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   421313篇
  免费   6178篇
  国内免费   1512篇
电工技术   8125篇
综合类   1134篇
化学工业   61522篇
金属工艺   15364篇
机械仪表   13237篇
建筑科学   10656篇
矿业工程   1792篇
能源动力   10037篇
轻工业   38442篇
水利工程   4026篇
石油天然气   4479篇
武器工业   76篇
无线电   52258篇
一般工业技术   76330篇
冶金工业   84706篇
原子能技术   7366篇
自动化技术   39453篇
  2021年   2755篇
  2019年   2787篇
  2018年   4786篇
  2017年   5121篇
  2016年   5786篇
  2015年   3969篇
  2014年   5945篇
  2013年   17259篇
  2012年   11088篇
  2011年   14881篇
  2010年   10534篇
  2009年   11973篇
  2008年   12996篇
  2007年   13109篇
  2006年   11850篇
  2005年   13514篇
  2004年   12500篇
  2003年   11751篇
  2002年   10385篇
  2001年   10264篇
  2000年   9368篇
  1999年   9719篇
  1998年   24759篇
  1997年   17680篇
  1996年   13794篇
  1995年   10548篇
  1994年   9354篇
  1993年   9094篇
  1992年   6941篇
  1991年   6575篇
  1990年   6341篇
  1989年   6081篇
  1988年   5808篇
  1987年   5099篇
  1986年   4972篇
  1985年   5825篇
  1984年   5368篇
  1983年   4921篇
  1982年   4672篇
  1981年   4743篇
  1980年   4456篇
  1979年   4227篇
  1978年   4043篇
  1977年   5217篇
  1976年   6912篇
  1975年   3733篇
  1974年   3520篇
  1973年   3555篇
  1972年   2884篇
  1971年   2711篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
41.
Current ammonia production technologies have a significant carbon footprint. In this study, we present a process synthesis and global optimization framework to discover the efficient utilization of renewable resources in ammonia production. Competing technologies are incorporated in a process superstructure where biomass, wind, and solar routes are compared with the natural gas-based reference case. A deterministic global optimization-based branch-and-bound algorithm is used to solve the resulting large-scale nonconvex mixed-integer nonlinear programming problem (MINLP). Case studies for Texas, California, and Iowa are conducted to examine the effects of different feedstock prices and availabilities. Results indicate that profitability of ammonia production is highly sensitive to feedstock and electricity prices, as well as greenhouse gas (GHG) restrictions. Under strict 75% GHG reductions, biomass to ammonia route is found to be competitive with natural gas route, whereas wind and solar to ammonia routes require further improvement to compete with those two routes. © 2018 American Institute of Chemical Engineers AIChE J, 65: e16498 2019  相似文献   
42.
Metallurgical and Materials Transactions A - The influence of the chemical composition on the crystallization process, amorphous phase formation, and the anticorrosion properties of Al-Zr-Ni-Fe-Y...  相似文献   
43.
44.
Here we report some recent biophysical issues on the preparation of solute-filled lipid vesicles and their relevance to the construction of “synthetic cells.” First, we introduce the “semi-synthetic minimal cells” as the liposome-based cell-like systems, which contain a minimal number of biomolecules required to display simple and complex biological functions. Next, we focus on recent aspects related to the construction of synthetic cells. Emphasis is given to the interplay between the methods of synthetic cell preparation and the physics of solute encapsulation. We briefly introduce the notion of structural and compositional “diversity” in synthetic cell populations.  相似文献   
45.
The viability and β‐galactosidase activity of four Lactobacillus strains in milk drink containing gums during 28 days of refrigerated storage at 4 °C were assessed. The population of Lactobacillus rhamnosus GGB101 and Lactobacillus rhamnosus GGB103 were maintained, whereas the population of Lactobacillus reuteri DSM20016 and Lactobacillus reuteri SD2112 significantly decreased. The recommended level of 6 log CFU g?1 was exceeded for all tested trains throughout storage. The highest viable number of Lactobacillus rhamnosus GGB103 (8.76 ± 0.03 log CFU mL?1) was obtained in the product containing carrageenan–maltodextrin. The addition of guar–locust bean–carrageenan led to 20‐fold increase in the level of β‐galactosidase activity for L. rhamnosus GGB101 (1208 ± 2.12 Miller units mL?1) compared to the control (61 ± 2.83 Miller units mL?1). Our results suggested that gums could be added to milk to improve viability and enhance β‐galactosidase activity of Lactobacillus.  相似文献   
46.
47.
48.
49.
Colour remains one of the key factors in presenting an object and, consequently, has been widely applied in retrieval of images based on their visual contents. However, a colour appearance changes with the change of viewing surroundings, the phenomenon that has not been paid attention yet while performing colour‐based image retrieval. To comprehend this effect, in this article, a chromatic contrast model, CAMcc, is developed for the application of retrieval of colour intensive images, cementing the gap that most of existing colour models lack to fill by taking simultaneous colour contrast into account. Subsequently, the model is applied to the retrieval task on a collection of museum wallpapers of colour‐rich images. In comparison with current popular colour models including CIECAM02, HSI and RGB, with respect to both foreground and background colours, CAMcc appears to outperform the others with retrieved results being closer to query images. In addition, CAMcc focuses more on foreground colours, especially by maintaining the balance between both foreground and background colours, while the rest of existing models take on dominant colours that are perceived the most, usually background tones. Significantly, the contribution of the investigation lies in not only the improvement of the accuracy of colour‐based image retrieval but also the development of colour contrast model that warrants an important place in colour and computer vision theory, leading to deciphering the insight of this age‐old topic of chromatic contrast in colour science. © 2014 Wiley Periodicals, Inc. Col Res Appl, 40, 361–373, 2015  相似文献   
50.
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