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   357837篇
  免费   29042篇
  国内免费   15778篇
电工技术   20994篇
技术理论   45篇
综合类   25468篇
化学工业   59944篇
金属工艺   20895篇
机械仪表   22531篇
建筑科学   27768篇
矿业工程   11759篇
能源动力   9736篇
轻工业   24241篇
水利工程   6785篇
石油天然气   23493篇
武器工业   2809篇
无线电   38921篇
一般工业技术   39470篇
冶金工业   18574篇
原子能技术   3646篇
自动化技术   45578篇
  2024年   1474篇
  2023年   5604篇
  2022年   9963篇
  2021年   13907篇
  2020年   10516篇
  2019年   8601篇
  2018年   9916篇
  2017年   11133篇
  2016年   10192篇
  2015年   13944篇
  2014年   17520篇
  2013年   21005篇
  2012年   22807篇
  2011年   25290篇
  2010年   22358篇
  2009年   21131篇
  2008年   20723篇
  2007年   19759篇
  2006年   20137篇
  2005年   17710篇
  2004年   12002篇
  2003年   10732篇
  2002年   9937篇
  2001年   8835篇
  2000年   8778篇
  1999年   9418篇
  1998年   7196篇
  1997年   6154篇
  1996年   5827篇
  1995年   4790篇
  1994年   3897篇
  1993年   2629篇
  1992年   2076篇
  1991年   1581篇
  1990年   1235篇
  1989年   996篇
  1988年   831篇
  1987年   526篇
  1986年   410篇
  1985年   258篇
  1984年   206篇
  1983年   164篇
  1982年   128篇
  1981年   76篇
  1980年   98篇
  1979年   43篇
  1978年   17篇
  1977年   23篇
  1976年   28篇
  1973年   9篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
121.
Cerebral microbleeds (CMBs) are small hemosiderin deposits indicative of prior cerebral microscopic hemorrhage and previously thought to be clinically silent. Recent population‐based cross‐sectional studies and prospective longitudinal cohort studies have revealed association between CMB and cognitive dysfunction. In the general population, CMBs are associated with age, hypertension, and cerebral amyloid angiopathy. In the chronic kidney disease (CKD) population, diminished estimated glomerular filtration rate has been found to be an independent risk factor for CMB, raising the possibility that a uremic milieu may predispose to microbleeds. In the end‐stage renal disease (ESRD) population on hemodialysis, the incidence of microbleeds is significantly higher compared with a control group without history of CKD or stroke. We present an ESRD patient on chronic hemodialysis with a history of gradual cognitive decline and progressive CMBs. Through this case and literature review, we illustrate the need to develop detection and prediction models to treat this frequent development in ESRD patients.  相似文献   
122.
123.
It is of great urgency to design inexpensive and high-performance oxygen reduction reaction (ORR) electrocatalysts derived from biowastes as substitutes for Pt-based materials in electrochemical energy-conversion devices. Here we propose a strategy to synthesize three-dimensional (3D) porous nitrogen-doped network carbons to catalyze the ORR from two-step pyrolysis engineering of biowaste scale combined with the use of a ZnCl2 activator and a FeCl2 promotor. Electrochemical tests show that the synthesized network carbons have exhibited comparable ORR catalytic activity with a half-wave potential (~0.85 V vs. RHE) and outstanding cyclical stability in comparison to the Pt/C catalyst. Beyond that, a high electron transfer number (~3.8) and a low peroxide yield (<7.6%) can be obtained, indicating a four-electron reaction pathway. The maximum power density is ~68 mW cm?2, but continuous discharge curves (at a constant potential of ~1.30 V) for 12 h are not obviously declined in Zn-air battery tests using synthesized network carbons as the cathodic catalyst. The formation of 3D porous structures with high BET surface area can effectively expose the surface catalytic sites and promote mass transportation to boost the ORR activity. This work may open a new idea to prepare porous carbon-based catalysts for some important reactions in new energy devices.  相似文献   
124.
Mitochondrial oxidative damage and dysfunction contribute to a wide range of human diseases. Considering the limitation of conventional antioxidants and that mitochondria are the main source of reactive oxygen species (ROS) which induce oxidative damage, mitochondria-targeted antioxidants which can selectively block mitochondrial oxidative damage and prevent various types of cell death have been widely developed. As a lipophilic cation, triphenylphosphonium (TPP) has been commonly used in designing mitochondria-targeted antioxidants. Conjugated with the TPP moiety, antioxidants can achieve more than 1000-fold higher mitochondrial concentration depending on cell membrane potentials and mitochondrial membrane potentials. Herein we discuss the deficiencies of conventional antioxidants and the advantages of mitochondrial targeting, and review various types of TPP-based mitochondria-targeted antioxidants. These provide theoretical and background support for the design of new anti-oxidant.  相似文献   
125.
In this study, in vitro digestion and fermentation of Flammulina velutipes -derived polysaccharides (FVP) were investigated. It was found that FVP mainly consisted of 48.45% glucose, 15.40% mannose, 14.60% xylose, 11.80% fucose and 9.90% galactose. The -human saliva, simulated gastric and small intestinal juices conditions did not break down the FVP. Based on in vitro fermentation tests, FVP modulated the composition of gut microbiota by elevating the amounts of Bifidobacteriaceae and Bacteroidaceae and reducing the numbers of genera Lachnospiraceae and Enterococcaceae. Meanwhile, FVP affected the synthesis of short-chain fatty acids derived from gut microbiota.  相似文献   
126.
127.
文章简述了IT运维的发展趋势,举例说明了综合运维软件的功能特点,并阐述了综合运维软件在供水企业中的应用案例及应用效果,由此提出综合运维软件的重要作用。  相似文献   
128.
129.
130.
通过对HP295封头冲压开裂件缺陷光电镜分析,查找到缺陷产生部位及其导致原因。对多组铸坯低倍样检查,发现中间裂纹是缺陷根源。此后,根据现场生产情况,分析钢中磷、硫含量、钢水过热度、铸机设备精度、拉速和二次冷却强度等因素对铸坯中间裂纹的影响。通过降低磷、硫,控制过热度,调整设备精度,降低拉速以及优化二次冷却等措施,HP295铸坯中间裂纹得到有效控制,用户加工开裂现象完全杜绝。  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