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   36336篇
  免费   1300篇
  国内免费   63篇
电工技术   371篇
综合类   29篇
化学工业   7236篇
金属工艺   725篇
机械仪表   739篇
建筑科学   1964篇
矿业工程   114篇
能源动力   1054篇
轻工业   2883篇
水利工程   430篇
石油天然气   117篇
武器工业   5篇
无线电   2475篇
一般工业技术   6117篇
冶金工业   6598篇
原子能技术   268篇
自动化技术   6574篇
  2023年   214篇
  2022年   440篇
  2021年   683篇
  2020年   463篇
  2019年   617篇
  2018年   780篇
  2017年   695篇
  2016年   835篇
  2015年   757篇
  2014年   1040篇
  2013年   2372篇
  2012年   1681篇
  2011年   2092篇
  2010年   1651篇
  2009年   1547篇
  2008年   1801篇
  2007年   1774篇
  2006年   1591篇
  2005年   1439篇
  2004年   1174篇
  2003年   1122篇
  2002年   1051篇
  2001年   702篇
  2000年   549篇
  1999年   595篇
  1998年   583篇
  1997年   574篇
  1996年   549篇
  1995年   572篇
  1994年   525篇
  1993年   510篇
  1992年   500篇
  1991年   288篇
  1990年   418篇
  1989年   389篇
  1988年   319篇
  1987年   355篇
  1986年   310篇
  1985年   418篇
  1984年   416篇
  1983年   318篇
  1982年   295篇
  1981年   281篇
  1980年   269篇
  1979年   270篇
  1978年   247篇
  1977年   225篇
  1976年   206篇
  1975年   194篇
  1974年   173篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
In hopes of promoting college success among Mexican Americans, researchers have identified factors related to their academic performance. A gap in the literature exists between the interactive role of acculturation, enculturation, and generation status in predicting college self-efficacy and college performance (grade-point average, or GPA). To fill this void, this study investigated the relation of demographic variables (e.g., age, gender, socioeconomic status) and cultural variables (e.g., acculturation, enculturation, generation status) on academic outcomes (e.g., college self-efficacy, college performance) among 408 Mexican-American college students. Results of a series of hierarchical regression analyses indicated socioeconomic status, generation status, enculturation, and acculturation had significant positive effects on college self-efficacy; socioeconomic status and the interaction of higher enculturation and first-generation status were positively and significantly related to GPA. Post-hoc analyses indicated college self-efficacy predicted college performance for students who were second generation and beyond. Implications for research and practice are discussed. (PsycINFO Database Record (c) 2011 APA, all rights reserved)  相似文献   
992.
A great deal of developmental research has relied on self-reports solicited using the “some/other” question format (“Some students think that… but other students think that…”). This article reports tests of the assumptions underlying its use: that it conveys to adolescents that socially undesirable attitudes, beliefs, or behaviors are not uncommon and legitimizes reporting them, yielding more valid self-reports than would be obtained by “direct” questions, which do not mention what other people think or do. A meta-analysis of 11 experiments embedded in four surveys of diverse samples of adolescents did not support the assumption that the some/other form increases validity. Although the some/other form led adolescents to think that undesirable attitudes, beliefs, or behaviors were more common and resulted in more reports of those attitudes and behaviors, answers to some/other questions were lower in criterion validity than were answers to direct questions. Because some/other questions take longer to ask and answer and require greater cognitive effort from participants (because they involve more words), and because they decrease measurement accuracy, the some/other question format seems best avoided. (PsycINFO Database Record (c) 2011 APA, all rights reserved)  相似文献   
993.
Objective: To use multitrait analysis to determine the measurement structure of the Caregiver Empowerment Scale (CES). Participants: An American sample of 87 adult primary family caregivers of persons with traumatic brain injury (TBI). Results: A four-factor structure was identified including factor 1 (Advocacy Self-Efficacy), factor 2 (Community Self-Efficacy), factor 3 (Caregiver Self-Efficacy), and factor 4 (Personal Self-Efficacy). Conclusions: The CES provides clinicians and researchers a means to assess self-perceived coping abilities of family caregivers of persons with TBI. (PsycINFO Database Record (c) 2011 APA, all rights reserved)  相似文献   
994.
In the face of prejudice against an ingroup, common ground for communication exists when people use similar social categories to understand the situation. Three studies tested the hypothesis that describing perceptions of prejudice can fundamentally change those perceptions because communicators account for the common ground in line with conversational norms. When women (Study 1), African Americans (Study 2), and Americans (Study 3) simply thought about suspected prejudice against their ingroup, categorization guided their perceptions: Participants assimilated their views of the prejudiced event toward the perceptions of ingroup members but contrasted away from the perceptions of outgroup members. Conversely, when participants described their perceptions, they contrasted away from the given category information and actually arrived at the opposite perceptions as those who merely thought about the prejudiced event. Study 3 identified an important qualification of these effects by showing that they were obtained only when participants could assume their audience was familiar with the common ground. Implications are discussed for understanding the role of communication in facilitating and inhibiting collective action about prejudice. (PsycINFO Database Record (c) 2011 APA, all rights reserved)  相似文献   
995.
