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   2282篇
  免费   113篇
  国内免费   8篇
电工技术   23篇
综合类   3篇
化学工业   580篇
金属工艺   33篇
机械仪表   47篇
建筑科学   80篇
矿业工程   5篇
能源动力   95篇
轻工业   250篇
水利工程   38篇
石油天然气   10篇
无线电   171篇
一般工业技术   327篇
冶金工业   239篇
原子能技术   15篇
自动化技术   487篇
  2024年   5篇
  2023年   33篇
  2022年   92篇
  2021年   116篇
  2020年   78篇
  2019年   65篇
  2018年   69篇
  2017年   75篇
  2016年   79篇
  2015年   79篇
  2014年   66篇
  2013年   153篇
  2012年   156篇
  2011年   157篇
  2010年   107篇
  2009年   114篇
  2008年   99篇
  2007年   101篇
  2006年   92篇
  2005年   77篇
  2004年   63篇
  2003年   42篇
  2002年   52篇
  2001年   28篇
  2000年   16篇
  1999年   27篇
  1998年   57篇
  1997年   40篇
  1996年   24篇
  1995年   20篇
  1994年   17篇
  1993年   18篇
  1992年   8篇
  1991年   14篇
  1990年   8篇
  1989年   18篇
  1988年   8篇
  1987年   15篇
  1986年   12篇
  1985年   7篇
  1984年   11篇
  1983年   10篇
  1982年   4篇
  1981年   8篇
  1980年   15篇
  1979年   4篇
  1976年   9篇
  1975年   4篇
  1974年   7篇
  1972年   4篇
排序方式: 共有2403条查询结果,搜索用时 15 毫秒
91.
Data gathered from energy audits, phone surveys and smart meter readings are used to derive regression models of the electricity consumption of housing units in Oshawa (Ontario, Canada). The database used comprises 59 predictors, for 62 observations. To address the problem of multi-collinearities among the predictors and at the same time reduce the number of needed predictors, a methodology is developed based on the latent root regression technique of Hawkins [5]. Contrary to other variable selection techniques such as the stepwise method, the technique used in this paper allows an easy identification of alternative subsets. Using this technique, a reduction of 85% in the number of predictors is obtained, leaving only nine of them in the final subset. These nine variables are the number of occupants, the house status (owned or rented), the number of weeks of vacation per year, the type of fuel used in the pool heater, the type of fuel used in the heating system, the type of fuel used in the domestic hot water heater, the existence or not of an air conditioning system, the type of air conditioning system, and the number of air changes per hour at 50 Pa. A regression with these nine predictors leads to an R2 of 0.79, with an adjusted R2 of 0.75 and all regression coefficients statistically significant at the 95% confidence level.  相似文献   
92.
This exploratory study examines the link between generativity and an interpersonal aspect of religion and spirituality, spiritual disclosure, in close relationships. Three hundred seventy-eight adults aged 18 to 85 years were asked about their use of spiritual disclosure with close friends, views on their own generativity, questions related to personality characteristics, and level of general self-disclosure. This community sample’s reports on higher levels of spiritual disclosure were tied to higher levels of generativity and general self-disclosure. Spiritual disclosure also predicted unique variance in generativity beyond general self-disclosure, personality, and intrapersonal aspects of religion and spirituality. These findings suggest spiritual disclosure in close relationships is an important part of the religious/spiritual landscape, which merits further study in relation to generativity and other prosocial indices. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
93.
In this paper, we propose a number of non-radial, output-oriented, centralised DEA models to determine individual and collective output target levels, input slacks and input reallocations as well as additional inputs acquisitions under a capital budget constraint. The application of the proposed approach to the Spanish Port Agency is presented. The overall amount of inefficiency currently found in the system allows for the determination of potential total output increases ranging from 24% to 114% without additional resources. Considering inputs reallocation would allow for an additional 20% output expansion. The acquisition of additional input resources would make feasible to expand outputs further, to levels whose exact values monotonously depend on the capital budget considered.  相似文献   
94.
95.
96.
97.
Intraoperative imaging technologies recently entered the operating room, and their implementation is revolutionizing how physicians plan, monitor, and perform surgical interventions. In this work, we present a novel surgical imaging reporter system: intraoperative chemiluminescence imaging (ICI). To this end, we have leveraged the ability of a chemiluminescent metal complex to generate near‐infrared light upon exposure to an aqueous solution of Ce4+ in the presence of reducing tissue or blood components. An optical camera spatially resolves the resulting photon flux. We describe the construction and application of a prototype imaging setup, which achieves a detection limit as low as 6.9 pmol cm?2 of the transition‐metal‐based ICI agent. As a proof of concept, we use ICI for the in vivo detection of our transition metal tracer following both systemic and subdermal injections. The very high signal‐to‐noise ratios make ICI an interesting candidate for the development of new intraoperative imaging technologies.  相似文献   
98.
Ammonia electrooxidation reaction involving multistep electron-proton transfer is a significant reaction for fuel cells, hydrogen production and understanding nitrogen cycle. Platinum has been established as the best electrocatalyst for ammonia oxidation in aqueous alkaline media. In this study, Pt/nitrogen-doped graphene (NDG) and Pt/tungsten monocarbide (WC)/NDG are synthesized by a wet chemistry method and their ammonia oxidation activities are compared to commercial Pt/C. Pt/NDG exhibits a specific activity of 0.472 mA∙cm–2, which is 44% higher than commercial Pt/C, thus establishing NDG as a more effective support than carbon black. Moreover, it is demonstrated that WC as a support also impacts the activity with further 30% increase in comparison to NDG. Surface modification with Ir resulted in the best electrocatalytic activity with Pt-Ir/WC/NDG having almost thrice the current density of commercial Pt/C. This work adds insights regarding the role of NDG and WC as efficient supports along with significant impact of Ir surface modification.  相似文献   
99.
A theoretical analysis of the power loss and series resistance of the front side emitter in silicon solar cells is presented. Existing 1D models (infinitely long finger) and 2D models (including the effect of busbars) of emitter series resistance contribution are extended to the case of selective emitters. The general case of different current densities for both emitters in the selective emitter scheme is considered in these extensions. The resulting models depend on the individual sheet resistances and current densities in both emitters and the device's overall grid geometry. The models are corroborated by finite element simulation of the potential in the emitter. An excellent agreement is found between the analytical models, and the simulations for a wide range of sheet resistances typically encountered in silicon solar cells. Grid simulations using the 2D model are applied to solar cells with selective emitters, where the width of the low‐resistive emitter was varied. The simulations demonstrate that the 2D model can explain the absolute change in fill factor observed in these cells. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   
100.
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