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   16462篇
  免费   629篇
  国内免费   4篇
  2019年   214篇
  2018年   259篇
  2017年   222篇
  2016年   260篇
  2015年   173篇
  2014年   261篇
  2013年   1276篇
  2012年   437篇
  2011年   494篇
  2010年   297篇
  2009年   320篇
  2008年   421篇
  2007年   450篇
  2006年   425篇
  2005年   351篇
  2004年   377篇
  2003年   335篇
  2002年   330篇
  2001年   452篇
  2000年   513篇
  1999年   344篇
  1998年   213篇
  1997年   164篇
  1996年   171篇
  1995年   172篇
  1992年   285篇
  1991年   292篇
  1990年   303篇
  1989年   288篇
  1988年   274篇
  1987年   247篇
  1986年   257篇
  1985年   271篇
  1984年   199篇
  1983年   212篇
  1982年   175篇
  1981年   161篇
  1980年   164篇
  1979年   262篇
  1978年   222篇
  1975年   218篇
  1974年   254篇
  1973年   279篇
  1972年   229篇
  1971年   220篇
  1970年   167篇
  1969年   203篇
  1968年   251篇
  1967年   242篇
  1966年   213篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
Only recently has determining the child-rearing concerns of parents been considered an important research objective. Existing efforts have, for the most part, either employed small sample sizes or surveyed parents already in the process of seeking help or advice. It was, therefore, felt that additional, more representative data were needed. In the present study, 583 mothers with children aged 59 months or younger were surveyed regarding their concerns about their children's development. On the „Specific Needs Assessment Report”︁ (SNAR) (copyright © 1975, by Karl F. Riem, J. Jeffrey Crisco, and Kathy Willms), mothers rated their concerns for 60 developmental-behavioral items about their children's health, attending skills, problem behaviors, communication skills, motor skills, cognitive skills, self-help skills, and social skills. Mothers were most frequently concerned to a moderate or major degree about at least one item of the problem behavior category. For this category, parent-child management, crying-whining, and temper tantrums were the individual items of greatest concern. Mothers of girls more frequently indicated health concerns than mothers of boys. These results support those of previous investigations, which suggested the need for parent education programs to help parents manage their children.  相似文献   
992.
Aggressive and sexual behavior was studied in 5-minute paired encounters between testosterone-treated castrated boars and estrogen-treated ovariectomized gilts. The boars were either 15 kg heavier (N = 6), or lighter (N = 6), than the gilts (N = 8). Tests were carried out over a 4-week period, during which time each boar was paired once with each gilt; the procedure was replicated over a further 4 weeks. Gilts usually initiated the aggression, especially in the first 4-week period; however, the degree of aggression was positively correlated with body size, irrespective of sex. Aggression was reduced in the second 4-week period in both sexes in tests with large, but not with small, boars. Large boars were more sexually active than small boars, and their sexual performance improved markedly with time, unlike that of the small boars. Champing was positively correlated with aggression duration in pigs of both sexes, and salivation was seen more often in boars than gilts.  相似文献   
993.
Female rats, chronically treated with Testosterone Propionate (TP), were injected with Fluprazine (DU 27716) or saline and tested for social aggression, masculine and feminine sexual behavior. Fluprazine-treated females were less aggressive than saline-treated females, as indicated by a shift from offensive to less offensive parameters of aggression. At the same time, mounting in Fluprazine-treated females was almost totally abolished, both in aggression tests and in tests for sexual behavior. Feminine sexual responses increased during aggressive encounters but were slightly inhibited when females were confronted with sexually active males. Females treated with Fluprazine and tested for mounting with a receptive female showed a substantial increase of offensive aggression directed at the receptive stimulus female. It is concluded that Fluprazine does not selectively inhibit offensive aggression in TP-treated female rats.  相似文献   
994.
The development of hand preference in infancy was investigated longitudinally by using a visually-directed reaching task. Thirty-two infants, equally divided into groups of familial right- and left-handed boys and girls, were tested every 3 weeks from 24 to 39 weeks of age and once again at 52 weeks. Group trends for the development of hand preference were differentiated by familial handedness and sex of the infant. At all ages, test object position (to the infant's right or left) strongly influenced the hand used for reaching. Marked variability both between and within infants demonstrated an instability of early hand preference, an effect that could be appreciated fully only with a prospective longitudinal design. The results thus suggest that the development of hand preference for reaching is highly variable, discontinuous, and related to the interaction of sex and familial handedness.  相似文献   
995.
Aggressive and sexual behaviour was studied in 5-min paired encounters between castrated prepubertal boars (N = 14) and normal (N = 2) or bulbectomized (N = 2) oestrogen-treated ovariectomized gilts. The boars were made sexually active by treatment with 17β-oestradiol + 5α-dihydrotestosterone. Half of the boars were sprayed on the snout with a solution containing a mixture of the boar pheromones 3α-androstenol and 5α-androstenone immediately before testing, and the remainder were treated with the vehicle solution. Aggression was almost always initiated by the gilts, and neither bulbectomy nor pheromone treatment of the boars reduced its occurrence. The results suggest that the display of aggression by gilts towards boars of similar body size is unlikely to be suppressed by the steroidal pheromones present in boar saliva.  相似文献   
996.
997.
Integrity of both cerebral hemispheres is required to control in-phase or anti-phase coupling of ipsilateral hand and foot oscillations, as shown by the impairment of these tasks when performed on the healthy side of hemiplegic patients. On this basis, coupling of hand–foot movements was analysed in a right-handed subject (ME) who underwent a total resection of the corpus callosum. Oscillations of the prone hand and foot, paced by a metronome at different frequencies, as well as EMG activity in extensor carpi radialis (ECR) and tibialis anterior (TA) muscles were analysed by measuring the average phase difference between the hand and foot movements and EMG cycles.

