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   1347篇
  免费   74篇
电工技术   5篇
化学工业   510篇
金属工艺   13篇
机械仪表   48篇
建筑科学   36篇
矿业工程   1篇
能源动力   34篇
轻工业   357篇
水利工程   21篇
石油天然气   5篇
无线电   22篇
一般工业技术   129篇
冶金工业   100篇
原子能技术   1篇
自动化技术   139篇
  2024年   6篇
  2023年   22篇
  2022年   119篇
  2021年   88篇
  2020年   47篇
  2019年   52篇
  2018年   54篇
  2017年   53篇
  2016年   68篇
  2015年   42篇
  2014年   59篇
  2013年   100篇
  2012年   87篇
  2011年   94篇
  2010年   71篇
  2009年   50篇
  2008年   54篇
  2007年   43篇
  2006年   34篇
  2005年   36篇
  2004年   27篇
  2003年   20篇
  2002年   17篇
  2001年   7篇
  2000年   10篇
  1999年   7篇
  1998年   16篇
  1997年   19篇
  1996年   13篇
  1995年   10篇
  1994年   7篇
  1993年   13篇
  1991年   3篇
  1990年   3篇
  1989年   3篇
  1988年   5篇
  1987年   4篇
  1985年   4篇
  1984年   3篇
  1983年   2篇
  1982年   7篇
  1981年   2篇
  1980年   4篇
  1979年   5篇
  1978年   4篇
  1977年   3篇
  1976年   6篇
  1975年   2篇
  1974年   3篇
  1973年   6篇
排序方式: 共有1421条查询结果,搜索用时 15 毫秒
91.
Although a wide array of variables has been found to predict harsh parenting, less is known about the linkages among these variables. It is suggested here that stress reactivity, as reflected in cortisol changes, is an important mediating variable. In a high-risk population, mothers (N = 60) with low perceived power (as measured by the Parent Attribution Test; D. B. Bugental, J. B. Blue, & M. Cruzcosa, 1989), were highly reactive to infants and toddlers with a difficult temperament pattern. In response to such children, they (a) manifested high cortisol reactivity and (b) reported greater use of harsh control practices (e.g., spanking). Cortisol reactivity was found to mediate the observed relationship between the predictor variable (the interaction between maternal "powerlessness" and the child's temperament) and parental harshness. These findings have clinical implications for the ways in which parental empowerment (via early interventions) can serve to reduce stress and thus the negative outcomes at-risk children may experience. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
92.
We have developed a new method that allows the purification of large numbers of both authentic osteoclasts (OCs) and in vitro differentiated osteoclast-like cells (OCLs) from rabbits. We characterized the OCLs in terms of the expression of different phenotypic markers of OC differentiation and their ability to resorb bone. The method provides a system for performing biochemical and molecular studies of OC differentiation and function in a single species. We used this system to characterize the effect of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) on the expression of proteins that bind to the serum response element (SRE) of the c-fos promoter. We found that OCLs and OCs displayed similar SRE-binding activities, including the serum response factor (SRF). This pattern is established in a time-dependent and cell-specific manner in response to long-term treatment of rabbit bone marrow by 1,25(OH)2D3. Thus, 1,25(OH)2D3 can modulate SRF and/or SRF-related protein. This finding may contribute to understanding the role of c-Fos in the regulation of OC differentiation.  相似文献   
93.
Placental protein 5 (PP5), pregnancy-specific glycoprotein (SP1), pregnancy-associated alpha 2-glycoprotein (SP3) and chorionic gonadotrophin could not be demonstrated in appreciable molar quantities in the soluble fraction from microvillous plasma membrane preparations isolated from the syncytiotrophoblast of full-term human placentae. However, progesterone, total oestriol and placental lactogen may have some association with this membrane.  相似文献   
94.
Hypothesized that women and Chicanos would make less internal and more external attributions for their own successful performance than would Anglo males. 40 Chicano male, 40 Chicano female, 40 Anglo male, and 40 Anglo female undergraduates participated as managers in an industrial simulation study. Ss were randomly assigned to 1 of 4 experimental conditions: designated powers vs unspecified powers, and supervision of male or female workers. Following the managerial task, Ss completed a questionnaire assessing their own performance and that of their workers. All Anglos devalued their workers as a function of controlling power and attributed workers' performance to external factors. All Ss tended to use their power to persuade workers. Males attempted to influence workers to a greater degree than did females. The predicted sex differences in terms of attribution were evident only among Anglos. (25 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
95.
