2003年   25606篇
  2002年   24202篇
  2001年   23618篇
  2000年   22405篇
  1999年   23287篇
  1998年   58622篇
  1997年   41384篇
  1996年   30915篇
  1995年   24113篇
  1994年   21280篇
  1993年   20905篇
  1992年   15205篇
  1991年   14546篇
  1990年   14362篇
  1989年   13839篇
  1988年   13072篇
  1987年   11638篇
  1986年   11453篇
  1985年   13038篇
  1984年   11805篇
  1983年   10875篇
  1982年   10035篇
  1981年   10301篇
  1980年   9739篇
  1979年   9613篇
  1978年   9380篇
  1977年   10974篇
  1976年   14356篇
  1975年   8270篇
  1974年   7882篇
  1973年   8003篇
  1972年   6750篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Multimedia Tools and Applications - Discovering the relevant web services for specific applications in the dynamically changing business world becomes very critical. Researchers have used many...  相似文献   
82.
Theoretical Foundations of Chemical Engineering - The effect of the electrolyte composition, mass-transfer conditions, pore diameter, interpore distance, and electric parameters on the formation of...  相似文献   
83.
Journal of Inorganic and Organometallic Polymers and Materials - This paper reports the performance of alizarin based SnO2 dye-sensitized solar cells. A novel template assisted method has been...  相似文献   
84.
Applied Composite Materials - Determining the impact behavior of adhesive joints allows the designing of high-strength joints. Therefore, the dynamic behavior of adhesive joints has recently become...  相似文献   
85.
In flash sintering experiments, the thermal history of the sample is key to understanding the mechanisms underlying densification rate and final properties. By combining robust temperature measurements with current-ramp-rate control, this study examined the effects of the thermal profile on the flash sintering of yttria-stabilized zirconia, with experiments ranging from a few seconds to several hours. The final density was maximized at slower heating rates, although processes slower than a certain threshold led to grain growth. The amount of grain growth observed was comparable to a similar conventional thermal process. The bulk electrical conductivity correlated with the maximum temperature and cooling rate. The only property that exhibited behavior that could not be attributed to solely the thermal profile was the grain boundary conductivity, which was consistently higher than conventional in flash sintered samples. These results suggest that, during flash sintering, athermal electric field effects are relegated to the grain boundary.  相似文献   
86.
Ce:Y3Al5O12 transparent ceramics (TCs) with appropriate emission light proportion and high thermal stability are significant to construct white light emitting diode devices with excellent chromaticity parameters. In this work, strategies of controlling crystal-field splitting around Ce3+ ion and doping orange-red emitting ion, were adopted to fabricate Ce:(Y,Tb)3(Al,Mn)5O12 TCs via vacuum sintering technique. Notably, 85.4 % of the room-temperature luminescence intensity of the TC was retained at 150 °C, and the color rendering index was as high as 79.8. Furthermore, a 12 nm red shift and a 16.2 % increase of full width at half maximum were achieved owing to the synergistic effects of Tb3+ and Mn2+ ions. By combining TCs with a 460 nm blue chip, a warm white light with a low correlated color temperature of 4155 K was acquired. Meanwhile, the action mechanism of Tb3+ ion and the energy transfer between Ce3+ and Mn2+ ions were verified in prepared TCs.  相似文献   
87.
A new TiO2-containing bioactive glass and glass-ceramics based on 50SiO2-(45-X)CaO-(XTiO2)-5P2O5 system was designed using a sol–gel technique (where X = 5, 7.5 and 10 wt %). The roles of the crystallization behavior and physicochemical characteristics of the designed glass and glass-ceramics which were played in the introduction of TiO2 substitutions were investigated. Moreover, cell proliferation and differentiation were evaluated against human osteosarcoma cells (Saos-2). The TiO2/CaO replacements led to the formation of a stronger glass structure and thus increased thermal parameters and the chemical stabilization of the designed materials. The FTIR data confirmed the existence of Ti within the glass and glass-ceramics samples, and no remarkable effect on their chemical integrity was observed. The XRD patterns indicated that calcium-containing minerals, including Ca2SiO4,Ca3(PO4)2, Ca(Ti,Si)O5, CaTiSiO5, and Ca15(PO4)2·(SiO4)6 phases were developed as a role of structure/texture under the applied heat-treatment. The results of the cytotoxicity test proved that a safe sample dose is 12–50 μg/ml, at which cell viability is ≥ 85%. The cell differentiation determined by ALP test proved the superiority of glass-ceramics compared with their native glasses. Therefore, the obtained materials could be safely used as novel biocompatible materials for the regeneration of bone tissue.  相似文献   
88.
One of the drawbacks of fusible clays is the narrow sintering interval due to a sharp increase in the amount of iron-silicate melt at a temperature of 1000–1100 °C, which hardens in the form of a glass phase upon cooling. This leads to a relatively low mechanical strength of the calcined samples and causes the danger of melting the granular material surface from such clays during the firing process. To increase the strength of samples of fusible clays, the influence of diabase and granitoid rocks was considered. It was found that the strengthening effect of diabase and granitoid rock additives in an amount of 20–50% in a mixture with fusible clay is due to an increase of total content of the crystalline phase (mullite, cristobalite and residual quartz) from 18–20% in clays without additives to 22–28 % - in mixtures with diabase and to 28–34% - with granitoid additives) at a temperature of 1050–1100 °C. This increase is due to the activation of synthesis processes of secondary mullite and crystallization from alkali-rich feldspar melt of amorphous silica, released from the structure of clay minerals. The established influence of the igneous rocks used made it possible to develop compositions and propose process flow sheet for producing aluminosilicate proppants based on fusible clays. The use of granitoid and diabase rocks in an amount of 20–70% with fusible clays produces lightweight aluminosilicate proppants with bulk density of 1.40–1.46 g/cm3 at temperature range of 1050–1100 °C, which can endure destructive pressures up to 34.5–52 MPa.  相似文献   
89.
Theoretical Foundations of Chemical Engineering - The corona onset voltage is an important operating parameter in the electrostatic precipitation of nanoparticulate, however, its experimental...  相似文献   
90.
Chronic stress is a combination of nonspecific adaptive reactions of the body to the influence of various adverse stress factors which disrupt its homeostasis, and it is also a corresponding state of the organism’s nervous system (or the body in general). We hypothesized that chronic stress may be one of the causes occurence of several molecular and cellular types of stress. We analyzed literary sources and considered most of these types of stress in our review article. We examined genes and mutations of nuclear and mitochondrial genomes and also molecular variants which lead to various types of stress. The end result of chronic stress can be metabolic disturbance in humans and animals, leading to accumulation of reactive oxygen species (ROS), oxidative stress, energy deficiency in cells (due to a decrease in ATP synthesis) and mitochondrial dysfunction. These changes can last for the lifetime and lead to severe pathologies, including neurodegenerative diseases and atherosclerosis. The analysis of literature allowed us to conclude that under the influence of chronic stress, metabolism in the human body can be disrupted, mutations of the mitochondrial and nuclear genome and dysfunction of cells and their compartments can occur. As a result of these processes, oxidative, genotoxic, and cellular stress can occur. Therefore, chronic stress can be one of the causes forthe occurrence and development of neurodegenerative diseases and atherosclerosis. In particular, chronic stress can play a large role in the occurrence and development of oxidative, genotoxic, and cellular types of stress.  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