首页 | 官方网站   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   530428篇
  免费   6079篇
  国内免费   1725篇
工业技术   538232篇
  2021年   3872篇
  2019年   3728篇
  2018年   12795篇
  2017年   13151篇
  2016年   10464篇
  2015年   4671篇
  2014年   7516篇
  2013年   20621篇
  2012年   14014篇
  2011年   22967篇
  2010年   19141篇
  2009年   19812篇
  2008年   20363篇
  2007年   22036篇
  2006年   13506篇
  2005年   14890篇
  2004年   13478篇
  2003年   12849篇
  2002年   11912篇
  2001年   11392篇
  2000年   10965篇
  1999年   11143篇
  1998年   26545篇
  1997年   18927篇
  1996年   14560篇
  1995年   11209篇
  1994年   9911篇
  1993年   9799篇
  1992年   7327篇
  1991年   6898篇
  1990年   6995篇
  1989年   6849篇
  1988年   6401篇
  1987年   5717篇
  1986年   5772篇
  1985年   6526篇
  1984年   6098篇
  1983年   5608篇
  1982年   5251篇
  1981年   5367篇
  1980年   5246篇
  1979年   4995篇
  1978年   5041篇
  1977年   5604篇
  1976年   7337篇
  1975年   4376篇
  1974年   4208篇
  1973年   4307篇
  1972年   3671篇
  1971年   3315篇
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
1.
2.
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   
3.
4.
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   
5.
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   
6.

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   
7.
This study presents the development and characterization of PVDF-conjugated polymer nanofiber-based systems. Five different conducting polymers (CPs) were synthesized successfully and used to create the nanofiber systems. The CPs used are polyaniline (PANI), polypyrrole (PPY), polyindole (PIN), polyanthranilic acid (PANA), and polycarbazole (PCZ). Nanofiber systems were produced utilizing the Forcespinning® technique. The nanofiber systems were developed by mechanical stretching. No electrical field or post-process poling was used in the nanofiber systems. The morphology, structure, electrochemical and piezoelectric performance was characterized. All of the nanofiber PVDF/CP systems displayed higher piezoelectric performance than the fine fiber PVDF systems. The PVDF/PPY nanofiber system displays the highest piezoelectric performance of 15.56 V. The piezoelectric performance of the PVDF/CP nanofiber systems favors potential for an attractive source of energy where highly flexible membranes could be used in power actuators, sensors and portable, and wireless devices to mention some.  相似文献   
8.
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   
9.
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   
10.
Journal of Communications Technology and Electronics - A statistical study of the effectiveness of the non-threshold search procedure for a noise-like phase-shift keyed signal by the delay time is...  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-23

京公网安备 11010802026262号