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   27337篇
  免费   1666篇
  国内免费   2849篇
电工技术   854篇
综合类   1301篇
化学工业   4961篇
金属工艺   11875篇
机械仪表   839篇
建筑科学   1785篇
矿业工程   311篇
能源动力   490篇
轻工业   158篇
水利工程   224篇
石油天然气   3176篇
武器工业   137篇
无线电   275篇
一般工业技术   3368篇
冶金工业   1664篇
原子能技术   343篇
自动化技术   91篇
  2024年   135篇
  2023年   433篇
  2022年   729篇
  2021年   924篇
  2020年   994篇
  2019年   880篇
  2018年   724篇
  2017年   1127篇
  2016年   1058篇
  2015年   1029篇
  2014年   1519篇
  2013年   1676篇
  2012年   1796篇
  2011年   2192篇
  2010年   1671篇
  2009年   1801篇
  2008年   1279篇
  2007年   1652篇
  2006年   1639篇
  2005年   1297篇
  2004年   1303篇
  2003年   1143篇
  2002年   937篇
  2001年   751篇
  2000年   624篇
  1999年   519篇
  1998年   367篇
  1997年   344篇
  1996年   268篇
  1995年   253篇
  1994年   200篇
  1993年   142篇
  1992年   109篇
  1991年   59篇
  1990年   71篇
  1989年   65篇
  1988年   32篇
  1987年   23篇
  1986年   17篇
  1985年   7篇
  1984年   7篇
  1983年   5篇
  1982年   7篇
  1981年   7篇
  1980年   14篇
  1979年   4篇
  1978年   6篇
  1975年   2篇
  1959年   5篇
  1951年   4篇
排序方式: 共有10000条查询结果,搜索用时 12 毫秒
991.
Hydrogen's widespread use is fraught with many difficulties. The challenges currently are to do with safety concerns in gas storage and transportation, and low rate of production leading to non-viability of technologies at the point-of-use. Another global concern of immediate relevance involves heavy-metal ion pollution. Viable processes which can simultaneously remove and result in beneficiation of the contaminants are hitherto rarely reported. In this context we report a single-step, in situ co-reduction approach which has the dual advantage of (i) Hg contaminant removal, and (ii) room temperature hydrogen production. Hydrogen is produced via galvanic corrosion of in situ synthesized nanoaluminium amalgam. The production rate (720 mL/min for 0.5 g-Al salt) is far superior to what would be expected from the use of pure hydrides, and/or using bulk amalgams at room temperature. The method is simple, chimie douce (i.e soft chemical), hence potentially affordable, and capable of providing a means of beneficiating Hg contaminated water present in effluents from certain industries (for example, industries which uses chlor-alkali process). The in situ co-reduction approach helps in bypassing the usual rate limiting step which involves formation of an alumina passivation layer on hydrolytic material surface. Given the potential that exists in scale down and up, this approach offers a method to address the long standing challenge of point-of-use hydrogen availability.  相似文献   
992.
Magnesium and magnesium alloys are attracting considerable interest as biodegradable materials with high potential for application as temporary implants. The high corrosion rate of Mg-based implants is considered a serious drawback, and it is crucial to design novel surface protection strategies that minimize the detrimental effects of corrosion, while contributing for introducing additional functionalities on the material surface. In this work, a layer-by-layer coating architecture composed of an inner poly(lactic-co-glycolic) acid layer, working as adhesion promoter, and additional polycaprolactone (PCL) layers working as reservoirs for antibiotic (levofloxacin) and for nanohydroxyapatite (nanoHA) particles was applied on the Mg alloy AZ31. The results demonstrate that the composition and number of PCL layers can tailor the biodegradation of the bare magnesium alloy, surface wettability, and the kinetics of release of antibiotic (levofloxacin). The distribution of nanoHA in the coating architecture plays a crucial role on tailoring the desired biocompatible functionalities and corrosion protection of the bare alloy.  相似文献   
993.
Flexible aluminum moisture barrier films are shown to meet ultra-barrier requirements with water vapor transmission rates as low as 1*10−4 g/m2/day at 38 °C and 90% R.H. These low transmission rates are achieved by lamination of two films that are independently processed on individual substrates. The integration in organic electronic devices like organic solar cells or OLEDs is particularly easy in a single lamination step, since an existing aluminum electrode can be utilized as one half of the moisture barrier. The resulting laminate maintains flexibility of the device and improves the barrier quality by an order of magnitude compared to conventional stacking of two barriers. Organic solar cells with this type of encapsulation are manufactured and aged in controlled climate. They do not exhibit significant extrinsic degradation.  相似文献   
994.
陈涛 《山西建筑》2014,(5):39-40
依据相关标准及规范,对11G101-1图集中关于制图规则、钢筋锚固、搭接、节点构造等内容的变化作了分析,以便于设计人员掌握11G101-1图集内容,解决如何执行11G101-1图集的问题。  相似文献   
995.
996.
997.
Stability of the passive state was assessed for pure Zr and four Zr–Nb alloys (2.5, 5.0, 10.0, 25.0 at.% Nb) after 24 h exposure to naturally aerated 3.5% NaCl solution (pH = 6). Open circuit potential values indicated that all the Zr–Nb alloys studied and the pure Zr undergo spontaneous passivation due to spontaneously formed oxide film passivating the metallic surface. It also indicated that the addition of increasing Nb contents to pure Zr seems to improve the protection characteristics of its spontaneous oxides. Potentiodynamic polarization curves showed an increase of the breakdown potential and the extent of the passive range following an increased niobium amount in the alloy. This leads to the conclusion that a progressive increase of niobium content positively affects the localized corrosion behaviour of the Zr–Nb alloys by enhancing the electrochemical stability of the passive film. Electrochemical impedance spectroscopy (EIS) studies showed high impedance values for all the samples, and its increase on increased niobium content in the alloy indicated an improvement in the corrosion resistance of the spontaneous oxide film. The fit obtained suggests a single passive film present on the metal surface, with resistance improving with the increase of niobium amount in the alloy. All these electrochemical results show the beneficial effect of increasing niobium contents on the passive state stability of the Zr–Nb alloys.  相似文献   
998.
999.
This study is aimed to find the fatigue behavior of Glass Reinforced Plastics, a material which is a widely preferred material for small marine crafts, as well as several other applications. The type of composite tested is hand‐laid E‐glass non‐crimp reinforcements with an polyester resin matrix. The specimens were produced in two standard thicknesses and with these material directions and were tested both under atmospheric and simulated seawater environments for fatigue. It was seen that the results of fatigue lifetime obtained by testing the material in seawater is much lower than the results obtained from testing similar specimens under atmospheric conditions. However, the stress curves indicate the same slope, suggesting that the fatigue failure mechanism of both testing conditions is the same and the fiber‐related factors dominate. It was found that the thickness and material direction did not have a significant effect on the fatigue behavior of the material.  相似文献   
1000.
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