全文获取类型
收费全文 | 34000篇 |
免费 | 477篇 |
国内免费 | 414篇 |
专业分类
测绘学 | 1400篇 |
大气科学 | 2616篇 |
地球物理 | 6614篇 |
地质学 | 12162篇 |
海洋学 | 2582篇 |
天文学 | 7879篇 |
综合类 | 186篇 |
自然地理 | 1452篇 |
出版年
2022年 | 208篇 |
2021年 | 331篇 |
2020年 | 330篇 |
2019年 | 380篇 |
2018年 | 1005篇 |
2017年 | 941篇 |
2016年 | 1168篇 |
2015年 | 680篇 |
2014年 | 1092篇 |
2013年 | 1862篇 |
2012年 | 1156篇 |
2011年 | 1386篇 |
2010年 | 1163篇 |
2009年 | 1482篇 |
2008年 | 1280篇 |
2007年 | 1202篇 |
2006年 | 1223篇 |
2005年 | 1006篇 |
2004年 | 900篇 |
2003年 | 887篇 |
2002年 | 877篇 |
2001年 | 779篇 |
2000年 | 765篇 |
1999年 | 690篇 |
1998年 | 629篇 |
1997年 | 638篇 |
1996年 | 573篇 |
1995年 | 539篇 |
1994年 | 519篇 |
1993年 | 436篇 |
1992年 | 388篇 |
1991年 | 428篇 |
1990年 | 423篇 |
1989年 | 395篇 |
1988年 | 364篇 |
1987年 | 439篇 |
1986年 | 367篇 |
1985年 | 457篇 |
1984年 | 485篇 |
1983年 | 466篇 |
1982年 | 448篇 |
1981年 | 358篇 |
1980年 | 365篇 |
1979年 | 318篇 |
1978年 | 311篇 |
1977年 | 297篇 |
1976年 | 261篇 |
1975年 | 260篇 |
1974年 | 292篇 |
1973年 | 310篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
J.Aramendia L.Gomez-Nubla M.L.Tuite K.H.Williford K.Castro J.M.Madariaga 《地学前缘(英文版)》2021,12(5):421-426
Nitrogen-containing heterocyclic compounds are fundamental biochemical components of all life on Earth and, presumably, life elsewhere in our solar system. Dete... 相似文献
72.
73.
K. R. Muraleedharan P. K. Dinesh Kumar S. Prasanna Kumar Sebin John B. Srijith K. Anil Kumar K. Naveen Kumar S. Gautham V. Samiksha 《Estuaries and Coasts》2018,41(4):1021-1035
Mud bank formation during the southwest monsoon along the southwest coast of India remains an enigma to the researchers and coastal community in spite of several earlier studies. The present study attempts to unravel the mystery through a high-frequency, season-long time-series observation at Alappuzha, located at the southern part of the west coast of India, a region of frequent occurrence of mud bank. Using 7-month-long weekly time-series observation, we identified strong winds and high waves associated with onset of the southwest monsoon and subsequent three episodic atmospheric low-pressure events (LPEs).With the help of in situ time-series data, we show that the strong winds and high waves associated with southwest monsoon pre-conditions the near shore bottom sediment to bring it into suspension. The high amplitude waves associated with the southwest monsoon, while propagating from the deep water to shallow water region, interact with the bottom initiating bottom-sediment movement and its suspension due to wave refraction and shoaling. The sporadic occurrence of the atmospheric LPEs enhances the process of suspension of bottom sediment in the near shore region leading to the formation of fluid mud. Simulations with a cohesive sediment transport model yielded realistic estimates of sediment transport, in the presence of an onshore current, a pre-requisite for transporting the fluid mud toward the coast. The prevailing onshore upwelling current during the southwest monsoon provides the favorable pre-requisite conditions for transporting the fluid mud through depression channel network towards the coast. Once sufficient quantity and thickness of fluid mud is accumulated in the near shore region, it acts as a wave damper for subsequent high monsoon waves, as indicated by the time-series wave data, leading to the formation of tranquil mud bank region. Depression channel networks extending from the shelf to the coast off Alappuzha, Kochi, Ponnani, Beypore, and Ullal were found in the bathymetric charts, thus explaining why mud banks occur only at few locations in spite of the prevalence of similar monsoon conditions. 相似文献
74.
