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   251590篇
  免费   7615篇
  国内免费   2485篇
电工技术   6851篇
技术理论   1篇
综合类   2608篇
化学工业   36984篇
金属工艺   10336篇
机械仪表   8689篇
建筑科学   7855篇
矿业工程   2499篇
能源动力   6385篇
轻工业   22476篇
水利工程   3178篇
石油天然气   5222篇
武器工业   421篇
无线电   27866篇
一般工业技术   47524篇
冶金工业   43888篇
原子能技术   5601篇
自动化技术   23306篇
  2022年   2342篇
  2021年   4051篇
  2020年   2897篇
  2019年   2885篇
  2018年   4458篇
  2017年   4416篇
  2016年   4636篇
  2015年   4114篇
  2014年   5671篇
  2013年   12630篇
  2012年   8526篇
  2011年   10499篇
  2010年   8587篇
  2009年   9177篇
  2008年   9222篇
  2007年   9120篇
  2006年   7702篇
  2005年   6884篇
  2004年   6164篇
  2003年   5891篇
  2002年   5472篇
  2001年   5392篇
  2000年   5226篇
  1999年   5358篇
  1998年   13287篇
  1997年   9299篇
  1996年   7256篇
  1995年   5252篇
  1994年   4711篇
  1993年   4467篇
  1992年   3421篇
  1991年   3238篇
  1990年   3020篇
  1989年   3121篇
  1988年   2969篇
  1987年   2542篇
  1986年   2439篇
  1985年   2913篇
  1984年   2679篇
  1983年   2493篇
  1982年   2207篇
  1981年   2359篇
  1980年   2194篇
  1979年   2239篇
  1978年   2218篇
  1977年   2555篇
  1976年   3589篇
  1975年   1904篇
  1974年   1839篇
  1973年   1873篇
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
51.
52.
Sequencing of rice genome has facilitated the understanding of rice evolution and has been utilized extensively for mining of DNA markers to facilitate marker-assisted breeding. Simple sequence repeat (SSR) markers that are tandemly repeated nucleotide sequence motifs flanked by unique sequences are presently the maker of choice in rice improvement due to their abundance, co-dominant inheritance, high levels of allelic diversity, and simple reproducible assay. The current level of genome coverage by SSR markers in rice is sufficient to employ them for genotype identification and marker-assisted selection in breeding for mapping of genes and quantitative trait loci analysis. This review provides comprehensive information on the mapping and applications of SSR markers in investigation of rice cultivars to study their genetic divergence and marker-assisted selection of important agronomic traits.  相似文献   
53.
  Qing  Xu  Bin  Yu  Yang  Zhan  Wei  Zhao  Yu  Zheng  Jun  Ji  Jian 《Bulletin of Engineering Geology and the Environment》2021,80(8):6513-6525
Bulletin of Engineering Geology and the Environment - Many uncertainties exist in pile-stabilized slopes which make their design substantially complicated. In this paper, a first-order reliability...  相似文献   
54.
55.
Ischemic and hemorrhagic strokes are associated with severe functional disability and high mortality. Except for recombinant tissue plasminogen activator, therapies targeting the underlying pathophysiology of central nervous system (CNS) ischemia and hemorrhage are strikingly lacking. Sur1-regulated channels play essential roles in necrotic cell death and cerebral edema following ischemic insults, and in neuroinflammation after hemorrhagic injuries. Inhibiting endothelial, neuronal, astrocytic and oligodendroglial sulfonylurea receptor 1–transient receptor potential melastatin 4 (Sur1–Trpm4) channels and, in some cases, microglial KATP (Sur1–Kir6.2) channels, with glibenclamide is protective in a variety of contexts. Robust preclinical studies have shown that glibenclamide and other sulfonylurea agents reduce infarct volumes, edema and hemorrhagic conversion, and improve outcomes in rodent models of ischemic stroke. Retrospective studies suggest that diabetic patients on sulfonylurea drugs at stroke presentation fare better if they continue on drug. Additional laboratory investigations have implicated Sur1 in the pathophysiology of hemorrhagic CNS insults. In clinically relevant models of subarachnoid hemorrhage, glibenclamide reduces adverse neuroinflammatory and behavioral outcomes. Here, we provide an overview of the preclinical studies of glibenclamide therapy for CNS ischemia and hemorrhage, discuss the available data from clinical investigations, and conclude with promising preclinical results that suggest glibenclamide may be an effective therapeutic option for ischemic and hemorrhagic stroke.  相似文献   
56.
Endotoxin exacerbates asthma. We designed the Louisa Environmental Intervention Project (LEIP) and assessed its effectiveness in reducing household endotoxin and improving asthma symptoms in rural Iowa children. Asthmatic school children (N = 104 from 89 homes) of Louisa and Keokuk counties in Iowa (aged 5-14 years) were recruited and block-randomized to receive extensive (education + professional cleaning) or educational interventions. Environmental sampling collection and respiratory survey administration were done at baseline and during three follow-up visits. Mixed-model analyses were used to assess the effect of the intervention on endotoxin levels and asthma symptoms in the main analysis and of endotoxin reduction on asthma symptoms in exploratory analysis. In the extensive intervention group, dust endotoxin load was significantly reduced in post-intervention visits. The extensive compared with the educational intervention was associated with significantly decreased dust endotoxin load in farm homes and less frequent nighttime asthma symptoms. In exploratory analysis, dust endotoxin load reduction from baseline was associated with lower total asthma symptoms score (Odds ratio: 0.52, 95% confidence interval: 0.29-0.92). In conclusion, the LEIP intervention reduced household dust endotoxin and improved asthma symptoms. However, endotoxin reductions were not sustained post-intervention by residents.  相似文献   
57.
58.
59.
60.
顾凯 《建筑学报》2021,(11):35-40
进入更广泛的历史语境探讨清乾隆时期镜清斋假山的营造思路,追溯至晚明江南的两种假山营造来源.在整体构思上,承续了17世纪前期张南垣所创的追求画意真山的"天然"假山;而在局部营造中,则采纳了16世纪后期盛行的追求胜景无穷的"人巧"假山.除镜清斋之外,在稍晚的苏州环秀山庄假山中也有显著表达,是清代假山发展高峰的体现.清末和1970年代对该假山的两次改造,未能很好理解原初的思路取向,一定程度上损害了当初追求的山意.  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