全文获取类型
收费全文 | 1855篇 |
免费 | 24篇 |
专业分类
公路运输 | 641篇 |
综合类 | 70篇 |
水路运输 | 515篇 |
铁路运输 | 59篇 |
综合运输 | 594篇 |
出版年
2023年 | 22篇 |
2022年 | 52篇 |
2021年 | 18篇 |
2020年 | 9篇 |
2019年 | 21篇 |
2018年 | 53篇 |
2017年 | 41篇 |
2016年 | 84篇 |
2015年 | 23篇 |
2014年 | 86篇 |
2013年 | 290篇 |
2012年 | 94篇 |
2011年 | 102篇 |
2010年 | 92篇 |
2009年 | 113篇 |
2008年 | 79篇 |
2007年 | 45篇 |
2006年 | 43篇 |
2005年 | 38篇 |
2004年 | 29篇 |
2003年 | 26篇 |
2002年 | 31篇 |
2001年 | 27篇 |
2000年 | 26篇 |
1999年 | 30篇 |
1998年 | 15篇 |
1997年 | 24篇 |
1996年 | 22篇 |
1995年 | 31篇 |
1994年 | 15篇 |
1993年 | 17篇 |
1992年 | 15篇 |
1991年 | 16篇 |
1990年 | 8篇 |
1989年 | 9篇 |
1988年 | 11篇 |
1987年 | 9篇 |
1986年 | 9篇 |
1985年 | 17篇 |
1984年 | 11篇 |
1983年 | 18篇 |
1982年 | 9篇 |
1981年 | 19篇 |
1980年 | 20篇 |
1979年 | 18篇 |
1978年 | 11篇 |
1977年 | 19篇 |
1976年 | 16篇 |
1975年 | 20篇 |
1974年 | 13篇 |
排序方式: 共有1879条查询结果,搜索用时 312 毫秒
941.
The precise estimation of the annual average daily traffic (AADT) is a task of significant interest for many transportation authorities and Departments of Transportation. In this study, three methods are developed to improve the assignment of short‐term counts to seasonal adjustment factor (SAF) groupings: the traditional functional classification, a discriminant analysis (DA), and a new statistical approach based on a weighted coefficient of variation (WCV). The data analyzed within this study are generated from all available continuous counters within the State of Ohio between 2002 and 2006. The analysis is conducted using SAFs that are separately calculated for the total volume and the directional specific volumes of a site. The results show that the directionally based assignment errors are statistically lower at a 95% confidence interval when compared with those generated by the total volume analysis. It is also found that the hourly time‐of‐day factors are more important in the assignment process than the average daily traffic. The directionally based WCV produces a decline in the average mean absolute percentage error (MAPE) over the roadway functional classification by 58% and in the standard deviation of the absolute error (SDAE) by 70%. On the contrary, the directionally based DA lowers the MAPE and the SDAE by 35% and 60%, respectively. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
942.
Y. H. Venus Lun Kee-hung Lai Christina W. Y. Wong T. C. E. Cheng 《Maritime Policy and Management》2014,41(2):134-148
Global economic development is facilitated by the commercial shipping industry. Shipping operations contribute to the growth of international trade activities, which heavily count on ships to carry cargoes from places of production to places of consumption. Despite its importance, there have been growing concerns about the environmental impacts caused by shipping activities in international trade. To balance environmental protection and productivity, many shipping firms have begun to adopt green shipping practices (GSPs) to improve their operations in a more environmentally friendly manner. GSP consists of six dimensions, namely, company policy and procedure (CPP), shipping documentation (SD), shipping equipment (SE), shipper cooperation (SC), shipping materials (SM), and shipping design and compliance (SDC). GSP is becoming an important aspect of shipping operations. It is timely for the shipping industry to evaluate firm capability in carrying out greening operations, that is, firms’ “greening” capability. Firm capability comprises two key elements: one is embedded in firms’ business routines or activities, and the other concerns firms’ ability in transforming inputs into outputs. GSPs can be considered as inputs while firm performance measures as outputs. This study uses an input/output approach to examine the greening capability (GC) of shipping firms. The results indicate that shipping firms are relatively weak in the practices of SC and SE, while the capability scores of SM, CPP, SDC, and SD are all close to 1, with an average score of 0.927, 0.920, 0.924, and 0.978, respectively. Academic and managerial significance of the findings are highlighted. 相似文献
943.
944.
945.
