全文获取类型
收费全文 | 16046篇 |
免费 | 2081篇 |
国内免费 | 2481篇 |
专业分类
测绘学 | 1618篇 |
大气科学 | 2082篇 |
地球物理 | 2144篇 |
地质学 | 5333篇 |
海洋学 | 2280篇 |
天文学 | 128篇 |
综合类 | 1331篇 |
自然地理 | 5692篇 |
出版年
2024年 | 74篇 |
2023年 | 205篇 |
2022年 | 631篇 |
2021年 | 731篇 |
2020年 | 729篇 |
2019年 | 768篇 |
2018年 | 632篇 |
2017年 | 766篇 |
2016年 | 737篇 |
2015年 | 765篇 |
2014年 | 914篇 |
2013年 | 1227篇 |
2012年 | 1044篇 |
2011年 | 1009篇 |
2010年 | 801篇 |
2009年 | 913篇 |
2008年 | 897篇 |
2007年 | 1007篇 |
2006年 | 882篇 |
2005年 | 774篇 |
2004年 | 699篇 |
2003年 | 603篇 |
2002年 | 544篇 |
2001年 | 460篇 |
2000年 | 462篇 |
1999年 | 361篇 |
1998年 | 283篇 |
1997年 | 300篇 |
1996年 | 235篇 |
1995年 | 188篇 |
1994年 | 179篇 |
1993年 | 153篇 |
1992年 | 163篇 |
1991年 | 91篇 |
1990年 | 75篇 |
1989年 | 52篇 |
1988年 | 51篇 |
1987年 | 30篇 |
1986年 | 36篇 |
1985年 | 28篇 |
1984年 | 25篇 |
1983年 | 25篇 |
1982年 | 16篇 |
1981年 | 10篇 |
1980年 | 5篇 |
1979年 | 1篇 |
1978年 | 12篇 |
1977年 | 12篇 |
1976年 | 1篇 |
1972年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
论述旅游目的地形象形成的 8个阶段 ,并结合南京郊区旅游地的实际情况 ,对目的地形象的推广思路进行分析。从旅游者心理特征出发 ,提出了目的地形象的生命周期问题 ,通过对南京郊区旅游地形象现状的评估 ,认为钟山风景区形象趋于老化 ,面临形象的重新定位。 相似文献
992.
大都市政府和都市议会是发达国家对大都市区和都市连绵区进行宏观管理的重要机构,本文简要介绍了各种类型的大都市政府和都市议会的形成与发展,在此基础上提出了我国相应的宏观管理机构为城镇密集区政府和都市区规划局,最后,对我国城镇密集区规划管理的可行性与规划管理体系问题进行了讨论。 相似文献
993.
1 IntroductionSand-dust storms include both sand storms and dust storms[1]. When the visibility in local areas is greater than or equal to 50 m but less than 200 m, they are called severe sand-dust storms. When extremely severe sand-dust storm, the most severest type of sand-dust storm, occurs, the local instantaneous maximum wind speed can be greater than 25 m/s and a local visibility be less than 50 m or even descend to 0 m[2].Sand-dust storm is a critical environmental problem and is also a… 相似文献
994.
We examined the abundance and distribution of Eleodes extricata (Tenebrionidae) in a semi-arid region of West Texas. During the 2-year study, climatic conditions were extreme but opposite, with 1997 being unusually wet and mild, and 1998 being unusually dry and hot. These conditions were associated with striking differences in the population structure of the beetles. Under identical pitfall-sampling efforts, we captured 1562 and 671 individuals in 1997 and 1998, respectively. Capture rates were lowest in grassland, and highest in sand shinnery oak, and within the latter, they were lowest in blowouts, intermediate along the edges of blowouts, and highest under vegetative cover. Sex ratios were consistently female-biased, and the degree of bias increased from spring through fall in both years. These increases were more pronounced in 1998, with the sex ratios of early and late sampling periods differing by over four-fold, from 1·15 to 5·00. Females were heavier than males, and the dry masses of both sexes increased from spring though fall in both years. As with sex ratios, these increases were more pronounced in 1998. Only the largest beetles survived the drought, illustrating how extreme conditions can exert especially strong directional selection, and affect sex ratios in populations with sexual size dimorphism. 相似文献
995.
The idea that the emergence of writing was necessity due to the increase in both the number of economic transactions and political complexity has been recently emphasized by Matthews, who also underlines that writing acted as a feedback in enabling and encouraging the growth of ever more complex modes of exchange. The intertwinement of trade and writing suggests that clay tablets left by the civilizations from the third millennium B.C. in Mesopotamia, where writing was invented, may be considered as traces of trade links and transactions between cities. We estimate a gravity model based on clay tablets, as if they represented trade flows. The parameters lead us to conclude that Mesopotamia formed a strongly integrated market. 相似文献
996.
