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   95620篇
  免费   8452篇
  国内免费   4952篇
电工技术   5584篇
技术理论   2篇
综合类   8366篇
化学工业   15331篇
金属工艺   5347篇
机械仪表   5972篇
建筑科学   6939篇
矿业工程   2363篇
能源动力   2649篇
轻工业   8036篇
水利工程   1908篇
石油天然气   3986篇
武器工业   747篇
无线电   11303篇
一般工业技术   10712篇
冶金工业   4091篇
原子能技术   1324篇
自动化技术   14364篇
  2024年   292篇
  2023年   1204篇
  2022年   2176篇
  2021年   3181篇
  2020年   2496篇
  2019年   2146篇
  2018年   2304篇
  2017年   2673篇
  2016年   2549篇
  2015年   3485篇
  2014年   4570篇
  2013年   5559篇
  2012年   6395篇
  2011年   6900篇
  2010年   6353篇
  2009年   6208篇
  2008年   6141篇
  2007年   5857篇
  2006年   5732篇
  2005年   4975篇
  2004年   3874篇
  2003年   3477篇
  2002年   3957篇
  2001年   3436篇
  2000年   2520篇
  1999年   2059篇
  1998年   1516篇
  1997年   1239篇
  1996年   1206篇
  1995年   1021篇
  1994年   784篇
  1993年   588篇
  1992年   465篇
  1991年   372篇
  1990年   295篇
  1989年   206篇
  1988年   198篇
  1987年   139篇
  1986年   75篇
  1985年   80篇
  1984年   67篇
  1983年   43篇
  1982年   29篇
  1981年   31篇
  1980年   28篇
  1979年   23篇
  1978年   12篇
  1977年   14篇
  1976年   20篇
  1959年   10篇
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
61.
Background: Epilepsy is a chronic neurological disorder characterized by the recurrence of seizures. One-third of patients with epilepsy may not respond to antiseizure drugs. Purpose: We aimed to examine whether D-limonene, a cyclic monoterpene, exhibited any antiseizure activity in the pentylenetetrazole (PTZ)-induced kindling mouse model and in vitro. Methods: PTZ kindling mouse model was established by administering PTZ (30 mg/kg) intraperitoneally to mice once every 48 h. We performed immunoblot blots, immunohistochemistry (IHC), and high-performance liquid chromatography (HPLC) analysis after the behavioral study. Results: An acute injection of PTZ (60 mg/kg) induced seizure in mice, while pretreatment with D-limonene inhibited PTZ-induced seizure. Repeated administration of PTZ (30 mg/kg) increased the seizure score gradually in mice, which was reduced in D-limonene (10 mg/kg)-pretreated group. In addition, D-limonene treatment increased glutamate decarboxylase-67 (GAD-67) expression in the hippocampus. Axonal sprouting of hippocampal neurons after kindling was inhibited by D-limonene pretreatment. Moreover, D-limonene reduced the expression levels of Neuronal PAS Domain Protein 4 (Npas4)-induced by PTZ. Furthermore, the adenosine A2A antagonist SCH58261 and ZM241385 inhibited anticonvulsant activity and gamma-aminobutyric acid (GABA)ergic neurotransmission-induced by D-limonene. Conclusion: These results suggest that D-limonene exhibits anticonvulsant activity through modulation of adenosine A2A receptors on GABAergic neuronal function.  相似文献   
62.
The {100} facet of single-crystalline TiO2(B) is an ideal platform for inserting Li ions, but it is hard to be obtained due to its high surface energy. Here, the single-crystalline TiO2(B) nanobelts from H2Ti3O7 with nearly 70% {100} facets exposed are synthesized, which significantly enhances Li-storage capacity. The first-principle calculations demonstrate an ab in-plane 2D diffusion through the exposed {100} facets. As a consequence, the nanobelts can significantly accommodate Li ions in LiTiO2 formula with specific capacity up to 335 mAh g−1, which is in good agreement with the electrochemical characterizations. Coating with conductive and protective poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate), the cut-off discharge voltage is as low as 0.5 V, leading to a capacity of 160.7 mAh g−1 after 1500 cycles with a retention rate of 66% at 1C. This work provides a practical strategy to increase the Li-ion capacity and cycle stability by tailoring the crystal orientation and nanostructures.  相似文献   
63.
Journal of Mechanical Science and Technology - Skidding is a phenomenon that frequently occurs in ball–raceway contact areas of bearings and often leads to their early failure. This paper...  相似文献   
64.
Ethanol steam reforming (ESR) is one of the potential processes to convert ethanol into valuable products. Hydrogen produced from ESR is considered as green energy for the future and can be an excellent alternative to fossil fuels with the aim of mitigating the greenhouse gas effect. The ESR process has been well studied, using transition metals as catalysts coupled with both acidic and basic oxides as supports. Among various reported transition metals, Ni is an inexpensive material with activity comparable to that of noble metals, showing promising ethanol conversion and hydrogen yields. Additionally, different promoters and supports were utilized to enhance the hydrogen yield and the catalyst stability. This review summarizes and discusses the influences of the supports and promoters of Ni-based catalysts on the ESR process.  相似文献   
65.
JOM - The Isa/Ausmelt smelting technology with a top submerged lance (TSL) has been extensively used in copper smelting processes. However, the TSL is extremely vulnerable to damage and failure...  相似文献   
66.
User Modeling and User-Adapted Interaction - Personality plays a pivotal role at work. Many scholars have investigated the association between personality and language usage habits in the English...  相似文献   
67.
综述了氰酸钾的合成方法,并对各种方法进行了评价,其中液固相反应法具有原料易得,操作简便,产物纯度较高、易与溶剂分离、经济性好等特点,适用于工业化生产。  相似文献   
68.
针对ca油田多层状砂泥薄互层稠油油藏的特点,开展了热采和非热采条件下储层变化特征研究、钻井和固井过程入井液的研究、采油工艺技术等系统保护油气层研究,了解各种变化的作用过程和原因,有效地预防现场施工中可能发生的储层伤害,从而达到储层保护、提高采收率的目的。  相似文献   
69.
炼油达标污水回用处理试验研究   总被引:1,自引:0,他引:1  
采用曝气生物滤池、多介质过滤、超滤、反渗透工艺,对炼油达标外排污水进行回用处理中试试验。结果表明,曝气生物滤池对油、COD和浊度去除效果良好,超滤、反渗透膜化学清洗周期达到 2个月以上,脱盐率稳定在98%以上,产水品质达到回用要求。  相似文献   
70.
根据水平井三维渗流特征,在底水油藏情形仍假定顶面为不渗透隔层所封闭,底部则是恒压边界,水平井渗流表现为早期径向流以及稳定流动期,由此进行常规试井分析。以TKxxDH井为例,通过水平井的静压、压恢试井资料结果的对比分析,阐述了不稳定试井资料的应用,为此类油藏油井模型的选择及效果评价提供了可借签的经验。  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