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   82509篇
  免费   8822篇
  国内免费   5253篇
电工技术   6450篇
技术理论   4篇
综合类   6709篇
化学工业   12240篇
金属工艺   5332篇
机械仪表   5805篇
建筑科学   6380篇
矿业工程   2880篇
能源动力   2585篇
轻工业   6957篇
水利工程   2214篇
石油天然气   3761篇
武器工业   921篇
无线电   9150篇
一般工业技术   8547篇
冶金工业   3653篇
原子能技术   1618篇
自动化技术   11378篇
  2024年   394篇
  2023年   1361篇
  2022年   2803篇
  2021年   3812篇
  2020年   2767篇
  2019年   2248篇
  2018年   2524篇
  2017年   2644篇
  2016年   2457篇
  2015年   3610篇
  2014年   4556篇
  2013年   5224篇
  2012年   6316篇
  2011年   6653篇
  2010年   5992篇
  2009年   5735篇
  2008年   5497篇
  2007年   5292篇
  2006年   4888篇
  2005年   3944篇
  2004年   2939篇
  2003年   2461篇
  2002年   2548篇
  2001年   2255篇
  2000年   1714篇
  1999年   1372篇
  1998年   865篇
  1997年   666篇
  1996年   621篇
  1995年   548篇
  1994年   387篇
  1993年   334篇
  1992年   258篇
  1991年   189篇
  1990年   154篇
  1989年   101篇
  1988年   112篇
  1987年   54篇
  1986年   69篇
  1985年   30篇
  1984年   33篇
  1983年   16篇
  1982年   16篇
  1981年   23篇
  1980年   14篇
  1979年   19篇
  1977年   8篇
  1970年   7篇
  1959年   18篇
  1951年   9篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
In this study, 30 subjects were exposed to different combinations of air temperature (Ta: 24, 27, and 30°C) and CO2 level (8000, 10 000, and 12 000 ppm) in a high-humidity (RH: 85%) underground climate chamber. Subjective assessments, physiological responses, and cognitive performance were investigated. The results showed that as compared with exposure to Ta = 24°C, exposure to 30°C at all CO2 levels caused subjects to feel uncomfortably warm and experience stronger odor intensity, while increased mental effort and greater intensity of acute health symptoms were reported. However, no significant effects of Ta on task performance or physiological responses were found. This indicated that subjects had to exert more effort to maintain their performance in an uncomfortably warm environment. Increasing CO2 from 8000 to 12 000 ppm at all Ta caused subjects to report higher rates of headache, fatigue, agitation, and feeling depressed, although the results were statistically significant only at 24 and 27°C. The text typing performance and systolic blood pressure (SBP) decreased significantly at this exposure, whereas diastolic blood pressure (DBP) and thermal discomfort increased significantly. These effects suggest higher arousal/stress. No significant interaction effect of Ta and CO2 concentration on human responses was identified.  相似文献   
32.
33.
34.
Liu  Song  Cui  Yuan-Zhen  Zou  Nian-Jun  Zhu  Wen-Hao  Zhang  Dong  Wu  Wei-Guo 《计算机科学技术学报》2019,34(2):456-475
Journal of Computer Science and Technology - DOACROSS loops are significant parts in many important scientific and engineering applications, which are generally exploited pipeline/wave-front...  相似文献   
35.
Replacement of precious single metal catalysts with cost-effective, highly-dispersed composite catalysts for catalytic hydrothermal conversion of residue holds tremendous promise for the residue upgrading technologies. Organic metals were added to the feed as the oil-soluble precursors, and transformed into the catalytic active phases in this work. Physical properties and structures of the composite catalysts had been investigated by X-ray fluorescence spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscope and transmission electron microscopy. The composite catalysts were found to be highly efficient in the catalytic hydrothermal conversion of both model compound and residue. Increased metal dispersion and synergistic effects of two metals played indispensable roles in such catalytic system. Results showed that under the test conditions in the article, the catalyst had the best catalytic performance when the mass ratio of molybdenum to iron was 1.5.  相似文献   
36.
Neural Computing and Applications - Traffic identification is currently an important challenge for network management and security. In this paper, we propose a novel application identification...  相似文献   
37.
Basins with various mineral resources coexisting and enriching often occupy an important strategic position. The exploration of various mineral resources is repetitive at present due to unshared data and imperfect management mechanism. This situation greatly increases the cost of energy exploitation in the country. Traditional data-sharing mode has several disadvantages, such as high cost, difficulty in confirming the right of data, and lack of incentive mechanism, which make achieving real data sharing difficult. In this paper, we propose a data-sharing mechanism based on blockchain and provide implementation suggestions and technical key points. Compared with traditional data-sharing methods, the proposed data-sharing mechanism can realize data sharing, ensure data quality, and protect intellectual property. Moreover, key points in the construction are stated in the case study section to verify the feasibility of the data-sharing system based on blockchain proposed in this paper.  相似文献   
38.
Toxicity caused by the accumulation of butanol in fermentation media is an important factor limiting the concentration of butanol. There is currently no systematic research in place investigating the butanol tolerance mechanism of bacteria such as Clostridium acetobutylicum, which adapts to butanol stress and regulates its growth and metabolism. Here, research results related to the butanol tolerance of C. acetobutylicum are reviewed to understand the molecular basis of changes in butanol-tolerant strains. Organic solvent-tolerant bacteria play an important role in the fields of biofuel production, enzyme preparation and bioremediation. An analysis of limitations of the application of organic solvent-tolerant bacteria has revealed that future research should focus on combining the microbial tolerance phenotype with specific utilization to achieve an optimal balance between organic solvent tolerance and production. This review serves as a reference for the improvement and engineering of strains that tolerate organic solvents. © 2019 Society of Chemical Industry  相似文献   
39.
刘喜武  董宁  刘宇巍 《石油物探》2015,(2):210-217,225
由于尺度的限制,利用地震方法进行裂缝参数定量表征一直是地球科学的难题。基于裂缝性孔隙介质动态等效理论的频变AVAZ反演方法给出了研究思路。首先介绍了裂缝性孔隙介质的等效介质理论研究进展,分析比较了各种裂缝性储层岩石静态等效介质模型和动态等效介质模型;然后给出了基于Chapman模型的裂缝参数和渗透率定量表征的正问题数学模型以及反演问题求解的方法和策略,以及基于模型数据的数值计算结果;最后讨论了频变AVAZ反演方法目前存在的问题和进一步研究方向。  相似文献   
40.
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