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   1558篇
  免费   182篇
  国内免费   1篇
电工技术   17篇
综合类   1篇
化学工业   368篇
金属工艺   24篇
机械仪表   87篇
建筑科学   52篇
矿业工程   7篇
能源动力   59篇
轻工业   450篇
水利工程   13篇
石油天然气   4篇
无线电   74篇
一般工业技术   218篇
冶金工业   37篇
原子能技术   5篇
自动化技术   325篇
  2024年   9篇
  2023年   20篇
  2022年   41篇
  2021年   106篇
  2020年   69篇
  2019年   80篇
  2018年   106篇
  2017年   95篇
  2016年   92篇
  2015年   85篇
  2014年   96篇
  2013年   248篇
  2012年   124篇
  2011年   132篇
  2010年   122篇
  2009年   92篇
  2008年   52篇
  2007年   30篇
  2006年   24篇
  2005年   6篇
  2004年   9篇
  2003年   11篇
  2002年   16篇
  2001年   6篇
  2000年   9篇
  1999年   7篇
  1998年   13篇
  1997年   10篇
  1996年   3篇
  1995年   5篇
  1993年   4篇
  1992年   1篇
  1990年   1篇
  1989年   1篇
  1983年   1篇
  1982年   1篇
  1981年   2篇
  1980年   1篇
  1979年   1篇
  1978年   1篇
  1977年   1篇
  1975年   1篇
  1965年   2篇
  1964年   1篇
  1963年   2篇
  1938年   2篇
排序方式: 共有1741条查询结果,搜索用时 15 毫秒
151.
In this paper, we present a Computer Aided Diagnosis and image biomarker identification system for cocaine dependence, which selects relevant regions from a set of brain structural magnetic resonance images (sMRI). After sMRI volume preprocessing for spatial normalization, we compute Pearson’s correlation between pixel values across volumes and the indicative variable, obtaining a volume of correlation values (VCV). We calculate the gradient of the VCV which is used to perform a watershed segmentation of the brain volume into regions. A region selection stage finds the most relevant watershed regions. We propose two different approaches to characterize region relevance: (a) a wrapper procedure using extreme learning machines (ELM), and (b) apply correlation distribution percentiles to select most discriminant regions. Next, we consider three different procedures to extract the image features corresponding to selected regions: (1) collecting the sMRI intensity values of all the voxels that compose each region, compute (2) the mean or (3) the median of the sMRI intensity value of the voxels contained in each selected region. Extracted feature vectors are used to build a classifier aiming to discriminate between cocaine dependent patients and healthy controls. We compare results of several classifiers: ELM, OP-ELM, SVM and 1NN. Also, we visualize the brain locations of selected regions, checking if these locations are in accordance with previous findings in the medical literature.  相似文献   
152.
This paper aims to contribute to the literature of Cournot spatial equilibria in two-dimensional spaces by considering branching. We study the case in which two firms compete on a circle and each one has the possibility of opening one or more branches. An innovative method—polar coordinates—is employed to obtain the complex profit functions. We show that there exists a symmetric subgame perfect Nash equilibrium where both firms place their n branches alternately and at the same distance from the center of the circle. Additionally, we show that this is, up to rotation, the unique symmetric equilibrium location.  相似文献   
153.
154.
Zusammenfassung Unter Verhältnissen, wie sie praktisch bei Induktionsmaschinen vorkommen, ist für ungesättigte, unendlich dünne Zahnkopfstege und bei gegebenem LuftspaltB min/B max nur von dem Nutenschlitz abhängig. Für die offene Nut mit derselben Schlitzöffnung istB min/B max größer, der Cartersche Faktor kleiner als für die oben gekennzeichnete Nut. Der von Weber angegebene Verlauf der Induktion im Luftspalt [13] entspricht auch bei gesättigten Zahnspitzen nicht der Wirklichkeit.  相似文献   
155.
Redesigning an assembly line through lean manufacturing tools   总被引:1,自引:1,他引:0  
The implementation of a lean manufacturing strategy represents a robust contribution to the phase sequence that leads to operational excellence and the continuous improvement through the elimination of nonvalue-added activities. Therefore, lean practices contribute substantially to plant operational performance. This paper studies the use of value stream mapping (VSM) as a tool in lean manufacturing implementation and a framework of improvement activities, in particular for an efficient introduction of kanban and milkrun techniques. A case study illustrates VSM use, as well as kanban and milkrun systems application on an assembly line. Finally, the results obtained show the path of improvement, measured through the lean rate (LR) and dock-to-dock time (DtD).  相似文献   
156.
