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   462篇
  免费   21篇
  国内免费   17篇
测绘学   7篇
大气科学   36篇
地球物理   9篇
地质学   50篇
海洋学   41篇
综合类   32篇
自然地理   325篇
  2023年   12篇
  2022年   35篇
  2021年   30篇
  2020年   25篇
  2019年   28篇
  2018年   26篇
  2017年   24篇
  2016年   22篇
  2015年   19篇
  2014年   10篇
  2013年   38篇
  2012年   21篇
  2011年   19篇
  2010年   13篇
  2009年   11篇
  2008年   13篇
  2007年   17篇
  2006年   21篇
  2005年   11篇
  2004年   13篇
  2003年   14篇
  2002年   11篇
  2001年   10篇
  2000年   9篇
  1999年   7篇
  1998年   9篇
  1997年   7篇
  1996年   2篇
  1995年   2篇
  1994年   5篇
  1993年   1篇
  1992年   1篇
  1991年   1篇
  1989年   1篇
  1988年   2篇
  1987年   4篇
  1985年   2篇
  1984年   2篇
  1983年   1篇
  1980年   1篇
排序方式: 共有500条查询结果,搜索用时 767 毫秒
341.
赵多平  孙根年 《地理科学》2017,37(12):1815-1822
以宁夏与阿拉伯国家为例,提出了入境旅游与贸易互动机理与路径假设,采用结构方程方法,对宁夏与阿拉伯国家的入境旅游与贸易的微观互动机理与路径关系进行了实证研究。结果发现:旅游与贸易互动路径假设均在1%或5%的置信水平上得到了验证,即关系链接对知识关联有正向路径影响,商贸关联对知识关联和广告效应有正向路径影响,信息传播对广告效应有正向路径影响。商贸关联、广告效应以及知识关联对商贸行为有正向路径影响。主要存在商贸关联引发商贸行为的直接路径和两条间接路径关系:关系链接→知识关联→商贸行为和信息传播→广告效应→商贸行为。旅游与贸易的互动机理来看,文化关联拉近了心理感知距离,通过旅游构建了良好的人际关系和商贸关系,增加了贸易便利性、削减交易成本、消除商务距离、培育合作商机、构建商业纽带,开启了宁夏与阿拉伯国家之间的贸易规模的提升,尤其是出口贸易的迅猛增长。贸易的增长提高了旅游的便利化程度,进一步拉近了感知距离,消除了旅游成本,构建了中介关联,增加了更多旅游需求。  相似文献   
342.
While much has been written about the history of mobility and trade in the Indian Ocean, recent trading connections between Eastern Africa and Asia have so far only gained very little attention. However, in Zanzibar alone, hundreds of traders regularly embark on journeys reviving old routes and further develop them, in order to take advantage of the way the global economy works today. By providing an ethnographic account of such a journey undertaken by four Zanzibari traders to Jakarta, this article gives an insight into the organization, calculations and imaginations involved in contemporary Indian Ocean trading networks. Although this trade journey clearly marks a new form of translocal mobility among Zanzibari traders, this mobile ethnography highlights how the journey is at the same time closely linked to, evokes and enlivens very old processes of mobility across the Indian Ocean, thus highlighting the dialectics between old and new mobilities, and between familiarity and strangeness.  相似文献   
343.
This paper analyzes Hungary's export linkages of the interwar and Cold War periods using gravity model and historical analyses. Hungary is a useful example of former Soviet satellites because it combines relative political stability (since 1956) and experimentation with the New Economic Mechanism (NEM) during the 1970s and 1980s. Historical analysis reveals seven events since World War I that changed Hungary's trade patterns. Gravity model analysis for 1955, 1965, 1975, and 1985 shows the dramatic cleavage of the “Iron Curtain,” the effect of the NEM, and particularly strong and weak linkages for Hungarian trade that may result from historical legacies, complementarity, or specific political contacts.  相似文献   
344.
Discuss as the significance of the Taiwan Strait Tunnel from the perspective of cross-strait economic and trade relations. Points out major problems and development of proper ways to assist both sides in such economic and trade relations.  相似文献   
345.
Land borders connecting Canada and the United States are vital transportation facilities for the two countries. Truck crossing times at these facilities can have a significant impact on the performance of the economy. To date, knowledge about border crossing times has been limited due to lack of detailed data on the Canadian border. This article explores and models the patterns of crossing times at the three major land crossings connecting Canada to the United States: Ambassador Bridge, Blue Water Bridge, and Peace Bridge. The analysis is based on 387,775 border crossing truck trips that were generated between Canada and the United States over a course of twelve months. Seemingly unrelated regression (SUR) models are estimated to evaluate the seasonal and hourly crossing times of Canada- and U.S.-bound trips on each border crossing, controlling for traffic intensity in the models. The SUR modeling approach is chosen to control for potential cross-model correlations. The results suggest that crossing times at the border vary by season and hour of the day. Crossing times also vary by direction of traffic and by type of day (i.e., weekday vs. weekend). Traffic intensity has a significant influence on crossing times at two of the crossings but not the Blue Water Bridge. Finally, crossing times are more variable during the summer season and tend to be higher during the late evening hours and past midnight.  相似文献   
346.
