全文获取类型
收费全文 | 11779篇 |
免费 | 151篇 |
专业分类
11930篇 |
出版年
2020年 | 139篇 |
2019年 | 201篇 |
2018年 | 453篇 |
2017年 | 424篇 |
2016年 | 542篇 |
2015年 | 218篇 |
2014年 | 206篇 |
2013年 | 2610篇 |
2012年 | 302篇 |
2011年 | 448篇 |
2010年 | 456篇 |
2009年 | 310篇 |
2008年 | 306篇 |
2007年 | 301篇 |
2006年 | 217篇 |
2005年 | 164篇 |
2004年 | 153篇 |
2003年 | 128篇 |
2002年 | 141篇 |
2001年 | 153篇 |
2000年 | 153篇 |
1999年 | 192篇 |
1998年 | 136篇 |
1997年 | 90篇 |
1996年 | 101篇 |
1995年 | 111篇 |
1994年 | 102篇 |
1993年 | 112篇 |
1992年 | 113篇 |
1991年 | 82篇 |
1990年 | 89篇 |
1989年 | 93篇 |
1988年 | 104篇 |
1987年 | 105篇 |
1986年 | 113篇 |
1985年 | 139篇 |
1984年 | 141篇 |
1983年 | 147篇 |
1982年 | 113篇 |
1981年 | 122篇 |
1980年 | 135篇 |
1979年 | 120篇 |
1978年 | 104篇 |
1977年 | 129篇 |
1976年 | 99篇 |
1975年 | 105篇 |
1974年 | 110篇 |
1973年 | 91篇 |
1971年 | 85篇 |
1969年 | 79篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Steven M. Manson Heather A. Sander Debarchana Ghosh J. Michael Oakes Myron W. Orfield Jr William J. Craig Thomas F. Luce Jr Eric Myott Shipeng Sun 《Geography Compass》2009,3(2):698-726
Parcel data, or information about individual plots of land, may be used to examine a broad range of social and environmental issues. While analog parcel information has long been available, the move towards digital georeferenced data offers a more readily available means of using detailed structural and land use information. Parcels map onto useful units of analysis such as individuals and households, and serve as the foci of policy institutions tasked with functions such as taxation, schooling, zoning, or public health. The promise of digital parcel data is offset by challenges related to format, availability, maintenance, quality, augmentation, and confidentiality. We examine the use of digital parcel data in research and policy with special reference to land use, public health, education, and environmental applications. We also make recommendations for improving and using parcel datasets. 相似文献
993.
Historia, Antropología y Fuentes Orales (HAYFO) is aSpanish-language journal for the study of oral data across diversedisciplinary traditions, such as history, anthropology, andsociology. The journal is edited by Asociación Historiay Fuente Oral, Arxiu Històric de la Ciutat de Barcelona,and Editorial Universidad de Granada. HAYFO first saw the lightin 1989 and is published biannually in Spain. The thirty-seventh issue of the journal is an exciting mix ofarticles with a variety of theoretical and empirical merits.This issue is divided into four main sections. The first sectionis entitled \"Denouncement and opacity.\" This section 相似文献
994.
Abstract This paper sets out to explore the phenomenon that the authors have entitled Dark Tourism and to analyse evidence of its existence in the context of sites associated with the life and death of the former US President, John F. Kennedy (JFK). These sites present front‐line staff, curators, and development bodies with dilemmas concerning legitimacy of presentation/representation and lead to questions about the, often cited, educational mission, of such attractions. The media has had a central role in the development of this phenomenon and documentation and illustration via news and film has been central to much of the interpretation of JFK and the Kennedys. This paper considers media fascination with this subject and examines exploitation of this interest at three, contrasting sites. 相似文献
995.
Michael J. Turner 《Journal of Victorian Culture》2013,18(4):531-548
AbstractVictorian attitudes to the past were varied and in some cases irreconcilable. Newer standards of expertise and objectivity coexisted with older approaches, and the idea that history should be used for present purposes remained intact. Throughout the Victorian age there were circumstances in which history was a polemical tool, designed to give one set of interpretations or values or policies an advantage over its rivals. This article explores the work of a relatively neglected figure in Victorian historiography – the reform-minded historian and lawyer Andrew Bisset (1803–1891) – whose primary goal was to illustrate and advance what he called ‘the principle of representation’. He discussed people and events of the past to this end, offending reviewers along the way because of his obvious political agenda, but also developing a rigorous source-based style, usefully evaluating for his readers the work of Macaulay, Carlyle, and others, and helping to shape Victorian opinion about, in particular, the political and religious crises of seventeenth-century Britain. Like others, Bisset believed that the disputes of that period had relevance to the public controversies of his own day. This article is designed to contribute to ongoing debates about the Victorians’ relationship with the past. 相似文献
996.
