全文获取类型
收费全文 | 10669篇 |
免费 | 104篇 |
国内免费 | 19篇 |
专业分类
教育 | 7219篇 |
科学研究 | 1260篇 |
各国文化 | 61篇 |
体育 | 1036篇 |
综合类 | 4篇 |
文化理论 | 83篇 |
信息传播 | 1129篇 |
出版年
2023年 | 59篇 |
2022年 | 90篇 |
2021年 | 152篇 |
2020年 | 187篇 |
2019年 | 265篇 |
2018年 | 428篇 |
2017年 | 390篇 |
2016年 | 384篇 |
2015年 | 216篇 |
2014年 | 343篇 |
2013年 | 1685篇 |
2012年 | 306篇 |
2011年 | 328篇 |
2010年 | 298篇 |
2009年 | 256篇 |
2008年 | 293篇 |
2007年 | 256篇 |
2006年 | 249篇 |
2005年 | 211篇 |
2004年 | 230篇 |
2003年 | 167篇 |
2002年 | 176篇 |
2001年 | 231篇 |
2000年 | 224篇 |
1999年 | 207篇 |
1998年 | 121篇 |
1997年 | 145篇 |
1996年 | 120篇 |
1995年 | 83篇 |
1994年 | 105篇 |
1993年 | 78篇 |
1992年 | 177篇 |
1991年 | 133篇 |
1990年 | 130篇 |
1989年 | 150篇 |
1988年 | 136篇 |
1987年 | 106篇 |
1986年 | 116篇 |
1985年 | 116篇 |
1984年 | 88篇 |
1983年 | 96篇 |
1982年 | 63篇 |
1981年 | 78篇 |
1980年 | 65篇 |
1979年 | 111篇 |
1978年 | 70篇 |
1977年 | 69篇 |
1975年 | 61篇 |
1974年 | 67篇 |
1973年 | 58篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
981.
982.
In this article, we discuss at length a combinatorial problem which has been of historic interest. It has appeared as a puzzle in several different versions with varying degrees of difficulty. It can be simply stated as follows: We are given a number of coins which are otherwise identical except that there may be at most one fake coin among them which is either slightly heavier or slightly lighter than the other genuine coins. Using only a two-pan weighing balance, we must devise a weighing scheme to identify the counterfeit coin and determine whether it is heavier or lighter (or declare that all coins are normal). We construct both sequential and non-sequential (that is, simultaneously declared) weighing plans for any given number of coins containing at most one fake coin using the minimum number of weighings needed. 相似文献
983.
Wootton-Gorges SL Stein-Wexler R Walton JW Rosas AJ Coulter KP Rogers KK 《Child abuse & neglect》2008,32(6):659-663
PURPOSE: Chest radiographs (CXR) are the standard method for evaluating rib fractures in abused infants. Computed tomography (CT) is a sensitive method to detect rib fractures. The purpose of this study was to compare CT and CXR in the evaluation of rib fractures in abused infants. METHODS: This retrospective study included all 12 abused infants identified from 1999 to 2004 who had rib fractures and both CXR and CT (8 abdomen CTs, 4 chest CTs). CT exams had been performed for clinical indications, and were obtained within one day of the CXR. Studies were reviewed by two pediatric radiologists to determine the number, locations, and approximate ages of the rib fractures. A total of 225 ribs were completely (192) or partially (33) seen by CT, and the matched ribs on CXR were used for the analysis. RESULTS: The mean patient age was 2.5 months (1.2-5.6), with seven females and five males. While 131 fractures were visualized by CT, only 79 were seen by CXR (p<.001). One patient had fractures only seen by CT. There were significantly (p<.05) more early subacute (24 vs. 4), subacute (47 vs. 26), and old fractures (4 vs. 0) seen by CT than by CXR. Anterior (42 vs. 11), anterolateral (21 vs. 12), posterolateral (9 vs. 3) and posterior (39 vs. 24) fractures were better seen by CT than by CXR (p<.01). Bilateral fractures were detected more often by CT (11) than by CXR (6). CONCLUSIONS: While this study group is small, these findings suggest that CT is better than CXR in visualizing rib fractures in abused infants. 相似文献
984.
