全文获取类型
收费全文 | 58128篇 |
免费 | 910篇 |
国内免费 | 791篇 |
专业分类
测绘学 | 1478篇 |
大气科学 | 4656篇 |
地球物理 | 12004篇 |
地质学 | 19733篇 |
海洋学 | 5068篇 |
天文学 | 12888篇 |
综合类 | 150篇 |
自然地理 | 3852篇 |
出版年
2020年 | 375篇 |
2019年 | 362篇 |
2018年 | 849篇 |
2017年 | 781篇 |
2016年 | 1217篇 |
2015年 | 868篇 |
2014年 | 1190篇 |
2013年 | 2862篇 |
2012年 | 1431篇 |
2011年 | 2075篇 |
2010年 | 1709篇 |
2009年 | 2480篇 |
2008年 | 2211篇 |
2007年 | 2118篇 |
2006年 | 2062篇 |
2005年 | 1855篇 |
2004年 | 1806篇 |
2003年 | 1738篇 |
2002年 | 1661篇 |
2001年 | 1450篇 |
2000年 | 1462篇 |
1999年 | 1381篇 |
1998年 | 1281篇 |
1997年 | 1298篇 |
1996年 | 1106篇 |
1995年 | 1022篇 |
1994年 | 933篇 |
1993年 | 857篇 |
1992年 | 830篇 |
1991年 | 758篇 |
1990年 | 800篇 |
1989年 | 668篇 |
1988年 | 697篇 |
1987年 | 770篇 |
1986年 | 721篇 |
1985年 | 948篇 |
1984年 | 1046篇 |
1983年 | 1013篇 |
1982年 | 878篇 |
1981年 | 838篇 |
1980年 | 817篇 |
1979年 | 732篇 |
1978年 | 767篇 |
1977年 | 662篇 |
1976年 | 664篇 |
1975年 | 645篇 |
1974年 | 673篇 |
1973年 | 675篇 |
1972年 | 407篇 |
1971年 | 341篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
941.
Roger W. Stump 《The Professional geographer》1987,39(4):438-449
This study examines the hypothesis that the determinants of denominational switching vary regionally among white American Protestants. Data for the analysis are taken from the National Opinion Research Center's General Social Survey for 1974 through 1984. Using logistic regression, the analysis compares the determinants of switching among respondents residing in the nine Census regions of the U.S. Results reveal significant regional differences in the determinants of switching, especially in the effects of conversion, childhood affiliation and interdenominational marriage. 相似文献
942.
MATTHEW C. LaFEVOR 《Geographical review》2012,102(2):202-224
The discovery, extraction, and monopolistic control of key natural resources was a priority of New Spain's colonial administration. Managing the region's abundant resources, however, often proved difficult for the Spanish Crown. Human and environmental challenges impeded protoindustrial growth and development, and monopolistic control of resources often met resistance. In this article I examine these processes in the context of New Spain's little‐known monopoly on sulphur—a yellow, powdery mineral the Crown jealously guarded as its own. Sulphur was critical for gunpowder and explosives production, yet the Crown often failed to produce enough of it to meet the growing demand by its military and the silver blast‐mining industry. Colonial documents reveal administrators’ attempts to improve sulphur production through reform measures, which included advising sulphur miners on how to discover sulphur deposits and, eventually, how to develop their mines. Efforts to improve sulphur production were moderately successful, although the process was messy and inefficient. 相似文献
943.
944.
The Myth of Location Privacy in the United States: Surveyed Attitude Versus Current Practices 总被引:1,自引:0,他引:1
In the United States, legal steps have been taken to protect personal privacy, which is viewed as an individual's fundamental right. Location privacy (i.e., protection of personal and location information), however, has not received equal attention in the legal system. Given the recent popularity of location-based services (e.g., cell phones), it is possible to obtain an individual's location information easily and precisely. An investigation of public perception of privacy in the United States indicated that survey responders (1) were unaware of legal implications of location privacy violation and (2) believed that there should be location privacy protection similar to that provided by the Health Insurance Portability and Accountability Act and the Family Educational Rights and Privacy Act. 相似文献
945.
Jason C. Senkbeil David A. Scott Pilar Guinazu-Walker Meganne S. Rockman 《The Professional geographer》2013,65(4):610-620
The 27 April 2011 EF4 Tuscaloosa tornado directly impacted more than 50,000 residents, causing forty-five fatalities within the city and sixty-five in total. It was a rare urban tornado with varying impacts on the three major ethnic and racial groups within the city. A hybrid survey and interview of open-ended and closed questions was conducted with 211 Tuscaloosa area residents in a two-week period after the tornado. Results indicate significant differences in risk perception, preparedness, and shelter lead time among the three ethnic and racial groups. Furthermore, results were still significant for perception after controlling for the effects of age, education, and experience. 相似文献
946.