This research examines the possibility that people's choices in the service of an explicit focal goal may also reflect their tendency to fulfill implicit background goals and in that sense are multifinal. We carried out 5 experimental studies to investigate this notion. In Experiment 1, a primed implicit goal affected individuals' choices even when those avowedly served an explicit “focal” goal. Experiment 2 replicated this finding with a different type of implicit goals. Experiment 3 found that primed implicit goals had no effect on choices where the options that served them undermined the explicit goal. Experiment 4 found that a primed implicit goal served by a multifinal option does not privilege it over a unifinal option if that goal had been already attained by a different means. Finally, Experiment 5, via 3 types of control groups, showed that choices were affected by both the explicit and implicit goals in isolation, and they shifted toward multifinality when these goals were conjointly present. The discussion considers the integrative potential of the multifinality framework and its implications for a variety of phenomena in the domain of motivated cognition. (PsycINFO Database Record (c) 2011 APA, all rights reserved)  相似文献   
996.
Objective: As emotion regulation is widely considered to be a primary motive in the misuse of alcohol, our aim in the study was to investigate whether deficits in adaptive emotion-regulation skills maintain alcohol dependence (AD). Method: A prospective study investigated whether emotion-regulation skills were associated with AD and whether these skills predicted alcohol use during and after treatment for AD. Participants were 116 individuals treated for AD with cognitive–behavioral therapy. Emotion regulation and severity of AD symptoms were assessed by self-report. Alcohol use during treatment was assessed by Breathalyzer and urine analysis for ethyl glucuronide; alcohol use during the 3-month follow-up interval was assessed by self-report. Results: Pretreatment emotion-regulation skills predicted alcohol use during treatment, and posttreatment emotion-regulation skills predicted alcohol use at follow-up, even when controlling for other predictors potentially related to emotion regulation. Among a broad range of specific emotion-regulation skills, the ability to tolerate negative emotions was the only skill that negatively predicted subsequent alcohol consumption when controlling for the other skills. Individuals in the AD sample reported significantly larger deficits in emotion-regulation skills than did those in a nonclinical control sample but significantly less than did those in a sample of individuals exclusively meeting criteria for major depressive disorder. Conclusions: Enhancement of general emotion-regulation skills, especially the ability to tolerate negative emotions, appears to be an important target in the treatment of AD. (PsycINFO Database Record (c) 2011 APA, all rights reserved)  相似文献   
997.
Although evidence has suggested that synchronized movement can foster cooperation, the ability of synchrony to increase costly altruism and to operate as a function of emotional mechanisms remains unexplored. We predicted that synchrony, due to an ability to elicit low-level appraisals of similarity, would enhance a basic compassionate response toward victims of moral transgressions and thereby increase subsequent costly helping behavior on their behalf. Using a manipulation of rhythmic synchrony, we show that synchronous others are not only perceived to be more similar to oneself but also evoke more compassion and altruistic behavior than asynchronous others experiencing the same plight. These findings both support the view that a primary function of synchrony is to mark others as similar to the self and provide the first empirical demonstration that synchrony-induced affiliation modulates emotional responding and altruism. (PsycINFO Database Record (c) 2011 APA, all rights reserved)  相似文献   
998.
To mitigate the damaging impacts caused by interference and hidden terminals, it has been proposed to use orthogonal channels in wireless multi-hop mesh networks. We demonstrate however that even if these issues are completely eliminated with perfectly assigned channels, gross unfairness can still exist amongst competing flows which traverse multiple hops. We propose the use of 802.11e’s TXOP mechanism to restore/enforce fairness. The proposed scheme is simple, implementable using off-the-shelf devices and fully decentralised (requires no message passing).  相似文献   
999.
The magnitude and direction of the permanent electric polarization in the non‐crystalline, polar phase (termed quasi‐amorphous) of SrTiO3 in SiSiO2MeSrTiO3Me, (Me = Cr or W), SiSrRuO3SrTiO3, and SiSrTiO3 layered structures were investigated. Three potential sources of the polarization which appears after the material is pulled through a temperature gradient were considered: a) contact potential difference; b) a flexoelectric effect due to a strain gradient caused by substrate curvature; and c) a flexoelectric effect due to the thermally induced strain gradient that develops while pulling through the steep temperature gradient. Measurements show that options a) and b) can be eliminated from consideration. In most cases studied in this (SiSrTiO3, SiSiO2MeSrTiO3Me, M = Cr or W) and previous works (SiBaTiO3, SiBaZrO3), the top surface of the quasi‐amorphous phase acquires a negative charge upon heating. However, in SiSrRuO3SrTiO3 structures the top surface acquires a positive charge upon heating. On the basis of the difference in the measured expansion of the upper and lower surfaces of the SrTiO3 layer in the presence and absence of SrRuO3, we contend that the magnitude and direction of the pyroelectric effect are determined by the out‐of‐plane gradient of the in‐plane strain in the SrTiO3 layer while pulling through the temperature gradient.  相似文献   
1000.
Biogenic single‐crystal composites, such as sea urchin spines and calcitic prisms from mollusk shells, contain organic macromolecules inside of inorganic single‐crystal matrices. The nanoscale internal structure of these materials, however, is poorly understood, especially how the biomacromolecules are distributed within the crystals without significantly disrupting the crystalline lattice. Here, annular dark‐field scanning transmission electron microscopy and electron tomography reveal, in three dimensions, how biomacromolecules are distributed within the calcitic prisms from Atrina rigida shells. Disk‐like nanopatches, whose scattering intensity is consistent with organic inclusions, are observed to be anisotropically arranged within a continuous, single‐crystalline calcite matrix. These nanopatches are preferentially aligned with the (000l) planes of calcite. Along the crystallographic c‐axis, there are alternating organic‐rich and ‐poor regions on a length scale of tens of nanometers, while, in the ab plane, the distribution of nanopatches is more random and uniform. The structural features elucidated in this work have relevance to understanding the structure–property relationships and formation mechanisms of biominerals, as well as to the development of bio‐inspired strategies to extrinsically tune the properties of single‐crystals.  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