Although water, at least for basic needs, should be accessible to everyone, many families have trouble paying their water bill. Assessments of water affordability inform the design of water tariffs aimed at ensuring universal access to water. In order to carry out such assessments, managers must have instruments available that accurately reflect the state of water affordability. In this article, a critique is presented of one of the indicators traditionally used to measure water affordability and a proposal of an alternative way of measuring water affordability is put forward. The empirical analysis is applied to data from 301 communities in southern Spain.  相似文献   
157.
Multistandard channelisation for base stations is a big application of generalised discrete Fourier transform modulated filter banks (GDFT‐FBs) in digital communications. For technologies such as software‐defined radio and cognitive radio, nonuniform channelisers must be used if frequency bands are shared by different standards. However, GDFT‐FB‐based nonuniform channelisers can suffer from high filter orders when applied to wideband input signals. In this paper, various combinations of GDFT‐FB with the frequency response masking technique are proposed and evaluated for both uniform and nonuniform channelisation applications. Results show that the proposed techniques achieve savings in both the number of filter coefficients and the number of operations per input sample. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   
158.
Novel, environmentally friendly waterborne coatings were obtained from the filmification of nanostructured latex particles reinforced with inorganic nanotubes. The latex used to form the coatings consists of core-shell particles with a shell functionalized with different amounts of acrylic acid (AA). This external polymer layer was doped, in some cases, with TiO2 nanotubes at three different concentrations: 100, 500 and 1000 ppm. The composite particles were synthesized in two steps by semi-continuous emulsion polymerization at 75°C. A series of films was prepared by employing core-shell particles with different sizes, core cross-linking and shell functionalization. The coatings obtained were characterized by infrared spectroscopy (FTIR), tapping mode atomic force microscopy (TM-AFM), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and thermogravimetrical analysis (TGA). Drying rates and tests were also performed to further evaluate these films. It was observed that the addition of small amounts of TiO2 nanotubes contributes to improve the application properties, mainly adhesion to metallic substrates and water impermeability. The resistance to thermal degradation was also strongly increased, as showed by the DSC and TGA analyses.  相似文献   
159.
The human enzymes aldose reductase (AR) and AKR1B10 have been thoroughly explored in terms of their roles in diabetes, inflammatory disorders, and cancer. In this study we identified two new lead compounds, 2‐(3‐(4‐chloro‐3‐nitrobenzyl)‐2,4‐dioxo‐3,4‐dihydropyrimidin‐1(2H)‐yl)acetic acid (JF0048, 3 ) and 2‐(2,4‐dioxo‐3‐(2,3,4,5‐tetrabromo‐6‐methoxybenzyl)‐3,4‐dihydropyrimidin‐1(2H)‐yl)acetic acid (JF0049, 4 ), which selectively target these enzymes. Although 3 and 4 share the 3‐benzyluracil‐1‐acetic acid scaffold, they have different substituents in their aryl moieties. Inhibition studies along with thermodynamic and structural characterizations of both enzymes revealed that the chloronitrobenzyl moiety of compound 3 can open the AR specificity pocket but not that of the AKR1B10 cognate. In contrast, the larger atoms at the ortho and/or meta positions of compound 4 prevent the AR specificity pocket from opening due to steric hindrance and provide a tighter fit to the AKR1B10 inhibitor binding pocket, probably enhanced by the displacement of a disordered water molecule trapped in a hydrophobic subpocket, creating an enthalpic signature. Furthermore, this selectivity also occurs in the cell, which enables the development of a more efficient drug design strategy: compound 3 prevents sorbitol accumulation in human retinal ARPE‐19 cells, whereas 4 stops proliferation in human lung cancer NCI‐H460 cells.  相似文献   
160.

Literature suggests that urban regeneration policies might contribute towards improving mental health of residents, but to date there is a lack of empirical research on how these policies and downward social mobility can interact and influence health outcomes. The current study aims to explicitly test whether regeneration policies implemented in deprived Andalusian urban places (southern Spain) moderate the use of anxiolytics and/or antidepressants, taking into consideration families’ downward social mobility during the recent period of economic crisis in Spain. We designed a post intervention survey to retrospectively compare the evolution of psychotropic drug consumption in target and comparison areas. We observe a general increase in the use of anxiolytics and/or antidepressants from 2008 to 2015, specifically for people in whose families the economic crisis had the greatest impact (odds ratio?=?2.18; p value?<?0.001). However, better evolution is observed among residents of the target areas compared with residents of similar urban areas where this kind of polices have been not in force (odds ratio?=?0.50; p value?<?0.05). Therefore, urban regeneration policies might act as moderators of the risk of mental health, particularly when people are subject to the loss of individual/family resources in urban vulnerable contexts.

  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