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   849篇
  免费   78篇
电工技术   1篇
综合类   1篇
化学工业   301篇
金属工艺   15篇
机械仪表   14篇
建筑科学   25篇
矿业工程   3篇
能源动力   20篇
轻工业   205篇
水利工程   7篇
石油天然气   1篇
无线电   48篇
一般工业技术   79篇
冶金工业   123篇
原子能技术   3篇
自动化技术   81篇
  2024年   3篇
  2023年   18篇
  2022年   68篇
  2021年   62篇
  2020年   40篇
  2019年   40篇
  2018年   26篇
  2017年   45篇
  2016年   45篇
  2015年   35篇
  2014年   29篇
  2013年   65篇
  2012年   51篇
  2011年   53篇
  2010年   38篇
  2009年   35篇
  2008年   27篇
  2007年   36篇
  2006年   24篇
  2005年   28篇
  2004年   22篇
  2003年   16篇
  2002年   14篇
  2001年   15篇
  2000年   10篇
  1999年   9篇
  1998年   5篇
  1997年   6篇
  1996年   9篇
  1995年   9篇
  1994年   5篇
  1993年   2篇
  1992年   3篇
  1991年   4篇
  1990年   2篇
  1989年   3篇
  1988年   3篇
  1987年   1篇
  1986年   1篇
  1984年   1篇
  1983年   3篇
  1982年   3篇
  1981年   2篇
  1980年   3篇
  1979年   3篇
  1978年   2篇
  1974年   2篇
  1973年   1篇
排序方式: 共有927条查询结果,搜索用时 15 毫秒
81.
Nowadays, students often practice problem-solving skills in online learning environments with the help of examples and problems. This requires them to self-regulate their learning. It is questionable how novices self-regulate their learning from examples and problems and whether they need support. The present study investigated the open questions (1) to what extent students' (novices) task selections align with instructional design principles and (2) whether informing them about these principles would improve their task selections, learning outcomes, and motivation. Higher education students (N = 150) learned a problem-solving procedure by fixed sequences of examples and problems (FS-condition), or by self-regulated learning (SRL). The SRL participants selected tasks from a database, varying in format, complexity, and cover story, either with (ISRL-condition) or without (SRL-condition) watching a video detailing the instructional design principles. Students' task-selection patterns in both SRL conditions largely corresponded to the principles, although tasks were built up in complexity more often in the ISRL-condition than in the SRL-condition. Moreover, there was still room for improvement in students' task selections after solving practice problems. The video instruction helped students to better apply certain principles, but did not enhance learning and motivation. Finally, there were no test performance or motivational differences among conditions. Although these findings might suggest it is relatively ‘safe’ to allow students to independently start learning new problems-solving tasks using examples and problems, caution is warranted: It is unclear whether these findings generalize to other student populations, as the students participating in this study have had some experience with similar tasks or learning with examples. Moreover, as there was still room for improvement in students' task selections, follow-up research should investigate how we can further improve self-regulated learning from examples and practice problems.  相似文献   
82.
Systems biologists use interaction graphs to model the behavior of biological systems at the molecular level. In an iterative process, such biologists obser ve the reactions of living cells under various experimental conditions, view the results in the context of the interaction graph, and then propose changes to the graph model. These graphs ser ve as a form of dynamic knowledge representation of the biological system being studied and evolve as new insight is gained from the experimental data. While numerous graph layout and drawing packages are available, these tools did not fully meet the needs of our immunologist collaborators. In this paper, we describe the data information display needs of these immunologists and translate them into design decisions. These decisions led us to create Cerebral, a system that uses a biologically guided graph layout and incor porates experimental data directly into the graph display. Small multiple views of different experimental conditions and a data-driven parallel coordinates view enable correlations between experimental conditions to be analyzed at the same time that the data is viewed in the graph context. This combination of coordinated views allows the biologist to view the data from many different perspectives simultaneously. To illustrate the typical analysis tasks performed, we analyze two datasets using Cerebral. Based on feedback from our collaboratorsweconcludethat Cerebral is a valuable tool for analyzing experimental data in the context of an interaction graph model.   相似文献   
83.
84.
We extend the popular force-directed approach to network (or graph) layout to allow separation constraints, which enforce a minimum horizontal or vertical separation between selected pairs of nodes. This simple class of linear constraints is expressive enough to satisfy a wide variety of application-specific layout requirements, including: layout of directed graphs to better show flow; layout with non-overlapping node labels; and layout of graphs with grouped nodes (called clusters). In the stress majorization force-directed layout process, separation constraints can be treated as a quadratic programming problem. We give an incremental algorithm based on gradient projection for efficiently solving this problem. The algorithm is considerably faster than using generic constraint optimization techniques and is comparable in speed to unconstrained stress majorization. We demonstrate the utility of our technique with sample data from a number of practical applications including gene-activation networks, terrorist networks and visualization of high-dimensional data  相似文献   
85.
Corporate and academic communities have focused a great deal of attention on formalized approaches for creating, capturing, and propagating knowledge. Far less attention has been paid to the informal mechanisms that individuals share and employ to help them navigate complex processes in order to ‘get things done.’ In this paper, we examine the creation, use, and content of informal documents for supporting users of an enterprise resource planning system in a Fortune 500 company. We contend that such notes, which are commonly used for supporting information systems-related work, are an overlooked source of knowledgeability about organizational practices. This study is a first but necessary step in analyzing the types of information that can be derived from informal notes so that organizations can more fully utilize this largely untapped resource.  相似文献   
86.
