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   4798篇
  免费   268篇
  国内免费   10篇
电工技术   55篇
综合类   4篇
化学工业   1007篇
金属工艺   178篇
机械仪表   301篇
建筑科学   99篇
矿业工程   1篇
能源动力   211篇
轻工业   444篇
水利工程   16篇
石油天然气   3篇
无线电   843篇
一般工业技术   975篇
冶金工业   342篇
原子能技术   63篇
自动化技术   534篇
  2024年   8篇
  2023年   65篇
  2022年   102篇
  2021年   185篇
  2020年   98篇
  2019年   138篇
  2018年   157篇
  2017年   148篇
  2016年   170篇
  2015年   149篇
  2014年   224篇
  2013年   296篇
  2012年   294篇
  2011年   372篇
  2010年   269篇
  2009年   283篇
  2008年   247篇
  2007年   200篇
  2006年   197篇
  2005年   164篇
  2004年   158篇
  2003年   114篇
  2002年   121篇
  2001年   84篇
  2000年   98篇
  1999年   90篇
  1998年   134篇
  1997年   96篇
  1996年   75篇
  1995年   64篇
  1994年   53篇
  1993年   24篇
  1992年   31篇
  1991年   24篇
  1990年   22篇
  1989年   18篇
  1988年   15篇
  1987年   16篇
  1986年   19篇
  1985年   8篇
  1984年   3篇
  1983年   5篇
  1982年   4篇
  1981年   3篇
  1977年   7篇
  1976年   6篇
  1975年   3篇
  1974年   3篇
  1973年   3篇
  1966年   2篇
排序方式: 共有5076条查询结果,搜索用时 15 毫秒
81.
82.
The low-density-lipoprotein receptor (LDLr) removes low-density lipoprotein (LDL), an endovascular transporter that carries cholesterol from the bloodstream to peripheral tissues. The maintenance of cholesterol content in the brain, which is important to protect brain function, is affected by LDLr. LDLr co-localizes with the insulin receptor and complements the internalization of LDL. In LDLr deficiency, LDL blood levels and insulin resistance increase, leading to abnormal cholesterol control and cognitive deficits in atherosclerosis. Defects in brain cholesterol metabolism lead to neuroinflammation and blood–brain-barrier (BBB) degradation. Moreover, interactions between endoplasmic reticulum stress (ER stress) and mitochondria are induced by ox-LDL accumulation, apolipoprotein E (ApoE) regulates the levels of amyloid beta (Aβ) in the brain, and hypoxia is induced by apoptosis induced by the LDLr defect. This review summarizes the association between neurodegenerative brain disease and typical cognitive deficits.  相似文献   
83.
A low-cost broadband millimetre-wave planar 30/spl times/30 array antenna is presented. The antenna is fed by a microstrip feed network in the H-plane to decrease fabrication costs, and a waveguide feed network in the E-plane to reduce the feed line loss. The waveguide and microstrip feed network are coupled through the proposed slot pair. The slots are placed one quarter of a guided-wavelength distance apart, so that the reflected waves from the slots cancel each other. A conductive bar is laid above the slots to increase the coupling, which increases the antenna gain by about 1 dBi. The maximum gain is 30.5 dBi at 41.5 GHz. The measured bandwidth is as broad as 7.1%.  相似文献   
84.
Chip-on-glass (COG) interconnection using anisotropic conductive film (ACF) is susceptible to open failures. Open failures can be induced by the absence of conductive particles or an insufficient contact. Experimental results as well as statistical approaches were used to understand the conditions for open failures in COG bonding. The binomial distribution was used to predict the probability of the open failure due to the deficiency of conductive particles. The probability of an open failure decreased with increasing bump area and decreasing particle size. The bump height variation was also an important factor that affected the probability of the open failure together with the bump-to-electrode gap and the particle size. The variation in bump height should be minimized to avoid open failures in fine-pitch applications where a smaller particle size is required.  相似文献   
85.
