首页 | 官方网站   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   196982篇
  免费   2355篇
  国内免费   629篇
工业技术   199966篇
  2021年   1234篇
  2019年   1281篇
  2018年   2126篇
  2017年   2104篇
  2016年   2172篇
  2015年   1495篇
  2014年   2618篇
  2013年   7961篇
  2012年   4470篇
  2011年   6124篇
  2010年   4936篇
  2009年   5775篇
  2008年   6157篇
  2007年   6205篇
  2006年   5635篇
  2005年   5314篇
  2004年   5260篇
  2003年   5095篇
  2002年   4902篇
  2001年   5311篇
  2000年   4922篇
  1999年   5447篇
  1998年   15641篇
  1997年   10332篇
  1996年   7937篇
  1995年   5757篇
  1994年   4990篇
  1993年   4989篇
  1992年   3352篇
  1991年   3235篇
  1990年   3200篇
  1989年   3002篇
  1988年   2760篇
  1987年   2207篇
  1986年   2275篇
  1985年   2594篇
  1984年   2300篇
  1983年   2049篇
  1982年   1889篇
  1981年   2029篇
  1980年   1779篇
  1979年   1645篇
  1978年   1644篇
  1977年   2015篇
  1976年   2701篇
  1975年   1419篇
  1974年   1359篇
  1973年   1307篇
  1972年   1114篇
  1971年   941篇
排序方式: 共有10000条查询结果,搜索用时 473 毫秒
41.
Potential mGAT4 inhibitors derived from the lead substance (S)-SNAP-5114 have been synthesized and characterized for their inhibitory potency. Variations from the parent compound included the substitution of one of its aromatic 4-methoxy and 4-methoxyphenyl groups, respectively, with a more polar moiety, including a carboxylic acid, alcohol, nitrile, carboxamide, sulfonamide, aldehyde or ketone function, or amino acid partial structures. Furthermore, it was investigated how the substitution of more than one of the aromatic 4-methoxy groups affects the potency and selectivity of the resulting compounds. Among the synthesized test substances (S)-1-{2-[(4-formylphenyl)bis(4-methoxyphenyl)-methoxy]ethyl}piperidine-3-carboxylic acid, that features a carbaldehyde function in place of one of the aromatic 4-methoxy moieties of (S)-SNAP-5114, was found to have a pIC50 value of 5.89±0.07, hence constituting a slightly more potent mGAT4 inhibitor than the parent substance while showing comparable subtype selectivity.  相似文献   
42.
43.
44.
45.
46.
47.
48.
49.
Spinel LiSr0·1Cr0·1Mn1·8O4 was synthesised by high temperature solid state method in order to enhance the electrochemical performance. The LiSr0·1Cr0·1Mn1·8O4 (LSCMO) materials were characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical tests. The XRD and SEM studies confirm that LSCMO had spinel crystal structure with a space group of Fd3m, and the particle of LSCMO shows irregular shape. The cyclic voltammetry data illustrated that the heavy current charge–discharge performance of LMO was improved by Sr2+ and Cr3+ doping. The galvanostatic charge–discharge of LSCMO cathode materials was measured at 1, 5, 10 and 20 C. The results indicated that LSCMO improved the capacity retention.  相似文献   
50.
WO3 is a potential material candidate for construction of photoanode for solar driven water splitting. In this work, μm-thick porous WO3 photoanode is prepared by depositing a stable ink made of WO3 nanoparticles and Aristoflex velvet polymer in water using the doctor blade technique, followed by a sintering in air. The nature of WO3 nanoparticles, its loading mass on F-doped tin oxide electrode as well as sintering temperature are examined in order to optimize the photocatalytic activity of the resultant WO3 photoanode. The operation of WO3 photoanode is investigated by varying the light illumination direction and light incident intensity as well as changing the nature of the electrolyte. Dissolved tungsten in electrolyte is quantified by ICP-MS providing insights into the influences of electrolyte nature and operating conditions to the corrosion of WO3. It is proposed that the H2O2 and OH. radical generated as by-products of the photo-driven water oxidation on the photoanode surface are harmful species that accelerate the dissolution of WO3.  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-23

京公网安备 11010802026262号