96.
97.
Investigation of travel-domain dialogues reveals travel-agent (System) utterances with intonational contours characterized by late-timed focal accents on given information. These accents occur on content words in utterance-initial position. The accentuation can be assumed to be related to the interactive nature of the dialogue in which the travel agent links back to a domain-related concept introduced by the client (User) and comments on it in an engaged manner. A perception test using constructed human-machine dialogues in which the machine (synthesized) responses vary as to the type of accent pattern on the initial words was developed to test listeners' preference for accent type. Results indicate that i) focal accents on domain-related utterance-initial given concepts are indeed preferred to nonfocal accents and that ii) late-timed focal accents are preferred to early-timed focal accents. These results have implications for the design of the prosody-generating component of human-machine dialogue systems.  相似文献   
98.
Owing to the dynamic nature of collaborative environments, the software intended to support collaborative work should adapt itself to the different situations that may occur. This requirement is related to the concept of “context of use”, which has been considered as an important aspect in the design of interactive systems. Nevertheless, two main problems about this concept have been identified by current research in context-aware computing: (1) most of the studies have mainly focused on the context of a single user, so the context of multiple users involved in a common endeavor remains little explored, and (2) adaptability in context-aware systems generally takes into account a reduced number of contextual variables (mainly the user’s location and platform). In this paper, we firstly re-conceptualize the notion of “context of use”, in order to consider the main characteristics of collaborative environments. Based on this new notion, we then design and implement a framework that allows application developers to specify the adaptability of groupware systems in terms of the state of activities, roles, collaborators’ location, available resources, and other typical variables of working groups. This framework has been generalized from scenarios that highlight dynamic situations presented in real collaborative settings. Finally, we validate our proposal by a set of applications that are able to adapt their user interface and functionality, when significant changes are produced in the environment, the working group, and/or the used devices.  相似文献   
99.
Traditional ‘in situ’ measurement techniques often fail to record the spatial distribution of floodplains. In that case, remote sensing provides inexpensive and reliable methodologies to map flooded areas and compute flood damage. The identification and monitoring of floods, due to their highly dynamic nature, require the use of high-time-resolution satellite images with the drawback that such images usually have low to medium spatial resolution. In this context, the traditional classification techniques would not be suitable for delineating floods because they use ‘hard methods’ of classification, where the coarse pixel is assigned to a unique land cover class, generating inaccurate maps of the flooded area. In contrast, the ‘soft methods’ assign several land cover classes within the coarse pixels. In this article, the theoretical basis regarding an innovative methodology of sub-pixel analysis (SA) to identify flooded areas is developed. The improvement in flood delineation is achieved with the use of primary topographic attributes, which stem from a digital elevation model (DEM). The methodology was applied to the monitoring of flood events in the lower Senegal River Valley, using satellite images with moderate spatial resolution. The proposed methodology was demonstrated to be effective for mapping the flood extent: the correct mapping of flooded areas was about 80% in all considered regions, whilst the better performance of supervised classification was 53%.  相似文献   
100.
Although steam–water capillary pressure is of central importance in geothermal reservoir engineering, it is nevertheless still poorly understood because of the difficulties involved in making direct measurements. To this end, we have conducted some experimental and theoretical studies. Unique methods have been developed to measure capillary pressures in order to overcome the complications in laboratory procedures associated with mass transfer as temperature and pressure changes. Both steam–water and air–water capillary pressures were measured and compared. Significant differences were found; in the cases studied, the steam–water capillary pressures were smaller. The drainage capillary pressure was greater than the imbibition capillary pressure, as was expected. Using experimental data, an empirical model was derived to calculate steam-water capillary pressure directly. Also developed was a generalized capillary pressure model based on fractal modeling of a porous medium; it encompasses the frequently used Brooks–Corey model (Brooks, R.H., Corey, A.T., 1964. Hydraulic Properties of Porous Media. Colorado State University, Hydro paper No. 3, Fort Collins, CO, USA, 24 pp.) as well as others. Recent studies on the topic are summarized and reviewed.  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