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   181311篇
  免费   7961篇
  国内免费   164篇
  189436篇
  2021年   1534篇
  2020年   2826篇
  2019年   3504篇
  2018年   3699篇
  2017年   4137篇
  2016年   4796篇
  2015年   4002篇
  2014年   4874篇
  2013年   23971篇
  2012年   5020篇
  2011年   4164篇
  2010年   4146篇
  2009年   4946篇
  2008年   4375篇
  2007年   3946篇
  2006年   4462篇
  2005年   4376篇
  2004年   3878篇
  2003年   3480篇
  2002年   3314篇
  2001年   3465篇
  2000年   3277篇
  1999年   3280篇
  1998年   2895篇
  1997年   2728篇
  1996年   2619篇
  1995年   2483篇
  1994年   2435篇
  1993年   2381篇
  1992年   2737篇
  1991年   2525篇
  1990年   2432篇
  1989年   2300篇
  1988年   2284篇
  1987年   2294篇
  1986年   2257篇
  1985年   2458篇
  1984年   2593篇
  1983年   2402篇
  1982年   2417篇
  1981年   2384篇
  1980年   2224篇
  1979年   2288篇
  1978年   2242篇
  1977年   2187篇
  1976年   2010篇
  1975年   2070篇
  1974年   2122篇
  1973年   2017篇
  1972年   1549篇
排序方式: 共有10000条查询结果,搜索用时 5 毫秒
141.
142.
Are different responses differentially associable with their consequences? An overshadowing design was used to try to answer this question for three responses previously studied in golden hamsters. In Experiment I, scrabbling was rapidly suppressed by electric shock punishment, and it overshadowed a tone which occurred between scrabbling and shock. In Experiment II, no evidence of response-shock association was obtained when open rearing was the punished response, and open rearing did not overshadow the tone. Punishment had some effect on face washing, but there was no statistically significant overshadowing with this response. These results are consistent with the idea that differences in punishment suppression among these three responses have an associative basis. They also demonstrate the usefulness of a novel paradigm for studying “preparedness” of response-reinforcer associations.  相似文献   
143.
144.
145.
146.
147.
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   
148.
149.
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   
150.
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