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   14375篇
  免费   582篇
  国内免费   3篇
  2020年   173篇
  2019年   228篇
  2018年   271篇
  2017年   306篇
  2016年   330篇
  2015年   260篇
  2014年   305篇
  2013年   1433篇
  2012年   528篇
  2011年   535篇
  2010年   367篇
  2009年   338篇
  2008年   462篇
  2007年   440篇
  2006年   419篇
  2005年   366篇
  2004年   372篇
  2003年   355篇
  2002年   410篇
  2001年   305篇
  2000年   295篇
  1999年   281篇
  1998年   193篇
  1997年   168篇
  1996年   159篇
  1995年   165篇
  1994年   143篇
  1993年   153篇
  1992年   218篇
  1991年   210篇
  1990年   197篇
  1989年   175篇
  1988年   157篇
  1987年   160篇
  1986年   164篇
  1985年   184篇
  1984年   192篇
  1983年   189篇
  1982年   163篇
  1981年   196篇
  1980年   157篇
  1979年   224篇
  1978年   179篇
  1977年   167篇
  1976年   163篇
  1975年   176篇
  1974年   205篇
  1973年   153篇
  1972年   139篇
  1969年   137篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
The increasing number of companies providing internet services and auction tools helped popularize the online reverse auction trend for purchasing commodities and services in the last decade. As a result, a number of owners, both public and private, accepted the online reverse auctions as the bidding technique for their construction projects. Owners, while trying to minimize their costs for construction projects, are also required to address their ethical responsibilities to the shareholders. In the case of online reverse auctions for construction projects, the ethical issues involved in the bidding technique directly reflects on the owner’s ethical and social responsibilities to their shareholders. The goal of this paper is to identify the shareholder ethics and responsibilities in online reverse auctions for construction projects by analyzing the ethical issues for the parties involved in the process. The identification of the ethical issues and responsibilities requires clear definition and understanding of professional ethics and the roles of the involved parties. In this paper, first, the concept of professional ethics and social responsibility is described in a general form. To illustrate the ethical issues and responsibilities, a sample case of bidding for a construction project using online reverse auction techniques is presented in which the shareholders were actively involved in questioning the ethical issues. The issues involved in the bidding process and their reflection on the shareholder responsibilities are described and analyzed for each stage of the process. A brief discussion of the overall process is also included to address the general ethical issues involved in online reverse auctions. An earlier version of this paper was presented at the “Ethics and Social Responsibility in Engineering and Technology” meeting, New Orleans, 2003.  相似文献   
994.
Event-related potentials (ERPs) to tone pairs and single tones were measured for 16 participants with specific language impairment (SLI) and 16 age-matched controls aged from 10 to 19 years The tone pairs were separated by an inter-stimulus interval (ISI) of 20, 50 or 150 ms. The intraclass correlation (ICC) was computed for each participant between the ERP to a single tone and the ERP to the tone pair. A high ICC indicates that the brain response to a tone pair is similar to that for a single tone. ICCs were significantly higher at short than at long ISIs. At 50-ms ISI, ICCs were higher for younger than older participants. Age and ISI interacted with SLI status: ERPs of older participants with SLI differed from age-matched controls, and resembled ERPs of younger controls, consistent with a theory of immature auditory processing in SLI.  相似文献   
995.
In order to examine the concurrent and criterion validity of the questionnaire version of the Eating Disorders Examination (EDE-Q), self-report and interview formats were administered to a community sample of women aged 18-45 (n = 208). Correlations between EDE-Q and EDE subscales ranged from 0.68 for Eating Concern to 0.78 for Shape Concern. Scores on the EDE-Q were significantly higher than those of the EDE for all subscales, with the mean difference ranging from 0.25 for Restraint to 0.85 for Shape Concern. Frequency of both objective bulimic episodes (OBEs) and subjective bulimic episodes (SBEs) was significantly correlated between measures. Chance-corrected agreement between EDE-Q and EDE ratings of the presence of OBEs was fair, while that for SBEs was poor. Receiver operating characteristic (ROC) analysis, based on a sample of 13 cases, indicated that a score of 2.3 on the global scale of the EDE-Q in conjunction with the occurrence of any OBEs and/or use of exercise as a means of weight control, yielded optimal validity coefficients (sensitivity = 0.83, specificity = 0.96, positive predictive value = 0.56). A stepwise discriminant function analysis yielded eight EDE-Q items which best distinguished cases from non-cases, including frequency of OBEs, use of exercise as a means of weight control, use of self-induced vomiting, use of laxatives and guilt about eating. The EDE-Q has good concurrent validity and acceptable criterion validity. The measure appears well-suited to use in prospective epidemiological studies.  相似文献   
996.
