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   415184篇
  免费   29680篇
  国内免费   15351篇
电工技术   21307篇
技术理论   59篇
综合类   24202篇
化学工业   67494篇
金属工艺   21444篇
机械仪表   24508篇
建筑科学   30253篇
矿业工程   12513篇
能源动力   11483篇
轻工业   24049篇
水利工程   6781篇
石油天然气   24862篇
武器工业   2932篇
无线电   43029篇
一般工业技术   46966篇
冶金工业   41016篇
原子能技术   4002篇
自动化技术   53315篇
  2024年   1265篇
  2023年   5735篇
  2022年   9999篇
  2021年   14120篇
  2020年   10858篇
  2019年   9073篇
  2018年   10643篇
  2017年   12240篇
  2016年   11252篇
  2015年   14620篇
  2014年   18284篇
  2013年   21939篇
  2012年   24900篇
  2011年   27511篇
  2010年   22478篇
  2009年   21495篇
  2008年   20959篇
  2007年   20310篇
  2006年   21047篇
  2005年   21107篇
  2004年   14477篇
  2003年   13302篇
  2002年   12017篇
  2001年   10754篇
  2000年   9580篇
  1999年   11232篇
  1998年   14797篇
  1997年   11011篇
  1996年   9298篇
  1995年   7147篇
  1994年   5725篇
  1993年   4381篇
  1992年   2899篇
  1991年   2352篇
  1990年   1875篇
  1989年   1559篇
  1988年   1344篇
  1987年   882篇
  1986年   735篇
  1985年   510篇
  1984年   312篇
  1983年   278篇
  1982年   325篇
  1981年   307篇
  1980年   324篇
  1979年   132篇
  1978年   130篇
  1977年   646篇
  1976年   1374篇
  1975年   118篇
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
81.
The Fe/C/SiCN composite ceramics were synthesized by polymer-derived method to obtain the integration of structure and functions. The electromagnetic waves (EMW) absorption properties at X and Ku bands were investigated. The addition of nano-sized Fe particles improved the magnetic loss and impedance matching, and the carbon nanotubes generated by the iron in-situ catalysis increased the internal relaxation polarization and interfacial polarization, which together improved the EMW absorption properties significantly. In particular, the Fe/C/SiCN-9 showed the optimum reflection loss (RL) of ?31.06 dB at 10.03 GHz with an effective absorption bandwidth (EAB, RL < ?10 dB) of 3.03 GHz at 2.51 mm, indicating the excellent EMW absorption properties of Fe/C/SiCN composite ceramics.  相似文献   
82.
83.
We used scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to observe the oral organelle, cytopharynx, and subpellicular structure of a Dileptus sp. The main results were as follows: (a) the cytostome was located on the ventral surface of the base of the beak, surrounded by a periportal matrix that integrated 135 microtube bundles. When these microtube bundles contract, radially arranged into a disk, the cytostome was closed. When these microtube bundles were stretch, they fell into the cytostome and opens. The diameter of the cytostome was about 16 μm regardless of its closure or opening, indicating that the contraction or elongation of these microtube bundles did not change the size of the cytostome, which was only related to whether it blocked the cytostome, thus determining the opening and closing of the cytostome. There were many microtube bundles on two sides of the feeding trough, which could widen or narrow the feeding trough and facilitate beak feeding. (b) The cytopharynx was basket‐like without a bottom with a diameter of about 6 μm and was woven from two kind fibers about 0.08 and 0.19 μm. (c) There were two types of extrusomes under the pellicle. Using transmission electron microscopy,the Type I extrusomes showed narrow and long egg shape, its cross section was circular which is composed by various electronic density of concentric. Using the scanning electron microscope, they were two slightly thin clavate, the length was about 5 μm, the diameter of the middle section was about 0.75 μm, and the diameter of the two ends was about 0.32 μm, they were distributed abundantly between the microtubule fasciculi which were located on both sides of the gap on the feeding groove. Using transmission electron microscopy, the Type II extrusomes showed egg shape. Using the scanning electron microscopy, they were about 1.6 × 0.8 μm in size, they were distributed abundantly under the body pellicle while rarely the proboscis. In addition, many different of developmental stages two types of extrusomes could be also seen in the cytoplasm. (d) There were very well‐developed fibrous systems under the pellicle that were woven from fibers about 0.14 μm in diameter that attached to the pellicle and bound some organelles in the cytoplasm (e.g., mitochondria, extrusomes) and other structures to the cytoplasm and maintained cell morphology. The results of this study not only supplement and enrich the morphological contents of the Dileptus sp., but also provide the basis for the study of the taxonomy of the Dileptus sp. It also provides a new method for researchers to explore the morphology and structure of ciliate cells under the cortex by SEM.  相似文献   
84.
In this paper, we present a novel memory access reduction scheme (MARS) for two-dimension fast cosine transform (2-D FCT). It targets programmable DSPs with high memory-access latency. It reduces the number of memory accesses by: 1) reducing the number of weighting factors and 2) combining butterflies in vector-radix 2-D FCT pruning diagram from two stages to one stage with an efficient structure. Hardware platform based on general purpose processor is used to verify the effectiveness of the proposed method for vector-radix 2-D FCT pruning implementation. Experimental results validate the benefits of the proposed method with reduced memory access, less clock cycle and fewer memory space compared with the conventional implementation.  相似文献   
85.
Wei  Shaowei  Yu  Guoxian  Wang  Jun  Domeniconi  Carlotta  Zhang  Xiangliang 《Machine Learning》2021,110(6):1505-1526
Machine Learning - Traditional clustering algorithms focus on a single clustering result; as such, they cannot explore potential diverse patterns of complex real world data. To deal with this...  相似文献   
86.
针对和成矿业井下原矿含泥量和含水量较大,且矿泥中存在绿泥石、高岭土等黏土类矿物,造成供矿系统粘堵严重,系统台时量仅为设计水平一半的问题,对原矿进行了洗矿工艺研究。通过洗矿工艺,将原矿中的矿块和矿泥分离,实现矿块和矿泥按粒度分选,彻底解决了供矿系统粘堵严重的问题,稳定了磨选系统给矿量。  相似文献   
87.
88.
为了综合回收现有南非铜尾矿中的有价铁元素,在试验室对该铜尾矿进行了回收铁的可选性试验研究。研究结果表明:该铜尾矿铁品位为59.36%,磁性铁含量为57.99%,当原矿磨矿细度为-0.074 mm 58%时,经两次磁选后,可获得产率为88.95%,铁品位为65.69%,铁回收率为98.43%的铁精矿。  相似文献   
89.
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