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   7824篇
  免费   222篇
  国内免费   6篇
电工技术   94篇
综合类   1篇
化学工业   1213篇
金属工艺   120篇
机械仪表   214篇
建筑科学   276篇
矿业工程   20篇
能源动力   289篇
轻工业   602篇
水利工程   95篇
石油天然气   30篇
武器工业   2篇
无线电   573篇
一般工业技术   1230篇
冶金工业   2324篇
原子能技术   45篇
自动化技术   924篇
  2022年   48篇
  2021年   91篇
  2020年   78篇
  2019年   95篇
  2018年   98篇
  2017年   100篇
  2016年   121篇
  2015年   101篇
  2014年   140篇
  2013年   336篇
  2012年   281篇
  2011年   468篇
  2010年   366篇
  2009年   282篇
  2008年   387篇
  2007年   378篇
  2006年   320篇
  2005年   303篇
  2004年   245篇
  2003年   242篇
  2002年   253篇
  2001年   139篇
  2000年   130篇
  1999年   145篇
  1998年   460篇
  1997年   322篇
  1996年   237篇
  1995年   186篇
  1994年   159篇
  1993年   159篇
  1992年   94篇
  1991年   60篇
  1990年   79篇
  1989年   76篇
  1988年   67篇
  1987年   57篇
  1986年   92篇
  1985年   73篇
  1984年   58篇
  1983年   53篇
  1982年   49篇
  1981年   50篇
  1980年   52篇
  1979年   38篇
  1978年   44篇
  1977年   75篇
  1976年   97篇
  1975年   42篇
  1974年   32篇
  1972年   31篇
排序方式: 共有8052条查询结果,搜索用时 712 毫秒
171.
172.
Proteomics has long been thought to hold the promise of producing results of clinical utility which will influence patient treatment and outcomes. A recent Wellcome Trust/EBI meeting and retreat--“Perspectives in Clinical Proteomics”--brought together experts from a broad range of stakeholder groups with an interest in ensuring proteomics achieves this aim. This viewpoint presents views derived from these forums, proposing a pathway for the development of next-generation proteomic analyses in the clinical setting from selection of candidates through to their validation and ultimate demonstration of utility through health technology assessments. Although not meant to be all encompassing, important elements for proteomics researchers to consider are presented.  相似文献   
173.
Bryophytes are the dominant ground cover vegetation layer in many boreal forests and in some of these forests the net primary production of bryophytes exceeds the overstory. Therefore it is necessary to quantify their spatial coverage and species composition in boreal forests to improve boreal forest carbon budget estimates. We present results from a small exploratory test using airborne lidar and multispectral remote sensing data to estimate the percentage of ground cover for mosses in a boreal black spruce forest in Manitoba, Canada. Multiple linear regression was used to fit models that combined spectral reflectance data from CASI and indices computed from the SLICER canopy height profile. Three models explained 63-79% of the measured variation of feathermoss cover while three models explained 69-92% of the measured variation of sphagnum cover. Root mean square errors ranged from 3-15% when predicting feathermoss, sphagnum, and total moss ground cover. The results from this case study warrant further testing for a wider range of boreal forest types and geographic regions.  相似文献   
174.
The current study examined problematic Internet use (PIU) among people who play MMO games and sought to determine whether aspects of the MMO experience are useful predictors of PIU. The study sought to determine whether game-related variables could predict PIU scores after accounting for their relationships with psychosocial well-being. Novel methods allowed us, for the first time, to connect in-game behaviors with survey results of over 4000 MMO players. The results revealed that MMO gaming variables contributed a substantively small, but statistically significant amount of explained variance to PIU scores.  相似文献   
175.
Many software systems fail to address their intended purpose because of a lack of user involvement and requirements deficiencies. This paper discusses the elaboration of a requirements-analysis process that integrates a critical-parameter-based approach to task modeling within a user-centric design framework. On one hand, adapting task models to capture requirements bridges the gap between scenarios and critical parameters which benefits design from the standpoint of user involvement and accurate requirements. On the other hand, using task models as a reusable component leverages requirements reuse which benefits design by increasing quality while simultaneously reducing development costs and time-to-market. First, we present the establishment of both a user-centric and reuse-centric requirements process along with its implementation within an integrated design tool suite. Secondly, we report the design, procedures, and findings of two user studies aimed at assessing the feasibility for novice designers to conduct the process as well as evaluating the resulting benefits upon requirements-analysis deliverables, requirements quality, and requirements reuse.  相似文献   
176.
