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   335165篇
  免费   3779篇
  国内免费   1023篇
电工技术   5586篇
综合类   2472篇
化学工业   46263篇
金属工艺   17609篇
机械仪表   14040篇
建筑科学   7920篇
矿业工程   2485篇
能源动力   6769篇
轻工业   21109篇
水利工程   4182篇
石油天然气   5673篇
武器工业   8篇
无线电   36928篇
一般工业技术   70304篇
冶金工业   45023篇
原子能技术   6245篇
自动化技术   47351篇
  2021年   1681篇
  2019年   1631篇
  2018年   22162篇
  2017年   21773篇
  2016年   15255篇
  2015年   2829篇
  2014年   3436篇
  2013年   9375篇
  2012年   9973篇
  2011年   22128篇
  2010年   19338篇
  2009年   17111篇
  2008年   17765篇
  2007年   20362篇
  2006年   5897篇
  2005年   9591篇
  2004年   7753篇
  2003年   7388篇
  2002年   5659篇
  2001年   4875篇
  2000年   4890篇
  1999年   4840篇
  1998年   11479篇
  1997年   8205篇
  1996年   6503篇
  1995年   4744篇
  1994年   4363篇
  1993年   4163篇
  1992年   3294篇
  1991年   3149篇
  1990年   2909篇
  1989年   2996篇
  1988年   2868篇
  1987年   2433篇
  1986年   2343篇
  1985年   2754篇
  1984年   2532篇
  1983年   2371篇
  1982年   2110篇
  1981年   2226篇
  1980年   2041篇
  1979年   2149篇
  1978年   2132篇
  1977年   2376篇
  1976年   3193篇
  1975年   1840篇
  1974年   1765篇
  1973年   1773篇
  1972年   1449篇
  1971年   1344篇
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
101.
X-ray diffraction analysis has been used to study the structure of the α-Zr matrix phase and the precipitation of β-Nb particles upon the annealing of a Zr–2.5% Nb deformed alloy. It has been found that the process of the precipitation of the strengthening β-Nb particles in the alloy is accompanied by the appearance of fields of elastic interphase deformations in the matrix α phase of the alloy due to the difference in the specific atomic volumes of the crystal structures of the matrix and precipitated phases. It has been shown experimentally that, as a result of the presence of interphase deformations in the alloy, the bcc crystal structure of the precipitating β-Nb particles undergoes monoclinic distortions.  相似文献   
102.
103.
The cracks in the workpiece specimens can reduce the fatigue life of any machine components. Since the residual stress has a considerable amount of influence on determining crack formation over the machined surface, it is very essential to analyze the residual stress developed in any machining process. However, it is a very tedious process to compute the residual stress over the machined surface. In the present study, an endeavor has been made to measure and analyze the residual stress of machined silicon steel as a workpiece using the EDM process with different energy distribution. The nano-indentation method was used to compute the residual stress produced over the machined surface. From the experimental results, it was found that the uniform energy distribution has produced higher compressive residual stress owing to the tiny and uniform spark energy distribution. It has also been observed that the tool electrode has a considerable amount of influence on determining development of residual stress in the EDM process.  相似文献   
104.
105.
Russian Engineering Research - The theoretically possible reconfigurable parallel mechanisms are classified, in terms of the layout of guides on the base. Formulas are derived for the...  相似文献   
106.
107.
We show that in the presence of magnetic field, two superconducting phases with the center-of-mass momentum of Cooper pair parallel to the magnetic field are induced in Dresselhaus spin–orbit-coupled superconductor. Specifically, at small magnetic field, the center-of-mass momentum is induced due to the energy-spectrum distortion and no unpairing region with vanishing singlet correlation appears. We refer to this superconducting state as the drift-BCS state. By further increasing the magnetic field, the superconducting state falls into the Fulde–Ferrell state with the emergence of the unpairing regions. The observed abrupt enhancement of the center-of-mass momenta and suppression on the order parameters during the transition indicate the occurrence of a first-order phase transition. Enhanced Pauli limit and hence enlarged magnetic-field regime of the Fulde–Ferrell state, due to the spin-flip terms of the spin–orbit coupling, are revealed. We also address the triplet correlations induced by the spin–orbit coupling, and show that the Cooper-pair spin polarizations, generated by the magnetic field and center-of-mass momentum with the triplet correlations exhibit totally different magnetic-field dependences between the drift-BCS and Fulde–Ferrell states.  相似文献   
108.