We evaluated computerized training and testing programs with children who were having difficulties learning prereading skills. The programs were derived from equivalence research and were written in authoring software designed for educators. After learning to match uppercase and lowercase printed letters to the corresponding letter names (Tasks 1 and 2), the children matched the letters to one another (Tasks 4 and 5). Then, after learning to match uppercase letters to sounds (Task 3), they also matched lowercase letters to sounds (Task 6) and matched printed to spoken words (Tasks 7 and 8). The results recommend equivalence-based protocols and user-friendly software in further development of prereading instruction.  相似文献   
997.
Eight crows were taught to discriminate overlapping pairs of visual stimuli (A+ B-, B+ C-, C+ D-, and D+ E-). For 4 birds, the stimuli were colored cards with a circle of the same color on the reverse side whose diameter decreased from A to E (ordered feedback group). These circles were made available for comparison to potentially help the crows order the stimuli along a physical dimension. For the other 4 birds, the circles corresponding to the colored cards had the same diameter (constant feedback group). In later testing, a novel choice pair (BD) was presented. Reinforcement history involving stimuli B and D was controlled so that the reinforcement/nonreinforcement ratios for the latter would be greater than for the former. If, during the BD test, the crows chose between stimuli according to these reinforcement/nonreinforcement ratios, then they should prefer D; if they chose according to the diameter of the feedback stimuli, then they should prefer B. In the ordered feedback group, the crows strongly preferred B over D; in the constant feedback group, the crows' choice did not differ significantly from chance. These results, plus simulations using associative models, suggest that the orderability of the postchoice feedback stimuli is important for crows' transitive responding.  相似文献   
998.
The authors examined participants' estimates of own and parental psychometric intelligence (IQ) and emotional intelligence (EI). The authors asked 224 participants (82 men, 138 women, 4 people who did not report their gender) to estimate their own and their parents' IQ and EI scores on a normal distribution ranging from 55 to 145 points. The authors hypothesized that men would give higher IQ but lower EI self-estimates than women and that participants, regardless of gender, would rate their fathers as higher on IQ but lower on EI than their mothers. The results confirmed the hypotheses, supporting the view that people perceive psychometric intelligence as a primarily masculine attribute in contrast with emotional intelligence, which they perceive as a primarily feminine attribute. The results also showed that the intensity of the stereotypical perception of EI as a feminine attribute diminished when the authors asked participants to estimate their scores on a range of specific EI facets instead of providing a direct overall self-estimate.  相似文献   
999.
In two experiments, we examined the effects of task and location switching on the accuracy of reporting target characters in an attentional blink (AB) paradigm. Single-character streams were presented at a rate of 100 msec per character in Experiment 1, and successive pairs of characters on either side of fixation were presented in Experiment 2. On each trial, two targets appeared that were either white letters or black digits embedded in a stream of black letter distractors, and they were separated by between zero and five items in the stream (lags 1-6). Experiment 1 showed that report of the first target was least accurate if it immediately preceded the second target and if the two targets were either both letters or both digits (task repetition cost). Report of the second target was least accurate if one or two distractors intervened between the two targets (the U-shaped AB lag effect) and if one target was a letter and the other a digit (task switch cost). Experiment 2 added location uncertainty as a factor and showed similar effects as Experiment 1, with one exception. Lag 1 sparing (the preserved accuracy in reporting the second of two targets if the second immediately follows the first) was completely eliminated when the task required attention switching across locations. Two-way additive effects were found between task switching and location switching in the AB paradigm. These results suggests separate loci for their attentional effects. It is likely that the AB deficit is due mainly to central memory limitations, whereas location-switching costs occur at early visual levels. Task-switching costs occur at an intermediate visual level, since the present task switch involved encoding differences without changes in stimulus-response mapping rules (i.e., the task was character identification for both letters and digits).  相似文献   
1000.
Two experiments are reported in which linear separability was investigated in superordinate natural language concept pairs (e.g., toiletry-sewing gear). Representations of the exemplars of semantically related concept pairs were derived in two to five dimensions using multidimensional scaling (MDS) of similarities based on possession of the concept features. Next, category membership, obtained from an exemplar generation study (in Experiment 1) and from a forced-choice classification task (in Experiment 2) was predicted from the coordinates of the MDS representation using log linear analysis. The results showed that all natural kind concept pairs were perfectly linearly separable, whereas artifact concept pairs showed several violations. Clear linear separability of natural language concept pairs is in line with independent cue models. The violations in the artifact pairs, however, yield clear evidence against the independent cue models.  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