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   416642篇
  免费   6333篇
  国内免费   1831篇
电工技术   8104篇
综合类   575篇
化学工业   63383篇
金属工艺   17766篇
机械仪表   11871篇
建筑科学   10742篇
矿业工程   1451篇
能源动力   10690篇
轻工业   40497篇
水利工程   3492篇
石油天然气   4416篇
武器工业   15篇
无线电   48836篇
一般工业技术   76777篇
冶金工业   84190篇
原子能技术   7734篇
自动化技术   34267篇
  2021年   3198篇
  2019年   2853篇
  2018年   4847篇
  2017年   4717篇
  2016年   5084篇
  2015年   3965篇
  2014年   6226篇
  2013年   18863篇
  2012年   10377篇
  2011年   14225篇
  2010年   11477篇
  2009年   12884篇
  2008年   13473篇
  2007年   13449篇
  2006年   11919篇
  2005年   10982篇
  2004年   10382篇
  2003年   10092篇
  2002年   10021篇
  2001年   10096篇
  2000年   9328篇
  1999年   10130篇
  1998年   26920篇
  1997年   18818篇
  1996年   14412篇
  1995年   10721篇
  1994年   9300篇
  1993年   9083篇
  1992年   6416篇
  1991年   6264篇
  1990年   5762篇
  1989年   5683篇
  1988年   5603篇
  1987年   4842篇
  1986年   4745篇
  1985年   5625篇
  1984年   5069篇
  1983年   4646篇
  1982年   4309篇
  1981年   4384篇
  1980年   4130篇
  1979年   3958篇
  1978年   3868篇
  1977年   4795篇
  1976年   6864篇
  1975年   3339篇
  1974年   3250篇
  1973年   3301篇
  1972年   2702篇
  1971年   2502篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Tian  J. Y.  Xu  G.  Hu  H. J.  Zhou  M. X. 《Strength of Materials》2019,51(3):439-449
Strength of Materials - A metallographic method, dilatometry, and X-ray diffraction were applied to investigate the effects of undercooling and holding time on bainitic transformation,...  相似文献   
92.
Wireless Personal Communications - Current mobile communications technology relies heavily on efficient design of antennas, where the operational characteristics of the wireless communication...  相似文献   
93.
In this work, the sintering behaviour of fluorapatite (FAp)–silicate composites prepared by mixing variable amounts of natural quartz (2.5 wt% to 20 wt%) and FAp was studied. The composites were pressureless sintered in air at temperatures from 1000 °C to 1350 °C. The effects of temperatures on the densification, phase formation, chemical bonding and Vickers hardness of the composites were evaluated. All the samples exhibited mixed phase, comprising FAp and francolite as the major constituents along with some minor phases of cristobalite, wollastonite, dicalcium silicate and/or whitlockite dependent on the quartz content and sintering temperature. The composite containing 2.5 wt% quartz exhibited the best sintering properties. The highest bulk density of 3 g/cm3 and a Vickers hardness of >4.2 GPa were obtained for the 2.5 wt% quartz–FAp composite when sintered at 1100 °C. The addition of quartz was found to alter the microstructure of the composites, where it exhibited a rod-like morphology when sintered at 1000 °C and a regular rounded grain structure when sintered at 1350 °C. A wetted grain surface was observed for composites containing high quartz content and was believed to be associated with a transient liquid phase sintering.  相似文献   
94.
95.
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   
96.
International Journal of Computer Vision - Anticipating future situations from streaming sensor data is a key perception challenge for mobile robotics and automated vehicles. We address the problem...  相似文献   
97.
Radiation therapy is a technology-driven cancer treatment modality that has experienced significant advances over the last decades, due to multidisciplinary contributions that include engineering and computing. Recent technological developments allow the use of noncoplanar volumetric modulated arc therapy (VMAT), one of the most recent photon treatment techniques, in clinical practice. In this work, an automated noncoplanar arc trajectory optimization framework designed in two modular phases is presented. First, a noncoplanar beam angle optimization algorithm is used to obtain a set of noncoplanar irradiation directions. Then, anchored in these directions, an optimization strategy is proposed to compute an optimal arc trajectory. The computational experiments considered a pool of twelve difficult head-and-neck tumor cases. It was possible to observe that, for some of these cases, the optimized noncoplanar arc trajectories led to significant treatment planning quality improvements, when compared with coplanar VMAT treatment plans. Although these experiments were done in a research environment treatment planning software (matRad), the conclusions can be of interest for a clinical setting: automated procedures can simplify the current treatment workflow, produce high-quality treatment plans, making better use of human resources and allowing for unbiased comparisons between different treatment techniques.  相似文献   
98.
Journal of Inorganic and Organometallic Polymers and Materials - This work aimed to investigate the impact of Lead-fluoride based glasses via theoretical and simulation techniques on mechanical and...  相似文献   
99.
100.
High Temperature - Experimental findings suggest that a strongly ionized, arc He plasma of atmospheric pressure does not exist in the state of the local thermodynamic equilibrium (LTE) expected for...  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