The presentation of extraneous (i.e., irrelevant or unnecessary) information may hamper learning with multimedia. The present study examined whether people can learn to ignore unnecessary information with increasing experience with the task and whether this depends on the layout of that information. In two experiments, participants learned about the process of mitosis from a multimedia slideshow, with each slide presenting a combination of expository text and a picture on one of the stages in the process. Slides either contained no unnecessary text (control condition) or unnecessary text (i.e., merely describing the picture) either integrated in the picture (integrated condition) or presented underneath the picture (separated condition). Knowledge about the studied mitosis phase was tested immediately after each slide using a cloze test. Across Experiments 1 and 2, we did not find a reliable negative effect of the unnecessary text on cloze test performance. As a result, the question of whether task experience would reduce or eliminate that negative effect could not be answered. The eye movement data did confirm, however, that participants attended less to the unnecessary information with increasing task experience, suggesting that students can adapt their study strategy and learn to ignore unnecessary information.  相似文献   
87.
The front-line antituberculosis drug isoniazid (INH) inhibits InhA, the NADH-dependent fatty acid biosynthesis enoyl ACP-reductase from Mycobacterium tuberculosis, via formation of covalent adducts with NAD (INH-NAD adducts). While ring tautomers were found the main species formed in solution, only the 4S chain INH-NAD tautomer was evidenced in the crystallized InhA:INH-NAD complex. In this study we attempted to explore the modes of interaction and energy binding of the different isomers placed in the active site of InhA with the help of various molecular modelling techniques. Ligand and enzyme models were generated with the help of the Vega ZZ program package. Resulting ligands were then docked into the InhA active site individually using computational automated docking package AUTODOCK 3.0.5. The more relevant docked conformations were then used to compute the interaction energy between the ligands and the InhA cavity. The AM1 Hamiltonian and the QM/MM ONIOM methodologies were used and the results compared. The various tautomers were found docked in almost the same place where INH-NAD was present as predicted by earlier X-ray crystallographic studies. However, some changes of ligand conformation and of the interactions ligand-protein were evidenced. The lower binding energy was observed for the 4S chain adduct that probably represents the effective active form of the INH-NAD adducts, as compared to the 4R epimer. The two 4S,7R and 4R,7S ring tautomers show intermediate and similar binding energies contrasting with their different experimental inhibitory potency on InhA. As a possible explanation based on calculated conformations, we formulated the hypothesis of an initial binding of the two ring tautomers to InhA followed by opening of only the ring hemiamidal 4S,7R tautomer (possibly catalyzed by Tyr158 phenolate basic group) to give the 4S chain INH-NAD tight-binding inhibitor. The predictions of ligand-protein interactions at the molecular level can be of primary importance in elucidating the mechanisms of action of isoniazid and InhA-related resistances, in identifying the effective mycobactericidal entities and, in further step, in the design of a new generation of antitubercular drugs.  相似文献   
88.
In today’s competitive business environment, Intellectual Capital (IC) management is ever more recognized as a fundamental factor in gaining competitive advantage. Actually, most firms have only a vague idea of how to manage investments in IC and what they should obtain from these investments. As a result, many companies overlook to balance IC investments, overinvesting in some IC components and neglecting other ones. Following this lead, the aim of the paper is to assess the relative importance of IC components, with respect to their contribution to the company value creation, in order to obtain guidelines for IC management and investments.We propose a model for IC evaluation by integrating Fuzzy Logic and Analytic Hierarchy Process (AHP). This Fuzzy AHP approach allows to capture and foster IC dynamics: experts and managers are greatly supported by the use of linguistic variables in the evaluation process of the company intangible assets. Finally, the application of the Fuzzy AHP methodology to a group of ICT service companies is presented.  相似文献   
89.
Learner-controlled instruction is often found to be less effective for learning than fixed or adaptive system-controlled instruction. One possible reason for that finding is that students – especially novices – might not able to accurately assess their own performance and select tasks that fit their learning needs. Therefore, this explorative study investigated the differences in self-assessment and task-selection processes between effective and ineffective learners (i.e., in terms of learning gains) studying in a learner-controlled instructional environment. Results indicated that although effective learners could more accurately assess their own performance than ineffective learners, they used the same task aspects to select learning tasks. For effective learners, who were also more accurate self-assessors, the self-assessment criteria predicted subsequent task selection. The results are discussed, particularly with regard to their potential to provide guidelines for the design of a self-assessment and task-selection training.  相似文献   
90.
This study examined connections between college students' adjustment and success and characteristics of their relationships with their parents. A sample of 236 students completed the Student Attitudes and Perceptions Survey, a 135-item anonymous self-report instrument. Students' grades, confidence level, persistence, task involvement, and rapport with their teachers were generally predicted by both current and childhood levels of parental autonomy granting, demandingness, and supportiveness. Ratings of parenting characteristics were equally predictive of adjustment and success among students living with their parents and those living on their own. They were somewhat less predictive of seniors' adjustment and success than they were for freshmen, sophomores, and juniors. These findings suggest that parenting style continues to play an important role in the academic lives of college students. (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