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   292831篇
  免费   24731篇
  国内免费   5465篇
电工技术   9496篇
技术理论   5篇
综合类   7714篇
化学工业   54538篇
金属工艺   15437篇
机械仪表   12860篇
建筑科学   12119篇
矿业工程   5010篇
能源动力   6096篇
轻工业   21739篇
水利工程   5078篇
石油天然气   13303篇
武器工业   920篇
无线电   32005篇
一般工业技术   58594篇
冶金工业   32574篇
原子能技术   8104篇
自动化技术   27435篇
  2022年   3609篇
  2021年   5823篇
  2020年   5692篇
  2019年   7096篇
  2018年   8578篇
  2017年   9443篇
  2016年   9809篇
  2015年   9494篇
  2014年   11747篇
  2013年   17092篇
  2012年   13506篇
  2011年   14777篇
  2010年   13334篇
  2009年   13402篇
  2008年   12868篇
  2007年   12045篇
  2006年   10797篇
  2005年   9333篇
  2004年   7785篇
  2003年   7405篇
  2002年   7284篇
  2001年   6660篇
  2000年   5402篇
  1999年   4876篇
  1998年   8227篇
  1997年   6163篇
  1996年   4676篇
  1995年   3791篇
  1994年   3295篇
  1993年   3230篇
  1992年   2642篇
  1991年   2653篇
  1990年   2640篇
  1989年   2493篇
  1988年   2451篇
  1987年   2262篇
  1986年   2313篇
  1985年   2333篇
  1984年   2227篇
  1983年   2150篇
  1981年   2206篇
  1980年   2091篇
  1979年   2270篇
  1978年   2433篇
  1977年   2431篇
  1976年   3088篇
  1975年   2243篇
  1974年   2302篇
  1973年   2337篇
  1972年   2155篇
排序方式: 共有10000条查询结果,搜索用时 38 毫秒
1.
Fiber production from inorganic industrial solid wastes is an effective waste management strategy. Because of cost considerations, most enterprises generally use local solid wastes as raw materials to produce fibers. In this study, we explored the feasibility of producing fibers using fly ash and magnesium slag. The results show that the melting temperature of the blends composed of fly ash, magnesium slag, and a small amount of calcined dolomite first decreased and then increased with an increase in acidity coefficient (Mk) from 1.0 to 2.4. The samples could form a eutectic system in the Mk range of 1.4–1.8, and therefore have a relatively low melting temperature in this Mk range. Fly ash could react with magnesium slag and calcined dolomite to form akermanite, gehlenite-magnesium, and anorthite at temperatures close to the melting temperature; therefore, these crystalline phases were the main reaction products formed in the samples with Mk values lower than 1.80. Anorthite reacted further with some Na-containing and Si-containing spieces to produce labradorite. Thus, the content of anorthite and labradorite rapidly increased and they became the major crystal phases in the blend samples with Mk values greater than 1.80. MAS-NMR spectroscopic analysis revealed that the network structure of the melts depended on the ratio of bridging oxygen to non-bridging oxygen; a high ratio of bridging oxygen to non-bridging oxygen could lead to the formation of a dense network structure in the melt. The blends of fly ash and magnesium slag can be used to produce wool fibers and continuous fibers. In addition, the suitable temperature ranges for the production of both types of fibers were determined. The drawing temperature for continuous fiber production depended on the degree of polymerization and structure of the melt.  相似文献   
2.
张梁  欧阳联格  刘金武  欧阳莎 《机械》2021,48(11):25-33
为了解决新型铰接式弯管的变形问题,利用ANSYS软件对铰接式弯管进行建模和流固耦合分析,发现原始弯管两侧中部内凹、弯径增大、最大应力超过许用应力,据此提出了导流器错位排布方案.结果 表明:采用方案三错位排布导流器方案、将导流器间距设为70 mm时得到最优方案,优化后的弯管4最大应力由178.12 MPa降低到92.4 MPa、降低了52%,弯管12最大应力由289.52 MPa降低到135.4 MPa、降低了47%,取得了较好的优化效果,为180°弯管导流器设计提供了一种新方案.  相似文献   
3.