A waveguide polarization splitter is demonstrated based on a low-loss polymer waveguide and a birefringent polyimide. Crosslinkable fluorinated polymers with an excellent stability and a low absorption loss are utilized for the device. The polyimide is buried under one branch of the Y-branch waveguide to enhance the birefringence between the TE and TM modes. By the adiabatic mode evolution, the TE mode is coupled to the branch with the polyimide strip, while the TM mode propagates through the other branch without the polyimide. For the device with a branch angle of 1/400 rad, we obtained a crosstalk less than -20 dB and a fiber-to-fiber insertion loss of 3.8 dB  相似文献   
86.
Non-alcoholic steatohepatitis (NASH) has pathological characteristics similar to those of alcoholic hepatitis, despite the absence of a drinking history. The greatest threat associated with NASH is its progression to cirrhosis and hepatocellular carcinoma. The pathophysiology of NASH is not fully understood to date. In this study, we investigated the pathophysiology of NASH from the perspective of glycolysis and the Warburg effect, with a particular focus on microRNA regulation in liver-specific macrophages, also known as Kupffer cells. We established NASH rat and mouse models and evaluated various parameters including the liver-to-body weight ratio, blood indexes, and histopathology. A quantitative phosphoproteomic analysis of the NASH rat model livers revealed the activation of glycolysis. Western blotting and immunohistochemistry results indicated that the expression of pyruvate kinase muscle 2 (PKM2), a rate-limiting enzyme of glycolysis, was upregulated in the liver tissues of both NASH models. Moreover, increases in PKM2 and p-PKM2 were observed in the early phase of NASH. These observations were partially induced by the downregulation of microRNA122-5p (miR-122-5p) and occurred particularly in the Kupffer cells. Our results suggest that the activation of glycolysis in Kupffer cells during NASH was partially induced by the upregulation of PKM2 via miR-122-5p suppression.  相似文献   
87.
The aim of this study is to extract landslide-related factors from remote-sensing data, such as Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) satellite imagery, and to examine their applicability to landslide susceptibility near Boun, Korea, using a geographic information system (GIS). Landslide was mapped from interpretation of aerial photographs and field surveying. Factors that influence landslide occurrence were extracted from ASTER imagery. The slope, aspect and curvature were calculated from the digital elevation model (DEM) with 25.77 m root mean square error (RMSE), which was derived from ASTER imagery. Lineaments, land-cover and normalized difference vegetation index (NDVI) layers were also estimated from ASTER imagery. Landslide-susceptible areas were analysed and mapped using the occurrence factors by a frequency ratio and logistic regression model. Validation results were 84.78% in frequency ratio and 84.20% in logistic regression prediction accuracy for the susceptibility map with respect to ground-truth data.  相似文献   
88.
This paper describes the design and implementation of SAPPHIRE – a novel middleware and software development kit for stream programing on a heterogeneous system of multi-core multi-CPUs with optional hardware accelerators such as graphics processing unit (GPU). A stream program consists of a set of tasks where the same tasks are repeated over multiple iterations of data (e.g., video frames). Examples of such programs are video analysis applications for computer-aided diagnosis and computer-assisted surgeries. Our design goal is to reduce the implementation efforts and ease collaborative software development of stream programs while supporting efficient execution of the programs on the target hardware. To validate the toolkit, we implemented EM-Automated-RT software with the toolkit and reported our experience. EM-Automated-RT performs real-time video analysis for quality of a colonoscopy procedure and provides visual feedback to assist the endoscopist to achieve optimal inspection of the colon during the procedure. The software has been deployed in a hospital setting to conduct a clinical trial.  相似文献   
89.
This letter proposes an open‐ended waveguide antenna with a single split‐ring resonator. In contrast to the waveguide antennas incorporating multiple rings reported in a previous study, which exhibited narrow bandwidth, the proposed antenna uses only one ring to achieve broader bandwidth while keeping the aperture small. A single ring has a relatively low quality factor compared to multiple rings. The simulated and measured fractional bandwidth was 4.13% and 4.03%, respectively, which is much broader than the fractional bandwidth of about 1% demonstrated in a previous study. This simple technique can be used in many applications that require small apertures including near‐field probes and array elements.  相似文献   
90.
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