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   63126篇
  免费   1728篇
  国内免费   31篇
  2020年   490篇
  2019年   652篇
  2018年   4134篇
  2017年   3519篇
  2016年   3025篇
  2015年   852篇
  2014年   862篇
  2013年   3894篇
  2012年   1915篇
  2011年   3779篇
  2010年   3314篇
  2009年   2404篇
  2008年   2944篇
  2007年   3348篇
  2006年   1289篇
  2005年   1308篇
  2004年   1190篇
  2003年   1184篇
  2002年   1086篇
  2001年   1450篇
  2000年   1418篇
  1999年   1058篇
  1998年   562篇
  1997年   504篇
  1996年   478篇
  1995年   449篇
  1994年   442篇
  1993年   437篇
  1992年   847篇
  1991年   836篇
  1990年   785篇
  1989年   717篇
  1988年   663篇
  1987年   682篇
  1986年   660篇
  1985年   756篇
  1984年   622篇
  1983年   498篇
  1982年   413篇
  1981年   424篇
  1979年   556篇
  1978年   450篇
  1977年   419篇
  1976年   399篇
  1975年   501篇
  1974年   517篇
  1973年   552篇
  1972年   438篇
  1968年   403篇
  1966年   410篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
A growing literature has observed a significant reduction in pain sensitivity among hypertensive animals and humans. It is uncertain whether a reduced sensitivity to pain can be observed in nonnotensive individuals who go on to develop high blood pressure. Blood pressure (BP) was reassessed in one hundred fifteen 19-year-old boys initially tested at age 14, when they were also presented with a pain stimulus (mechanical finger pressure). Hierarchical regression analyses indicated that information regarding pain tolerance improved prediction of changes in systolic and diastolic blood pressure beyond that afforded by differences in BP at age 14, parental history of hypertension, and body mass index. These analyses suggest that pain sensitivity may be associated with physiological processes involved in the development of sustained high blood pressure.  相似文献   
62.
63.
64.
65.
66.
Main clause phenomena (MCPs) are syntactic constructions that occur predominantly or exclusively in main clauses. I propose a processing explanation for MCPs. Sentence processing is easiest at the beginning of the sentence (requiring less search); this follows naturally from widely held assumptions about sentence processing. Because of this, a wider variety of constructions can be allowed at the beginning of the sentence without overwhelming the sentence‐processing mechanism. Unlike pragmatic and grammatical accounts of MCPs, the processing account predicts avoidance of MCPs in non‐initial main clauses (non‐initial coordinate clauses and premodified clauses). A corpus study supports these predictions, but it is somewhat inconclusive. A further corpus study examines another type of syntactic construction, premodifying adjunct phrases (“openers”); the prediction here is that less common types of opener will be especially avoided in non‐initial contexts. The prediction is confirmed, supporting the processing view of rare constructions.  相似文献   
67.
Suicides among older adults in the United States and Canada in the last decade have accounted for an increasing share of all suicides. In both countries the use of firearms among older adults has steadily increased. Despite these trends, little is known about the extent to which crisis centers are prepared to prevent elder suicide. A survey of AAS-listed crisis prevention centers examined the training, knowledge, and current practices relevant to elder suicide among personnel in 321 crisis prevention centers in both countries. Results revealed insufficient training, a lack of familiarity with recent suicide trends, and limited outreach to older adults.  相似文献   
68.
Cancellation tests are commonly used in the clinical assessment of visuospatial function, but there has been little study of task characteristics influencing performance. This study was designed to assess factors which affect cancellation performance. Sixteen healthy subjects sequentially performed four random-array letter cancellation tasks. The forms contained 50 and 100 stimuli and target:distractor (T/D) ratios of 1:4 and 1:9 with target letter “A” and randomly selected letter distractors. The primary performance measure was calculated as the number of correctly cancelled targets divided by the time to complete the task, corrected for accuracy. This measure revealed a strong effect of T/D ratio (p< .0001), with performance adversely affected by higher proportion of distractors. There was no effect of stimulus number. This suggests that T/D ratio should be considered in cancellation test design and interpretation.  相似文献   
69.
70.
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