全文获取类型
收费全文 | 26248篇 |
免费 | 388篇 |
国内免费 | 335篇 |
专业分类
测绘学 | 742篇 |
大气科学 | 1882篇 |
地球物理 | 5103篇 |
地质学 | 9040篇 |
海洋学 | 2379篇 |
天文学 | 6373篇 |
综合类 | 73篇 |
自然地理 | 1379篇 |
出版年
2021年 | 207篇 |
2020年 | 261篇 |
2019年 | 310篇 |
2018年 | 632篇 |
2017年 | 614篇 |
2016年 | 759篇 |
2015年 | 423篇 |
2014年 | 732篇 |
2013年 | 1351篇 |
2012年 | 847篇 |
2011年 | 1087篇 |
2010年 | 993篇 |
2009年 | 1286篇 |
2008年 | 1160篇 |
2007年 | 1186篇 |
2006年 | 1159篇 |
2005年 | 862篇 |
2004年 | 863篇 |
2003年 | 781篇 |
2002年 | 745篇 |
2001年 | 637篇 |
2000年 | 649篇 |
1999年 | 577篇 |
1998年 | 567篇 |
1997年 | 537篇 |
1996年 | 399篇 |
1995年 | 400篇 |
1994年 | 416篇 |
1993年 | 324篇 |
1992年 | 315篇 |
1991年 | 266篇 |
1990年 | 316篇 |
1989年 | 283篇 |
1988年 | 264篇 |
1987年 | 288篇 |
1986年 | 243篇 |
1985年 | 323篇 |
1984年 | 343篇 |
1983年 | 335篇 |
1982年 | 321篇 |
1981年 | 253篇 |
1980年 | 272篇 |
1979年 | 226篇 |
1978年 | 213篇 |
1977年 | 222篇 |
1976年 | 180篇 |
1975年 | 195篇 |
1974年 | 178篇 |
1973年 | 171篇 |
1972年 | 116篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
Actual surface fields of meteorological variables 1–3 hours before the heavy showers are analyzed in detail for the purpose
of their specification with WRF-ARW model. The complex of hygrothermodynamic characteristics needed for this purpose is discovered.
The detailed satellite, radar, and synoptic data are also considered. 相似文献
103.
104.
D. A. Burney R. V. DeCandido L. P. Burney F. N. Kostel-Hughes T. W. Stafford Jr. H. F. James 《Journal of Paleolimnology》1995,13(3):209-217
A sediment core from a high-elevation bog on Maui in the Hawaiian Islands contains evidence for drier conditions between 9.4–5.8 kyr BP, followed by a wetter interval between 5.8–2.2 kyr BP, and a variable late Holocene. These precipitation changes may be a reflection of vertical displacements of the upper boundary of the mid-Pacific Trade Wind Inversion (TWI) cloud layer. Fires, probably volcanically ignited, occurred in the forests prior to human arrival. Polynesian activity in this high-elevation, remote site was apparently limited, with no pollen, charcoal, or sedimentological evidence for local anthropogenic disturbance. After European contact, grass fires increased and introduced plant species invaded the site. Values for Cd, Cu, Pb, and Zn in sediments throughout the Holocene indicate low trace-metal deposition from atmospheric particulates at the site, even in the twentieth century.This paper is one of a series of papers guest edited by Dr. Mark Brenner on tropical paleolimnology 相似文献
105.
Dan?HammarlundEmail author Svante?Bj?rck Bj?rn?Buchardt Charlotte T.?Thomsen 《Journal of Paleolimnology》2005,34(4):471-480
Highly resolved sediment stratigraphic and stable isotope records from a lake in south-central Sweden give evidence of relatively humid summers during the wide-spread cold event at c. 8200 cal. BP. A transient lake-level rise led to increased catchment erosion followed by enhanced phytoplankton production and disturbance of the Chara-dominated algal community. An associated increase in the deposition of organic material resulted in hypolimnetic oxygen deficit and methane formation as inferred from elevated sulphur content of the sediments and strong depletion in 13C of bulk organic material. In combination with dry and cold winter conditions as revealed by other proxy records, these data suggest the development of a strongly seasonal climate in northwestern Europe in response to altered atmospheric circulation at this stage. Enhanced zonal circulation with frequent cyclonic activity and increased effective humidity probably characterized the summer climate of southern and central Scandinavia, consistent with conditions inferred for continental Europe. In contrast, the winter climate was dominated by blocking high-pressure circulation, giving rise to cold and dry conditions. 相似文献
106.
In this paper we present the H map, the 2D velocity field and the rotation curve of the galaxy NGC 784 obtained with the ByuFOSC2 scanning Fabry-Perot interferometer, attached at the prime focus of the 2.6-m telescope of Byurakan Observatory. The H image shows several HII condensations along the major axis of the galaxy. The galaxy has an asymmetric distribution of the H emission. The rotation curve is quite symmetric with a low gradient in the central part of the galaxy. 相似文献
107.
The Cryogenian succession of the Northern Flinders Ranges reveals a complex sedimentary record between the Sturtian and Marinoan glacial deposits. A major unconformity separates the Sturtian and Marinoan-aged sedimentary successions in the area. This forms a subaerial erosion surface with terrestrial and marginal marine infill directly above the Angepena and Balcanoona Formations in their respective localities. This exposure surface is here correlated with the previously documented submarine unconformity between the Yankaninna Formation and the underlying deep marine Tapley Hill Formation. This erosional event provides a chronostratigraphic marker horizon that coincides approximately with thepreviously defined Sturtian–Marinoan Time Series boundary in the Northern Flinders Ranges. These stratigraphic relationships also constrain lateral facies relationships between the Oodnaminta ReefComplex (Balcanoona Formation) and the Angepena Formation. Similarly, the shallow-water Weetootla Dolomite is correlated with the deeper water carbonates of the Yankaninna Formation. 相似文献
108.
109.
Horizontal and vertical zones of influence for root systems of four Mojave Desert shrubs 总被引:3,自引:0,他引:3
Horizontal and vertical zones of influence for root systems of four Mojave Desert shrubs were characterized using 32P as a nutrient tracer. Larrea tridentata's horizontal zone of influence was sparse near the plant's stem base, with a maximum probability of accessing 32P (Pmax) of 41%. However, its horizontal zone of influence extended beyond 5 m, and the distance from the stem base at which the probability of accessing 32P was half Pmax (L503 m) was significantly greater than the other three shrubs. Ambrosia dumosa's zone of influence was dense near the plant's stem base (Pmax78%), but was rare at distances >2 m (L501 m). Zones of influence for Lycium andersonii and Lycium pallidum were intermediate between those of L. tridentata and A. dumosa. For vertical zones of influence, L. tridentata was more likely to obtain 32P from 5 m soil depths than A. dumosa, but L. pallidum was not significantly different from either A. dumosa or L. tridentata. Horizontal zones of influence did not change with treatments that altered soil water and nitrogen availability, but vertical zones of influence increased with a flood irrigation treatment that increased water availability to 5 m soil depth. These differences among species likely reflect compromises between their shoot growth strategies and their need to acquire spatially and temporally limited soil resources, especially through competitive interactions. 相似文献
110.