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   1573篇
  免费   83篇
  国内免费   3篇
电工技术   22篇
综合类   2篇
化学工业   302篇
金属工艺   29篇
机械仪表   28篇
建筑科学   86篇
矿业工程   2篇
能源动力   45篇
轻工业   127篇
水利工程   15篇
石油天然气   2篇
无线电   85篇
一般工业技术   426篇
冶金工业   216篇
原子能技术   12篇
自动化技术   260篇
  2023年   11篇
  2022年   27篇
  2021年   43篇
  2020年   23篇
  2019年   28篇
  2018年   38篇
  2017年   34篇
  2016年   39篇
  2015年   48篇
  2014年   70篇
  2013年   95篇
  2012年   94篇
  2011年   136篇
  2010年   90篇
  2009年   82篇
  2008年   103篇
  2007年   116篇
  2006年   90篇
  2005年   87篇
  2004年   55篇
  2003年   48篇
  2002年   39篇
  2001年   30篇
  2000年   18篇
  1999年   18篇
  1998年   19篇
  1997年   19篇
  1996年   11篇
  1995年   11篇
  1994年   8篇
  1993年   11篇
  1992年   8篇
  1991年   3篇
  1990年   14篇
  1989年   9篇
  1988年   10篇
  1987年   8篇
  1985年   2篇
  1984年   5篇
  1983年   6篇
  1982年   8篇
  1981年   5篇
  1979年   3篇
  1978年   4篇
  1977年   4篇
  1976年   4篇
  1975年   3篇
  1974年   2篇
  1967年   2篇
  1960年   7篇
排序方式: 共有1659条查询结果,搜索用时 15 毫秒
981.
Huntington’s disease (HD) is one of at least nine polyglutamine diseases caused by a trinucleotide CAG repeat expansion, all of which lead to age-onset neurodegeneration. Mitochondrial dynamics and function are disrupted in HD and other polyglutamine diseases. While multiple studies have found beneficial effects from decreasing mitochondrial fragmentation in HD models by disrupting the mitochondrial fission protein DRP1, disrupting DRP1 can also have detrimental consequences in wild-type animals and HD models. In this work, we examine the effect of decreasing mitochondrial fragmentation in a neuronal C. elegans model of polyglutamine toxicity called Neur-67Q. We find that Neur-67Q worms exhibit mitochondrial fragmentation in GABAergic neurons and decreased mitochondrial function. Disruption of drp-1 eliminates differences in mitochondrial morphology and rescues deficits in both movement and longevity in Neur-67Q worms. In testing twenty-four RNA interference (RNAi) clones that decrease mitochondrial fragmentation, we identified eleven clones—each targeting a different gene—that increase movement and extend lifespan in Neur-67Q worms. Overall, we show that decreasing mitochondrial fragmentation may be an effective approach to treating polyglutamine diseases and we identify multiple novel genetic targets that circumvent the potential negative side effects of disrupting the primary mitochondrial fission gene drp-1.  相似文献   
982.
Scanning electron microscopy (SEM) has been used to classify and quantify the types of damage evident in a population potato starch granules following ball milling. Whilst the majority of granules remained undamaged, a significant (p<0.01) increase in the number of granules with localized damage was observed (1.6% to 15.1%). A variety fo types of localised damage were discernable, ranging from areas where small amounts of granule surface material had been removed, to large areas possessing coarse surfaces caused by extensive removal of material. The generation of this latter category termed ‘rough faces’, was the most significant and predominant change following ball milling (p <0.05). Ball-milling was therefore attributed to the penetration of an outer granule layer, via the removal of surface material at existing points of weakness. This produced rough, disrupted areas of the granule surface, which are more likely to be susceptible to hydration and enzyme attack.  相似文献   
983.
984.
在工厂生产层使用以太网之前,必须了解它的七个要素。这里,我们以Profinet标准为例,为大家一一进行介绍。1.网络布局办公室的网络拓扑布局并不适用于工厂生产层,那里采用的是工厂/机器的以太网拓扑布局。办公室以太网的基础架构通常是由商业级的产品构建,它们在恒温的环境和星型拓扑构建的交换网络中可以很好地发挥作用;而与此不同,工业以太网架构常常要面对多变的意  相似文献   
985.
The oxygen electrodes from two solid oxide electrolysis stacks that performed high-temperature steam electrolysis (HTSE) and produced hydrogen for 1000 and 2000 h, respectively, were examined using X-ray fluorescence, X-ray absorption near edge structure (XANES), four-point resistivity, scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction and Raman micro-spectroscopy to determine possible causes for the degradation in stack performance over the test periods. These techniques yielded information such as elemental distribution, oxidation state, phases present, electrode delamination, and porosity within the electrode layers. From these studies, we found two phenomena that were likely the cause of increasingly poor oxygen electrode performance over time. The first source of degradation was chromium substitution into the oxygen electrode bond layer, which serves to bond the cell to the flow field and interconnect. This is caused by migration of a chromium species from the bipolar plate. The effect of this is a significant increase in the electrical resistance of the bond layer material. The other source of degradation identified was oxygen electrode delamination. The cause of electrode delamination, which is locally catastrophic to the operation of the cell, is unclear; however, we will discuss two possible mechanisms that might cause this phenomenon.  相似文献   
986.
