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   5199篇
  免费   431篇
  国内免费   154篇
电工技术   69篇
综合类   167篇
化学工业   1837篇
金属工艺   670篇
机械仪表   39篇
建筑科学   125篇
矿业工程   76篇
能源动力   93篇
轻工业   1277篇
水利工程   29篇
石油天然气   472篇
武器工业   5篇
无线电   93篇
一般工业技术   276篇
冶金工业   454篇
原子能技术   16篇
自动化技术   86篇
  2025年   47篇
  2024年   137篇
  2023年   104篇
  2022年   204篇
  2021年   223篇
  2020年   176篇
  2019年   169篇
  2018年   145篇
  2017年   181篇
  2016年   204篇
  2015年   185篇
  2014年   236篇
  2013年   295篇
  2012年   305篇
  2011年   411篇
  2010年   284篇
  2009年   285篇
  2008年   239篇
  2007年   275篇
  2006年   277篇
  2005年   227篇
  2004年   188篇
  2003年   176篇
  2002年   126篇
  2001年   125篇
  2000年   104篇
  1999年   55篇
  1998年   60篇
  1997年   40篇
  1996年   36篇
  1995年   23篇
  1994年   34篇
  1993年   33篇
  1992年   27篇
  1991年   20篇
  1990年   23篇
  1989年   13篇
  1988年   6篇
  1987年   12篇
  1986年   7篇
  1985年   15篇
  1984年   13篇
  1983年   5篇
  1981年   4篇
  1977年   3篇
  1964年   3篇
  1961年   2篇
  1960年   2篇
  1958年   3篇
  1955年   2篇
排序方式: 共有5784条查询结果,搜索用时 15 毫秒
1.
Water extracts from leaves of date palm, phoenix dactylifera, henna, Lawsonia inermis, and corn, Zea mays, were tested as corrosion inhibitors for steel, aluminum, copper and brass in acid chloride and sodium hydroxide solutions using weight loss, solution analysis and potential measurements. The inhibition action was found to critically depend on metal type and solution composition. Only, date palm and henna extracts were found highly effective in reducing corrosion rate of steel in acid chloride solutions and aluminum in sodium hydroxide solutions. The inhibition efficiency increased with increasing the concentration of the extract. The inhibition was interpreted in terms of chemisorption of some active ingredients in the leaves according to Temkin isotherm.  相似文献   
2.
The catalytic activity of fresh Pd and Pt catalysts supported on γ-alumina in the complete oxidation of CH4 traces under lean-burn conditions was studied in the presence or the absence of water or H2S. Steam-aged catalysts were also studied in order to simulate long-term ageing in real lean-burn natural gas fuelled vehicles (NGVs) exhaust conditions. Without water or H2S added to the feed, Pd catalysts exhibit a superior catalytic activity in methane oxidation compared to Pt ones, whatever the catalysts were fresh or aged. The addition of 10 vol.% water vapour to the feed strongly affects the activity of the fresh Pd catalyst, thus being only slightly more efficient than the fresh Pt one. H2S has a strong poisoning effect on the catalytic activity of Pd catalysts, while Pt catalysts are more resistant. The fresh H2S-poisoned Pd/Al2O3 catalyst was studied by TPD in O2/He. Poisoning species decompose above 873 K as SO2 and O2 in relative concentrations consistent with the decomposition of surface sulphate species. However, a treatment in O2/He at temperatures as high as 923 K does not allow the complete regeneration of the catalytic activity of H2S-poisoned Pd/Al2O3. A mechanism involving the poisoning of PdO by sulphate species is proposed. Different diffusion processes by which these sulphate species can migrate back and forth between PdO and the support, depending on the experimental conditions, are suggested.  相似文献   
3.
Uniform, crack-free vanadium-based corrosion inhibitor films were grown on aluminum alloy 2024. Neutron and X-ray reflectivity were utilized to investigate the structure, water-barrier properties and speciation of the inhibitor film. The top part of the alloy participates in the formation of vanadate film. The similarity of films prepared from H2O and D2O implies the vanadate film is not hydrated. The film has a layered structure with vanadium enriched at the alloy interface. The film behaves as an effective water barrier when the thickness is greater than 800 Å. Films grown without K3Fe[CN]6 accelerator are found to be extremely thin.  相似文献   
4.