K C Faller 《Child abuse & neglect》1985,9(1):63-69
While the United States child protection system is widely recognized as probably the most sophisticated and wide-ranging in the world, it nevertheless has some inherent problems. This article addresses some of the negative effects of mandatory reporting and the lack of fit of a short-term crisis intervention treatment approach for a substantial proportion of the protective services population. Reporting may have detrimental effects on the client-reporter relationship. Further, over half of the cases investigated are not substantiated. Of concern are the impact on innocent families of being investigated and the waste of scarce worker resources on investigation. While some protective services families are well suited to a crisis intervention model, a large number are multiproblem families who are always in crisis and families with chronic problems for whom crisis intervention is totally inadequate. Furthermore, because of high caseload size, workers are often not available to intervene after they have investigated the case. The problems described have been exacerbated by funding cutbacks under the current United States administration. The child protection system, along with other social welfare programs, is at risk for being dismantled by the Reagan administration. 相似文献
985.
Judith K. Bernhard Luz Bascunan Rodolfo Arenas Nury Rugeles Verga Daniel Gana 《Early Years: An International Journal of Research and Development》2004,24(1):49-62
Thirty‐eight Latin American mothers with young children tell of their perceptions of school discipline and comportment issues and talk of their children's encounters with ‘zero tolerance’ legislation, and related rules for conduct, implemented by the local school boards. The purpose of this exploratory study is to understand: (a) parents' views of and concern about disciplinary practices at school; (b) parents' ideas about the connection between home and school discipline; and (c) parents' understanding of the officially prescribed consequences of behaviour identified as non‐tolerable. Implications of the findings are discussed with regard to professional practice. 相似文献
986.
A K Shukla 《Resonance》2001,6(11):49-62
Road transportation as an important requirement of modern society is presently faced with restrictions in mainly two respects,
namely the ever tightening emission legislation as well as the availability of petroleum fuels, and as a consequence the fuel
cost. But in any review of power sources for future road transport vehicles, the performance of the existing internal combustion
engine is likely to be the yardstick against which other power sources will be compared. The power sources most likely to
provide favourable comparison are those, which can display comparable range and speed, long and reliable life and manufactured
at a cost comparable to petrol engine. A vehicle which fails in any of these requirements is unlikely to achieve anything
but a niche market share. This article is an appraisal of a variety of proposed electrochemical systems, viz. rechargeable
batteries, fuel cells and supercapacitors, for an electric car. It is surmised that a viable electric car could be powered
with a fuel cell to provide power for cruising and climbing coupled in parallel with a supercapacitor/battery bank to deliver
additional short-term burst-power during acceleration.
A K Shukla is a Professor at the Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore. His current
research interests are in materials electrochemistry with special emphasis on batteries, fuel cells and supercapacitors. 相似文献
987.
Lauren A. Barth-Cohen Michelle K. Smith Daniel K. Capps Justin D. Lewin Jonathan T. Shemwell MacKenzie R. Stetzer 《Journal of Science Education and Technology》2016,25(1):50-61
There is a growing interest in using classroom response systems or clickers in science classrooms at both the university and K-12 levels. Typically, when instructors use this technology, students are asked to answer and discuss clicker questions with their peers. The existing literature on using clickers at the K-12 level has largely focused on the efficacy of clicker implementation, with few studies investigating collaboration and discourse among students. To expand on this work, we investigated the question: Does clicker use promote productive peer discussion among middle school science students? Specifically, we collected data from middle school students in a physical science course. Students were asked to answer a clicker question individually, discuss the question with their peers, answer the same question again, and then subsequently answer a new matched-pair question individually. We audio recorded the peer conversations to characterize the nature of the student discourse. To analyze these conversations, we used a grounded analysis approach and drew on literature about collaborative knowledge co-construction. The analysis of the conversations revealed that middle school students talked about science content and collaboratively discussed ideas. Furthermore, the majority of conversations, both ones that positively and negatively impacted student performance, contained evidence of collaborative knowledge co-construction. 相似文献
988.
Oshana D Harding K Friedman L Holton JK 《Child abuse & neglect》2005,29(3):219-28; author reply 241-9
989.
990.
Nelson ES Coleman PK Swager MJ 《The Journal of humanistic education and development》1997,35(4):217-224
College students completed a questionnaire that assessed their attitudes toward the level of male responsibility in abortion decisions. Overall, both men and women thought that men should have some degree of involvement in the abortion decision. However, as expected by the first hypothesis, men indicated a desire for more responsibility in the abortion decision than women thought the men should have. A second hypothesis predicted women would feel more strongly than men that abortion was strictly a woman's issue. Contrary to the hypothesis, women tended to disagree that abortion was strictly a women's issue. Implications of the findings are discussed. 相似文献