D. C. OVADIA 《International journal of geographical information science》2013,27(2):190-191
947.
CHI HO SHAM JOHN W. BRAWLEY MAX A. MORITZ 《International journal of geographical information science》2013,27(4):463-473
Abstract Waquoit Bay, a shallow bay on Cape Cod, Massachusetts, is exhibiting symptoms of eutrophication, largely attributed to septic nitrogen inputs. This study assessed septic nitrogen inputs by linking a three-dimensional ground-water model, a geographic information system (GIS), and a customized spatio-temporal nitrogen loading program. Owing to the slow speed of ground-water movement, the bulk of septic nitrogen entering the bay lags behind development by nearly a decade. Even if residential development is held at 1989 levels, nitrogen input from septic systems wilt increase by 36% over the current levels. At full residential build-out (i.e., development), septic nitrogen loading will eventually increase to more than twice the current levels. 相似文献
948.
Theo A. Arentze Aloys W. J. Borgers Harry J. P. Timmermans 《International journal of geographical information science》2013,27(2):219-236
Abstract. The traditional approach in DSS falls short of providing a highly interactive problem solving environment for planning. Often, cumbersome procedures are required to implement optional plans and obtain feedback information. In dynamic graphic systems, the user is able to view different linked graphic representations (e.g., spatial or statistical graphs) of statistical data and interact (e.g., selecting items) with these graphics. In this paper we describe the design of a DSS for planning facility locations, which uses principles of dynamic graphics to achieve a highly interactive problem solving environment. As in dynamic graphic systems, the user interacts with the DSS through active and linked views. However, where views in dynamic graphics are different representations of a given dataset, the views in the DSS are active data structures describing the facility system to be planned from different perspectives. The declarative and procedural forms of knowledge involved are identified by a logical analysis of planning problems. A frame-based formalism is proposed to represent the knowledge contained in the views. The main advantage of this view-based approach is that it offers the user a highly flexible and interactive environment for performing ‘what-if’ analyses. 相似文献
949.
Following deglaciation, the long-term pattern of change in diatom communities and the inferred history of the aquatic environment are affected by a hierarchy of environmental controls. These include direct climate impacts on a lake’s thermal and hydrologic budgets, as well as the indirect affects of climate on catchment processes, such as weathering, soil development, microbial activity, fire, and vegetation composition and productivity, which affect the transfer of solutes and particulates from the terrestrial ecosystem into the lake. Some of these catchment influences on lacustrine systems operate as time-dependent patterns of primary succession that are set in motion by glacier retreat. This paper provides a conceptual model of some dominant pathways of catchment influence on long-term lake development in glaciated regions and uses a series of paleolimnological examples from arctic, boreal, and temperate regions to evaluate the relative role of direct climate influences and of catchment processes in affecting the trajectory of aquatic ecosystems during the Holocene in different environmental contexts. 相似文献
950.
The Takla Makan Desert is one of the supposed sources of eolian deposits in the eastern China and the North Pacific Ocean. Lack of direct measurements hinders the theoretical interpretation of material exchange between the atmosphere and land surface as well as the sediment budget of the region. From 1992 to 1994, four measuring sites were established in the vicinity of 84°E meridian along a 380 km observation traverse from the northern margin to the central desert. Data were collected on quantities of dust fall and sedimentary characteristics of airborne sediments, including grain-size distributions as well as chemical and mineral compositions. The quantities of annual dust fall were 102 to 103 tons km-2 yr-1, increasing from the margin toward the central desert. Monthly concentrations of particles finer than 0.02 mm in diameter ranged from 0.06 to 1.25 mg m-3 over the three-year observation period. The elemental ratio and the element enrichment factor ruled out the Takla Makan Desert as possible sources of the dust in Hawaii and Alaska. The mean geometric diameter of airborne sediments in the 4 to 8 m surface layer from the Luntai oasis was 0.038 mm and from the interior ranged 0.064 to 0.067 mm being moderately to poorly sorted. Weight percent of particles finer than 0.063 mm in diameter were from 83.5% to 47.7%, decreasing toward the central desert. Distributions of the airborne particles were unimodal with peak diameters of 0.06 to 0.07 mm in the central desert and 0.02 to 0.06 mm in the sites toward the edge of the desert. [Key words: dust fall, sedimentary characteristics, Takla Makan Desert.] 相似文献