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   1563655篇
  免费   27693篇
  国内免费   7057篇
电工技术   35265篇
综合类   6452篇
化学工业   276672篇
金属工艺   66081篇
机械仪表   45814篇
建筑科学   47788篇
矿业工程   11890篇
能源动力   50610篇
轻工业   119095篇
水利工程   15871篇
石油天然气   38367篇
武器工业   147篇
无线电   199894篇
一般工业技术   296166篇
冶金工业   179768篇
原子能技术   34677篇
自动化技术   173848篇
  2021年   15686篇
  2020年   11960篇
  2019年   14786篇
  2018年   18693篇
  2017年   18490篇
  2016年   22855篇
  2015年   17652篇
  2014年   28845篇
  2013年   88388篇
  2012年   37682篇
  2011年   52540篇
  2010年   45763篇
  2009年   53703篇
  2008年   48362篇
  2007年   46166篇
  2006年   46273篇
  2005年   42057篇
  2004年   43310篇
  2003年   42974篇
  2002年   41750篇
  2001年   38107篇
  2000年   36433篇
  1999年   35554篇
  1998年   49300篇
  1997年   42058篇
  1996年   37123篇
  1995年   31858篇
  1994年   29667篇
  1993年   29495篇
  1992年   26531篇
  1991年   23657篇
  1990年   24017篇
  1989年   23101篇
  1988年   21611篇
  1987年   19869篇
  1986年   19210篇
  1985年   22592篇
  1984年   22578篇
  1983年   20551篇
  1982年   19453篇
  1981年   19517篇
  1980年   18152篇
  1979年   18679篇
  1978年   17890篇
  1977年   17846篇
  1976年   19009篇
  1975年   16133篇
  1974年   15611篇
  1973年   15723篇
  1972年   13179篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
111.
Ferroptosis is gaining followers as mechanism of selective killing cancer cells in a non-apoptotic manner, and novel nanosystems capable of inducing this iron-dependent death are being increasingly developed. Among them, polydopamine nanoparticles (PDA NPs) are arousing interest, since they have great capability of chelating iron. In this work, PDA NPs were loaded with Fe3+ at different pH values to assess the importance that the pH may have in determining their therapeutic activity and selectivity. In addition, doxorubicin was also loaded to the nanoparticles to achieve a synergist effect. The in vitro assays that were performed with the BT474 and HS5 cell lines showed that, when Fe3+ was adsorbed in PDA NPs at pH values close to which Fe(OH)3 begins to be formed, these nanoparticles had greater antitumor activity and selectivity despite having chelated a smaller amount of Fe3+. Otherwise, it was demonstrated that Fe3+ could be released in the late endo/lysosomes thanks to their acidic pH and their Ca2+ content, and that when Fe3+ was co-transported with doxorubicin, the therapeutic activity of PDA NPs was enhanced. Thus, reported PDA NPs loaded with both Fe3+ and doxorubicin may constitute a good approach to target breast tumors.  相似文献   
112.
At present, the development and implementation of digital transformation are the keys to promoting high-quality industry development. The new digital fabrication method of robotic 3D printing is a research area being studied by many to tackle the issue of the declining productivity of traditional construction methods. Although many studies have been done, most of the current 3D printing projects are facing limitations in terms of scale. In order to bridge the gap, this article proposed a mass customization 3D printing framework system for large-scale projects. This article discusses how mass customization is made possible through the joint operation of the FUROBOT software and 3D printing hardware. By taking the east gate of Nanjing Happy Valley Plaza as a case study, the article demonstrates and studies the feasibility of the large-scale mass customization 3D printing framework system.  相似文献   
113.
Cybernetics and Systems Analysis - The authors propose a method for solving the problem of approach of controlled objects in dynamic game problems with a terminal payoff function. The method is...  相似文献   
114.
Journal of Computer and Systems Sciences International - The solution of the problem of determining the trajectory control of the observation process of a mobile digital direction finder in the...  相似文献   
115.
Vieira  Elizabeth S. 《Scientometrics》2022,127(5):2747-2772

It is widely recognised that science in Africa will benefit from international research collaboration (IRC), and therefore studies have been done on IRC in Africa (hereafter: Africa-related IRC research). However, there is no information on the development of Africa-related IRC research, the geographical location of the scientists interested in the topic, the visibility of the literature and the themes researched. This information makes it possible to understand relevant aspects in the context of IRC in Africa, which are useful for identifying IRC strengths, weaknesses and opportunities. It also allows paving the way for future research on this topic. Using discipline–specific terms, bibliometric, and thematic analysis, I collected the literature on Africa-related IRC research indexed in the Web of Science Core Collection (WoS). The results showed that the number of publications on the topic has increased, few African countries have researched the topic, a third of the publications were written exclusively by African scientists, and the topic has high visibility. The panoply of publications revealed that patterns, driving factors, effects, networks, asymmetries, and policies concerning IRC were the main themes researched.

  相似文献   
116.
Marrone  Mauricio  Lemke  Sascha  Kolbe  Lutz M. 《Scientometrics》2022,127(7):3857-3878
Scientometrics - Computer-assisted methods and tools can help researchers automate the coding process of literature reviews and accelerate the literature review process. However, existing...  相似文献   
117.

Probabilistic topic modeling algorithms like Latent Dirichlet Allocation (LDA) have become powerful tools for the analysis of large collections of documents (such as papers, projects, or funding applications) in science, technology an innovation (STI) policy design and monitoring. However, selecting an appropriate and stable topic model for a specific application (by adjusting the hyperparameters of the algorithm) is not a trivial problem. Common validation metrics like coherence or perplexity, which are focused on the quality of topics, are not a good fit in applications where the quality of the document similarity relations inferred from the topic model is especially relevant. Relying on graph analysis techniques, the aim of our work is to state a new methodology for the selection of hyperparameters which is specifically oriented to optimize the similarity metrics emanating from the topic model. In order to do this, we propose two graph metrics: the first measures the variability of the similarity graphs that result from different runs of the algorithm for a fixed value of the hyperparameters, while the second metric measures the alignment between the graph derived from the LDA model and another obtained using metadata available for the corresponding corpus. Through experiments on various corpora related to STI, it is shown that the proposed metrics provide relevant indicators to select the number of topics and build persistent topic models that are consistent with the metadata. Their use, which can be extended to other topic models beyond LDA, could facilitate the systematic adoption of this kind of techniques in STI policy analysis and design.

  相似文献   
118.
Chemical and Petroleum Engineering - The hydrodynamics of oxidation towers used for bitumen production were studied using a model tower having transparent walls. Experiments were carried out in two...  相似文献   
119.
Journal of Engineering Physics and Thermophysics - A numerical investigation has been made into the interaction of slender (5–20 calibers) steel cylinder strikers with orthotropic compost...  相似文献   
120.
Journal of Engineering Physics and Thermophysics - Results of investigation into the influence of a corrosion process on thermotechnical characteristics of heat pipes of low-temperature range are...  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