全文获取类型
收费全文 | 111852篇 |
免费 | 1566篇 |
国内免费 | 797篇 |
专业分类
测绘学 | 2496篇 |
大气科学 | 7542篇 |
地球物理 | 21612篇 |
地质学 | 39787篇 |
海洋学 | 10281篇 |
天文学 | 25648篇 |
综合类 | 277篇 |
自然地理 | 6572篇 |
出版年
2022年 | 679篇 |
2021年 | 1227篇 |
2020年 | 1304篇 |
2019年 | 1474篇 |
2018年 | 3002篇 |
2017年 | 2779篇 |
2016年 | 3311篇 |
2015年 | 1738篇 |
2014年 | 3171篇 |
2013年 | 5792篇 |
2012年 | 3504篇 |
2011年 | 4615篇 |
2010年 | 4195篇 |
2009年 | 5428篇 |
2008年 | 4691篇 |
2007年 | 4804篇 |
2006年 | 4485篇 |
2005年 | 3350篇 |
2004年 | 3264篇 |
2003年 | 3062篇 |
2002年 | 3041篇 |
2001年 | 2668篇 |
2000年 | 2564篇 |
1999年 | 2074篇 |
1998年 | 2131篇 |
1997年 | 2011篇 |
1996年 | 1700篇 |
1995年 | 1691篇 |
1994年 | 1467篇 |
1993年 | 1429篇 |
1992年 | 1317篇 |
1991年 | 1314篇 |
1990年 | 1295篇 |
1989年 | 1194篇 |
1988年 | 1108篇 |
1987年 | 1290篇 |
1986年 | 1135篇 |
1985年 | 1387篇 |
1984年 | 1563篇 |
1983年 | 1479篇 |
1982年 | 1351篇 |
1981年 | 1320篇 |
1980年 | 1127篇 |
1979年 | 1097篇 |
1978年 | 1052篇 |
1977年 | 967篇 |
1976年 | 923篇 |
1975年 | 903篇 |
1974年 | 887篇 |
1973年 | 961篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
821.
Daniele Pedretti Roger D. Beckie 《Stochastic Environmental Research and Risk Assessment (SERRA)》2016,30(7):1933-1946
Two-station pairing approaches are routinely used to infill missing information in incomplete rainfall databases. We evaluated the performance of three simple methodologies to reconstruct incomplete time series in presence of variable nonlinear correlation between data pairs. Nonlinearity stems from the statistics describing the marginal peak-over-threshold (POT) values of rainfall events. A Monte Carlo analysis was developed to quantitatively assess expected errors from the use of chronological pairing (CP) with linear and nonlinear regression and frequency pairing (FP). CP is based on a priori selection of regression functions, while FP is based on matching the probability of non-exceedance of an event from one time series with the probability of non-exceedance of a similar event from another time series. We adopted a generalized Pareto (GP) model to describe POT events, and a t-copula algorithm to generate reference nonlinearly correlated pairs of random temporal distributions distributed according with the GP model. The results suggest that the optimal methodology strongly depends on GP statistics. In general, CP seems to provide the lowest errors when GP statistics were similar and correlation became linear; we found that a power-2 function performs well for the selected statistics when the number of missing points is limited. FP outperforms the other methods when POT statistics are different and variables are markedly nonlinearly correlated. Ensemble-based results seem to be supported by the analysis of observed precipitation at two real-world gauge stations. 相似文献
822.
823.
824.
A problem of convective cooling of both freshwater and saltwater lake is formulated. A transient one-dimensional turbulent model with variable layer depth is proposed to describe the process of freezing. The dependence of layer depth on time is determined by a universal equation describing the propagation of Deardorff convective layer. A combination of the main form of equations of Kolmogorov–Obukhov theory and available experimental data is shown to allow the construction of a universal profile of turbulent exchange coefficient, depending on the height. 相似文献
825.