Reconstruction of spectral information based on multi‐channel image system is a significant problem in color reproduction, detection, and recognition. A spectral radiance reconstruction from trichromatic digital camera responses is researched in this article. The mapping relationship between the trichromatic imaging system response and the incident spectral radiance is analyzed. Then, in order to remove the ill‐posedness of the problem, a regularized constraint solution model of spectral radiance reconstruction matrix is established. And the spectral radiance can be reconstructed by spectral radiance reconstruction matrices and trichromatic imaging system response. Finally, the spectral radiance reconstruction matrix is estimated by the system radiometric calibration experiment. The input radiance is offered by a LCD display. A 3‐factor and 9‐level orthogonal test is designed for the calibration experiment, and a test set of 24 colors is used for precision analysis. The results show that the average relative mean error of our method is 8.69%, it is lower than that of Wiener filtering method by 2.84%. The method can reconstruct spectral radiance information effectively.  相似文献   
4.
Atomic Energy - The physical aspects and main results of reactor tests of a two-stage core consisting of fresh fuel assemblies and a significant number of fuel assemblies from the previous core,...  相似文献   
5.
Journal of Communications Technology and Electronics - An option of multicriteria collision risk ranking of aircraft by data from an onboard radar station (OBRS) is proposed. This method can be...  相似文献   
6.
Protection of Metals and Physical Chemistry of Surfaces - Impedance spectroscopy was used to study the adsorption of the IFKhAN-92 inhibitor, a triazole derivative, on cathodically polarized...  相似文献   
7.
Combustion, Explosion, and Shock Waves - This paper touches upon the effect of a polyvinyl butyral content (0–2.3%) on the combustion of a Ti + C granular...  相似文献   
8.
以华能某2×1000 MW燃煤机组为例,对全厂原有工业废水处理系统进行升级改造,从而实现工业废水系统持续稳定运行.改造的重点在于脱水机的调试运行,实现脱水机在满足工业废水系统出力要求的基础上,连续稳定地产出合格的回用水和污泥.  相似文献   
9.
Chronic stress is a combination of nonspecific adaptive reactions of the body to the influence of various adverse stress factors which disrupt its homeostasis, and it is also a corresponding state of the organism’s nervous system (or the body in general). We hypothesized that chronic stress may be one of the causes occurence of several molecular and cellular types of stress. We analyzed literary sources and considered most of these types of stress in our review article. We examined genes and mutations of nuclear and mitochondrial genomes and also molecular variants which lead to various types of stress. The end result of chronic stress can be metabolic disturbance in humans and animals, leading to accumulation of reactive oxygen species (ROS), oxidative stress, energy deficiency in cells (due to a decrease in ATP synthesis) and mitochondrial dysfunction. These changes can last for the lifetime and lead to severe pathologies, including neurodegenerative diseases and atherosclerosis. The analysis of literature allowed us to conclude that under the influence of chronic stress, metabolism in the human body can be disrupted, mutations of the mitochondrial and nuclear genome and dysfunction of cells and their compartments can occur. As a result of these processes, oxidative, genotoxic, and cellular stress can occur. Therefore, chronic stress can be one of the causes forthe occurrence and development of neurodegenerative diseases and atherosclerosis. In particular, chronic stress can play a large role in the occurrence and development of oxidative, genotoxic, and cellular types of stress.  相似文献   
10.
For the purpose of developing biodegradable magnesium alloys with suitable properties for biomedical applications, Mg–Zn–Ca–Cu metallic glasses were prepared by copper mold injection methods. In the present work, the effect of Cu doping on mechanical properties, corrosion behavior, and glass-forming ability of Mg66Zn30Ca4 alloy was studied. The experimental findings demonstrated that the incorporation of Cu decreases the corrosion resistance of alloys, but increases the microhardness and degradation rate slightly. However, the addition of a trace amount of Cu can make the samples have antibacterial properties. Therefore, Mg–Zn–Ca–Cu has great advantages in clinical implantation and is the potential implant material.  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