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   156746篇
  免费   10082篇
  国内免费   4264篇
电工技术   5479篇
技术理论   1篇
综合类   6998篇
化学工业   27657篇
金属工艺   7123篇
机械仪表   9543篇
建筑科学   6929篇
矿业工程   1673篇
能源动力   5372篇
轻工业   12273篇
水利工程   1891篇
石油天然气   3027篇
武器工业   546篇
无线电   22917篇
一般工业技术   24753篇
冶金工业   11623篇
原子能技术   2002篇
自动化技术   21285篇
  2024年   224篇
  2023年   1440篇
  2022年   2362篇
  2021年   4135篇
  2020年   3123篇
  2019年   3063篇
  2018年   3682篇
  2017年   3801篇
  2016年   4295篇
  2015年   4374篇
  2014年   6439篇
  2013年   9262篇
  2012年   9780篇
  2011年   11262篇
  2010年   9562篇
  2009年   9714篇
  2008年   9446篇
  2007年   8501篇
  2006年   8074篇
  2005年   6840篇
  2004年   6054篇
  2003年   5552篇
  2002年   5856篇
  2001年   4943篇
  2000年   3888篇
  1999年   3241篇
  1998年   4195篇
  1997年   2877篇
  1996年   2503篇
  1995年   1981篇
  1994年   1519篇
  1993年   1338篇
  1992年   998篇
  1991年   915篇
  1990年   812篇
  1989年   712篇
  1988年   607篇
  1987年   503篇
  1986年   396篇
  1985年   383篇
  1984年   315篇
  1983年   233篇
  1982年   202篇
  1981年   180篇
  1980年   174篇
  1979年   144篇
  1978年   130篇
  1977年   170篇
  1976年   234篇
  1975年   105篇
排序方式: 共有10000条查询结果,搜索用时 890 毫秒
51.
52.
Over the past decades, the number of patients with dry eye disease (DED) has increased dramatically. The incidence of DED is higher in Asia than in Europe and North America, suggesting the involvement of cultural or racial factors in DED etiology. Although many definitions of DED have been used, discrepancies exist between the various definitions of dry eye disease (DED) used across the globe. This article presents a clinical consensus on the definition of DED, as formulated in four meetings with global DED experts. The proposed new definition is as follows: “Dry eye is a multifactorial disease characterized by a persistently unstable and/or deficient tear film (TF) causing discomfort and/or visual impairment, accompanied by variable degrees of ocular surface epitheliopathy, inflammation and neurosensory abnormalities.” The key criteria for the diagnosis of DED are unstable TF, inflammation, ocular discomfort and visual impairment. This definition also recommends the assessment of ocular surface epitheliopathy and neurosensory abnormalities in each patient with suspected DED. It is easily applicable in clinical practice and should help practitioners diagnose DED consistently. This consensus definition of DED should also help to guide research and clinical trials that, to date, have been hampered by the lack of an established surrogate endpoint.  相似文献   
53.
54.
55.
56.
Incorporating high level of potato flour into wheat flour enhances nutritional values of bread but induces a series of problems that lead to the decline of the bread quality. To overcome the barrier, wheat gluten and carboxymethylcellulose (CMC) were added into potato–wheat composite flour to improve dough machinability and bread quality. The rheological properties, thermo-mechanical properties and microstructures of dough were investigated. The results showed that the interaction between gluten and CMC mitigated the discontinuity of gluten matrix and gluten protein aggregation caused by the addition of potato flour, which yielded a more branched and compact gluten network. The compact three-dimensional viscoelastic structure induced improvements of gas retention capacity and dough stability, making it mimic the machinability properties of wheat flour dough. Bread qualities were apparently improved with the combined use of 4% gluten and 6% CMC, of which specific volume increased by 42.86%, and simultaneously, hardness reduced by 75.93%.  相似文献   
57.
Phytoalexins are inducible secondary metabolites possessing antimicrobial activity against phytopathogens. Rice produces a wide array of phytoalexins in response to pathogen attacks and environmental stresses. With few exceptions, most phytoalexins identified in rice are diterpenoid compounds. Until very recently, flavonoid sakuranetin was the only known phenolic phytoalexin in rice. However, recent studies have shown that phenylamides are involved in defense against pathogen attacks in rice. Phenylamides are amine-conjugated phenolic acids that are induced by pathogen infections and abiotic stresses including ultra violet (UV) radiation in rice. Stress-induced phenylamides, such as N-trans-cinnamoyltryptamine, N-p-coumaroylserotonin and N-cinnamoyltyramine, have been reported to possess antimicrobial activities against rice bacterial and fungal pathogens, an indication of their direct inhibitory roles against invading pathogens. This finding suggests that phenylamides act as phytoalexins in rice and belong to phenolic phytoalexins along with sakuranetin. Phenylamides also have been implicated in cell wall reinforcement for disease resistance and allelopathy of rice. Synthesis of phenolic phytoalexins is stimulated by phytopathogen attacks and abiotic challenges including UV radiation. Accumulating evidence has demonstrated that biosynthetic pathways including the shikimate, phenylpropanoid and arylmonoamine pathways are coordinately activated for phenolic phytoalexin synthesis, and related genes are induced by biotic and abiotic stresses in rice.  相似文献   
58.
Evaluation of kinetic distribution and behaviors of nanoparticles in vivo provides crucial clues into their roles in living organisms. Extracellular vesicles are evolutionary conserved nanoparticles, known to play important biological functions in intercellular, inter‐species, and inter‐kingdom communication. In this study, the first kinetic analysis of the biodistribution of outer membrane vesicles (OMVs)—bacterial extracellular vesicles—with immune‐modulatory functions is performed. OMVs, injected intraperitoneally, spread to the whole mouse body and accumulate in the liver, lung, spleen, and kidney within 3 h of administration. As an early systemic inflammation response, increased levels of TNF‐α and IL‐6 are observed in serum and bronchoalveolar lavage fluid. In addition, the number of leukocytes and platelets in the blood is decreased. OMVs and cytokine concentrations, as well as body temperature are gradually decreased 6 h after OMV injection, in concomitance with the formation of eye exudates, and of an increase in ICAM‐1 levels in the lung. Following OMV elimination, most of the inflammatory signs are reverted, 12 h post‐injection. However, leukocytes in bronchoalveolar lavage fluid are increased as a late reaction. Taken together, these results suggest that OMVs are effective mediators of long distance communication in vivo.  相似文献   
59.
介绍锚杆应用及常用的拆锚方法,针对现有前混合磨料射流退锚装置存在锚杆拆卸时间长、工人作业环境差、装置部件锈蚀维护性差等问题,提出了一种前混合磨料射流退锚改进装置,并进行现场试验,结果表明,所改进设计装置具有退锚时间短、对工人伤害小、操作简便、部件维护周期长和无需专门配备泵站等特点,对进一步提高锚杆拆除效率具有重要参考价值。  相似文献   
60.
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