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   150399篇
  免费   20852篇
  国内免费   15945篇
电工技术   13345篇
技术理论   8篇
综合类   20170篇
化学工业   12543篇
金属工艺   4738篇
机械仪表   10589篇
建筑科学   14337篇
矿业工程   4713篇
能源动力   6798篇
轻工业   4575篇
水利工程   8876篇
石油天然气   7559篇
武器工业   2224篇
无线电   13243篇
一般工业技术   14521篇
冶金工业   5082篇
原子能技术   1453篇
自动化技术   42422篇
  2024年   852篇
  2023年   2373篇
  2022年   4436篇
  2021年   5059篇
  2020年   5638篇
  2019年   4953篇
  2018年   4777篇
  2017年   5866篇
  2016年   6734篇
  2015年   6861篇
  2014年   9098篇
  2013年   10127篇
  2012年   11045篇
  2011年   11675篇
  2010年   9224篇
  2009年   9588篇
  2008年   9682篇
  2007年   10960篇
  2006年   9456篇
  2005年   8341篇
  2004年   6734篇
  2003年   5878篇
  2002年   4664篇
  2001年   3987篇
  2000年   3517篇
  1999年   2702篇
  1998年   2270篇
  1997年   1933篇
  1996年   1749篇
  1995年   1512篇
  1994年   1232篇
  1993年   886篇
  1992年   761篇
  1991年   588篇
  1990年   477篇
  1989年   378篇
  1988年   236篇
  1987年   145篇
  1986年   126篇
  1985年   116篇
  1984年   124篇
  1983年   57篇
  1982年   84篇
  1981年   46篇
  1980年   65篇
  1979年   59篇
  1978年   27篇
  1977年   16篇
  1959年   18篇
  1951年   14篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
M-learning is characterized as a powerful element of learning and education for facilitating the learning experiences. With enhanced and rapid advancements in technologies of ICTs (Information and Communication Technologies) and mobile, numerous innovative services and applications are being developed. Therefore, it becomes significant to investigate the factors influencing the intentions of m-learning to be used among the students of higher education institution. This study examines the “Technology Acceptance Model” (TAM), “Theory of Reasoned Action” (TRA) and “Unified Theory of Acceptance and Use of Technology” (UTAUT). The study is based on a survey being conducted across diverse groups of students, belonging to different communities and universities. The survey questionnaire was utilized for collecting the relevant data from 250 respondents. The results analyzed yields the impact that the proposed model of m-learning is comprehensive to study in the institutions of higher education.  相似文献   
22.
An engineered variant of the yeast Pichia pastoris was used to produce the potential malaria vaccine D1M1. This paper describes the implementation of an expanded bed adsorption chromatography step into a sequential cultivation process of the yeast in order to link protein expression, cell release, and product capture of the secreted protein in a fully automated plant. The process is operated with a semi-continuous strategy for an integrated production. Process improvements have been achieved using design of experiments. Resulting purities of product achieved up to 87% with recoveries of 51% in a single downstream operation. Furthermore, a multivariate analysis of historical batch data was used to develop a golden batch model for process monitoring.  相似文献   
23.
24.
The eutectic 80Au/20Sn solder alloy is widely used in high power electronics and optoelectronics packaging. In this study, low cycle fatigue behavior of a eutectic 80Au/20Sn solder alloy is reported. The 80Au/20Sn solder shows a quasi-static fracture characteristic at high strain rates, and then gradually transforms from a transgranular fracture (dominated by fatigue damage) to intergranular fracture (dominated by creep damage) at low strain rates with increasing temperature. Coffin-Manson and Morrow models are proposed to evaluate the low cycle fatigue behavior of the 80Au/20Sn solder. Besides, the 80Au/20Sn solder has enhanced fatigue resistance compared to the 63Sn/37Pb solder.  相似文献   
25.
To improve the electrochemical properties of rare-earth–Mg–Ni-based hydrogen storage alloys, the effects of stoichiometry and Cu-substitution on the phase structure and thermodynamic properties of the ...  相似文献   
26.
