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   459614篇
  免费   4468篇
  国内免费   882篇
电工技术   7798篇
综合类   310篇
化学工业   69203篇
金属工艺   25880篇
机械仪表   17285篇
建筑科学   9445篇
矿业工程   4965篇
能源动力   8984篇
轻工业   26416篇
水利工程   6518篇
石油天然气   15544篇
武器工业   33篇
无线电   44537篇
一般工业技术   105729篇
冶金工业   68461篇
原子能技术   14497篇
自动化技术   39359篇
  2021年   3989篇
  2019年   3936篇
  2018年   12408篇
  2017年   12824篇
  2016年   11232篇
  2015年   4801篇
  2014年   7800篇
  2013年   17824篇
  2012年   13003篇
  2011年   19730篇
  2010年   16760篇
  2009年   17208篇
  2008年   17635篇
  2007年   18670篇
  2006年   11105篇
  2005年   11932篇
  2004年   10981篇
  2003年   10709篇
  2002年   9508篇
  2001年   8983篇
  2000年   8957篇
  1999年   8468篇
  1998年   17680篇
  1997年   13233篇
  1996年   10266篇
  1995年   7887篇
  1994年   7292篇
  1993年   7266篇
  1992年   5972篇
  1991年   5971篇
  1990年   5844篇
  1989年   5802篇
  1988年   5593篇
  1987年   5228篇
  1986年   4976篇
  1985年   5534篇
  1984年   5285篇
  1983年   5014篇
  1982年   4632篇
  1981年   4796篇
  1980年   4669篇
  1979年   4895篇
  1978年   5075篇
  1977年   5343篇
  1976年   6559篇
  1975年   4578篇
  1974年   4558篇
  1973年   4641篇
  1972年   4015篇
  1971年   3718篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
Csáji  Balázs Cs.  Kis  Krisztián B. 《Machine Learning》2019,108(8-9):1677-1699
Machine Learning - We propose a data-driven approach to quantify the uncertainty of models constructed by kernel methods. Our approach minimizes the needed distributional assumptions, hence,...  相似文献   
152.
Russian Engineering Research - Thin-film vacuum technology permits the creation of new electrode materials on the basis of a flexible carbon matrix with a highly developed surface. Supercapacitor...  相似文献   
153.
Refractories and Industrial Ceramics - The effect of the addition of 2 and 5 mol.% Dy2O3 during spark-plasma sintering at a compaction loading of 60 MPa in the range of 1200 – 1600°C on...  相似文献   
154.
Refractories and Industrial Ceramics - Results of studying the rheotechnological properties of moldable refractory mixes based on bauxite suspensions plasticized with refractory clay are presented....  相似文献   
155.
The influence of phase composition and microstructure of Ti42.75Zr27Mn20.25V10 alloy on its hydrogenation kinetic and phase composition of hydrogenated product was studied. It is established that the process of dissociation of hydrogen molecules begins on the surface of Laves phase crystallites. The dissolution of atomic hydrogen in the material volume leads to the formation of cracks in the intermetallic crystallites, which further appear as additional centers of dissociation of hydrogen molecules and noticeably accelerate the diffusion of hydrogen into the bulk material. It was shown that the Laves phase acts as a donor of atomic hydrogen for the BCC solid solution during hydrogenation of two-phase structure, initiating intensive hydrogenation of the BCC phase at room temperature.  相似文献   
156.
With superior properties of Mg such as high hydrogen storage capacity (7.6 wt% H/MgH2), low price, and low density, Mg has been widely studied as a promising candidate for solid-state hydrogen storage systems. However, a harsh activation procedure, slow hydrogenation/dehydrogenation process, and a high temperature for dehydrogenation prevent the use of Mg-based metal hydrides for practical applications. For these reasons, Mg-based alloys for hydrogen storage systems are generally alloyed with other elements to improve hydrogen sorption properties. In this article, we have added Na to cast Mg–La alloys and achieved a significant improvement in hydrogen absorption kinetics during the first activation cycle. The role of Na in Mg–La has been discussed based on the findings from microstructural observations, crystallography, and first principles calculations based on density functional theory. From our results in this study, we have found that the Na doped surface of Mg–La alloy systems have a lower adsorption energy for H2 compared to Na-free surfaces which facilitates adsorption and dissociation of hydrogen molecules leading to improvement of absorption kinetic. The effect of Na on the microstructure of these alloys, such as eutectic refinement and a density of twins is not highly correlated with absorption kinetics.  相似文献   
157.
Power Technology and Engineering - The major results from the survey and geotechnical monitoring during the leveling of the model foundation of the Zagorsk PSP-2 in test site No. 3 are presented....  相似文献   
158.
Russian Engineering Research - The machining precision in grinding a flexible shaft by sharp and blunt wheels is compared for a CNC system with a specified cycle of radial supply velocities. To...  相似文献   
159.
The demand for food production has been constantly increasing due to rising population. In developed countries, for example, the emergence of regional production of old grains that are rarely utilized, along with the production of commonly consumed grains, has gained importance in recent years. These grains, known collectively as ancient or heirloom grains, have offered both farmers and consumers novel ways of cultivation and products with interesting taste, characteristics and nutritional value. Among the 30 000 plant species known, only five cereals currently provide more than 50% of the world's energy intake – bread wheat (Triticum aestivum), rice (Oryza sativa), sorghum (Sorghum bicolor), millets (Panicum sp.) and maize (Zea mays). The excessive utilization of these selected species has a great potential to cause genetic losses and difficulty in bridging future agricultural demands. Teff (Eragrostis tef), an ancient grain extensively cultivated in countries like Eritrea and Ethiopia, provides promising alternatives for new food uses since its nutritional value is significantly higher than most others cereal grains. The absence of gluten allows flexibility in food utilization since it can be directly substituted to gluten-containing products. The grain also offers an excellent balance of essential amino acids and minerals, which can fulfil the recommended daily intake and eliminates the need for fortification and enrichment. This review provides a general overview of the physical properties and nutritional composition of teff grains related to processing and applications in the food and feed industries. The current status of teff utilization, as well as the challenges in production and commercialization, and future opportunities is presented and discussed.  相似文献   
160.
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   
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