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   533592篇
  免费   6347篇
  国内免费   2249篇
电工技术   9467篇
综合类   3008篇
化学工业   77269篇
金属工艺   24816篇
机械仪表   19986篇
建筑科学   13080篇
矿业工程   3034篇
能源动力   11917篇
轻工业   40766篇
水利工程   5752篇
石油天然气   7900篇
武器工业   48篇
无线电   62996篇
一般工业技术   108440篇
冶金工业   78494篇
原子能技术   10507篇
自动化技术   64708篇
  2021年   2840篇
  2019年   2832篇
  2018年   23295篇
  2017年   22889篇
  2016年   16913篇
  2015年   4357篇
  2014年   6193篇
  2013年   17978篇
  2012年   14283篇
  2011年   27897篇
  2010年   23605篇
  2009年   22264篇
  2008年   23517篇
  2007年   26045篇
  2006年   11617篇
  2005年   14612篇
  2004年   12923篇
  2003年   12392篇
  2002年   10969篇
  2001年   10277篇
  2000年   9842篇
  1999年   9936篇
  1998年   21966篇
  1997年   16096篇
  1996年   12697篇
  1995年   9977篇
  1994年   8930篇
  1993年   8802篇
  1992年   6758篇
  1991年   6512篇
  1990年   6321篇
  1989年   6290篇
  1988年   5878篇
  1987年   5297篇
  1986年   5264篇
  1985年   5967篇
  1984年   5481篇
  1983年   5115篇
  1982年   4857篇
  1981年   4799篇
  1980年   4676篇
  1979年   4497篇
  1978年   4436篇
  1977年   5020篇
  1976年   6437篇
  1975年   3832篇
  1974年   3660篇
  1973年   3709篇
  1972年   3084篇
  1971年   2781篇
排序方式: 共有10000条查询结果,搜索用时 15 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.

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   
5.
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   
6.
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   
7.
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   
8.

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   
9.
Cell surface and secreted proteins provide essential functions for multicellular life. They enter the endoplasmic reticulum (ER) lumen co-translationally, where they mature and fold into their complex three-dimensional structures. The ER is populated with a host of molecular chaperones, associated co-factors, and enzymes that assist and stabilize folded states. Together, they ensure that nascent proteins mature properly or, if this process fails, target them for degradation. BiP, the ER HSP70 chaperone, interacts with unfolded client proteins in a nucleotide-dependent manner, which is tightly regulated by eight DnaJ-type proteins and two nucleotide exchange factors (NEFs), SIL1 and GRP170. Loss of SIL1′s function is the leading cause of Marinesco-Sjögren syndrome (MSS), an autosomal recessive, multisystem disorder. The development of animal models has provided insights into SIL1′s functions and MSS-associated pathologies. This review provides an in-depth update on the current understanding of the molecular mechanisms underlying SIL1′s NEF activity and its role in maintaining ER homeostasis and normal physiology. A precise understanding of the underlying molecular mechanisms associated with the loss of SIL1 may allow for the development of new pharmacological approaches to treat MSS.  相似文献   
10.
Analog Integrated Circuits and Signal Processing - As the 5G era beckons in the world of communication and information technology, there is a surge in demand for battery-operated, mobile wireless...  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