X区煤层气井生产过程中,井下设备存在着严重的结垢情况,给气井正常生产带来较大影响。为提高采收率,对X区垢样进行X-射线衍射成分分析,优选出了除垢泡沫酸体系,设计加工了泡沫酸现场施工配套设备。结果表明:X区垢成因复杂,泡沫酸酸溶率可高达95%,缓蚀性及配伍性良好,工艺存在问题得到相应改善,现场施工应用增产效果较好。  相似文献   
5.
The anti-listerial activity of Staphylococcus equorum SE3 isolated from cheese brine was tested in two different model cheese systems to ascertain its potential for use as a protective culture for smear cheese ripening. Co-cultivation of Listeria monocytogenes L129 and the antilisterial S. equorum SE3 was performed on “milk agar” or “modified milk agar” (model cheese surface systems). S. equorum inoculated at concentrations of 106 cfu/cm2 completely inhibited growth of L. monocytogenes inoculated at 10–500 cfu/cm2 on modified milk agar within 24 h of incubation, in the negative controls L129 grew to >107 cfu/cm2. At a higher inoculation level, growth inhibition was still more than 7 log units after 24 h. L. monocytogenes strains of different serotypes were also inhibited. Co-cultivation of S. equorum SE3 with other smear bacteria or yeasts, however, showed no growth inhibition of these important ripening microorganisms. The antilisterial effect was not diminished on the modified milk agar when co-cultivation was performed with the added smear cheese microbiota. However, on milk agar with no adjuncts (“green cheese model”), only a slight (<1 log unit) growth inhibition of L. monocytogenes was observed. Addition of peptides or amino acids to milk agar could restore growth inhibition of listeriae at different levels.  相似文献   
6.
基于侧抑制机制的一维多速度运动检测神经网络   总被引:1,自引:0,他引:1  
王爱群  郑南宁 《电子学报》1997,25(11):22-26
运动感知是生物视觉系统的一个重要组成部分。运动对自然界的认识一大部分是通过运动感知。本文通过对同时具有方向和速度选择性的视觉皮层运动区神经元的侧抑制机制的模拟,提出了一种新的乘积抑制速度检测子(Multiplicative Inhibitory Velocity-MIVD),其时空联合参数K决定了检测子的最优速度,基于MIVD的响应幅度差特性,我们构造了两个速度融合神经网络(一个简单神经网络和一个  相似文献   
7.
New sulfur analogs of the sex pheromone of the female processionary mothThaumetopoea pityocampa have been found to be effective inhibitors of the natural pheromone activity both in EAG bioassays and field tests. The structures of these analogs have been derived from replacement of the oxygen atom(s) of the acetate group by sulfur (compounds 3-5) and the olefinic moiety of the enyne function by the isosteric SCH2 group (compounds 6 and 7). The synthesis and biological activity of 3-[(Z)-12-pentadecen-10-ynylthio]-1,1,1-trifluoropropan-2-one (8), a closely related structure to the pheromone is also described.  相似文献   
8.
石墨烯具有独特的物理、化学性质,在钻井液领域得到了一定的研究.本文讨论了石墨烯及其衍生物的结构和特点,概述了石墨烯材料在提高钻井液封堵抑制性,改善钻井液滤失性、流变性和润滑性等方面的研究进展,并探讨了石墨烯材料在钻井液领域的研究和发展方向.  相似文献   
9.
10.
真菌产生的代谢产物可激活烟草体内抗病防御相兲酶的表达,诱导烟草产生系统抗性,增强烟草对病毒的抗性。本研究对38种植物病原真菌及45种分离自(恩施、襄樊)土壤、烟叶中的真菌进行了过敏性反应实验和系统抗性实验。结果表明,筛选出了对烟草花叶病毒抗性较强的真菌。在烟草上产生过敏反应的菌株有32个;系统抗性实验中对烟草花叶病毒抑制率较高的菌株有16个,其中,油茶炭疽菌、棉花黄萎病菌、esf-13、esf-3、小麦赤霉、立枯丝核菌、E1、esf-6、xfpf-6等菌株的抗性较高,枯斑抑制率均大于70%,最高可达96.44%。抗性较高的真菌可开发为烟草病毒病诱抗剂。  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