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   29780篇
  免费   1294篇
  国内免费   111篇
电工技术   391篇
综合类   229篇
化学工业   5383篇
金属工艺   678篇
机械仪表   613篇
建筑科学   1030篇
矿业工程   94篇
能源动力   986篇
轻工业   4057篇
水利工程   245篇
石油天然气   150篇
武器工业   6篇
无线电   2401篇
一般工业技术   4399篇
冶金工业   6325篇
原子能技术   252篇
自动化技术   3946篇
  2023年   148篇
  2022年   420篇
  2021年   824篇
  2020年   552篇
  2019年   624篇
  2018年   715篇
  2017年   790篇
  2016年   755篇
  2015年   587篇
  2014年   917篇
  2013年   1528篇
  2012年   1340篇
  2011年   1719篇
  2010年   1251篇
  2009年   1298篇
  2008年   1186篇
  2007年   1034篇
  2006年   844篇
  2005年   895篇
  2004年   947篇
  2003年   853篇
  2002年   827篇
  2001年   712篇
  2000年   563篇
  1999年   544篇
  1998年   2059篇
  1997年   1365篇
  1996年   940篇
  1995年   629篇
  1994年   489篇
  1993年   542篇
  1992年   225篇
  1991年   295篇
  1990年   229篇
  1989年   205篇
  1988年   211篇
  1987年   176篇
  1986年   165篇
  1985年   189篇
  1984年   135篇
  1983年   94篇
  1982年   123篇
  1981年   124篇
  1980年   121篇
  1979年   98篇
  1978年   84篇
  1977年   141篇
  1976年   233篇
  1975年   86篇
  1973年   53篇
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
21.
22.
23.
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   
24.
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   
25.
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   
26.
The objective of this study was to characterise the nutritional potential of leaves and identify a diversity centre with low cyanide and high nutrient content among 178 Latin American cassava genotypes. This field-based collection represents the seven diversity centres, held at The International Center for Tropical Agriculture (CIAT Palmira, Colombia) by the Cassava Program. The cyanide, all-trans-β-carotene and lutein concentrations in cassava leaves ranged from 346 to 7484 ppm dry basis (db), from 174–547 μg g−1 db and 15–181 μg g−1 db, respectively. Cassava leaves also showed significant levels of essential amino acids leucine, lysine, phenylalanine, valine and threonine, and average total protein content of 26.24 g 100 g−1 db. Among seven diversity centres, South American rainforest group showed low cyanide and high carotene content in leaves. In addition, VEN77 and PAN51 genotypes stood out for having low cyanide in leaves and roots and high carotene in leaves. This genetic diversity can be used to select high potential progenitors for breeding purposes.  相似文献   
27.
28.
29.
30.
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