全文获取类型
收费全文 | 12064篇 |
免费 | 138篇 |
国内免费 | 72篇 |
专业分类
测绘学 | 248篇 |
大气科学 | 759篇 |
地球物理 | 2285篇 |
地质学 | 4661篇 |
海洋学 | 1221篇 |
天文学 | 2559篇 |
综合类 | 50篇 |
自然地理 | 491篇 |
出版年
2022年 | 144篇 |
2021年 | 207篇 |
2020年 | 196篇 |
2019年 | 235篇 |
2018年 | 539篇 |
2017年 | 434篇 |
2016年 | 483篇 |
2015年 | 194篇 |
2014年 | 419篇 |
2013年 | 624篇 |
2012年 | 473篇 |
2011年 | 576篇 |
2010年 | 570篇 |
2009年 | 659篇 |
2008年 | 585篇 |
2007年 | 586篇 |
2006年 | 499篇 |
2005年 | 336篇 |
2004年 | 317篇 |
2003年 | 290篇 |
2002年 | 280篇 |
2001年 | 253篇 |
2000年 | 259篇 |
1999年 | 176篇 |
1998年 | 195篇 |
1997年 | 176篇 |
1996年 | 122篇 |
1995年 | 132篇 |
1994年 | 115篇 |
1993年 | 98篇 |
1992年 | 75篇 |
1991年 | 103篇 |
1990年 | 99篇 |
1989年 | 70篇 |
1988年 | 80篇 |
1987年 | 101篇 |
1986年 | 85篇 |
1985年 | 111篇 |
1984年 | 101篇 |
1983年 | 107篇 |
1982年 | 89篇 |
1981年 | 87篇 |
1980年 | 100篇 |
1979年 | 92篇 |
1978年 | 89篇 |
1977年 | 80篇 |
1976年 | 67篇 |
1975年 | 64篇 |
1974年 | 73篇 |
1973年 | 65篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
This study proposes a bootstrap-based space–time surveillance model. Designed to find emerging hotspots in near-real time, the bootstrap based model is characterized by its use of past occurrence information and bootstrap permutations. Many existing space–time surveillance methods, using population at risk data to generate expected values, have resulting hotspots bounded by administrative area units and are of limited use for near-real time applications because of the population data needed. However, this study generates expected values for local hotspots from past occurrences rather than population at risk. Also, bootstrap permutations of previous occurrences are used for significant tests. Consequently, the bootstrap-based model, without the requirement of population at risk data, (1) is free from administrative area restriction, (2) enables more frequent surveillance for continuously updated registry database, and (3) is readily applicable to criminology and epidemiology surveillance. The bootstrap-based model performs better for space–time surveillance than the space–time scan statistic. This is shown by means of simulations and an application to residential crime occurrences in Columbus, OH, year 2000. 相似文献
102.
Mudanyal O. Yldz S. Semerci O. Yapar A. Akduman I. 《Geoscience and Remote Sensing Letters, IEEE》2008,5(2):180-184
A microwave imaging method for nondestructive testing of perfectly conducting surfaces beyond a layered media is presented. The method is an adaptation of the surface reconstruction approach by Yapar et al. to the present problem. It is based on the analytical continuation of the measured data to the surface under test through a special representation of the scattered field in terms of Fourier transform and Taylor expansion. Then the problem is reduced to the solution of a nonlinear equation which is solved iteratively via the Newton method and regularization in the least squares sense. Numerical simulations show that defects as small as lambda/500 can be recovered through the presented algorithm. 相似文献
103.
104.
105.
106.
107.
A.E. Dodonov V.G. Trifonov T.P. Ivanova V.Yu. Kuznetsov F.E. Maksimov D.M. Bachmanov T.A. Sadchikova A.N. Simakova H. Minini A.-M. Al-Kafri O. Ali 《Quaternary International》2008,190(1):158
In order to provide new data on the neotectonics and geodynamic properties of western Syria, studies of marine terraces have been carried out. The most attention was paid to the lower terraces in the range of 3–5 to 30–35 m above sea level, because they have more complete distributions along the shore. The lower terraces were examined along the coastal area from Tartus to Latakia, and along the carbonate cliff on Arwad Island. Seven 230Th/U dates for these terraces are in the range of 85–130 ka, suggesting the age interval of the last interglacial (MIS 5). New dates on the lower terraces provide a basis for stratigraphical and geomorphological interpretation as well as neotectonic reconstruction. According to the geomorphological data and lithological composition of those terraces, two main uplifted blocks can be established. One coincides with the Latakia block, and another corresponds to the western margin of the Banias volcanic plateau. These blocks are divided by a subsided structure corresponding to the Nahr el Kebir graben. The amplitude of neotectonic uplifting in the Latakia and Banias blocks reaches 15–20 m for the Late Pleistocene. 相似文献
108.
109.
O. G. Den 《Astronomy Reports》2008,52(11):931-936
We analyze the flare events of October 28 and May 27, 2003 to examine the possible connection of solar flares with singularities in the differential characteristics of solar magnetic fields. The relation between flares and the behavior of F indicators (which describe structural singularities of the magnetic fields) introduced earlier is analyzed. It is shown that the generation of flares can be associated with self-intersections (or reconnection) of the F = 0 curves, where magnetic reconnection can occur. Consequently, the current sheets generated in such regions can be sources of energy release. 相似文献
110.
The region known as Pampa Plain, in Argentina, is a vast area characterized by slopes of less than 0.05%. The surface sediment is silty sand, mainly Aeolian, referred to as Pampean Loess, which is a phreatic aquifer unit of utmost importance for the water supply of the region. On account of the slight gradient, hydrogeological analyses using only hydraulic measurements are difficult to perform, often leading to confusing results. Thus, the study presented relies on hydrochemical modeling and isotopic determinations as well. The study area comprises three catchments in the inter-mountainous area corresponding to El Moro, Tamangueyú and Seco creeks, and covering 2,570 km2 in the province of Buenos Aires. Measurements of piezometric levels and samples of groundwater, surface water and rainwater were carried out between January and March 2005. Major ion results were analyzed by means of hydrochemical graphs and hydrogeochemical modelling using NETPATH. The resulting data show that it is possible to identify local changes in recharge, flow direction and stream/groundwater relationship by using hydrochemical and isotopic information, which may become a useful and more precise tool for the study of particularly flat landscapes. 相似文献