全文获取类型
收费全文 | 38849篇 |
免费 | 627篇 |
国内免费 | 240篇 |
专业分类
测绘学 | 754篇 |
大气科学 | 2580篇 |
地球物理 | 7630篇 |
地质学 | 14067篇 |
海洋学 | 3545篇 |
天文学 | 8720篇 |
综合类 | 87篇 |
自然地理 | 2333篇 |
出版年
2022年 | 257篇 |
2021年 | 440篇 |
2020年 | 499篇 |
2019年 | 576篇 |
2018年 | 1011篇 |
2017年 | 1013篇 |
2016年 | 1078篇 |
2015年 | 582篇 |
2014年 | 1035篇 |
2013年 | 1852篇 |
2012年 | 1191篇 |
2011年 | 1629篇 |
2010年 | 1441篇 |
2009年 | 1796篇 |
2008年 | 1629篇 |
2007年 | 1688篇 |
2006年 | 1557篇 |
2005年 | 1058篇 |
2004年 | 1075篇 |
2003年 | 1112篇 |
2002年 | 996篇 |
2001年 | 868篇 |
2000年 | 797篇 |
1999年 | 723篇 |
1998年 | 715篇 |
1997年 | 723篇 |
1996年 | 588篇 |
1995年 | 572篇 |
1994年 | 501篇 |
1993年 | 453篇 |
1992年 | 409篇 |
1991年 | 424篇 |
1990年 | 437篇 |
1989年 | 391篇 |
1988年 | 369篇 |
1987年 | 400篇 |
1986年 | 415篇 |
1985年 | 508篇 |
1984年 | 545篇 |
1983年 | 542篇 |
1982年 | 496篇 |
1981年 | 454篇 |
1980年 | 429篇 |
1979年 | 408篇 |
1978年 | 375篇 |
1977年 | 384篇 |
1976年 | 344篇 |
1975年 | 353篇 |
1974年 | 340篇 |
1973年 | 370篇 |
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
101.
P. J. Michaels P. J. Stenger D. E. Sappington 《Theoretical and Applied Climatology》1986,37(1-2):39-50
Summary This report details as statistical model that relates changes in areal coverage of the Southern Pine Beetle (Dendroctonus frontalis Zimm.) to a multivariate combination of temperature and moisture status indices. It is applicable to larger geographic areas than our previous work (Michaels 1984). Performance in a true test (predictive) mode detected the algebraic sign of major coverage changes in a highly significant fashion. The results are purely correlative, rather than causative.This report describes a test-proven tool that can be used by planners to determine whether coverage will change, based upon easily accessed climatic data. An example of its application is provided.
With 5 Figures 相似文献
Zusammenfassung Diese Untersuchung führt ein statistisches Modell aus, welches das flächenmäßige Auftreten vonDendroctonus frontalis Zimm. mit einer Kombination von Temperaturund Feuchteverhältnisindikatoren in Verbindung bringt. Es kann für größere Gebiete verwendet werden als ein früher vorgestelltes (Michaels 1984). Die Anwendung zur Vorhersage zeigte in einem Test gute Übereinstimmung mit der tatsächlich aufgetretenen Richtung der Veränderung in der Verbreitung des Käfers. Die Ergebnisse zeigen Korrelationen, keine Kausalitäten auf.Es wird also ein Werkzeug für den Planer vorgestellt, mit dem die Verbreitungsänderung mit Hilfe leicht zugänglicher klimatologischer Daten bestimmt werden kann. Ein Anwendungsbeispiel wird näher ausgeführt.
With 5 Figures 相似文献
102.
103.
104.
105.
E. K. Semenov N. N. Sokolikhina E. V. Sokolikhina 《Russian Meteorology and Hydrology》2013,38(10):661-668
The genetic and synoptic classifications of the Novorossiysk Bora are created using the data of daily observations at the Novorossiysk meteorological station and other available synoptic information. Obtained are the quantitative criteria of these classifications, and on this base worked out are the basic scenarios of the generation and evolution of this dangerous phenomenon on the Black Sea coast of Russia. According to the genetic classification, the Bora was divided into four types: frontal, air-mass, monsoon, and gravity. Quantitative criteria worked out for each type can be used for the more accurate forecast of this destructive phenomenon near Novorossiysk. According to the synoptic classification, four classes were distinguished: Azores, North Atlantic, Siberian, and Arctic. 相似文献
106.
107.
The coupled mechanics of fluid-filled granular media controls the physics of many Earth systems, for example saturated soils, fault gouge, and landslide shear zones. It is well established that when the pore fluid pressure rises, the shear resistance of fluid-filled granular systems decreases, and, as a result, catastrophic events such as soil liquefaction, earthquakes, and accelerating landslides may be triggered. Alternatively, when the pore pressure drops, the shear resistance of these geosystems increases. Despite the great importance of the coupled mechanics of grain–fluid systems, the basic physics that controls this coupling is far from understood. Fundamental questions that must be addressed include: what are the processes that control pore fluid pressurization and depressurization in response to deformation of the granular skeleton? and how do variations of pore pressure affect the mechanical strength of the grains skeleton? To answer these questions, a formulation for the pore fluid pressure and flow has been developed from mass and momentum conservation, and is coupled with a granular dynamics algorithm that solves the grain dynamics, to form a fully coupled model. The pore fluid formulation reveals that the evolution of pore pressure obeys viscoelastic rheology in response to pore space variations. Under undrained conditions elastic-like behavior dominates and leads to a linear relationship between pore pressure and overall volumetric strain. Viscous-like behavior dominates under well-drained conditions and leads to a linear relationship between pore pressure and volumetric strain rate. Numerical simulations reveal the possibility of liquefaction under drained and initially over-compacted conditions, which were often believed to be resistant to liquefaction. Under such conditions liquefaction occurs during short compactive phases that punctuate the overall dilative trend. In addition, the previously recognized generation of elevated pore pressure under undrained compactive conditions is observed. Simulations also show that during liquefaction events stress chains are detached, the external load becomes completely supported by the pressurized pore fluid, and shear resistance vanishes. 相似文献
108.
E. G. Krupa 《Water Resources》2007,34(6):712-717
Data on the Shardarinskoe Reservoir are used to assess the indicator role of zooplankton community under unstable hydrological regime. The structural characteristics of zooplankton featured significant seasonal variations. The averaged indices characterized reservoir water quality at the level of mesotrophic and eutrophic water bodies. The possible use of cyclopidas to characterize toxic pollution of water is discussed. 相似文献
109.
110.
This paper presents an integrated measurement technique based on DC methods (vertical electrical sounding, electrical resistivity tomography) which was used to identify faults and determine their geoelectric parameters in the western part of the Chuya basin. New information on the structure of the Chagan River valley located in the zone of the disastrous 27 September 2003 Chuya earthquake has been obtained from the results of these methods. Geoelectric cross-sections of the sedimentary sequence and the upper part of the basement were obtained from VES data, showing the block structure of the study area. Electrical resistivity tomography sections confirm the presence of a major fault between basement blocks of different heights and indicate the presence of faults bounding the valley on its right side and in the southwestern part. 相似文献