全文获取类型
收费全文 | 721篇 |
免费 | 74篇 |
国内免费 | 108篇 |
专业分类
测绘学 | 16篇 |
大气科学 | 123篇 |
地球物理 | 174篇 |
地质学 | 322篇 |
海洋学 | 60篇 |
天文学 | 20篇 |
综合类 | 24篇 |
自然地理 | 164篇 |
出版年
2024年 | 4篇 |
2023年 | 7篇 |
2022年 | 17篇 |
2021年 | 17篇 |
2020年 | 21篇 |
2019年 | 18篇 |
2018年 | 17篇 |
2017年 | 36篇 |
2016年 | 20篇 |
2015年 | 22篇 |
2014年 | 38篇 |
2013年 | 55篇 |
2012年 | 43篇 |
2011年 | 32篇 |
2010年 | 33篇 |
2009年 | 41篇 |
2008年 | 50篇 |
2007年 | 40篇 |
2006年 | 40篇 |
2005年 | 39篇 |
2004年 | 37篇 |
2003年 | 32篇 |
2002年 | 34篇 |
2001年 | 28篇 |
2000年 | 27篇 |
1999年 | 27篇 |
1998年 | 17篇 |
1997年 | 20篇 |
1996年 | 12篇 |
1995年 | 6篇 |
1994年 | 10篇 |
1993年 | 8篇 |
1992年 | 10篇 |
1991年 | 6篇 |
1990年 | 6篇 |
1989年 | 6篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 6篇 |
1985年 | 1篇 |
1984年 | 3篇 |
1983年 | 6篇 |
1981年 | 3篇 |
1979年 | 1篇 |
1977年 | 3篇 |
1976年 | 1篇 |
排序方式: 共有903条查询结果,搜索用时 15 毫秒
81.
Abstract An intercomparison of the Väisälä MicroCora system used in the Automated Shipboard Aerological Program (ASAP) and the Atmospheric Environment Service upper‐air system (GMD/ADRES) was conducted in May‐June 1983. Thirty‐three paired ascents were made. The ASAP system dry‐bulb temperatures averaged 0.3°C warmer. For the lowest 100 mb, the dew‐point temperature difference (ASAP ‐ GMD/ADRES) was near ‐1°C whereas for the 780–500 mb layer, the difference was 1°C. The wind component mean differences averaged were small but with a 4 m s?1 standard deviation. 相似文献
82.
应用EOF(经验正交函数)迭代方案,考虑多时次历史资料,在全球海区海温与四川盆地气温非同步联系的基础上,以海温为预报因子进行了夏季气温的长期预报。结果表明:西太平洋高温区等关键海区海温的异常对未来四川盆地夏季气温变化有重要影响,由此建立的引入多时次海温的EOF迭代长期温度预报方法,具有较强的预报能力 相似文献
83.
George B. McManus Kevin D. Wyman William T. Peterson Charles F. Wurster 《Estuarine, Coastal and Shelf Science》1983,17(4):421-430
The effects of feeding, egg laying, and fecal pellet production on the elimination of polychlorinated biphenyls (PCBs) from the marine copepod Acartia tonsa were studied in a series of experiments. Copepods were exposed to 14C-labelled Aroclor 1254 and allowed to depurate in clean seawater. Copepods fed during depuration eliminated PCBs more rapidly than unfed copepods whether or not the original PCB exposure medium had contained food. Both eggs and fecal pellets contained PCBs during depuration, with the weight specific concentration of PCB in the eggs (up to 407 ppm, dry weight) exceeding four times that in the females that produced them. Female copepods eliminated PCBs twice as rapidly as males, indicating that egg production is an important route for PCB elimination. 相似文献
84.
The results of the Midland Valley Investigation by Seismology (MAVIS) are described. The experiment consists of three refraction profiles of between 80 and 100 km length across the Upper Palaeozoic basins of the Scottish Midland Valley.
Three refractors are recognized, thus defining four upper crustal layers. The top two layers are interpreted as Carboniferous plus Upper Old Red Sandstone, and Lower Old Red Sandstone plus Lower Palaeozoic. The structure of the refractor, an unconformity, separating the two layers mirrors surface structure. Deeper refractors, associated with Midland Valley crystalline basement, show no correlation with surface structure. The MAVIS survey allows the refinement of earlier gross interpretation of upper crustal structure in the Midland Valley, but confirms the existence of anomalously shallow (6.4 km s–1 ) basement, and shows, in conjunction with results of previous work, that a large area of the central and southern Midland Valley is characterized by one velocity signature, probably indicative of a single terrane. 相似文献
Three refractors are recognized, thus defining four upper crustal layers. The top two layers are interpreted as Carboniferous plus Upper Old Red Sandstone, and Lower Old Red Sandstone plus Lower Palaeozoic. The structure of the refractor, an unconformity, separating the two layers mirrors surface structure. Deeper refractors, associated with Midland Valley crystalline basement, show no correlation with surface structure. The MAVIS survey allows the refinement of earlier gross interpretation of upper crustal structure in the Midland Valley, but confirms the existence of anomalously shallow (6.4 km s
85.
Summary. The largest earthquake-induced acceleration yet recorded occurred at the United States Geological Survey's (USGS) Strong Motion Array Station 6 during the 1979 October 15, Imperial Valley, California earthquake. This large acceleration (1.74 g, vertical component) is anomalously strong considering the low magnitude of the event ( M = 6.4), and the fact that receivers in the immediate neighbourhood of Station 6 recorded much lower accelerations. Previous studies of the records by other investigators have suggested a number of explanations for the anomaly, several of which implicate the near-receiver geological structure.
