全文获取类型
收费全文 | 85493篇 |
免费 | 1137篇 |
国内免费 | 528篇 |
专业分类
测绘学 | 1757篇 |
大气科学 | 5607篇 |
地球物理 | 16265篇 |
地质学 | 30798篇 |
海洋学 | 7869篇 |
天文学 | 19910篇 |
综合类 | 222篇 |
自然地理 | 4730篇 |
出版年
2022年 | 619篇 |
2021年 | 1048篇 |
2020年 | 1118篇 |
2019年 | 1247篇 |
2018年 | 2551篇 |
2017年 | 2363篇 |
2016年 | 2719篇 |
2015年 | 1353篇 |
2014年 | 2616篇 |
2013年 | 4486篇 |
2012年 | 2863篇 |
2011年 | 3693篇 |
2010年 | 3377篇 |
2009年 | 4266篇 |
2008年 | 3718篇 |
2007年 | 3832篇 |
2006年 | 3551篇 |
2005年 | 2525篇 |
2004年 | 2445篇 |
2003年 | 2285篇 |
2002年 | 2275篇 |
2001年 | 1969篇 |
2000年 | 1954篇 |
1999年 | 1535篇 |
1998年 | 1596篇 |
1997年 | 1465篇 |
1996年 | 1243篇 |
1995年 | 1242篇 |
1994年 | 1042篇 |
1993年 | 1007篇 |
1992年 | 934篇 |
1991年 | 967篇 |
1990年 | 935篇 |
1989年 | 817篇 |
1988年 | 751篇 |
1987年 | 883篇 |
1986年 | 773篇 |
1985年 | 946篇 |
1984年 | 1070篇 |
1983年 | 1031篇 |
1982年 | 950篇 |
1981年 | 891篇 |
1980年 | 792篇 |
1979年 | 748篇 |
1978年 | 726篇 |
1977年 | 619篇 |
1976年 | 626篇 |
1975年 | 613篇 |
1974年 | 589篇 |
1973年 | 656篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
341.
Darrell A. Norris 《The Professional geographer》1987,39(1):23-32
The commercial non-metropolitan exit clusters of America's interstate highway system exhibit regularities of basic form, scale, mix of services provided, and the ordinal placement of establishments relative to the exit proper. An examination of 354 exits serving 1-75 indicates the typical morphology of interstate exit clusters. 相似文献
342.
Potential implications of differential preservation of testate amoeba shells for paleoenvironmental reconstruction in peatlands 总被引:1,自引:0,他引:1
Edward A. D. Mitchell Richard J. Payne Mariusz Lamentowicz 《Journal of Paleolimnology》2008,40(2):603-618
Testate amoebae are now commonly used in paleoenvironmental studies but little is known of their taphonomy. There is some
experimental evidence for differential preservation of some testate amoeba shell types over others, but it is unclear what,
if any impact this has on palaeoenvironmental reconstruction. To investigate this issue we looked at palaeoecological evidence
for the preservation of different shell types. We then investigated the possible impact of selective preservation on quantitative
palaeoenvironmental inference. We first used existing palaeoecological data sets to assess the vertical patterns of relative
abundance in four testate amoeba shell types: (1) shells made of secreted biosilica plates (idiosomes, e.g. Euglypha), (2) idiosomes with thick organic coating (Assulina), (3) proteinaceous shells (e.g. Hyalosphenia), (4) shells built from recycled organic or mineral particles (xenosomes) (e.g. Difflugia, Centropyxis). In three diagrams a clear pattern of decay was only observed for the idiosome type. In order to assess the implications
of differential preservation of testate amoeba taxa for paleoenvironmental reconstruction we then carried out simulations
using three existing transfer functions and a wide range of scenarios, downweighting different test categories to represent
the impact of selective test decomposition. Simulation results showed that downweighting generally reduced overall model performance.
However downweighting a shell type only produced a consistent directional bias in inferred water table depth where that shell
type is both dominant and shows a clear preference along the ecological gradient. Applying a scenario derived from previous
experimental work did not lead to significant difference in inferred water table. Our results show that differential shell
preservation has little impact on paleohydrological reconstruction from Sphagnum-dominated peatlands. By contrast, for the minerotrophic peatlands data-set loss of idiosome tests leads to consistent underestimation
of water table depth. However there are few studies from fens and it is possible that idiosome tests are not always dominant,
and/or that differential decomposition is less marked than in Sphagnum peatlands. Further work is clearly needed to assess the potential of testate amoebae for paleoecological studies of minerotrophic
peatlands. 相似文献
343.
Di Baofeng Katsenis Loukas Stamatopoulos Constantine A. Panoskaltsis Vassilis P. 《Landslides》2021,18(6):2297-2307
Landslides - Earthquake-induced landslides involve excessive movement of slopes, usually along slip surfaces. This seismic movement of slopes may depend crucially on (a) the soil response along the... 相似文献
344.
高分辨率全球尺度水文模型发展综述 总被引:1,自引:0,他引:1
主要从高分辨率全球尺度水文模型(HRGHM)的发展历程、模型的一般结构与特点、模型数据集的发展和模型所面临的主要问题等几个方面对全球尺度水文模型的发展情况进行了综述。HRGHM能够使水文学家从全球的角度深入了解水资源的产生及循环过程,并且对相关环境问题的解决、气候的模拟与预报以及水资源的管理具有重要的意义。经过几十年的发展和努力,在全球尺度数据集的研究和发展方面已经取得了丰硕的成果,并且在HRGHM的实践中得以应用,但空间数据的缺乏仍然是其发展的最大羁绊。HRGHM所面临的问题除了数据的匮乏还在于非线性问题、尺度问题和确定性问题等水文机理和技术层面的问题。 相似文献
345.
An ecotoxicological assessment is given to the state of small lakes in specially protected natural areas in Northwestern and Central European Russia, which suffer from aerotechnogenic acidification. The toxicity of water and bottom sediments is shown to increase with decreasing water pH. The most sensitive characteristics of aquatic organisms in different trophic groups are chosen, allowing the state of lakes to be monitored. 相似文献
346.
A. V. Mityukov A. M. Nikishin O. A. Almendinger S. N. Bolotov V. A. Lavrishchev N. K. Myasoedov E. V. Rubtsova 《Moscow University Geology Bulletin》2012,67(2):81-92
This work is based on the results of 2-D and 3-D surveys in the Tuapse Basin and field works in the Crimea-Caucasus region. Seven zones were outlined in the model of sedimentation starting from the eroded mountain structure of the Greater Caucasus down to deep water sediments of the Tuapse Basin. The slope and deep-water sediments of channels and fan complexes are characterized. Volume models of the sedimentation system in the Black Sea are shown for the first time. 相似文献
347.
348.
WILLIAM A. KOELSCH 《Geographical review》2012,102(4):510-524
The conventional narrative regarding the American reception of George Perkins Marsh, author of Man and Nature (1864), is that his work and ideas were “lost,”“forgotten,” or “neglected” until Lewis Mumford “rediscovered” him and introduced him to geographers at the University of California‐Berkeley through The Brown Decades (Mumford [1931] 1955) and until Carl Sauer made him known to the profession at large beginning in 1938. This article upends the conventional narrative by looking at earlier references to Marsh's later versions of Man and Nature, which were published as The Earth as Modified by Human Action from 1874 to 1907. Analysis reveals that a number of geographers and historians cited these editions between 1875 and the early 1950s. Examining the legend of loss and rediscovery suggests the value of methods utilized in reception studies for research on the history of geography. 相似文献
349.
350.