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   118527篇
  免费   1633篇
  国内免费   990篇
测绘学   2853篇
大气科学   8074篇
地球物理   22862篇
地质学   42375篇
海洋学   10741篇
天文学   27374篇
综合类   354篇
自然地理   6517篇
  2022年   770篇
  2021年   1317篇
  2020年   1401篇
  2019年   1570篇
  2018年   3333篇
  2017年   3107篇
  2016年   3742篇
  2015年   1974篇
  2014年   3621篇
  2013年   6208篇
  2012年   3848篇
  2011年   5032篇
  2010年   4521篇
  2009年   5776篇
  2008年   5062篇
  2007年   5130篇
  2006年   4750篇
  2005年   3492篇
  2004年   3477篇
  2003年   3298篇
  2002年   3211篇
  2001年   2791篇
  2000年   2688篇
  1999年   2174篇
  1998年   2255篇
  1997年   2061篇
  1996年   1823篇
  1995年   1785篇
  1994年   1533篇
  1993年   1423篇
  1992年   1369篇
  1991年   1395篇
  1990年   1388篇
  1989年   1173篇
  1988年   1124篇
  1987年   1273篇
  1986年   1152篇
  1985年   1411篇
  1984年   1584篇
  1983年   1470篇
  1982年   1377篇
  1981年   1275篇
  1980年   1166篇
  1979年   1133篇
  1978年   1079篇
  1977年   915篇
  1976年   892篇
  1975年   882篇
  1974年   844篇
  1973年   913篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
681.
A paper devoted to the transformation of cartographic images based on nontraditional systems of scaling (travel time, transport effort, cost, etc.) describes the results of work to develop a more effective algorithm for such transformations, i.e., one which the authors claim provides for the more accurate determination of “transformed” line lengths than possible with earlier methods. Translated from: Izvestiya AN SSSR, seriya geograficheskaya, 1987, No. 4, pp. 105-111.  相似文献   
682.
Principles and objectives governing Soviet thematic mapping of nearby planets are outlined, types of information sources for such mapping categorized, and the suitability of different types of information sources for thematic mapping are evaluated. This is followed by a classification of thematic planetary maps according to type. The need for a standardized, systems approach to the determination of map scales, compilation and generalization, symbolization, and map design is emphasized as an essential prerequisite for the development of complex atlases of individual planets, atlases of “comparative planetology,” and the establishment of “planetary information systems.” Translated by Jay Mitchell; PlanEcon, Inc.; Washington, DC 20005 from: Vestnik Moskovskogo Universiteta, geografiya, 1987, No. 6, pp. 60-67.  相似文献   
683.
Spectral reflectances of artificial pastures are examined at various wavelengths and stages in the grazing/field work cycle to identify inadequately drained, marginally productive sites. Mesophytic pasture grasses and crops on well-drained sites are replaced by more hygrophytic species on poorly drained sites (each group with distinctive brightness values). This relationship, plus less significant spectral differences reflecting grazing intensity and soil moisture content at particular points in time, provided a methodological basis for the study. Poorly drained pastures are most reliably identified in the infrared and visible green portions of the spectrum during the middle of the grazing season. Translated from: Geografiya I prirodnyye resursy, 1988, No. 1, pp. 134-139.  相似文献   
684.
An effort is made at developing a theory of map readability, defined as the process of the user's representation of the information of the map in his/her own mind. This can be estimated quantitatively by surrogate measures, which include the speed of map comprehension and accuracy of map interpretation. Levels of psychological representation of map information are incorporated to determine at what stage particular aspects of map knowledge are understood. Thus what readability entails, and the approaches used to measure it (what types of things are comprehended, how fast, and how accurately) will depend upon the level of representation. Translated from: Vestnik Leningradskogo Universiteta, seriya 7 [geologiya, geografiya], 1988, No. 1, pp. 32-37.  相似文献   
685.
Shortcomings in the representation of bottom relief features on topographic maps of the continental shelves are examined, with particular attention given to submarine ridges and related features, the symbolization of which on such maps has been entirely ineffective. Specific recommendations are given on the form and color of symbols which can be used in upgrading the graphic impact of maps depicting such relief forms. Translated by Edward Torrey, Alexandria, VA 22308 from: Geodeziya i kartografiya, 1989, No. 1, pp. 35–40.  相似文献   
686.
687.
This paper explores how such characteristics as the polarization of reflected radiation, the angular characteristics of its reflectance, and its thermal properties can be used to supplement conventional remote sensing studies of the condition of the vegetation cover. One possible application is clarified by means of an experiment testing the relationship between the degree of polarization of radiation reflected from cultivated cotton fields and the condition of the crop in those fields. Empirical data demonstrate that changes in the geometric structure of (and reflectance from) fields occurs when cultivated plants are subjected to stress (disease or moisture deprivation). Translated by Edward Torrey, Alexandria, VA 22308 from: L. N. Vasil'yev, ed., Kosmicheskiye metody izucheniya biosfery [Remote Sensing Methods in the Study of the Biosphere]. Moscow: Nauka, 1990, pp. 77–82.  相似文献   
688.
Two general approaches for compiling maps of components of the water-ice budget in regions of glacier nourishment are compared and the resulting maps are analyzed. The compilation of raw data is based on field measurements rather than remote sensing information. Translated by Edward Torrey, Alexandria, VA 22308 from: Materialy glyatsiologicheskikh issledovaniy, 1991, No. 72, pp. 94-102.  相似文献   
689.
The article provides insights derived from conceptualization of the totality of elements (subsystems) of image interpretation as part of a larger system of scientific research. Among the elements discussed in some detail in terms of their impacts on the appearance of features interpreted on remote sensing imagery include solar radiation, the atmosphere, distinctive characteristics of the surface of the area being imaged, the remote sensors employed for image recording, processing techniques, the image medium, and the “human” element (interpreter). It then describes an evolutionary process in image interpretation by which knowledge gained in early stages represents an input leading to refinement of approaches employed in later stages. A final section describes factors contributing to dynamics (“scintillation” or “flickering”) of features on imagery of the same area but recorded at different times or under different imaging conditions. Translated by Edward Torrey, Alexandria, VA 22308 from: Izvestiya Akademii Nauk, seriya geograficheskaya, 1993, No. 3, pp. 102-109.  相似文献   
690.
Results are presented of analysis of Landsat MSS imagery for the purpose of assessing damage to northern taiga and tundra vegetation caused by emissions generated by nonferrous metallurgy on northwest Russia's Kola Peninsula. Unlike earlier studies, the present project attempts to provide spatially comprehensive coverage of vegetation impacts, according to a standardized methodology for their assessment. A reduction in the number of feature classes identifiable upon a change from visual interpretation to automated classification based on spectral brightness values made it necessary to test alternative classification procedures (based on brightness ratios and the normalized vegetation index).  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