We present a detailed time and frequency domain analysis of the acceleration records at Stations 6, 5, 7, 8 and Diff Array to suggest that the anomalous acceleration is the consequence of the focusing of the incoming body waves by the lens-like effect of the sedimentary wedge between Imperial Valley and Brawley faults. The analyses include a detailed comparison of observed particle motions between neighbouring stations. Narrow band-pass filtered particle motions at Station 6 reveal the interaction of multipath arrivals as well as the frequency-dependent interference between them. Three-dimensional ray tracing experiments confirm the fact that the faulted sedimentary wedge is capable of focusing P -waves near Station 6. The interpretation that best combines theoretical and observed results is that amplification was due to the formation of an elliptic umbilic caustic with focus near the surface. 相似文献
We present a detailed time and frequency domain analysis of the acceleration records at Stations 6, 5, 7, 8 and Diff Array to suggest that the anomalous acceleration is the consequence of the focusing of the incoming body waves by the lens-like effect of the sedimentary wedge between Imperial Valley and Brawley faults. The analyses include a detailed comparison of observed particle motions between neighbouring stations. Narrow band-pass filtered particle motions at Station 6 reveal the interaction of multipath arrivals as well as the frequency-dependent interference between them. Three-dimensional ray tracing experiments confirm the fact that the faulted sedimentary wedge is capable of focusing P -waves near Station 6. The interpretation that best combines theoretical and observed results is that amplification was due to the formation of an elliptic umbilic caustic with focus near the surface. 相似文献
86.
M.-P. Ledru D.-D. Rousseau F.W. Cruz Jr. C. Riccomini I. Karmann L. Martin 《Quaternary Research》2005,64(3):444-450
A long terrestrial record, Colônia CO-3, from the Atlantic rainforest region in Brazil (23°52′S, 46°42′20 W, 900 m a.s.l.) registrates variations in the forest expansion during the last 100,000 yr. The 780-cm depth core was analyzed at 2-cm intervals and arboreal pollen frequencies were compared to nearby speleothem stable isotope records and neighboring marine records from the tropical Atlantic. To evaluate regional versus global climate forcing, our record was compared with Greenland and Antarctic ice-core records. These comparisons suggest that changes in temperature seen in polar latitudes relate to moisture changes: e.g., to changes in the length of the dry season, in tropical and subtropical latitudes during glacial as well as interglacial times. These climatic changes result from changes in the frequency of polar air incursions to these latitudes inducing a permanent cloud cover and precipitation. This is an important result that should help define paleoclimatic features in the Southern Hemisphere for the last glaciation. 相似文献
87.
Medieval Warming, Little Ice Age, and European impact on the environment during the last millennium in the lower Hudson Valley, New York, USA 总被引:1,自引:0,他引:1
Dee Cabaniss Pederson Dorothy M. Peteet Dorothy Kurdyla Tom Guilderson 《Quaternary Research》2005,63(3):363-249
Establishing natural climate variability becomes particularly important in large urban areas in anticipation of droughts. We present a well-dated bi-decadal record of vegetation, climate, land use, and fire frequency from a tidal marsh in the Hudson River Estuary. The classic Medieval Warm Period is evident through striking increases in charcoal and Pinus dominance from 800–1300 A.D., paralleling paleorecords southward along the Atlantic seaboard. Higher inputs of inorganic sediment during this interval suggest increased watershed erosion during drought conditions. The presence of the Little Ice Age ensues with increases in Picea and Tsuga, coupled with increasing organic percentages due to cooler, moister conditions. European impact is manifested by a decline in arboreal pollen due to land clearance, increased weedy plant cover (i.e., Ambrosia, Plantago, and Rumex), and an increase in inorganic particles to the watershed. 相似文献
88.
89.
淮河流域5~6月降水的年际及年代际变化 总被引:1,自引:1,他引:1
对淮河流域降水异常进行分析对于预测黄海绿潮具有重要意义。选取淮河流域10个站,长江流域15个站,通过对国家气象信息中心1951~2011年的逐月降水数据进行分析,研究淮河流域和长江流域5~6月平均降水异常。2000~2010年,淮河流域5~6月降水呈现增加趋势,与长江流域降水呈反位相变化。分别对淮河流域5~6月平均降水异常与印度洋偶极子指数(Dipole Mode Index,DMI),以及太平洋年代际振荡(the Pacific Decadal Oscillation,PDO)指数做相关性分析,结果表明:淮河流域5~6月平均降水异常与6个月前的DMI指数达到最大正相关,与20个月前的北太平洋(20°N以北)SST呈现明显的负相关,与PDO指数达到最大负相关。这表明,PDO、DMI指数对淮河流域5~6月降水异常的年代际、年际变化具有明显的指示作用。 相似文献
90.
2003年江淮流域强降水过程与30—70d天低频振荡的联系 总被引:9,自引:1,他引:8
利用NCEP/NCAR再分析和地面观测站的逐日降水资料,研究了2003年夏季江淮流域强降水过程与低频振荡的联系。结果显示,主周期为30~70d的低频振荡对2003年江淮流域暴雨的形成具有重要贡献:低频涡旋在江淮地区降水期的对流层高、低层呈负、正配置,具有斜压结构,利于降水发生;850hPa上正涡度系统的传播具有明显的北传和西传特征;存在于西太平洋、西北太平洋及其以东地区的低频波列(P—J)的活动过程影响了我国2003年江淮低频强降水的形成;整层低频水汽通量显示来自副热带高压外围的西南季风对水汽输送的贡献较显著,且2003年江淮地区30-70d时间尺度上降水的水汽来源为南海而非孟加拉湾或西太平洋。 相似文献