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   8235篇
  免费   798篇
  国内免费   276篇
化学   4672篇
晶体学   85篇
力学   229篇
综合类   26篇
数学   443篇
物理学   1431篇
无线电   2423篇
  2024年   20篇
  2023年   127篇
  2022年   158篇
  2021年   244篇
  2020年   245篇
  2019年   246篇
  2018年   206篇
  2017年   184篇
  2016年   331篇
  2015年   310篇
  2014年   382篇
  2013年   560篇
  2012年   629篇
  2011年   648篇
  2010年   444篇
  2009年   428篇
  2008年   599篇
  2007年   512篇
  2006年   447篇
  2005年   428篇
  2004年   347篇
  2003年   298篇
  2002年   323篇
  2001年   208篇
  2000年   160篇
  1999年   135篇
  1998年   92篇
  1997年   65篇
  1996年   78篇
  1995年   68篇
  1994年   54篇
  1993年   42篇
  1992年   24篇
  1991年   22篇
  1990年   26篇
  1989年   18篇
  1988年   9篇
  1987年   17篇
  1986年   16篇
  1985年   16篇
  1984年   16篇
  1983年   14篇
  1982年   16篇
  1981年   11篇
  1980年   8篇
  1979年   8篇
  1978年   14篇
  1976年   10篇
  1974年   10篇
  1973年   8篇
排序方式: 共有9309条查询结果,搜索用时 15 毫秒
1.
2.
3.
Oral microbes have the capacity to spread throughout the gastrointestinal system and are strongly associated with multiple diseases. Given that tonsils are located between the oral cavity and the laryngopharynx at the gateway of the alimentary and respiratory tracts, tonsillar tissue may also be affected by microbiota from both the oral cavity (saliva) and the alimentary tract. Here, we analyzed the distribution and association of the microbial communities in the saliva and tonsils of Korean children subjected to tonsillectomy because of tonsil hyperplasia (n = 29). The microbiome profiles of saliva and tonsils were established via 16S rRNA gene sequencing. Based on the alpha diversity indices, the microbial communities of the two groups showed high similarities. According to Spearman’s ranking correlation analysis, the distribution of Treponema, the causative bacterium of periodontitis, in saliva and tonsils was found to have a significant positive correlation. Two representative microbes, Prevotella in saliva and Alloprevotella in tonsils, were negatively correlated, while Treponema 2 showed a strong positive correlation between saliva and tonsils. Taken together, strong similarities in the microbial communities of the tonsils and saliva are evident in terms of diversity and composition. The saliva microbiome is expected to significantly affect the tonsil microbiome. Furthermore, we suggest that our study creates an opportunity for tonsillar microbiome research to facilitate the development of novel microbiome-based therapeutic strategies.Subject terms: Comparative genomics, Metagenomics  相似文献   
4.
Analog Integrated Circuits and Signal Processing - Fault diagnosis of analog circuit is critical to improve safety and reliability in electrical systems and reduce losses. Traditional fault...  相似文献   
5.
The use of soft X-rays in a neutrahzer represents an alternative technique that could replace conventional radioactive sources.In this study,we evaluated the charging characteristics of a soft X-ray aerosol neutralize!".In addition,the results from the evaluation of the soft X-ray charger were compared with results obtained using a neutralizer incorporating an 241Am radioactive source.The tandem differential mobility analyzer technique was used previously to determine the size-dependent positive,negative,and neutral charge fractions of a soft X-ray neutralizer.This technique was used to show that the neutral fractions obtained using the soft X-ray charger agreed well with the predictions of bipolar diffusion charging theory,and that the soft X-ray charger could be used as a neutralizer for a scanning mobility particle sizer system.  相似文献   
6.
7.
The recent advancement in high- performance semiconductor packages has been driven by the need for higher pin count and superior heat dissipation. A one-piece cavity lid flip chip ball grid array (BGA) package with high pin count and targeted reliability has emerged as a popular choice. The flip chip technology can accommodate an I/O count of more than five hundreds500, and the die junction temperature can be reduced to a minimum level by a metal heat spreader attachment. None the less, greater expectations on these high-performance packages arose such as better substrate real estate utilization for multiple chips, ease in handling for thinner core substrates, and improved board- level solder joint reliability. A new design of the flip chip BGA package has been looked into for meeting such requirements. By encapsulating the flip chip with molding compound leaving the die top exposed, a planar top surface can be formed. A, and a flat lid can then be mounted on the planar mold/die top surface. In this manner the direct interaction of the metal lid with the substrate can be removed. The new package is thus less rigid under thermal loading and solder joint reliability enhancement is expected. This paper discusses the process development of the new package and its advantages for improved solder joint fatigue life, and being a multichip package and thin core substrate options. Finite-element simulations have been employed for the study of its structural integrity, thermal, and electrical performances. Detailed package and board-level reliability test results will also be reported  相似文献   
8.
9.
介绍了具有相同音频、视频编码方式的MPEG - 2节目流如何合并成一个节目流。合并后的文件播放流畅并且时间显示正确 ,它包括PATPMT表的重写 ,系统头部分相关字段的更改 ,PCR值的修改 ,解码时间标签 (DTS)和显示时间标签 (PTS)的重新确定 ,传送速率的修改以及添加相应的空包  相似文献   
10.
A novel fabrication process using a hot embossing technique has been developed for micromechanical passive alignment of polymer planar lightwave circuit (PLC) devices. With only one step of embossing, single-mode waveguide straight channels and micropedestals for passive aligning are simultaneously defined on a polymer thin film with an accuracy of /spl plusmn/0.5 /spl mu/m. This process reduces the steps for fabricating alignment structures. A fabricated polymer PLC chip and fibers are combined on a v-grooved silicon optical bench (SiOB) in a flip-chip manner. The process provides a coupling loss as low as 0.67 dB per coupling face and a cost-effective packaging solution for various polymer PLC devices.  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