In the presence of biofilms, stainless steels(SS) exhibits an increase in corrosion potential, called ennoblement. In the present study, the corrosion potential(Ecorr) behavior of the duplex SS UNS S32760 was recorded simultaneously with the in situ marine biofilm formation in two areas at Arraial do Cabo,Southeastern Brazil. The biofilm at Forno Harbor(an anthropogenically disturbed area) was characterized by higher relative abundances of Bacteria at day 2, followed by diatoms(especially Navicula sp.) on day 10 and dinoflagellates on day 18,whereas no clear trend was recorded at Cabo Frio Island(an undisturbed area). The ennoblement of Ecorr values was site-dependent. In a complementary laboratory assay, biofilms were removed and the Ecorr values registered in sterile conditions for the subsequent 10 days and corroborated in situ results. Understanding biofilms and SS interactions has important implications for materials science and engineering decisions as well as helping to fill in important gaps in this knowledge. 相似文献
946.
The Cocos (Keeling) Islands are located on an isolated atoll in the Indian Ocean and have a strong Malay culture owing to the translocation of a substantial plantation workforce in the early 19th century. The atoll became one of Australia's External Territories in 1955. Meeting the marine resource needs of the atoll residents within an Australian legislative system by formulating an integrated marine management plan presented several challenges. Key factors in drafting a culturally meaningful plan were a commitment to understanding and accommodating the cultural and subsistence needs of the community, innovative communication strategies, and a simple approach to management. Development of the plan highlighted the limitations of current Australian marine planning legislation in cross-cultural settings and for sustainable development. 相似文献
947.
James H. Stone Leonard M. Bahr Jr. John W. Day Jr. R. Eugene Turner Paul H. Templet 《Coastal management》2013,41(1):9-35
Abstract Preliminary management guidelines have been derived for oil and gas activities in coastal Louisiana. Derivation of these guidelines was done in terms of the natural function of the coastal ecosystem; this means that all economic activities should be designed to complement natural function as much as possible. The guidelines range in scope from very specific, almost performance standards, to very general admonitions. For example, we have suggested that spoil banks, produced as a result of dredging, should not be higher than the height of the daily tide or roughly 15 cm in coastal Louisiana, and at the other extreme, we have suggested that all dredging should be done with great care during wildlife migrations, spawning, and nesting times. 相似文献
948.
The concept of accessibility has been variously interpreted as being the “nearness to places,” the “nearness to activities” and more recently the “ease of participating in activities.” With each of these qualitative interpretations, there has also been a variety of quantitative definitions of accessibility. This paper shows that many of the proposed definitions of accessibility can in fact be gathered together to form a spectrum of accessibility measures. These measures differ with respect to the factors included in their formulation and their degree of behavioural interpretation. Existing measures of accessibility are shown to be deficient in one major aspect. That is, they assume that for any one measure of accessibility there is but one origin of trips. Thus, in estimating the accessibility of a point within a region it is assumed that all potential trips, which contribute to the accessibility of that point, start from that single point. In view of the considerable amount of evidence demonstrating the widespread, and increasing, occurrence of trip‐linking such a proposition must be viewed as being rather doubtful. In the light of this, the paper proceeds to develop a measure of accessibility which explicitly accounts for the linking of trips. The implications of this measure, compared to a conventional unlinked‐trip accessibility measure, are discussed as are some problems which are foreseen in the practical implementation of such a measure. 相似文献
949.
Robert J. Johnston Thomas A. Grigalunas James J. Opaluch Marisa Mazzotta Jerry Diamantedes 《Coastal management》2013,41(1):47-65
This article summarizes four integrated economic studies undertaken to contribute to resource preservation and restoration decisions for the Peconic Estuary System of Suffolk County, NY. Completed as part of the National Estuary Program, the studies apply distinct resource valuation methods to a wide range of resource issues. The principal goals of this article are to highlight different methodologies that may be used to assess nonmarket economic values in a coastal management context, and characterize differences in the results that one may expect from each approach. We also emphasize potential relationships among values estimated by different nonmarket methodologies, and comment on the implications of these relationships for the interpretation and use of economic value estimates. 相似文献
950.
Hui Ding Haigen Xu Jun Wu W. J. F. Le Quesne C. J. Sweeting N. V. C. Polunin 《Coastal management》2013,41(5):443-457
Marine ecosystems of the East China Sea are rich in biodiversity, with 12,933 species of which approximately 47.7% are endemic. As anthropogenic impacts are intensifying, fishery resources and biodiversity in the East China Sea are under threat from overfishing, habitat loss, pollution, and biological invasions. Marine protected areas (MPAs) and other spatial management measures are believed useful tools to protect and restore biological resources. Seventeen nature reserves, seven special marine reserves, and three fishery resource conservation zones covering a combined area of 102,156 km2 have so far been established in the Chinese East China Sea in order to protect fishery resources, biodiversity, and marine landscapes. This article provides a review and inventory of MPAs in the Chinese East China Sea as implemented by the People's Republic of China. 相似文献