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   189322篇
  免费   8337篇
  国内免费   158篇
  197817篇
  2020年   2804篇
  2019年   3459篇
  2018年   3694篇
  2017年   4131篇
  2016年   4735篇
  2015年   3950篇
  2014年   4822篇
  2013年   23641篇
  2012年   4934篇
  2011年   4201篇
  2010年   4143篇
  2009年   4887篇
  2008年   4438篇
  2007年   3926篇
  2006年   4390篇
  2005年   4320篇
  2004年   3777篇
  2003年   3468篇
  2002年   3232篇
  2001年   4212篇
  2000年   4064篇
  1999年   3723篇
  1998年   2913篇
  1997年   2728篇
  1996年   2642篇
  1995年   2468篇
  1994年   2445篇
  1993年   2394篇
  1992年   3086篇
  1991年   2922篇
  1990年   2787篇
  1989年   2647篇
  1988年   2597篇
  1987年   2598篇
  1986年   2600篇
  1985年   2827篇
  1984年   2790篇
  1983年   2512篇
  1982年   2456篇
  1981年   2429篇
  1980年   2266篇
  1979年   2507篇
  1978年   2345篇
  1977年   2275篇
  1976年   2091篇
  1975年   2297篇
  1974年   2376篇
  1973年   2313篇
  1972年   1859篇
  1971年   1739篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
141.
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   
142.
143.
144.
145.
146.
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   
147.
148.
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   
149.
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