ME performed in-phase movements (right-hand extension coupled to right-foot dorsal flexion) at frequencies up to 3 Hz, though the hand cycle progressively lagged the foot cycle as the frequency increased. At 3 Hz the hand lag reached −142° (as compared to about 25° in healthy subjects). The lag increased even further after application of an inertial load to the hand, reaching 180° at 1.8 Hz (about 50° in healthy subjects). ME's hand lag is caused by the lack of any anticipatory reaction in hand movers. In contrast to healthy subjects, which activate the ECR earlier than the TA when the frequency increases, ME activated the ECR later than TA at all frequencies higher than 0.9 Hz.

Anti-phase movements (hand extension coupled to foot plantar flexion) were performed only upto 1 Hz in unloaded conditions. At 0.6 Hz, movements were in tight phase-opposition (3°), but at 1 Hz, the hand lag reached −34° because of a delayed ECR activation. After hand loading ME was unable to couple movements in anti-phase. In contrast, normal subjects maintain a tight anti-phase coupling up to 2.0 Hz, both with an unloaded or loaded hand. Similar deficits were observed by ME when performing in-phase and anti-phase coupling on the left side, as well as when he was blindfolded.

In normal subjects, an anticipated muscular activation of hand movers compensates for hand loading. Since this compensation must depend on monitoring the hand delay induced by loading, the absence in ME of such compensatory reaction suggests that callosal division had apparently compromised the mechanisms sustaining feedback compensation for differences in the biomechanical limb properties. They also confirm and reinforce the idea that elaboration of the afferent message, aiming at controlling the phase of the movement association, needs the co-operation of both cerebral hemispheres.  相似文献   

998.
This longitudinal study examined adolescent girls' perception of control over sexually transmitted disease (STD) acquisition. Participants were asked questions regarding their perception of their STD locus of control (internal control; control by parents, partners, peers, and health care providers; and chance) at two waves of data collection. Of the 116 participants (mean age = 17 years), 82% were African-American and 18% were Caucasian. Responses to the measure of locus of control were significantly correlated across a 6-month interval. The responses regarding internal control, control by partner, and chance were not related to the acquisition of an STD in the next 6 months. Further, they were not influenced by an STD in the preceding 6 months. These results indicate that responses to a locus of control measure were stable over a 6-month period, and internal, partner, and chance locus of control perceptions seem to be neither determined by STD experience nor directly related to future STD acquisition. However, understanding an individual's locus of control may be helpful in providing appropriate counseling. Future research could examine how adolescent girls form their perceptions of control over STD acquisition.  相似文献   
999.
The literature suggests that a multitude of psychological and social factors can interact to place adolescents at risk for aggression and violence. This study examined three of these factors: personality, affect, and family. Using a heterogeneous sample of male adolescents at risk for violence, a hierarchical, agglomerative cluster analysis was conducted to categorize these adolescents in terms of personality characteristics. Results of the analysis suggested three clusters of at-risk adolescents. Examination of the three cluster types found distinctions between groups on anger expression, trait anger, and trait anxiety, but not family control. It was concluded that, among male delinquents, elevated psychopathology is associated with higher anger and anxiety, but not higher family control.  相似文献   
1000.
Zaff JF  Blount RL  Phillips L  Cohen L 《Adolescence》2002,37(148):751-773
Much coping research has been conducted comparing members of different ethnic groups using discrete racial classifications. However, the past two decades have seen the construct of ethnicity evolve into a complex variable that must be assessed in a more comprehensive way. This study explored how ethnicity, a discrete variable, and the continuous variables of a person's ethnic identity and self-construal contribute to the use of particular coping strategies across various situations. One hundred twelve seventh graders (67 African Americans and 45 Caucasian Americans) from three suburban middle schools completed questionnaires assessing ethnic identity, self-construal, and coping strategies for medical, test, and social criticism stressors. Results supported the hypothesis that ethnicity as a discrete variable is not associated with coping, but that ethnic identity and self-construal are. It was also found that high scores on the ethnic identity and self-construal scales were indicative of more positive psychological adjustment. Implications for future research and methodological considerations are discussed.  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