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   81965篇
  免费   3102篇
  国内免费   27篇
  2019年   907篇
  2018年   1359篇
  2017年   1376篇
  2016年   1533篇
  2015年   1082篇
  2014年   1231篇
  2013年   5817篇
  2012年   2442篇
  2011年   2616篇
  2010年   1522篇
  2009年   1497篇
  2008年   2171篇
  2007年   2147篇
  2006年   1996篇
  2005年   2827篇
  2004年   2189篇
  2003年   1910篇
  2002年   1760篇
  2001年   2409篇
  2000年   2361篇
  1999年   1819篇
  1998年   897篇
  1997年   840篇
  1996年   840篇
  1995年   757篇
  1992年   1588篇
  1991年   1482篇
  1990年   1474篇
  1989年   1352篇
  1988年   1337篇
  1987年   1270篇
  1986年   1392篇
  1985年   1384篇
  1984年   1177篇
  1983年   1066篇
  1982年   761篇
  1981年   769篇
  1979年   1253篇
  1978年   924篇
  1976年   765篇
  1975年   1041篇
  1974年   1179篇
  1973年   1284篇
  1972年   1049篇
  1971年   1015篇
  1970年   911篇
  1969年   959篇
  1968年   1197篇
  1967年   1075篇
  1966年   983篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Differential K Theory is proposed to help systematize individual and group differences in life histories, social behaviour and physiological functioning. K refers to one end of a continuum of reproductive strategies organisms can adopt, characterized by the production of very few offspring with a large investment of energy in each. At the opposite extreme is the r-strategy in which organisms produce a large number of offspring but invest little energy in any one. Between-species comparisons demonstrate that these reproductive strategies correlate with a variety of life history traits including: litter size, birth-spacing, parental care, infant mortality, developmental precocity, life span, intelligence, social organization and altruism. As a species, humans are at the K end of the continuum. Some people, however, are postulated to be more K than others. The more K a person is, the more likely he or she is to come from a smaller sized family, with a greater spacing of births, a lower incidence of DZ twinning, and more intensive parental care. Moreover, he or she will tend to be intelligent, altruistic, law-abiding, behaviourally restrained, maturationally delayed, lower in sex drive and longer lived. Thus diverse organismic characteristics, not otherwise relatable, are presumed to covary along the K dimension. Group differences are also hypothesized, such that, in terms of K: higher socio-economic > lower socio-economic; and Mongoloids > Caucasoids > Negroids.  相似文献   
992.
993.
994.
The present study explored the factors that contribute to mothers' decisions to seek urgent medical attention for their children when symptoms are not of a traumatic nature. One hundred mothers seeking treatment for their children at a prepaid clinic completed a questionnaire eliciting their expectations regarding the course of their children's problems, seriousness of the problems, perceived responsibility for the symptoms, and extent to which a variety of factors contributed to their decisions to seek treatment. Demographic data and information about each child's symptoms and medical history were also obtained. Four major "reasons for seeking treatment" factors were identified: family history of the presenting complaint, worry regarding the symptoms, situational variables, and the extent of the child's illness behavior. The appropriateness of the visit, delay in seeking treatment, and frequency of mothers' use of the pediatric clinic were predicted by the nature of the presenting symptoms (particularly the presence of fever), the ages of the mother and child, and two of the reasons for seeking treatment factors (i.e., family history and child's illness behavior). The present study suggests that mothers pay more attention to presenting symptoms and to the children's behavior than to psychosocial stressors in deciding to seek urgent care.  相似文献   
995.
In an earlier study, we found that men who smoked a cigarette and then engaged in a mildly stressful activity (video game) evidenced pronounced increases in heart rate and blood pressure, which were approximately equal to the sum of the effects produced by either smoking alone or stress alone. In the present study, a 2 (smoke vs. sham smoke) X 2 (stress vs. no stress) factorial design was used to evaluate the impact of stress and smoking on the cardiovascular responses of young women. The results revealed that the combination of stress and cigarette smoking produced blood pressure and heart rate responses that were larger than the additive effects of smoking and stress taken separately.  相似文献   
996.
Previous studies have examined intra-individual aggregation in the use of cigarettes, alcohol, and coffee by examining the co-occurrent use of any pair of these three substances. A recent literature review failed to find a single investigation that studied use of all three in the same sample. In the present study, co-occurrent use of all three of these substances was examined in crossvalidated subsamples of 226 male and 245 female healthy, community-living, middle-class Americans. A log-linear analysis was used to compare the proportion of smokers, ex-smokers, and nonsmokers categorized as users of more or less amounts of coffee and alcohol. Although most of the intercorrelations were not strong, the results indicate that for both sexes, smokers and ex-smokers were more likely than nonsmokers to drink greater amounts of alcohol and coffee. Furthermore, for smokers, ex-smokers, and nonsmokers, a majority of individuals who reported drinking more alcohol also reported drinking more coffee. Interestingly, the coffee and alcohol consumption levels of ex-smokers resembled those of smokers more than those of nonsmokers. Also, ex-smokers reported drinking more wine and decaffeinated coffee than either smokers or nonsmokers. Finally, the number of cigarettes smoked per day (daily quantity) was positively related to total alcohol and coffee consumption in men, but not in women. Further studies are recommended to examine the role of individual differences in the development, maintenance, and modification of these three appetitive habits and their co-occurrence.  相似文献   
997.
The Jenkins Activity Survey (JAS) and the Framingham Type A Scale (FTAS) have been found to have different psychological correlates. The JAS is typically unrelated to anxiety, while the FTAS is consistently correlated with trait anxiety. The present study of 200 male and female college students clarifies further the psychological heterogeneity of these measures. Enhanced motivation to control the environment has been suggested as an underlying psychological component of Type A behavior (Glass, 1977). Dysphoric emotions and the perception of more environmental stresses, on the other hand, are typical of neuroticism or negative affectivity (Watson & Clark, 1984). Although the results indicate that the JAS and FTAS are highly correlated, the JAS is more closely related to control motivation than is the FTAS. Further, compared to the JAS, the FTAS is more closely correlated with dysphoric emotions and perceived daily stresses. Thus, the results indicate that the JAS is closely correlated with core psychological components of the Type A pattern, while the FTAS has a relatively unique association with general emotional distress. Such differences may account for the fact that these measures are related to different disease end points.  相似文献   
998.
Two adult male chimpanzees reached through a hole in the wall of their home cage and, by tracking the images of their hands and of an otherwise hidden target object in a mirror or closed-circuit television picture, moved their hands in whichever direction was necessary to make contact with the target object. They discriminated between live video images and tapes and performed effectively when the target objects were presented in novel locations and when the video picture was presented at random in different orientations. There was thus no consistent relation between the location of images on the monitor and the location of their real-world counterparts. Comparable performances in monkeys and nonprimates seem unlikely.  相似文献   
999.
Due to the death of a severely disabled infant from Bloomington, Indiana, a series of events set in motion by the U.S. Department of Health and Human Services has resulted in cautions to health care providers. The resulting policies and procedures warn hospital personnel against withholding nutritional sustenance or medical treatment from severely disabled infants. This article presents dimensions that might serve as a background for counselors to assist families in considering options related to disabled infants. These dimensions include the meaning of life, cost to benefit ratio, medical options, legal precedent, and a theological perspective. This issue is related to counseling practice through counselor ethics, values, and the need for information that counselors can provide to parents during the decision process.  相似文献   
1000.
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