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   9216篇
  免费   506篇
  国内免费   11篇
电工技术   123篇
综合类   38篇
化学工业   2205篇
金属工艺   230篇
机械仪表   185篇
建筑科学   626篇
矿业工程   21篇
能源动力   281篇
轻工业   875篇
水利工程   88篇
石油天然气   43篇
武器工业   1篇
无线电   698篇
一般工业技术   1582篇
冶金工业   651篇
原子能技术   64篇
自动化技术   2022篇
  2023年   83篇
  2022年   74篇
  2021年   337篇
  2020年   188篇
  2019年   209篇
  2018年   277篇
  2017年   243篇
  2016年   330篇
  2015年   249篇
  2014年   359篇
  2013年   666篇
  2012年   507篇
  2011年   637篇
  2010年   448篇
  2009年   507篇
  2008年   480篇
  2007年   438篇
  2006年   358篇
  2005年   316篇
  2004年   299篇
  2003年   268篇
  2002年   204篇
  2001年   152篇
  2000年   156篇
  1999年   136篇
  1998年   181篇
  1997年   161篇
  1996年   117篇
  1995年   95篇
  1994年   88篇
  1993年   91篇
  1992年   64篇
  1991年   65篇
  1990年   68篇
  1989年   72篇
  1988年   54篇
  1987年   53篇
  1986年   50篇
  1985年   56篇
  1984年   61篇
  1983年   49篇
  1982年   41篇
  1981年   38篇
  1980年   40篇
  1979年   33篇
  1978年   36篇
  1977年   38篇
  1976年   50篇
  1975年   41篇
  1973年   39篇
排序方式: 共有9733条查询结果,搜索用时 15 毫秒
941.
Ceria- and yttria-doped tetragonal polycrystalline zirconia ceramics were ground at temperatures as high as 1100°C. X-ray diffraction revealed that the intensity ratio I (002)/ I (200) increased (to as high as ∼4.5) compared with that from the as-sintered surfaces (∼0.55). The enhancement in I (002)/ I (200) at temperatures well above the m → t transition temperature shows that it is not related to transformation, reversible or otherwise, but can be explained by ferroelastic domain switching.  相似文献   
942.
Energy savings certificates (ESCs) are potentially a major tool that can be used by regulators and policy makers in reducing greenhouse gas (GHG) emissions. In this paper, we present our findings on the experience to date with ESCs, outline potential program opportunities in the US, and conclude with our perspective on how to proceed with the use of ESCs, particularly as a component of GHG reduction programs.  相似文献   
943.
Summary A reproducible and sensitive gas Chromatographic method has been developed for the trace analysis of fluazifop-butyl, haloxyfop-ethoxyethyl and quizalofop-ethyl as well as their main metabolites (corresponding acids analysed after conversion to methyl esters) in some fruits and vegetables treated with herbicidal sprays. Comparable detection limits (0.01 mg/kg) were achieved when mass fragmentography and/or the electron capture detector were employed. However, in the latter case, bromination of fluazifop esters had to be carried out prior to GC analysis. By means of the nitrogen-phosphorus detector, determination of residues at a level of 0.05 mg/kg was possible. The residue values found in strawberries, cabbages, cauliflowers and carrots were used to discuss the degree of metabolic hydrolysis of parent esters, i.e. active ingredients of herbicides.
Bestimmung von Aryloxyphenoxypropionsäure-Derivaten in mit Herbicidsprays behandelten Produkten
Zusammenfassung Es wurde eine gaschromatographische Methode zur quantitativen und selektiven Bestimmung von Fluazifop-butyl, Haloxyfop-ethoxyethyl und Quizalofop-ethyl sowie von ihren Hauptmetaboliten (den entsprechenden Säuren, die zu Methylestern umgesetzt werden müssen) in mit Herbiciden behandelten Obst- und Gemüseproben entwickelt. Eine Nachweisgrenze von 0,01 mg/kg wurde durch Elektroneneinfanggaschromatographie oder durch Massenfragmentographie erzielt. Um die gleiche Empfindlichkeit des EC-Detektors bei Fluazifop zu erreichen, wurden die beiden Ester mit Brom umgesetzt. Mit Hilfe des NP-Detektors konnte eine Nachweisgrenze von 0,05 mg/kg erreicht werden. Die festgestellten Rückstandsgehalte in Erdbeeren, Kohl, Blumenkohl und Möhren wurden gleichzeitig zur Beurteilung der metabolischen Hydrolyse der diskutierten Ester (der Wirkstoffe der Herbicide) herangezogen.
  相似文献   
944.
Joint investigation of concrete at high rates of loading   总被引:2,自引:0,他引:2  
Uniaxial tensile tests have been carried out on a micro-concrete with strain rates between 0.5 and 1.25 s−1. The investigation is described and the results are discussed with respect to the influence of water content on the strain-rate sensitivity.  相似文献   
945.
The azalea lace bug secretes a clear fluid from secretory setae on the antennae and globulated spines on the dorsal and lateral aspects of the abdomen. The secretion contains 2-alkyl-5-hydroxychromones, the corresponding chromanones and diketones, and straight-chain aldehydes and ketones.  相似文献   
946.
947.
All-solid-state batteries based on fast Li+ conducting solid electrolytes such as Li7La3Zr2O12 (LLZO) give perspective on safe, non-inflammable, and temperature tolerant energy storage. Despite the promise, ceramic processing of whole battery assemblies reaching close to theoretical capacities and finding optimal strategies to process large-scale and low cost battery cells remains a challenge. Here, we tackle these issues and report on a solid-state battery cell composed of Li4Ti5O12 / c-Li6.25Al0.25La3Zr2O12 / metallic Li delivering capacities around 70–75 Ah/kg with reversible cycling at a rate of 8 A/kg (for 2.5–1.0 V, 95 °C). A key aspect towards the increase in capacity and Li+ transfer at the solid electrolyte-electrode interface is found to be the intimate embedding of grains and their connectivity, which can be implemented by the isostatic pressing of cells during their preparation. We suggest that simple adaption of ceramic processing, such as the applied pressure during processing, strongly alters the electrochemical performance by assuring good grain contacts at the electrolyte-electrode interface. Among the garnet-type all-solid-state ceramic battery assemblies in the field, considerably improved capacities and cycling properties are demonstrated for Li4Ti5O12 / c-Li6.25Al0.25La3Zr2O12 / metallic Li pressed cells, giving new perspectives on cheap ceramic processing and up-scalable garnet-based all-solid-state batteries.  相似文献   
948.
949.
950.
In 1974, (E)‐1‐nitropentadec‐1‐ene, a strong lipophilic contact poison of soldiers of the termite genus Prorhinotermes, was the first‐described insect‐produced nitro compound. However, its biosynthesis remained unknown. In the present study, we tested the hypothesis that (E)‐1‐nitropentadec‐1‐ene biosynthesis originates with condensation of amino acids with tetradecanoic acid. By using in vivo experiments with radiolabeled and deuterium‐labeled putative precursors, we show that (E)‐1‐nitropentadec‐1‐ene is synthesized by the soldiers from glycine or L ‐serine and tetradecanoic acid. We propose and discuss three possible biosynthetic pathways.  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