A double optimal projection method that involves projections for intra-cluster and inter-cluster dimensionality reduction are proposed for video fingerprinting. The video is initially set as a graph with frames as its vertices in a high-dimensional space. A similarity measure that can compute the weights of the edges is then proposed. Subsequently, the video frames are partitioned into different clusters based on the graph model. Double optimal projection is used to explore the optimal mapping points in a low-dimensional space to reduce the video dimensions. The statistics and geometrical fingerprints are generated to determine whether a query video is copied from one of the videos in the database. During matching, the video can be roughly matched by utilizing the statistics fingerprint. Further matching is thereafter performed in the corresponding group using geometrical fingerprints. Experimental results show the good performance of the proposed video fingerprinting method in robustness and discrimination.  相似文献   
27.
This paper introduces two novel nonlinear stochastic attitude estimators developed on the Special Orthogonal Group with the tracking error of the normalized Euclidean distance meeting predefined transient and steady‐state characteristics. The tracking error is confined to initially start within a predetermined large set such that the transient performance is guaranteed to obey dynamically reducing boundaries and decrease smoothly and asymptotically to the origin in probability from almost any initial condition. The proposed estimators produce accurate attitude estimates with remarkable convergence properties using measurements obtained from low‐cost inertial measurement units. The estimators proposed in continuous form are complemented by their discrete versions for the implementation purposes. The simulation results illustrate the effectiveness and robustness of the proposed estimators against uncertain measurements and large initialization error, whether in continuous or discrete form.  相似文献   
28.
This study addresses the problem of choosing the most suitable probabilistic model selection criterion for unsupervised learning of visual context of a dynamic scene using mixture models. A rectified Bayesian Information Criterion (BICr) and a Completed Likelihood Akaike’s Information Criterion (CL-AIC) are formulated to estimate the optimal model order (complexity) for a given visual scene. Both criteria are designed to overcome poor model selection by existing popular criteria when the data sample size varies from small to large and the true mixture distribution kernel functions differ from the assumed ones. Extensive experiments on learning visual context for dynamic scene modelling are carried out to demonstrate the effectiveness of BICr and CL-AIC, compared to that of existing popular model selection criteria including BIC, AIC and Integrated Completed Likelihood (ICL). Our study suggests that for learning visual context using a mixture model, BICr is the most appropriate criterion given sparse data, while CL-AIC should be chosen given moderate or large data sample sizes.  相似文献   
29.
提出了对暴露在任意外场中的传输线进行时频分析的新方法,这种方法非常稳定,它能够与任意的传输线模型和电路仿真方法兼容,并且使用这种方法得到的仿真值和实际值之间的差别小于1%。  相似文献   
30.
Reports an error in "Tradeoffs and Theory: The Double-Mediation Model" by Marc Scholten and Steven J. Sherman (Journal of Experimental Psychology: General, 2006 May, Vol 135[2], 237-261). This article was inadvertently printed with the incorrect title. The original title was "Tradeoffs and Conflict: The Double-Mediation Model." This title highlights the relation between tradeoffs and conflict as investigated by the authors and accounted for by their model. However, readers are asked to refer to the article by the title with which it was printed to facilitate its retrieval.. (The following abstract of the original article appeared in record 2006-06642-006.) Most theories of decision making suggest that, when options imply tradeoffs between their attributes, conflict increases as tradeoff size increases, because greater sacrifices are to be incurred in choosing one option instead of another. An alternative view is that conflict decreases as tradeoff size increases, because stronger arguments can be made for any decision. The authors propose a unified model, the double-mediation model, which combines the mediating effects of sacrifice and argumentation. Our model generally predicts an inverse U-shaped relation between tradeoff size and conflict. Results support this prediction. Also, when the decision situation increases the mediating effect of sacrifice relative to that of argumentation, the relation between tradeoff size and conflict changes in an upward direction; conversely, when the decision situation increases the mediating effect of argumentation relative to that of sacrifice, the relation changes in a downward direction. Results support these predictions as well. Commonalities and differences between our model and other formulations are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  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