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   212058篇
  免费   18540篇
  国内免费   10683篇
电工技术   14716篇
技术理论   4篇
综合类   14788篇
化学工业   27873篇
金属工艺   10936篇
机械仪表   12331篇
建筑科学   14999篇
矿业工程   5910篇
能源动力   5467篇
轻工业   14642篇
水利工程   4802篇
石油天然气   8269篇
武器工业   2011篇
无线电   22197篇
一般工业技术   19999篇
冶金工业   30078篇
原子能技术   2113篇
自动化技术   30146篇
  2024年   753篇
  2023年   2770篇
  2022年   5456篇
  2021年   7619篇
  2020年   5607篇
  2019年   4367篇
  2018年   5269篇
  2017年   6327篇
  2016年   5954篇
  2015年   8270篇
  2014年   9919篇
  2013年   11680篇
  2012年   15355篇
  2011年   16157篇
  2010年   13445篇
  2009年   12776篇
  2008年   12476篇
  2007年   11843篇
  2006年   10723篇
  2005年   11261篇
  2004年   8075篇
  2003年   6713篇
  2002年   5310篇
  2001年   4679篇
  2000年   3440篇
  1999年   3196篇
  1998年   8434篇
  1997年   5480篇
  1996年   3983篇
  1995年   2636篇
  1994年   2023篇
  1993年   1754篇
  1992年   680篇
  1991年   628篇
  1990年   567篇
  1989年   513篇
  1988年   467篇
  1987年   340篇
  1986年   311篇
  1985年   222篇
  1984年   105篇
  1983年   111篇
  1982年   159篇
  1981年   226篇
  1980年   245篇
  1979年   87篇
  1978年   113篇
  1977年   654篇
  1976年   1426篇
  1975年   110篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Circulating nucleic acids (CNAs) are under investigation as a liquid biopsy in cancer as potential non-invasive biomarkers, as stable structure in circulation nucleosomes could be valuable sources for detection of cancer-specific alterations in histone modifications. Our interest is in histone methylation marks with a focus on colorectal cancer, one of the leading cancers respective the incidence and mortality. Our previous work included the analysis of trimethylations of lysine 9 on histone 3 (H3K9me3) and of lysine 20 on histone 4 (H4K20me3) by chromatin immuno- precipitation-related PCR in circulating nucleosomes. Here we asked whether global immunologic measurement of histone marks in circulation could be a suitable approach to show their potential as biomarkers. In addition to H3K9me3 and H4K20me3 we also measured H3K27me3 in plasma samples from CRC patients (n = 63) and cancer free individuals (n = 40) by ELISA-based methylation assays. Our results show that of three marks, the amounts of H3K27me3 (p = 0.04) and H4K20me3 (p < 0.001) were significantly lower in CRC patients than in healthy controls. For H3K9me3 similar amounts were measured in both groups. Areas under the curve (AUC) in receiver operating characteristic (ROC) curves indicating the power of CRC detection were 0.620 for H3K27me3, 0.715 for H4K20me3 and 0.769 for the combination of both markers. In conclusion, findings of this preliminary study reveal the potential of blood-based detection of CRC by quantification of histone methylation marks and the additive effect of the marker combination.  相似文献   
92.
93.
孙伟  王绪滨 《内燃机车》2015,(2):28-30,4
针对机车走行部关键部位存在的风险及日常机车运用和检修存在的问题,进行了调查分析并提出预防对策,保证了机车走行部的运行安全。  相似文献   
94.
M1080B无心外圆磨床砂轮及导轮宽度较窄,磨削轴承套圈外圆时,磨削效率低,托板架调整较为繁琐、皮带打滑、磨损较为严重。针对上述问题,提出了相应的解决办法,提高了磨削效率。  相似文献   
95.
Structures and properties of myofibrillar protein gel prepared at different power (300–800 W) were evaluated. Amino acid analysis demonstrated that changes in microwave power did not alter primary structure of gel. However, an increase in microwave power could change higher structures of gel. As microwave power increased, α-helix content decreased and β-sheet content increased. Increased microwave power probably facilitated protein to unfold and expose the internal groups, causing surface hydrophobicity and the formation of disulphide bonds were enhanced, which indicated changes in tertiary and quaternary structures of protein. At 500 W, gel had the best ultrastructure where surface morphology, springiness and water holding capacity reached the optimum. Our findings suggested that microwave at an appropriate power (500 W) could change higher structures of myofibrillar protein gel to achieve desired processing and quality protein gel characteristics.  相似文献   
96.
97.
Multibody System Dynamics - A recently developed index reduction method is applied to comparatively complicated underactuated mechanical systems in the context of inverse dynamics. The inverse...  相似文献   
98.
From the perspectives of scientific researches and practical applications, it is desirable to explore high operating temperature ferromagnetic films. The effect of biaxial strain on magnetic properties of (110)-oriented La0.7Sr0.3MnO3 films was studied. High quality La0.7Sr0.3MnO3 films were grown on (110)-oriented perovskite single crystal substrates using pulsed laser deposition, varying substrate-induced misfit strains from ??2.27–0.75%. A remarkable enhancement of Curie temperature has been achieved for (110)-oriented La0.7Sr0.3MnO3 films clamped with small misfit strains (i.e., grown on LAST (110)). The enhanced Curie temperature of (110)-oriented La0.7Sr0.3MnO3 films could be attributed to the misfit strain between the films and the underlying substrates and may have technological implication for applications at high temperature environments.  相似文献   
99.
为降低烟草中噁霉灵检测中的基质干扰,提高检测灵敏度和和稳定性,通过试验建立了以QuEChERS为样品前处理方法、液相色谱串联质谱仪为检测仪器的烟草中噁霉灵残留检测方法。样品加水浸润后,经丙酮提取、盐析试剂包除水、石墨化炭黑除杂后,采用Agilent ZORBAX 300SB-C8液相色谱柱(2.1 mm×100 mm,1.8 μm)分离,甲醇-水程序洗脱,ESI雾化,串联质谱MRM检测。结果发现,该方法在0.0025~0.0500 mg/L范围内线性良好,决定系数r2=0.9996,定量检测限1.06 μg/L,回收率在90.8%~92.0%之间,相对标准偏差为5.1%。运用该方法测定烟草中的噁霉灵,操作简单,检测精度高,满足CORESTA对烟草农残检测的要求。  相似文献   
100.
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