Within the framework of a linear theory, the instability of an electron beam with a finite radius in a cold magnetised boundless plasma is considered. It is shown that a finite beam dimension influences the generation of quasi-potential waves in two aspects: the perpendicular wave number is quantised so that the frequencies of the waves are subjected to strong selection; a new kind of instability appears due to wave energy losses by emission into surrounding space. Growth rate dependence of wave numbers and frequencies is investigated for typical parameters of experiments with electron beams in space. 相似文献
826.
V. A. Marinov S. V. Meledina O. S. Dzyuba O. S. Urman O. V. Yazikova V. A. Luchinina A. G. Zamirailova A. N. Fomin 《Stratigraphy and Geological Correlation》2006,14(4):418-432
Paleontological study of Upper Jurassic and Lower Cretaceous sediments recovered by boreholes in the Agan-Vakh and Nadym-Vengapur interfluves clarified environments of their deposition. As is shown, influx of siliciclastic material to central areas of the West Siberian sea basin varied through time. Taxonomic composition and ecological structure of nektonic and benthic fossil assemblages are analyzed and considered in terms of environmental factors such as hydrodynamics, aeration, temperature, and salinity of seawater. 相似文献
827.
The composition, structure, and geochemical properties of the thickest, relatively deep-water Lower Miocene sediments developed in western Ciscaucasia are considered. Of particular interest are materials from the Kuban superdeep borehole SG-12000 that recovered the uppermost layers of the Maikop Group at 3148–3961 m in the central Indol-Kuban Trough west of Krasnodar. However, the borehole did not penetrate the whole Lower Miocene section of the Maikop Group. Therefore, characteristics of the Maikop Group are supplemented with new materials from several other boreholes drilled in the eastern Kuban region. Thus, the typical (reference) Lower Miocene section of central and western Ciscaucasia has been sufficiently well described. 相似文献
828.
829.
Donald A. Wilhite 《Natural Hazards》1996,13(3):229-252
Drought is a normal, recurrent feature of climate that affects virtually all countries to some degree. The number of drought-induced natural disasters has grown significantly since the 1960s, largely as a result of increasing vulnerability to extended periods of precipitation deficiency rather than because of an increase in the frequency of meteorological droughts. This increase in drought-induced natural disasters has resulted in a considerable growth of interest in drought mitigation and preparedness worldwide. The purpose of a national preparedness plan is to reduce societal vulnerability to drought through the adoption of preventive, anticipatory policies and programs. This paper describes a ten-step planning process that nations can follow to develop a drought preparedness plan. This process, originally developed in 1987, has been the basis of discussions at training seminars on drought preparedness for developing nations in Africa, Asia, and Latin America. It has also been adopted, with appropriate modifications, by state or provincial governments and by municipalities. The process is intended to be flexible so that governments can add, delete, or modify the suggested steps, as necessary.Published as Paper No. 10946, Journal Series, Nebraska Agricultural Research Division. The work reported here was conducted under Nebraska Agricultural Research Division Project 27-007. This material is based in part upon work supported by the National Science Foundation under Grant ATM-8704050. 相似文献
830.
M. V. Belyaeva A. S. Drofa V. N. Ivanov 《Izvestiya Atmospheric and Oceanic Physics》2013,49(2):154-161
Comparative estimates of the efficiency of hygroscopic reagents for the seeding of convective clouds to obtain additional precipitation are performed based on numerical simulation. It is shown that the use of polydisperse salt powders has many benefits over other known hygroscopic reagents. The effect of seeding with salt powders manifests itself at mass concentrations of hygroscopic particles an order of magnitude less than when pyrotechnic flares are used. With salt-powder seeding, it is possible to obtain precipitation from warm convective clouds of moderate thickness from which precipitation does not typically fall. In this case the effect of “reseeding” of clouds, which can be observed in seeding with hygroscopic reagents having narrow size distributions of particles, does not reveal itself. 相似文献