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   348340篇
  免费   7300篇
  国内免费   1453篇
电工技术   5498篇
综合类   788篇
化学工业   54522篇
金属工艺   12419篇
机械仪表   9855篇
建筑科学   8926篇
矿业工程   1738篇
能源动力   8963篇
轻工业   32523篇
水利工程   3606篇
石油天然气   6075篇
武器工业   53篇
无线电   38069篇
一般工业技术   67969篇
冶金工业   64491篇
原子能技术   7869篇
自动化技术   33729篇
  2022年   2514篇
  2021年   4076篇
  2020年   3047篇
  2019年   3560篇
  2018年   5896篇
  2017年   6003篇
  2016年   6373篇
  2015年   4318篇
  2014年   6928篇
  2013年   16618篇
  2012年   11064篇
  2011年   14011篇
  2010年   10729篇
  2009年   11843篇
  2008年   12241篇
  2007年   11897篇
  2006年   10053篇
  2005年   9227篇
  2004年   9097篇
  2003年   8675篇
  2002年   8337篇
  2001年   8017篇
  2000年   7499篇
  1999年   7836篇
  1998年   20497篇
  1997年   14260篇
  1996年   10757篇
  1995年   8027篇
  1994年   6992篇
  1993年   7033篇
  1992年   4791篇
  1991年   4656篇
  1990年   4507篇
  1989年   4425篇
  1988年   4133篇
  1987年   3685篇
  1986年   3694篇
  1985年   4096篇
  1984年   3746篇
  1983年   3436篇
  1982年   3293篇
  1981年   3331篇
  1980年   3294篇
  1979年   3032篇
  1978年   3048篇
  1977年   3454篇
  1976年   4679篇
  1975年   2557篇
  1974年   2490篇
  1973年   2524篇
排序方式: 共有10000条查询结果,搜索用时 31 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.
Transmission electron microscopy (TEM) is an important analysis technique to visualize (bio)macromolecules and their assemblies, including collagen fibers. Many protocols for TEM sample preparation of collagen involve one or more washing steps to remove excess salts from the dispersion that could hamper analysis when dried on a TEM grid. Such protocols are not standardized and washing times as well as washing solvents vary from procedure to procedure, with each research group typically having their own protocol. Here, we investigate the influence of washing with water, ethanol, but also methanol and 2-propanol, for both mineralized and unmineralized collagen samples via a protocol based on centrifugation. Washing with water maintains the hydrated collagen structure and the characteristic banding pattern can be clearly observed. Conversely, washing with ethanol results in dehydration of the fibrils, often leading to aggregation of the fibers and a less obvious banding pattern, already within 1 min of ethanol exposure. As we show, this process is fully reversible. Similar observations were made for methanol and propanol. Based on these results, a standardized washing protocol for collagenous samples is proposed.  相似文献   
4.
5.
6.
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   
7.
Objective

Neonatal brain and cardiac imaging would benefit from the increased signal-to-noise ratio levels at 7 T compared to lower field. Optimal performance might be achieved using purpose designed RF coil arrays. In this study, we introduce an 8-channel dipole array and investigate, using simulations, its RF performances for neonatal applications at 7 T.

Methods

The 8-channel dipole array was designed and evaluated for neonatal brain/cardiac configurations in terms of SAR efficiency (ratio between transmit-field and maximum specific-absorption-rate level) using adjusted dielectric properties for neonate. A birdcage coil operating in circularly polarized mode was simulated for comparison. Validation of the simulation model was performed on phantom for the coil array.

Results

The 8-channel dipole array demonstrated up to 46% higher SAR efficiency levels compared to the birdcage coil in neonatal configurations, as the specific-absorption-rate levels were alleviated. An averaged normalized root-mean-square-error of 6.7% was found between measured and simulated transmit field maps on phantom.

Conclusion

The 8-channel dipole array design integrated for neonatal brain and cardiac MR was successfully demonstrated, in simulation with coverage of the baby and increased SAR efficiency levels compared to the birdcage. We conclude that the 8Tx-dipole array promises safe operating procedures for MR imaging of neonatal brain and heart at 7 T.

  相似文献   
8.
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   
9.

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   
10.
Journal of Chemical Ecology - Biocontrol agents such as parasitic wasps use long-range volatiles and host-associated cues from lower trophic levels to find their hosts. However, this chemical...  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