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   240884篇
  免费   2787篇
  国内免费   1165篇
电工技术   3945篇
综合类   2408篇
化学工业   34522篇
金属工艺   13970篇
机械仪表   11285篇
建筑科学   6372篇
矿业工程   1973篇
能源动力   4417篇
轻工业   12748篇
水利工程   3081篇
石油天然气   4089篇
武器工业   43篇
无线电   23242篇
一般工业技术   51666篇
冶金工业   26013篇
原子能技术   4096篇
自动化技术   40966篇
  2021年   1272篇
  2020年   1018篇
  2019年   1170篇
  2018年   21613篇
  2017年   21244篇
  2016年   14741篇
  2015年   2365篇
  2014年   2553篇
  2013年   5861篇
  2012年   8326篇
  2011年   19477篇
  2010年   17309篇
  2009年   14546篇
  2008年   15348篇
  2007年   17892篇
  2006年   3578篇
  2005年   7389篇
  2004年   5590篇
  2003年   5264篇
  2002年   3755篇
  2001年   2449篇
  2000年   2547篇
  1999年   2196篇
  1998年   4301篇
  1997年   3120篇
  1996年   2577篇
  1995年   2077篇
  1994年   1886篇
  1993年   1908篇
  1992年   1496篇
  1991年   1413篇
  1990年   1501篇
  1989年   1467篇
  1988年   1318篇
  1987年   1298篇
  1986年   1250篇
  1985年   1441篇
  1984年   1261篇
  1983年   1201篇
  1982年   1134篇
  1981年   1129篇
  1980年   1006篇
  1979年   1005篇
  1978年   943篇
  1977年   1074篇
  1976年   1195篇
  1975年   892篇
  1974年   793篇
  1973年   819篇
  1972年   642篇
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
1.
Xiao  Zhu  Chen  Yanxun  Jiang  Hongbo  Hu  Zhenzhen  Lui  John C. S.  Min  Geyong  Dustdar  Schahram 《Wireless Networks》2022,28(7):3305-3322
Wireless Networks - Unmanned aerial vehicles (UAV) have been widely used in various fields because of their high mobility and portability. At the same time, due to the rapid development of...  相似文献   
2.
3.
Multimedia Tools and Applications - Mammograms are the images used by radiologists to diagnose breast cancer. Breast cancer is one of the most common cancers in women. The early detection of breast...  相似文献   
4.
Combustion, Explosion, and Shock Waves - Results of a numerical study of mixing, ignition, and combustion of a cold hydrogen jet propagating along the lower wall of a channel parallel to a...  相似文献   
5.
Cell surface proteoglycans are known to be important regulators of many aspects of cell behavior. The principal family of transmembrane proteoglycans is the syndecans, of which there are four in mammals. Syndecan-1 is mostly restricted to epithelia, and bears heparan sulfate chains that are capable of interacting with a large array of polypeptides, including extracellular matrix components and potent mediators of proliferation, adhesion and migration. For this reason, it has been studied extensively with respect to carcinomas and tumor progression. Frequently, but not always, syndecan-1 levels decrease as tumor grade, stage and invasiveness and dedifferentiation increase. This parallels experiments that show depletion of syndecan-1 can be accompanied by loss of cadherin-mediated adhesion. However, in some tumors, levels of syndecan-1 increase, but the characterization of its distribution is relevant. There can be loss of membrane staining, but acquisition of cytoplasmic and/or nuclear staining that is abnormal. Moreover, the appearance of syndecan-1 in the tumor stroma, either associated with its cellular component or the collagenous matrix, is nearly always a sign of poor prognosis. Given its relevance to myeloma progression, syndecan-1-directed antibody—toxin conjugates are being tested in clinical and preclinical trials, and may have future relevance to some carcinomas.  相似文献   
6.
Journal of Communications Technology and Electronics - In recent years, there has been a rapid improvement in photonics products due to the use of multilayer heterostructures grown on the basis of...  相似文献   
7.
Theoretical Foundations of Chemical Engineering - Calcium formate is widely used in construction, tanning, and textile manufacture and as an E238 biological additive in cosmetology and the food...  相似文献   
8.
The production of hydrogen, a favourable alternative to an unsustainable fossil fuel remains as a significant hurdle with the pertaining challenge in the design of proficient, highly productive and sustainable electrocatalyst for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Herein, the dysprosium (Dy) doped copper oxide (Cu1-xDyxO) nanoparticles were synthesized via solution combustion technique and utilized as a non-noble metal based bi-functional electrocatalyst for overall water splitting. Due to the improved surface to volume ratio and conductivity, the optimized Cu1-xDyxO (x = 0.01, 0.02) electrocatalysts exhibited impressive HER and OER performance respectively in 1 M KOH delivering a current density of 10 mAcm?2 at a potential of ?0.18 V vs RHE for HER and 1.53 V vs RHE for OER. Moreover, the Dy doped CuO electrocatalyst used as a bi-functional catalyst for overall water splitting achieved a potential of 1.56 V at a current density 10 mAcm?2 and relatively high current density of 66 mAcm?2 at a peak potential of 2 V. A long term stability of 24 h was achieved for a cell voltage of 2.2 V at a constant current density of 30 mAcm?2 with only 10% of the initial current loss. This showcases the accumulative opportunity of dysprosium as a dopant in CuO nanoparticles for fabricating a highly effective and low-cost bi-functional electrocatalyst for overall water splitting.  相似文献   
9.
Glass and Ceramics - An analysis of the specific mechanisms of the influence of the state of the grain structure on the thermoelectric properties (electrical resistivity and total thermal...  相似文献   
10.
This work presents the dielectric properties of YNbO4 (YNO)–TiO2 composites in the microwave range. X-ray diffraction analysis demonstrates that the addition of TiO2 to YNO results in the formation of a Y(Nb0.5Ti0.5)2O6 phase. In the microwave range, the values of permittivity and dielectric loss did not present major changes with the increment of TiO2. Moreover, the addition of TiO2 results in an improvement in the thermal stability of YNO, with YNO63 demonstrating a resonant frequency of ?8.96 ppm.°C?1. We utilised numerical simulations to evaluate the behaviour of these materials as dielectric resonator antennae and it is found that they exhibit a reflection coefficient below ?10 dB at the resonant frequency, with a realised gain of 4.94 – 5.76 dBi, a bandwidth of 665–1050 MHz and a radiation efficiency above 84%. Our results indicate that YNO–TiO2 composites are interesting candidates for microwave operating devices.  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