997.
The concept of equivalent linearization of nonlinear system response as applied to direct displacement-based design is evaluated. Until now, Jacobsen's equivalent damping approach combined with the secant stiffness method has been adopted for the linearization process in direct displacement-based design. Four types of hysteretic models and a catalog of 100 ground motion records were considered. The evaluation process revealed significant errors in approximating maximum inelastic displacements due to overestimation of the equivalent damping values in the intermediate to long period range. Conversely, underestimation of the equivalent damping led to overestimation of displacements in the short period range, in particular for effective periods less than 0.4 seconds. The scatter in the results ranged between 20% and 40% as a function of ductility. New equivalent damping relations for four structural systems, based upon nonlinear system ductility and maximum displacement, are proposed. The accuracy of the new equivalent damping relations is assessed, yielding a significant reduction of the error in predicting inelastic displacements. Minimal improvement in the scatter of the results was achieved, however. While many significant studies have been conducted on equivalent damping over the last 40 years, this study has the following specific aims: (1) identify the scatter associated with Jacobsen's equivalent damping combined with the secant stiffness as utilized in Direct Displacement-Based Design; and (2) improve the accuracy of the Direct Displacement-Based Design approach by providing alternative equivalent damping expressions. 相似文献
998.
Georgia E. Thermou Stavroula J. Pantazopoulou Amr S. Elnashai 《Journal of Earthquake Engineering》2013,17(4):582-606
This article presents a design methodology for seismic upgrading of existing reinforced concrete (RC) buildings. The methodology is based on the modification of the deflected shape of the structure so as to achieve a near-uniform distribution of interstorey drift along the building height, thereby eliminating damage localization. Yield Point Spectra are utilized for the definition of demand and a direct displacement-based design approach is implemented. The fundamental steps of the method are described in detail, including a systematic evaluation of assumptions and limitations. A full-scale tested structure is used as a case study for assessment and verification of the proposed methodology. Alternative retrofit scenarios are set according to target response and performance levels. The role of the target deflected response shape and its influence on the outcome of the retrofit strategy is investigated. The viability of the alternative retrofit scenarios is studied for different ground motions including near-fault earthquake records. 相似文献
999.
P-Δ effects can cause instability if they are not properly accounted for during the design of bridge piers and other structures. When a bridge pier is designed with the Direct Displacement-Based Design Method, P-Δ effects are evaluated at the end of the design process and compared to the flexural strength of the pier to find a stability index. If the stability index exceeds the specified value, the design must be repeated, iteratively reducing the target design displacement. This article presents a model that when used at the beginning of design (without knowledge of strength) allows the estimation of the maximum lateral displacement that a bridge pier can sustain without exceeding the specified value of the stability index, therefore eliminating the need for iteration. The examples that are presented prove that the model is accurate and very useful for design of extended pile bents. 相似文献
1000.
Da Ha Tarek H. Abdoun Michael J. O'Rourke Michael D. Symans Thomas D. O'Rourke Michael C. Palmer 《Journal of Earthquake Engineering》2013,17(5):646-669
Permanent ground deformation (PGD) is one of the most damaging hazards for continuous buried lifelines. This hazard is especially severe when the PGD results in net compression in the pipe. In that case, buckling of pipe material can occur. If buckling is moderate, deformation of the pipe cross-section can lead to flow restriction and high friction losses, and eventually require line replacement. If buckling is severe, high localized strains can lead to pipe rupture, loss of contents, and possible pollution of surrounding soil. In this article, centrifuge tests of buried pipelines subject to abrupt ground failure in the form of surface faulting are presented. The fault movement results in mostly compression in the pipe. The test results are compared with a case history of pipe failure in the 1999 Izmit, Turkey earthquake and also with the results from the centrifuge tests which result in net tension in the pipe. The experimental setup, procedures, and instrumentation are described in detail. Suggestions for design practice are offered based on the analysis of results from both the 1999 Izmit case history and the centrifuge modeling. 相似文献