Understanding semantic word shifts in scientific domains is essential for facilitating interdisciplinary communication. Using a data set of published papers in the field of information retrieval (IR), this paper studies the semantic shifts of words in IR based on mining per-word topic distribution over time. We propose that semantic word shifts not only occur over time, but also over topics. The shifts are examined from two perspectives, the topic-level and the context-level. According to the over-time word-topic distribution, stable words and unstable words are recognized. The diverging and converging trends in the unstable type reveal characteristics of the topic evolution process. The context-level shifts are further detected by similarities between word vectors. Our work associates semantic word shifts with the evolving of topics, which facilitates a better understanding of semantic word shifts from both topics and contexts.  相似文献   
109.
Research funding has been seen as one of the most important resource in the reward system of science. And usage of publications denotes an interesting perspective of user behavior in scientific communication. This study aims to address the relationship between funding and Usage Count, which is a new metrics item established on the platform of Web of Science. Full records of 300,010 articles published in 2013 were downloaded in October 2015, and divided into six disciplines, including information science library science, education educational research, economics, computer science, materials science, and chemistry. Seven indicators were proposed to measure the impact, including Funding rate, Citation per paper, Usage rate, Usage per paper, Citation difference, Usage difference, and Conversion rate. It concluded funding has impact on usage and citation, and funded papers attract more usage, but varying in different disciplines. Usage Count can be used in the extension of citation metrics but with limits. This study originally engages with usage metrics and detected that there is positive correlation between usage and funding.  相似文献   
110.
Lameness is one of the most prevalent diseases affecting the welfare of cows in modern dairy production. Lameness leads to behavioral changes in severely lame cows, which have been investigated in much detail. For early detection of lameness, knowledge of the effects of moderate lameness on cow behavior is crucial. Therefore, the behavior of nonlame and moderately lame cows was compared on 17 Swiss dairy farms. On each farm, 5 to 11 nonlame (locomotion score 1 of 5) and 2 to 7 moderately lame (locomotion score 3 of 5) cows were selected for data collection in two 48-h periods (A, B) separated by an interval of 6 to 10 wk. Based on visual locomotion scoring, 142 nonlame and 66 moderately lame cows were examined in period A and 128 nonlame and 53 moderately lame cows in period B. Between these 2 periods, the cows underwent corrective hoof trimming. Lying behavior, locomotor activity, and neck activity were recorded by accelerometers (MSR145 data logger, MSR Electronics GmbH, Seuzach, Switzerland), and feeding and rumination behaviors by noseband sensors (RumiWatch halter, ITIN + HOCH GmbH, Liestal, Switzerland). Furthermore, visits to the brush and the concentrate feeder, and the milking order position were recorded. In comparison with nonlame cows, moderately lame cows had a longer lying duration, a longer average lying bout duration, and a greater lateral asymmetry in lying duration. Average locomotor activity, locomotor activity during 1 h after feed delivery or push-ups, and average neck activity were lower in moderately lame cows. Eating time and the number of eating chews (jaw movements) were reduced in moderately lame compared with nonlame cows, whereas no effect of moderate lameness was evident for ruminating time, number of ruminating chews and boluses, and average number of ruminating chews per bolus. Moderately lame cows visited the concentrate feeder and the brush less frequently, and they were further back in the milking order compared with nonlame cows. In conclusion, nonlame and moderately lame cows differed in a biologically relevant way in many of the behavioral variables investigated in this study. Therefore, the use of these behavioral changes seems to be promising to develop a tool for early lameness detection.  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