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   116759篇
  免费   4926篇
  国内免费   75篇
  121760篇
  2019年   1484篇
  2018年   1996篇
  2017年   2067篇
  2016年   2197篇
  2015年   1595篇
  2014年   1916篇
  2013年   9779篇
  2012年   3437篇
  2011年   3621篇
  2010年   2331篇
  2009年   2370篇
  2008年   3253篇
  2007年   3262篇
  2006年   3001篇
  2005年   2642篇
  2004年   2490篇
  2003年   2403篇
  2002年   2436篇
  2001年   3539篇
  2000年   3357篇
  1999年   2647篇
  1998年   1357篇
  1997年   1197篇
  1996年   1344篇
  1995年   1258篇
  1994年   1209篇
  1993年   1204篇
  1992年   2362篇
  1991年   2178篇
  1990年   2168篇
  1989年   1963篇
  1988年   1932篇
  1987年   1917篇
  1986年   1934篇
  1985年   1937篇
  1984年   1722篇
  1983年   1530篇
  1982年   1181篇
  1979年   1761篇
  1978年   1293篇
  1975年   1472篇
  1974年   1560篇
  1973年   1714篇
  1972年   1494篇
  1971年   1365篇
  1970年   1226篇
  1969年   1278篇
  1968年   1584篇
  1967年   1412篇
  1966年   1264篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
52.
53.
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   
54.
55.
56.
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   
57.
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   
58.
59.
60.
Previous work on children's intuitive knowledge about the natural world has documented their difficulty in acquiring an overarching concept of biological life that includes plants as well as humans and non‐human animals. It has also suggested that the acquisition of fundamental biological concepts like alive and die may be influenced by the language used to describe them, as evidenced by differences between English‐ and Indonesian‐speaking children's performance in tasks involving these concepts. Here, we examine one particularly important source of linguistic information available to children during this acquisition process: everyday conversations with their parents. We take a cross‐linguistic approach in analysing the evidence available to English‐ and Indonesian‐speaking children as they acquire meanings for words corresponding to the concepts alive and die . Our analysis illustrates that young children acquiring English and Indonesian are faced with distinct problems, but that parental input in both languages does little to support the acquisition of broad, inclusive biological concepts.  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