Topographic and elevation data are essential in the development of supporting infrastructure around mining sites. The de facto standard for acquiring elevation data is through light detection and ranging (lidar). The high labour and monetary cost of acquiring lidar has fostered more cost-effective approaches for creating elevation models that use stereo photogrammetry. To assess the accuracy of stereo-photogrammetry-derived elevation models and their potential application, we benchmark satellite (Worldview-2) and aircraft (South Central Ontario Orthoimagery Project; SCOOP) stereo-derived digital surface models (DSMs) against a lidar-derived DSM. Our results show that both stereo-derived DSMs have strong monotonic correlations with lidar across a range of land-cover types and slopes. The overall vertical accuracy of Worldview-2 and SCOOP DSMs are similar and do not meet the United States National Digital Elevation Program (NDEP) standards. However, accuracy assessment across land-cover types and slope categories show that specific land cover types (i.e. grass, row crops/pasture, sparse vegetation and marsh) on gently sloping terrain compare well to lidar data and meet NDEP accuracy standards. We situate the presented research in the context of northern resource development and discuss opportunities to improve the vertical accuracy of stereo-derived DSMs, for example, through unmanned aerial systems.  相似文献   
177.
Physical activity monitoring for youth is an area of increasing scientific and public health interest due to the high prevalence of obesity and downward trend in physical activity. However, accurate assessment of such activity remains a challenging problem because of the complex nature in which certain activities are performed. In this study, we formulated the issue as a machine learning problem—using a diverse set of 19 physical activities commonly performed by youth—via two approaches: activity recognition and intensity estimation. With the aid of training data, we implemented a distance metric learning method called DML-KNN that utilizes time-frequency features and is capable of effectively classifying both continuous and intermittent movement in youth subjects. Four different time-frequency feature extraction methods were then systematically evaluated. Our results show that the DML-KNN method performed competitively, especially when using features extracted by the Tamura method for intensity estimation, and by the Square Coefficient method for activity recognition.  相似文献   
178.
Big data is being implemented with success in the private sector and science. Yet the public sector seems to be falling behind, despite the potential value of big data for government. Government organizations do recognize the opportunities of big data but seem uncertain about whether they are ready for the introduction of big data, and if they are adequately equipped to use big data. This paper addresses those uncertainties. It presents an assessment framework for evaluating public organizations’ big data readiness. Doing so demystifies the concept of big data, as it is expressed in terms of specific and measureable organizational characteristics. The framework was tested by applying it to organizations in the Dutch public sector. The results suggest that organizations may be technically capable of using big data, but they will not significantly gain from these activities if the applications do not fit their organizations and main statutory tasks. The framework proved helpful in pointing out areas where public sector organizations could improve, providing guidance on how government can become more big data ready in the future.  相似文献   
179.
Does visually perceived distance differ when objects are viewed in augmented reality (AR), as opposed to the real world? What are the differences? These questions are theoretically interesting, and the answers are important for the development of many tablet- and phone-based AR applications, including mobile AR navigation systems. This article presents a thorough literature review of distance judgment experimental protocols, and results from several areas of perceptual psychology. In addition to distance judgments of real and virtual objects, this section also discusses previous work in measuring the geometry of virtual picture space and considers how this work might be relevant to tablet AR. Then, the article presents the results of two experiments. In each experiment, observers bisected egocentric distances of 15 and 30 m in tablet-based AR and in the real world, in both indoor corridor and outdoor field environments. In AR, observers bisected the distances to virtual humans, while in the real world, they bisected the distances to real humans. This is the first reported research that directly compares distance judgments of real and virtual objects in a tablet AR system. Four key findings were: (1) In AR, observers expanded midpoint intervals at 15 m, but compressed midpoints at 30 m. (2) Observers were accurate in the real world. (3) The environmental setting—corridor or open field—had no effect. (4) The picture perception literature is important in understanding how distances are likely judged in tablet-based AR. Taken together, these findings suggest the depth distortions that AR application developers should expect with mobile and especially tablet-based AR.  相似文献   
180.
This report provides an overview of physical ergonomic exposures in highway construction work across trades and major operations. For each operation, the observational method “PATH” (Posture, Activity, Tools and Handling) was used to estimate the percentage of time that workers spent in specific tasks and with exposure to awkward postures and load handling. The observations were carried out on 73 different days, typically for about 4 h per day, covering 120 construction workers in 5 different trades: laborers, carpenters, ironworkers, plasterers, and tilers. Non-neutral trunk postures (forward or sideways flexion or twisting) were frequently observed, representing over 40% of observations for all trades except laborers (28%). Kneeling and squatting were common in all operations, especially tiling and underground utility relocation work. Handling loads was frequent, especially for plasterers and tilers, with a range of load weights but most often under 15 pounds. The results of this study provide quantitative evidence that workers in highway tunnel construction operations are exposed to ergonomic factors known to present significant health hazards. Numerous opportunities exist for the development and implementation of ergonomic interventions to protect the health and safety of construction workers.  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