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   61048篇
  免费   2388篇
  国内免费   25篇
  63461篇
  2020年   581篇
  2019年   819篇
  2018年   1077篇
  2017年   1149篇
  2016年   1123篇
  2015年   802篇
  2014年   965篇
  2013年   4663篇
  2012年   1747篇
  2011年   1888篇
  2010年   1198篇
  2009年   1178篇
  2008年   1687篇
  2007年   1611篇
  2006年   1525篇
  2005年   1331篇
  2004年   1255篇
  2003年   1230篇
  2002年   1226篇
  2001年   2008篇
  2000年   1889篇
  1999年   1415篇
  1998年   708篇
  1997年   585篇
  1992年   1188篇
  1991年   1144篇
  1990年   1099篇
  1989年   1060篇
  1988年   1042篇
  1987年   994篇
  1986年   1001篇
  1985年   1080篇
  1984年   877篇
  1983年   767篇
  1982年   624篇
  1981年   601篇
  1979年   930篇
  1978年   696篇
  1977年   613篇
  1976年   626篇
  1975年   807篇
  1974年   857篇
  1973年   930篇
  1972年   747篇
  1971年   658篇
  1970年   645篇
  1969年   687篇
  1968年   825篇
  1967年   718篇
  1966年   767篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
32.
Brain mapping studies using dynamic imaging methods demonstrate areas regional cerebral blood flow (rCBF) decreases, as well as areas where increases, during performance of various experimental tasks. Task holds for both sets of cerebral blood flow changes (CBF), providing the opportunity to investigate areas that become and “activated” in the experimental condition relative to control state. Such data yield the intriguing observation that in areas in emotional processing, such as the amygdala, the posteromedial cortex, and the ventral anterior cingulate cortex, although flow as expected during specific emotion-related tasks, flow decreases performance of some attentionally demanding, cognitive tasks. Conversely, in some of the areas that appear to subserve cognitive functions, as the dorsal anterior cingulate and the dorsolateral prefrontal cortices, increases while performing attentionally demanding cognitive tasks, but during some experimentally induced and pathological emotional Although the specific nature of such reciprocal patterns of regional remains unclear, they may reflect an important cross-modal interaction during mental operations. The possibility that neural activity is less in areas required in emotional processing during some higher cognitive processes holds implications for the mechanisms underlying interactions cognition and emotion. Furthermore, the possibility that neural in some cognitive-processing areas is suppressed during intense states suggests mechanisms by which extreme fear or severe may interfere with cognitive performance.  相似文献   
33.
Although perceived health risk plays a prominent role in theories of health behavior, its empirical role in risk taking is less clear. In Study 1 (N = 129), 2 measures of drivers' risk-taking behavior were found to be unrelated to self-estimates of accident concern but to be related to self-ratings of driving skill and the perceived thrill of driving. In Study 2 (N = 405), out of a wide range of potential influences, accident concern had the weakest relationship with risk taking. The authors concluded that although health risk is a key feature in many theories of health behavior and a central focus for researchers and policy makers, it may not be such a prominent factor for those actually taking the risk.  相似文献   
34.
Intention is theorized as the proximal determinant of behavior in some theories of motivation, but the need to understand predictors of action control (i.e., translating an intention into behavior) is warranted to tailor physical activity intervention efforts. The purpose of this study was to examine constructs of the transtheoretical model of behavior change (TTM) as predictors of physical activity intention-behavior profiles across 6 months in a large Canadian sample (N = 1,192). Results showed that 5 of the 8 possible intention-behavior profiles had a substantial number of participants: nonintenders, unsuccessful adopters, successful adopters, unsuccessful maintainers, and successful maintainers. Constructs of the TTM distinguished (p < .01) intention-behavior profiles. Self-efficacy and the behavioral processes of change were particularly good predictors of action control (p < .01), but disaggregated beliefs and processes identified specific intervention targets for successful physical activity adoption and maintenance. The results validate that both action planning and action control are important when understanding physical activity behavior.  相似文献   
35.
36.
37.
38.
39.
OBJECTIVE: This report reviews the evidence that informs the role of health and mental health care providers in addressing youth smoking cessation. DESIGN: Qualitative literature review. RESULTS: Physicians do not consistently screen adolescents for tobacco use and fail to provide recommended cessation advice. Challenges to addressing smoking cessation include the need for procedures to ensure confidentiality and the existence of competing demands to provide other services. Few published studies have specifically addressed the effectiveness of clinical interventions. Interventions that require return visits or follow-up phone contacts are technically difficult to implement in this population. Successful interventions may require resources not available in nonresearch settings. Most studies have used brief clinical intervention as a control condition, making it impossible to evaluate its effectiveness. CONCLUSION: There is little evidence that supports current clinical smoking cessation guidelines for adolescents. More research is needed to develop inexpensive, efficient clinical interventions that can provide youths access to smoking cessation help. Future challenges include reorganizing clinical systems to offer greater counseling by support staff or in electronic formats and to provide effective booster messages and follow-up care in a population that is difficult to track.  相似文献   
40.
An electronic apparatus using infrared beams for monitoring the movements of individual bees under dark conditions is described. The searching behavior of workers in an arena was monitored over 2-h periods. Mean ambulatory velocity for one bee over a distance of 100 mm was 45.6±1.51 mm/sec (n=45). Thigmokinesis and temporal activity patterns are illustrated.  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