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   118473篇
  免费   9858篇
  国内免费   4973篇
电工技术   7150篇
技术理论   7篇
综合类   7615篇
化学工业   20474篇
金属工艺   6487篇
机械仪表   7322篇
建筑科学   9653篇
矿业工程   3439篇
能源动力   3509篇
轻工业   7679篇
水利工程   2100篇
石油天然气   7304篇
武器工业   876篇
无线电   13436篇
一般工业技术   14306篇
冶金工业   5518篇
原子能技术   1291篇
自动化技术   15138篇
  2024年   556篇
  2023年   2030篇
  2022年   3531篇
  2021年   4888篇
  2020年   3738篇
  2019年   3154篇
  2018年   3393篇
  2017年   3929篇
  2016年   3300篇
  2015年   4695篇
  2014年   5718篇
  2013年   6789篇
  2012年   7428篇
  2011年   7981篇
  2010年   6964篇
  2009年   6653篇
  2008年   6423篇
  2007年   6094篇
  2006年   6356篇
  2005年   5526篇
  2004年   3775篇
  2003年   3293篇
  2002年   3084篇
  2001年   2815篇
  2000年   2965篇
  1999年   3175篇
  1998年   2684篇
  1997年   2280篇
  1996年   2104篇
  1995年   1833篇
  1994年   1475篇
  1993年   1059篇
  1992年   862篇
  1991年   681篇
  1990年   492篇
  1989年   439篇
  1988年   357篇
  1987年   246篇
  1986年   167篇
  1985年   97篇
  1984年   66篇
  1983年   49篇
  1982年   65篇
  1981年   39篇
  1980年   35篇
  1979年   10篇
  1978年   3篇
  1965年   3篇
  1959年   4篇
  1951年   1篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Clinical manifestations and peripheral blood lymphocyte subset changes were studied in patients with myasthenia gravis (MG) to elucidate the mechanism of clinical improvement following treatment, with thymectomy (Tx) or glucocorticoid (GC) therapy. The changes found were: 1. There was a significant increase in percentages of CD3+, CD29+ CD4+ cells and CD4/CD8 ratio and a significant decrease in percentages of CD8+ and CD16,56+ cells in patients who had never been treated with any immune therapy. 2. After Tx or GC therapy, CD3+ and CD4+, CD29+ cells were decreased, but the number CD19+ and CD16, CD56 cells did not change. 3. Tx had a special effect on CD8+ cells. In most of the patients who showed clinical improvement after Tx, CD8+ cells were increased and CD4/CD8 ratio wad decreased. 4. Anti-acetylcholine receptor (AChRAb) titers were markedly decreased after GC therapy. These results indicate that there were obvious abnormalities in cell-mediated immunity in addition to those in humoral immunity in myasthenia gravis. These abnormalities tended to be normalized after Tx or GC therapy.  相似文献   
42.
43.
44.
Brambilla  G. Xu  F. Feng  X. 《Electronics letters》2006,42(9):517-519
It is demonstrated for the first time that long nanowires with radii as small as 30 nm can be manufactured with a conventional coupler fabrication rig. The temporal deterioration of nanowire optical properties has been studied and correlated with its mechanical behaviour. The original transmission properties have been restored by a post-fabrication treatment.  相似文献   
45.
A ten-user truly asynchronous gigabit coherent-optical-code-division-multiple-access (OCDMA) transmission was experimentally demonstrated without using any timing coordination. The enabling technologies are a record-length 511-chip superstructured-fiber-Bragg-grating (SSFBG) en/decoder and a supercontinuum (SC)-based optical-thresholding technique to significantly suppress the signal interference beat noise as well as the multiple-access-interference (MAI) noise.  相似文献   
46.
The role of gas phase CH3 radicals in the oxidative coupling of CH4 over 1 wt% Sr/La2O3 is supported by the observations that (i) this is a very effective catalyst for the generation of CH3 · radicals and (ii) the concentration of CH3 · radicals increases with temperature over the range of 450 °C–800 °C.  相似文献   
47.
The NiFe2O4 and Pb(Zr0.52Ti0.48)O3 ceramic composites are prepared by conventional solid state reaction method. The microstructural and morphological properties of the composites are studied by X-ray diffraction analysis and scanning electron microscopy. Results indicate that the ferrite and piezoelectric phases can co-exist in the composites. The relationship between the dielectric constant and frequency (40 Hz–40 MHz) as well as temperature is also investigated. It is noted that the transition temperature of the composites is about 380 °C. A double electric hysteresis loop is observed in our composites. The magnetic properties are relatively weak according to the magnetic hysteresis loop. With increase in the content of the ferrite phase, the permeability increases. The electromagnetic properties of the as-prepared composites are tunable according to the content of the NiFe2O4 phase.  相似文献   
48.
49.
50.
Poly(ethylene terephthalate) (PET) is of excellent mechanical properties and melt processability and is widely used as raw material for textile fibers. However, the flame retardant properties of PET were rather poor, and both reactive and additive phosphorus- and halogen-containing compounds have been employed to enhance the reaction-to-fire properties while the meltdripping behaviour during burning hasn’t been handled properly with the flame retardants. In this work, fluoropolymer was blended with both pure PET (pPET) and reactive phosphorus-containing flame retarded copolyester (fPET), and the flame retardance and char formation and mechanical properties of the resulted pPET and fPET blends were investigated. The tensile strengths of modified pPET samples were worsen whereas those of modified fPET samples were improved at low concentrations. The initial thermal degradation in nitrogen was accelerated remarkably for the two polyesters with fluoropolymer. The oxygen indices of the all modified samples were reduced while char formation and meltdripping suppression were encouraged. The apparent melt viscosity and elasticity for the two polyesters were gained much with antidripping agent. Therefore, fluoropolymer improved char formation of the two polyesters based on the gaseous phase mechanism while the partial suppression of meltdripping behavior and the decrease of mechanical properties mainly originated from the increase of melt viscosity via fibrillation for pPET.  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