Danielle J. Marceau Luc Guindon Mireille Bruel Claude Marois 《The Professional geographer》2001,53(4):546-558
This article addresses the issue of linking temporal and spatial information into a GIS database structure to investigate the land‐use changes in a rural‐urban region over a thirty‐five‐year period. More specifically, it describes the application of a programming package developed to build temporal topology in an historical land‐use GIS database to efficiently perform spatiotemporal queries. The program was created within the MapInfo environment using MapBasic language. Different types of information, such as the rate of change, the relationship between the change of land use and zoning regulations, and land‐use succession were extracted from the database. A user‐friendly interface was also developed to easily address spatiotemporal queries to the database. This approach represents a flexible and performing tool for scientists and planners who need to efficiently capture essential spatiotemporal information required for geographical inquiry and decision‐making. 相似文献
997.
《The Professional geographer》2001,53(4):559-581
Books reviewed: Bassin, Mark, Imperial Visions: Nationalist Imagination and Geographical Expansion in the Russian Far East, 1840 – 1865 Shortridge, James R., Our Town on the Plains: J. J. Pennell's Photographs of Junction City, Kansas, 1893 – 1922 Jakle, John A. and Sculle, Keith A., Fast Food: Roadside Restaurants in the Automobile Age Boeschenstein, Walter, Historic American Towns along the Atlantic Coast McKee, Jesse O., Ethnicity in Contemporary America: A Geographical Appraisal Luciuk, Lubomyr Y., Searching for Place: Ukrainian Displaced Persons, Ottawa, and the Migration of Memory Hausladen, Gary, Places for Dead Bodies Phillips, Richard, Watt, Diane and Shuttleton, David, De‐Centering Sexualities: Politics and Representations beyond the Metropolis Goldin, Liliana R., Identities on the Move, Transnational Processes in North America and the Caribbean Basin McDonald, David A., On Borders: Perspectives on International Migration in Southern Africa Fox, Roddy and Rowntree, Kate, The Geography of South Africa in a Changing World Takeuchi, Keiichi, Modern Japanese Geography: An Intellectual History Amery, Hussein A., and Wolf, Aaron T., Water in the Middle East: A Geography of Peace Karl, Thomas R., Nicholls, Neville and Ghazi, Anver, Weather and Climate Extremes: Changes, Variations, and a Perspective from the Insurance Industry Pittman, Blair, Texas Caves 相似文献
998.
ABSTRACT. Recent attempts by U.S. politicians to reform the nation'sschools have shifted the goal of education to school accountability as assessed in standardized testing. Such an emphasis undermines geographical education in schools because of geography'ssuperficial representation in tests and in the social studies curriculum. Fieldwork done in the classroom can point to means of circumventing this dilemma. Collaborative fieldwork between college faculty members and public‐school teachers has the potential for adding geography to the social studies curriculum in a substantive way. Work conducted jointly by Hartwick College and the Oneonta (New York) Middle School exemplifies such a partnership. 相似文献
999.
通过对淮北市地质、水文地质条件的综合分析 ,建立了淮北市双含水层系统水文地质概念模型。引入准三维流数学模型进行地下水动态预报及建立地下水管理模型。用线性规划模型提出淮北市地下水资源的最佳管理方案。最后提出开展地下水回灌研究、建立岩溶含水层地下水库、限制发展耗水型工业及用法律和经济手段管理水资源开发等建议 相似文献
1000.
东太平洋CC区多金属结核物质来源和分布规律 总被引:5,自引:0,他引:5
对东太平洋CC区(Clarion-Clipperton Zone)多金属结核丰度、品位、多波束地形测量、深拖光学覆盖率探测、地震勘探等一系列调查资料综合研究表明:①东区和西区结核在其化学成分和形态上有差异,但是聚类分析结果表明不能按区域断然分开;②因子分析得出东、西两区结核4种主因子是Mn组元素Mn、Cu、Ni、Zn,Fe组元素Fe、Co、Ti、Sr,岩源组元素Si、Al、K,生物元素Ca、P;③西区结核成矿物质主要来源于上覆海水中金属元素的化学沉淀,火山成矿作用使结核富集和丰度增加,趋势面和人工神经网络分析表明结核主要分布在海底坡度≤5°地区,该地区的结核量占总结核量的89.62%,坡度>5°地区结核量占10.38%;④东区结核丰度、覆盖率、地形三者变化一致,重大相变距离为10~15km,来自地幔成矿物质通过玄武质洋壳裂隙和断层,为多金属结核的形成和生长提供了丰富的物质来源,地球深部地质作用过程如基底岩浆房活动可能对结核分布产生重要影响;⑤东太平洋CC区多金属结核矿带的形成应归于海底板块扩张活动的一种资源效应和经后期表生地质作用改造的结果。 相似文献