This paper presents a new method for image-guided surgery called image-enhanced endoscopy. Registered real and virtual endoscopic images (perspective volume renderings generated from the same view as the endoscope camera using a preoperative image) are displayed simultaneously; when combined with the ability to vary tissue transparency in the virtual images, this provides surgeons with the ability to see beyond visible surfaces and, thus, provides additional exposure during surgery. A mount with four photoreflective spheres is rigidly attached to the endoscope and its position and orientation is tracked using an optical position sensor. Generation of virtual images that are accurately registered to the real endoscopic images requires calibration of the tracked endoscope. The calibration process determines intrinsic parameters (that represent the projection of three-dimensional points onto the two-dimensional endoscope camera imaging plane) and extrinsic parameters (that represent the transformation from the coordinate system of the tracker mount attached to the endoscope to the coordinate system of the endoscope camera), and determines radial lens distortion. The calibration routine is fast, automatic, accurate and reliable, and is insensitive to rotational orientation of the endoscope. The routine automatically detects, localizes, and identifies dots in a video image snapshot of the calibration target grid and determines the calibration parameters from the sets of known physical coordinates and localized image coordinates of the target grid dots. Using nonlinear lens-distortion correction, which can be performed at real-time rates (30 frames per second), the mean projection error is less than 0.5 mm at distances up to 25 mm from the endoscope tip, and less than 1.0 mm up to 45 mm. Experimental measurements and point-based registration error theory show that the tracking error is about 0.5-0.7 mm at the tip of the endoscope and less than 0.9 mm for all points in the field of view of the endoscope camera at a distance of up to 65 mm from the tip. It is probable that much of the projection error is due to endoscope tracking error rather than calibration error. Two examples of clinical applications are presented to illustrate the usefulness of image-enhanced endoscopy. This method is a useful addition to conventional image-guidance systems, which generally show only the position of the tip (and sometimes the orientation) of a surgical instrument or probe on reformatted image slices.  相似文献   
987.
Pancreatic cancer (pancreatic ductal adenocarcinoma (PDAC/PC)) has been an aggressive disease that is associated with early metastases. It is characterized by dense and collagenous desmoplasia/stroma, predominantly produced by pancreatic stellate cells (PSCs). PSCs interact with cancer cells as well as other stromal cells, facilitating disease progression. A candidate growth factor pathway that may mediate this interaction is the hepatocyte growth factor (HGF)/c-MET pathway. HGF is produced by PSCs and its receptor c-MET is expressed on pancreatic cancer cells and endothelial cells. The current review discusses the role of the MET/HGF axis in tumour progression and dissemination of pancreatic cancer. Therapeutic approaches that were developed targeting either the ligand (HGF) or the receptor (c-MET) have not been shown to translate well into clinical settings. We discuss a two-pronged approach of targeting both the components of this pathway to interrupt the stromal–tumour interactions, which may represent a potential therapeutic strategy to improve outcomes in PC.  相似文献   
988.
Ceramic On-Demand Extrusion (CODE) process has been recently proposed for additive manufacturing of strong ceramic components via extrusion. This paper focuses on fabricating 3 mol% yttria-stabilized zirconia (3YSZ) components using CODE process, and enabling CODE to produce parts with support structures. A colloidal suspension of 3YSZ was developed and deposited through the main nozzle, and an organic feedstock was developed and deposited by means of another nozzle to fabricate supports. After printing and drying of raw parts, supports were removed by increasing the temperature and parts were then sintered to near theoretical (~99%) density. The maximum overhang angle that could be built with no support was also found out to be approximately 60 degrees. Three organic support materials, that is, polycaprolactone (PCL), silicone, and petrolatum were prepared and tested. PCL and petrolatum were identified as feasible support materials. Specimens were fabricated to validate the efficiency of the support materials and to evaluate CODE's capability for building parts with complex geometry. The microstructures of these parts were also analyzed via scanning electron microscopy.  相似文献   
989.
990.
Wang  Jeremy H.-S.  Yeh  Ming-Hua  Chao  Paul C.-P.  Tu  Tse-Yi  Kao  Yung-Hua  Pandey  Rajeev 《Microsystem Technologies》2020,26(11):3501-3516
Microsystem Technologies - A fast digital chip is designed and fabricated successfully to implement the algorithm for estimating blood pressure (BP) in real time by a non-invasive cuffless...  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