Pradeep Srivastava Indra Bir Singh Shikha Sharma Uma Kant Shukla Ashok Kumar Singhvi 《Geomorphology》2003,54(3-4):279-292
Abandoned channel belts, ponds and point bar deposits of palaeochannels in the interfluve regions of the central Ganga Plain suggest changes in the morphohydrologic conditions during the Latest Pleistocene–Holocene. Stratigraphy of these ponds comprises channel sand at the base overlain by shell-bearing clayey silt. The contact of the two facies marks the phase when channels converted into standing water bodies. Point bar deposits of some palaeochannels are overlain by oxidised aeolian sand, indicating that the channel abandonment possibly occurred due to the desiccation and aridity in the region.Optically stimulated luminescence (OSL) chronometry of the pond sediments suggests that the deposition of the basal channel sand started before 13 ka and continued up to 8 ka. The ponds formed around 8–6 ka when the channel activity ceased. Evidence from the point bar deposits also indicates that the fluvial activity in the region ended sometime during 7–5 ka. This was followed by aeolian aggradation. The present study thus suggests that the hydrologic conditions in the Gangetic plains, i.e. initiation of channels and their abandonment, formation of microgeomorphologic features such as ponds and their eventual siltation, were controlled largely by climatic changes (i.e. monsoon changes) supported by tectonic activity. For the past 2 ka, increasing human and related agricultural activity has substantially accentuated the natural siltation rate of ponds. 相似文献
75.
DNA from five tumors, three other-injured livers and two normal liver tissue samples from the European flounder were analyzed for mutations in exons 5-8 of the tumor suppressor gene p53 and at codons 12, 13 and 61 of Ha- and Ki-ras proto-oncogenes. No tumor-specific mutations were identified by direct sequencing and single-strand conformation polymorphism of these genes. A number of silent polymorphisms were noted in p53. In addition to a need for more extensive analyses of flounder liver tumor samples for ras or p53 mutations, other cancer-related genes should be investigated. 相似文献
76.
77.
Summary The change of rainfall totals with height has been the subject of much investigation in many parts of the world. The rates of increase or decrease vary with the climatic regime experienced. This study of Sri Lankan rainfall shows that the relationship between height and mean annual rainfall is complex. Examples of increases and decreases of rainfall with height are found. The climatic regime of the area is important in controlling the level of maximum rainfall.With 7 Figures 相似文献
78.
Impact of Sea-level Rise and Storm Surges on a Coastal Community 总被引:7,自引:7,他引:7
A technique to evaluate the risk of storm tides (the combination of a storm surge and tide) under present and enhanced greenhouse conditions has been applied to Cairns on the north-eastern Australian coast. The technique combines a statistical model for cyclone occurrence with a state-of-the-art storm surge inundation model and involves the random generation of a large number of storm tide simulations. The set of simulations constitutes a synthetic record of extreme sea-level events that can be analysed to produce storm tide return periods. The use of a dynamic storm surge model with overland flooding capability means that the spatial extent of flooding is also implicitly modelled. The technique has the advantage that it can readily be modified to include projected changes to cyclone behaviour due to the enhanced greenhouse effect. Sea-level heights in the current climate for return periods of 50, 100, 500 and 1000 years have been determined to be 2.0 m, 2.3 m, 3.0 m and 3.4 m respectively. In an enhanced greenhouse climate (around 2050), projected increases in cyclone intensity and mean sea-level see these heights increase to 2.4 m, 2.8 m, 3.8 m and 4.2 m respectively. The average area inundated by events with a return period greater than 100 years is found to more than double under enhanced greenhouse conditions. 相似文献
79.
Ostapchuk A. A. Kocharyan G. G. Morozova K. G. Pavlov D. V. Gridin G. A. 《Izvestiya Physics of the Solid Earth》2021,57(5):659-670
Izvestiya, Physics of the Solid Earth - Abstract—Granular media determine the dynamics of many natural systems including faults in the Earth’s crust. The paper addresses the laboratory... 相似文献
80.
Soumen Mondal Sandip K. Chakrabarti 《Monthly notices of the Royal Astronomical Society》2006,371(3):1418-1426
Standing, propagating or oscillating shock waves are common in accretion and winds around compact objects. We study the topology of all possible solutions using the pseudo-Kerr geometry. We present the parameter space spanned by the specific energy and angular momentum and compare it with that obtained from the full general relativity to show that the potential can work satisfactorily in fluid dynamics also, provided the polytropic index is suitably modified. We then divide the parameter space depending on the nature of the solution topology. We specifically study the nature of the standing Rankine–Hugoniot shocks. We also show that as the Kerr parameter is increased, the shock location generally moves closer to the black hole. In future, these solutions can be used as guidelines to test numerical simulations around compact objects. 相似文献