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   238497篇
  免费   28890篇
  国内免费   7744篇
电工技术   11964篇
技术理论   14篇
综合类   11202篇
化学工业   50949篇
金属工艺   10788篇
机械仪表   12717篇
建筑科学   17964篇
矿业工程   4889篇
能源动力   6666篇
轻工业   19356篇
水利工程   3475篇
石油天然气   10969篇
武器工业   1348篇
无线电   31565篇
一般工业技术   36527篇
冶金工业   11426篇
原子能技术   2157篇
自动化技术   31155篇
  2024年   671篇
  2023年   3080篇
  2022年   5343篇
  2021年   7988篇
  2020年   6914篇
  2019年   7610篇
  2018年   8048篇
  2017年   9129篇
  2016年   9095篇
  2015年   10812篇
  2014年   12982篇
  2013年   16677篇
  2012年   14707篇
  2011年   16080篇
  2010年   14064篇
  2009年   13822篇
  2008年   12851篇
  2007年   12278篇
  2006年   12434篇
  2005年   10931篇
  2004年   7839篇
  2003年   7030篇
  2002年   6465篇
  2001年   5781篇
  2000年   5917篇
  1999年   6089篇
  1998年   5384篇
  1997年   4431篇
  1996年   3989篇
  1995年   3343篇
  1994年   2801篇
  1993年   2218篇
  1992年   1721篇
  1991年   1301篇
  1990年   1046篇
  1989年   893篇
  1988年   705篇
  1987年   510篇
  1986年   393篇
  1985年   344篇
  1984年   207篇
  1983年   195篇
  1982年   159篇
  1981年   151篇
  1980年   135篇
  1979年   102篇
  1978年   64篇
  1977年   68篇
  1976年   88篇
  1975年   44篇
排序方式: 共有10000条查询结果,搜索用时 421 毫秒
171.
With excellent specific capacity, superior cycle stability, safety and strong practical, Nb2O5 has been considered as one of the prospective anode materials for lithium-ion batteries (LIBs). However, current study suggests that Nb2O5 electrode materials for LIBs still face the vital issues of low electrical conductivity and poor rate performance. Therefore, carbon-coated TT-Nb2O5 materials are designed and synthesized through solid state method in this work, which present high specific capacity (228 mA h g?1 at 0.2C), satisfactory rate properties (107 mA h g?1 at 20 C). The outstanding electrochemical property can not only give the credit to the pseudocapacitance effect of TT-Nb2O5, but also attribute to introduction of carbon. The homogeneous carbon-coated materials enhance the electrical conductivity, increase the electron transmission speed and alleviate particle crushing. This research not only offers a new method for preparing excellent electrode materials, but also provides a kind of excellent anode material with prospective application for LIBs.  相似文献   
172.
As haze intensifies in China, controlling haze emission has become the country's top priority for environmental protection. Because haze moves across different regions, it is necessary to develop a data envelopment analysis (DEA) model underpinned by both competition and cooperation to evaluate the haze emission efficiency in different provinces. This study innovatively adopts the spatial econometrics to construct the co-opetition matrices of Chinese provinces, then builds the co-opetition DEA model to evaluate the haze emission efficiency of them, and finally uses the haze data of 2015 as an example to assess the applicability of the model. The results of the study include the following: First, compared with the traditional CCR (A. Charnes & W. W. Cooper & E. Rhodes) model, this study constructs the co-opetition DEA cross-efficiency model that integrates haze's feature of cross-border moving; thus, it is more in line with the reality of haze emission and movement. Second, compared with the efficiency value gained from the CCR model, the haze emission efficiency values for Tianjin and Guangdong, two decision-making units, register greater variance when using the DEA model. The reason might lie in that they have a different spatial transportation relationship with their surrounding provinces. Third, the haze emission efficiency of provinces, according to the evaluation based on the co-opetition DEA method, varies greatly: Those with high efficiency are mostly inland provinces with slow economic growth and adverse climatic conditions, whereas many of the provinces with low efficiency are located in the relatively prosperous East China. The specific co-opetition DEA model constructed in this study enriches the research on the DEA model, which can be applied to the emission efficiency evaluation of similar pollutants around the world and can contribute empirical support to the haze reducing efforts of the government with its empirical results.  相似文献   
173.
Lipoxins (LXs) are autacoids, specialized proresolving lipid mediators (SPMs) acting locally in a paracrine or autocrine fashion. They belong to a complex superfamily of dietary small polyunsaturated fatty acid (PUFA)–metabolites, which direct potent cellular responses to resolve inflammation and restore tissue homeostasis. Together, these SPM activities have been intensely studied in systemic inflammation and acute injury or infection, but less is known about LX signaling and activities in the central nervous system. LXs are derived from arachidonic acid, an omega‐6 PUFA. In addition to well‐established roles in systemic inflammation resolution, they have increasingly become implicated in regulating neuroinflammatory and neurodegenerative processes. In particular, chronic inflammation plays a central role in Alzheimer's disease (AD) etiology, and dysregulated LX production and activities have been reported in a variety of AD rodent models and clinical tissue samples, yet with complex and sometimes conflicting results. In addition, reduced LX production following retinal injury has been reported recently by the authors, and an intriguing direct neuronal activity promoting survival and homeostasis in retinal and cortical neurons is demonstrated. Here, the authors review and clarify this growing literature and suggest new research directions to further elaborate the role of lipoxins in neurodegeneration.  相似文献   
174.
175.
176.
177.
178.
179.
The knowledge of turbo code's minimum Hamming distance (dmin) and its corresponding codeword multiplicity (Amin) is of a great importance because the error correction capability of a code is strongly tied to the values of dmin and Amin. Unfortunately, the computational complexity associated with the search for dmin and Amin can be very high, especially for a turbo code that has high dmin value. This paper introduces some useful properties of turbo codes that use structured interleavers together with circular encoding. These properties allow for a significant reduction of search space and thus reduce significantly the computational complexity associated with the determination of dmin and Amin values. © 2014 The Authors. International Journal of Communication Systems published by John Wiley & Sons, Ltd.  相似文献   
180.
In order to predict the wearing of stellite alloys,the related methods of rare metals data processing were discussed. The method of opposite degree(OD) algorithm was put forward to predict the wearing of stellite alloys.OD algorithm is based on prior numerical data, posterior numerical data and the opposite degree between numerical forecast data. To compare the performance of predicted results based on different algorithms, the back propagation(BP) and radial basis function(RBF) neural network methods were introduced. Predicted results show that the relative error of OD algorithm is smaller than those of BP and RBF neural network methods. OD algorithm is an effective method to predict the wearing of stellite alloys and it can be applied in practice.  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