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   285631篇
  免费   4051篇
  国内免费   1305篇
电工技术   4921篇
综合类   526篇
化学工业   41996篇
金属工艺   11253篇
机械仪表   8734篇
建筑科学   6734篇
矿业工程   1589篇
能源动力   7306篇
轻工业   23864篇
水利工程   3144篇
石油天然气   5818篇
武器工业   45篇
无线电   33993篇
一般工业技术   57652篇
冶金工业   51681篇
原子能技术   7547篇
自动化技术   24184篇
  2021年   2524篇
  2020年   1872篇
  2019年   2323篇
  2018年   3908篇
  2017年   4003篇
  2016年   4271篇
  2015年   2742篇
  2014年   4670篇
  2013年   12619篇
  2012年   7578篇
  2011年   10315篇
  2010年   7930篇
  2009年   9203篇
  2008年   9487篇
  2007年   9467篇
  2006年   8099篇
  2005年   7467篇
  2004年   7370篇
  2003年   7132篇
  2002年   6868篇
  2001年   6953篇
  2000年   6589篇
  1999年   6862篇
  1998年   16589篇
  1997年   11788篇
  1996年   9053篇
  1995年   6925篇
  1994年   6065篇
  1993年   6119篇
  1992年   4422篇
  1991年   4202篇
  1990年   4095篇
  1989年   4076篇
  1988年   3771篇
  1987年   3403篇
  1986年   3410篇
  1985年   3758篇
  1984年   3479篇
  1983年   3240篇
  1982年   3038篇
  1981年   3053篇
  1980年   3044篇
  1979年   2842篇
  1978年   2875篇
  1977年   3153篇
  1976年   4122篇
  1975年   2423篇
  1974年   2386篇
  1973年   2402篇
  1972年   2022篇
排序方式: 共有10000条查询结果,搜索用时 910 毫秒
1.
Wireless Personal Communications - Chronic kidney disease (CKD) is a gradual loss of kidney function over the period of time and it is irrevocable once functionality reaches the critical state....  相似文献   
2.
Food Science and Biotechnology - A rich source of nutrients, figs have a number of clinically validated benefits. This study aimed to evaluate the in vitro simulated gastrointestinal digestion, and...  相似文献   
3.
Multimedia Tools and Applications - In this work, a new fuzzy logic-based algorithm is proposed for the enhancement of low light color images. A generalization of a fuzzy set known as an...  相似文献   
4.
International Journal of Information Security - This paper deals with a well-known problem in the area of the smudge attacks: when a user draws a pattern to unlock the pattern lock on a smartphone...  相似文献   
5.

We discuss the temperature dependence of a common low temperature local thermometer, a tunnel junction between a superconductor and a normal metal (NIS junction). Towards the lowest temperatures its characteristics tend to saturate, which is usually attributed to selfheating effects. In this technical note, we reanalyze this saturation and show that the temperature independent subgap current of the junction alone explains in some cases the low temperature behavior quantitatively.

  相似文献   
6.
To investigate the evolution of the structural and enhanced magnetic properties of GdMnO3 systems induced by the substitution of Mn with Cr, polycrystalline GdMn1-xCrxO3 samples were synthesized via solid-state reactions. XRD characterization shows that all GdMn1-xCrxO3 compounds with single-phase structures crystallize well and that Cr3+ ions entering the lattice sites of GdMnO3 induce structural distortion. SEM results indicate that the grain size of the synthesized samples (a few microns) decreases as the Cr substitution concentration increases. Positron annihilation lifetime spectroscopy reveals that vacancy-type defects occur in GdMn1-xCrxO3 ceramics and that the vacancy size and concentration clearly change with the Cr content. The temperature and field dependence of the magnetization curves show that Cr substitution significantly influences the magnetic ordering of the gadolinium sublattice, improving the weak ferromagnetic transition temperature and magnetization of GdMn1-xCrxO3. The enhanced magnetization of GdMn1-xCrxO3 is closely related to the vacancy defect concentration.  相似文献   
7.
Semiconductors - Abstract—In our work, we carry out a structural-spectroscopic study of AlGaN/GaN epitaxial layers grown by molecular-beam epitaxy with nitrogen-plasma activation on a hybrid...  相似文献   
8.
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   
9.

In this work we analysed the stepwise charging technique to find the limits from which it is beneficial in terms of load capacitance and charge–discharge frequency. We included in the analysis practical limitations such as the consumption of auxiliary logic needed to implement the technique and the minimum size of auxiliary switches imposed by the technology. We proposed an ultra-low-power logic block to push these limits and to obtain benefits from this technique in small capacitances. Finally, we proposed to use a stepwise driver in the driving of the gate capacitance of power switches in switched-capacitor (SC) DC–DC converters. We designed and manufactured, in a 130 nm process, a SC DC–DC converter and measured a 29% energy reduction in the gate-drive losses of the converter. This accounts for an improvement of 4% (from 69 to 73%) in the overall converter efficiency.

  相似文献   
10.
This work aimed to examine the performance of the hybrid sintering of clay ceramic in a microwave furnace, compared to the sintering process in a conventional furnace. The raw materials were subjected to X-ray fluorescence, loss on ignition (LOI), X-ray diffraction, particle size distribution, real specific mass, and thermogravimetric analyses. The red clay ceramic mass was prepared, extruded, pre-sintered in a conventional furnace at 600°C/60 min, and sintered at temperatures between 700 °C and 1100 °C. The sintering conventional (resistive oven) was carried out for 60 min with a heating rate of 10°C/min. In the microwave furnace, the sintering times were 5, 10, and 15 min, with a heating rate of 50°C/min, with a sintering chamber coated with silicon carbide (susceptor). The sintered specimens were characterized according to linear shrinkage, water absorption, apparent porosity, apparent specific mass, X-ray diffraction, Raman spectroscopy analysis, spectroscopy analysis in the ultraviolet and visible regions, microhardness, and scanning electron microscopy. The results showed that microwave sintering promoted an increase in the microhardness and apparent specific mass, and reduction in water absorption and apparent porosity values, due to greater densification in the microstructure. The best results occurred for specimens sintered at 1100°C.  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