Agricultural land use to meet the demands of a growing population, changing diets, lifestyles and biofuel production is a significant driver of biodiversity loss. Globally applicable methods are needed to assess biodiversity impacts hidden in internationally traded food items. We used the countryside species area relationship (SAR) model to estimate the mammals, birds, amphibians and reptiles species lost (i.e. species ‘committed to extinction’) due to agricultural land use within each of the 804 terrestrial ecoregion. These species lost estimates were combined with high spatial resolution global maps of crop yields to calculate species lost per ton for 170 crops in 184 countries. Finally, the impacts per ton were linked with the bilateral trade data of crop products between producing and consuming countries from FAO, to calculate the land use biodiversity impacts embodied in international crop trade and consumption. We found that 83% of total species loss is incurred due to agriculture land use devoted for domestic consumption whereas 17% is due to export production. Exports from Indonesia to USA and China embody highest impacts (20 species lost at the regional level each). In general, industrialized countries with high per capita GDP tend to be major net importers of biodiversity impacts from developing tropical countries. Results show that embodied land area is not a good proxy for embodied biodiversity impacts in trade flows, as crops occupying little global area such as sugarcane, palm oil, rubber and coffee have disproportionately high biodiversity impacts.  相似文献   
347.
Zusammenfassung Im Mittleren Buntsandstein der Westeifel wurden etwa 4500 Schrägschichtungsmessungen aus aeolischen und fluviatilen Sandsteinen ausgewertet. Aeolische und fluviatile Sedimente werden kurz charakterisiert. Die Auswertung der Gefügedaten wird beschrieben. Paläowindrichtungen und Paläoströmungsrichtungen stimmen in großen Zügen überein. Die Paläoströmungsrichtungen passen sich in die vonWurster (1964, 1968) undGrumbt (1974) gegebene Zusammenstellung der Schüttungsrichtungen im germanischen Buntsandstein ein. Paläowindrichtungen werden hier erstmals aus dem westdeutschen Raum mitgeteilt. Nach Ermittlung von Paläobreite und Rotationsbetrag lassen sich die Paläowindrichtungen nur schwierig in das zentrale Passatwindsystem einfügen. Als mögliche Ursache der abweichenden Richtungen kommt am ehesten eine Verschiebung der intertropischen Konvergenzzone nach Norden im Sommer in Frage, evtl. auch Einflüsse von Luftströmen größerer Höhe oder lokale Faktoren.
In the Middle Buntsandstein of Western Eifel (Germany), about 4,500 cross-bedding measurements from aeolian and fluviatile sandstones were interpreted. Aeolian and fluviatile deposits are briefly characterized. The interpretation of the fabric data is described. Paleowind- and paleocurrent-directions fit together in broad outline. The paleocurrent-directions fit into the compilation of the cross-bedding data in the German Bunter given byWurster (1964, 1968) andGrumbt (1974). Paleowind-directions are here first described from Western Germany. According to paleolatitude and rotation the paleowind-directions fit only badly into the central trade wind system. Possible causes for this deviation are expected to be first of all a Northern shift of the intertropical convergence zone in summer, perhaps also the influences of air streams of greater height or local factors.

Résumé Dans le Buntsandstein moyen de l'Eifel occidental (Allemagne), 4500 mesures portant sur des structures sédimentaires entrecroisées dans des grès éoliens et fluviatiles ont fait l'objet d'interprétations; les sédiments éolièns et fluviatiles sont caracterisés brèvement; l'interprétation structurale des données est décrite. Les directions des paléovents et paléocourants concordent bien dans les grandes lignes. Les directions des paléocourants s'accordent avec les directions d'épandage compilées parWurster (1964, 1968) etGrumbt (1974) dans le Buntsandstein germanique. Les directions des paléovents sont données pour la première fois pour la région occidentale de l'Allemagne. D'après les données des paléolatitudes et de l'ampleur de la rotation, les directions des vents ne s'intègrent que difficilement dans le système central des alizés. Comme cause possible des écarts de direction, vient en premier lieu un déplacement vers le nord, durant l'été, des zones de convergence intertropicales, et éventuellement des influences de courants éoliens d'altitudes plus hautes ou des facteurs locaux.

4500 , . . , Wurster'a (1964, 1968) Grumbt'a (1974). . . , , , - . .
  相似文献   
348.
Western investment and trade in East-Central Europe is likely to play a key role in the economic fortunes of the region over the next decade. Currently, the capital cities and the western parts of Poland, Czechoslovakia, and Hungary are the primary beneficiaries of economic interaction with the West. As such, existing regional inequalities are being reinforced. Deepening regional socioeconomic disparities within individual states could complicate the economic restructuring process and jeopardize state stability in the years ahead.  相似文献   
349.
一、前言 西安市地表出现八条地裂缝带,总体走向N70°-80°E,间距2-2.5 km,长度约3-4 km,最长约8 km,近似于平行等间距展布在城区和近郊区的150 km2范围内,将西安市切割成规则条带,由于不断活动,二十多年来造成的破坏,相当于Ⅳ-Ⅶ度的地震。 1986-1987年,我们用Mini-Sosie高分辨反射波技术,在辛家庙(F1)、小寨(F7)  相似文献   
350.
运用层次分析法、变异系数法对1994,2003,2012年广东省各地级市城镇化与交通系统的发展水平进行测算,并借鉴物理耦合协调概念建立协调发展指数,对广东省域城镇化与交通系统协调发展程度进行定量分析。结果表明:1994—2012年间广东省城镇化加速发展,内部差异呈缩小趋势,珠三角为当前城镇化高值区,粤西为城镇化高速发展区,粤北为城镇化塌陷区;广东交通系统发展水平不断提高,但内部差异增大,粤东地区交通发展始终处于落后地位;各地级市城镇化与交通系统协调发展状况不断改善,但以低层次协调发展为主,城镇化与交通系统两者的关系由20世纪90年代的城镇化滞后转变为现阶段的交通滞后。  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