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   30981篇
  免费   1426篇
  国内免费   109篇
电工技术   411篇
综合类   228篇
化学工业   5803篇
金属工艺   670篇
机械仪表   648篇
建筑科学   1047篇
矿业工程   96篇
能源动力   1013篇
轻工业   4370篇
水利工程   271篇
石油天然气   162篇
武器工业   6篇
无线电   2384篇
一般工业技术   4523篇
冶金工业   6574篇
原子能技术   249篇
自动化技术   4061篇
  2024年   54篇
  2023年   155篇
  2022年   472篇
  2021年   945篇
  2020年   622篇
  2019年   681篇
  2018年   785篇
  2017年   876篇
  2016年   817篇
  2015年   628篇
  2014年   977篇
  2013年   1569篇
  2012年   1398篇
  2011年   1780篇
  2010年   1296篇
  2009年   1393篇
  2008年   1239篇
  2007年   1086篇
  2006年   858篇
  2005年   905篇
  2004年   976篇
  2003年   870篇
  2002年   844篇
  2001年   724篇
  2000年   579篇
  1999年   560篇
  1998年   2122篇
  1997年   1388篇
  1996年   967篇
  1995年   644篇
  1994年   502篇
  1993年   559篇
  1992年   236篇
  1991年   292篇
  1990年   241篇
  1989年   204篇
  1988年   216篇
  1987年   169篇
  1986年   174篇
  1985年   183篇
  1984年   137篇
  1983年   96篇
  1982年   121篇
  1981年   127篇
  1980年   121篇
  1979年   90篇
  1978年   78篇
  1977年   141篇
  1976年   235篇
  1975年   82篇
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
21.
22.
23.
24.
25.
26.
27.
Zhang  Xi  Wang  Xianhai  Zhao  Hongke  Ordóñez de Pablos  Patricia  Sun  Yongqiang  Xiong  Hui 《Scientometrics》2019,119(3):1311-1344
Scientometrics - Altmetrics indices are increasingly applied to measure scholarly influence in recent years because they can reflect the influence of research outputs more timely comparing with...  相似文献   
28.
Neat poly (lactic acid) (PLA) and PLA/cassava bagasse (CB) composites were used to produce seedling tubes by extrusion and injection molding. The tubes were buried in simulated soil, and their biodegradation was investigated by weight loss, scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR). After 180 days, the composites' biodegradation was higher than neat PLA material, and the higher the CB content, the higher the biodegradation, which caused fissures and voids in the material. The biodegradation of PLA/CB composites increased the phosphorus content in the soil after 180 days. Composites of PLA with CB, an abundant agro-industrial residue in Brazil, are promising because they can reduce the environmental impact due to CB's proper destination, and the composites' costs and biodegradation are faster than pure PLA material. Both the faster biodegradation of the tube and the higher P content are advantageous for seedling tubes.  相似文献   
29.
This study investigates the preparation of polyetherimide (PEI) – LaNi5 composites films for hydrogen storage. Prior to the polymer addition, LaNi5 was ball-milled at different conditions (250, 350, and 450 RPM) and annealed at 500 °C for 1 h under vacuum. The composites were produced with BM-LaNi5-350 (PEI/LaNi5-350) and annealed BM-LaNi5-350 (PEI/LaNi5-350-TT). Membranes were successfully produced through solvent casting assisted by an ultrasonic bath. The particles dispersion and the film morphology did not change after hydrogenation cycles. In the H2 sorption experiments at 43 °C and 20 bar, the films stored H2 without incubation time; both samples reached a capacity of ~0.6 wt%. The H2 sorption kinetics of PEI/LaNi5-350 was comparable to that of BM-LaNi5-350, whereas PEI/LaNi5-350-TT presented significantly slower kinetics. LaNi5 oxidation was hindered by PEI, showing that it can be explored to improve metal hydrides air resistance. The results demonstrated that PEI films filled with LaNi5 are promising materials for hydrogen storage.  相似文献   
30.
A series of 2-phenyloxazoles bearing an amide group at position 4 were designed and synthesized for evaluation as potential inhibitors of human recombinant monoamine oxidases (hrMAOs). Results of kinetics experiments demonstrated that all compounds behave as competitive MAO inhibitors, with good selectivity toward the MAO-B isoform. The most potent and selective derivatives are characterized by inhibition constant (Ki) values in the sub-micromolar range and a good selectivity index (Ki MAO-A/Ki MAO-B>50). Some derivatives were also found to be able to inhibit MAO activity in nerve growth factor (NGF)-differentiated PC12 cells, taken as a model of neuronal cells. In particular, 2-(2-hydroxyphenyl)-N-phenyloxazole-4-carboxamide (compound 4 a ) may be a promising new scaffold, exerting the highest selectivity and inhibitory effect toward MAOs in NGF-differentiated PC12 cell lysates, without compromising cell viability. Molecular docking analysis allowed a rationalization of the experimentally observed binding affinity and selectivity.  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