全文获取类型
收费全文 | 45169篇 |
免费 | 538篇 |
国内免费 | 312篇 |
专业分类
测绘学 | 917篇 |
大气科学 | 2258篇 |
地球物理 | 8920篇 |
地质学 | 17528篇 |
海洋学 | 4261篇 |
天文学 | 9960篇 |
综合类 | 117篇 |
自然地理 | 2058篇 |
出版年
2022年 | 528篇 |
2021年 | 795篇 |
2020年 | 866篇 |
2019年 | 938篇 |
2018年 | 1857篇 |
2017年 | 1704篇 |
2016年 | 1859篇 |
2015年 | 806篇 |
2014年 | 1604篇 |
2013年 | 2494篇 |
2012年 | 1854篇 |
2011年 | 2194篇 |
2010年 | 2058篇 |
2009年 | 2320篇 |
2008年 | 2077篇 |
2007年 | 2249篇 |
2006年 | 2044篇 |
2005年 | 1127篇 |
2004年 | 1098篇 |
2003年 | 1059篇 |
2002年 | 1003篇 |
2001年 | 933篇 |
2000年 | 792篇 |
1999年 | 553篇 |
1998年 | 576篇 |
1997年 | 573篇 |
1996年 | 447篇 |
1995年 | 470篇 |
1994年 | 461篇 |
1993年 | 393篇 |
1992年 | 395篇 |
1991年 | 395篇 |
1990年 | 435篇 |
1989年 | 355篇 |
1988年 | 344篇 |
1987年 | 378篇 |
1986年 | 291篇 |
1985年 | 460篇 |
1984年 | 479篇 |
1983年 | 435篇 |
1982年 | 394篇 |
1981年 | 377篇 |
1980年 | 368篇 |
1979年 | 326篇 |
1978年 | 357篇 |
1977年 | 303篇 |
1976年 | 270篇 |
1975年 | 273篇 |
1974年 | 237篇 |
1973年 | 288篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
81.
Considerable water leakages from reservoirs make it difficult to attain the planned storage capacity. In some cases water leakages give rise to suffusion followed by catastrophes. Until recently methods for locating water leakages were extremely imperfect. Geophysical methods offer good prospects in this direction. For solving these problems, it is effective to use streaming potential measurements, water flow rate observations and thermometry. Laboratory experiments were carried out in connection with the fact that water leakages from reservoirs are characterized by negative anomalies of natural currents; the more filtration discharge, the higher these anomalies are. As a result, the relationship governing the intensity of streaming potential and sand granulometric composition, electrolyte concentrations and other factors were revealed. To determine the velocity of water flowing to leakage sites, a special device, based on the relationship between the temperature of a heated body and its resistance, is applied. This device simultaneously makes it possible to measure the water medium temperature. Observations at reservoir sites were effected by moving along the reservoir non-polarizable potential electrodes and water velocity devices. Recordings were carried out automatically by the recording device of the logging apparatus. Under the conditions of ice cover on water surfaces, measurements were made through separate points by digging holes in the ice cover. Practical field observations were carried out at reservoir sites located in regions where fissured massive rocks as well as loose sediments predominate. In the first case field experiments were carried out in alpine reservoirs, in Armenia. The major water leakages were found to be concentrated on the right bank of the reservoir. In this connection it was not only possible to locate water leakage sites, but also to evaluate their relative intensity. These data were used for planning antifiltration measures. In the second case water leakages from a reservoir located in Uzbekistan in the submontane part of the Pamirs were studied. Streaming potential anomalies and high benthonic flow rates made it possible to discover high filtrations in the base and walls of the dam. Further perfection of these methods should not only permit the determination of water leakage sites and their relative intensity, but also filtration discharges in absolute units. 相似文献
82.
83.
Yu. V. Riznichenko 《Studia Geophysica et Geodaetica》1966,10(3):243-253
Резюме Описаны этапы развития сейсмического моделирования, взаимоотношения между сейсмическим моделированием, теоретическими разработками
и полевыми наблюдениями и формулированы перспективные задачи сейсмического моделирования.
Address: B. Gruzinskaja 10, Moskva G-242, USSR. 相似文献
Address: B. Gruzinskaja 10, Moskva G-242, USSR. 相似文献
84.
85.
Weakly non-linear free oscillations in a basin of variable depth filled with non-viscous fluid are investigated in terms of the long waves theory using the perturbation technique. Solutions to the initial two approximations for the horizontal velocity component and free surface departure are numerically derived. An attempt is made to determine the area of applicability of the linear theory by applying a parabolic bottom profile to the basin.Translated by V. Puchkin. 相似文献
86.
Linearized water wave theory is used to show that a submerged long circular cylinder suitably constrained by springs and dampers to make small harmonic oscillations, can be extremely efficient in absorbing the energy in an incident regular wave whose crests are parallel to the axis of the cylinder. Experimental results are described which confirm the theory for small amplitude waves and which suggest that the device can still be fairly efficient in waves of moderate amplitude. 相似文献
87.
We present a numerical model of the dynamics of Lake Donuzlav, which enables one to perform simultaneous numerical analyses
of the currents, sea level, waves, and sediment transport. The model is based on the hydrodynamic block and the spectral wave
model. For typical storm situations, we study the specific features of the integral circulation of waters and the three-dimensional
structure of currents, investigate the wind-induced wave fields, and evaluate the flows of sediments and deformations of the
bottom. The presence of intense eddy structures is revealed in the field of currents caused by the bottom topography. A significant
intensification of waves in the south part of the lake is established in the case of penetration of storm waves through the
strait. It is shown that the account of waves leads to qualitative changes in the structure of circulation in the lake and
to the formation of well-pronounced areas of wave-induced elevations and lowerings of the sea level.
__________
Translated from Morskoi Gidrofizicheskii Zhurnal, No. 2, pp. 43–65, March–April, 2006. 相似文献
88.
Lysosomal sequestration of polynuclear aromatic hydrocarbons (PNAHs), a major class of environmental contaminant, is a well-established phenomenon;1 considerably less is known about their pathological effects on lysosomes. Marine molluscs contain a number of lysosome-rich tissues and PNAHs are known to induce deleterious alterations in lysosomal structure and latency of lysosomal enzymes.2 The latter are presumed to involve destabilisation of the lysosomal membrane, resulting in increased permeability and reduced enzyme latency. If lysosomal injury involves derangement of membrane-lipid structure due to the interaction of PNAHs then it would be expected that membrane damage would be closely linked to the structural characteristics of the intruding molecule. Our results show that the effects of the isomeric PNAHs phenanthrene and anthracene on digestive cell lysosomal stability were markedly different in the marine mussel (Mytilus edulis) over the same range of tissue concentrations. Lysosomal membrane stability was determined using a cytochemical test for enzyme latency.3 相似文献
89.
The influence of inhomogeneities of surface currents on the intensity of breaking wind waves is considered and a model for the relation between whitecap contrasts and the tensor of current gradients is developed. The imagery of typical patterns of ocean currents is discussed. The results of field observations supporting this model are given.Translated by Mikhail M. Trufanov. 相似文献
90.
An application of a Markov-chain model of shore erosion for describing the dynamics of sediment flux
Acquisition of coastline retreat rate time sequences (RRTS) is an important component of Arctic coastal monitoring. These data can be used not only to estimate sediment input into the sea during a fixed time period, but also to dynamically simulate sediment flux intensity. The RRTS were investigated at the Marre-Sale (Kara Sea) and Malii Chukochii Cape (East Siberian Sea) key sites. Statistical analysis demonstrated that the RRTS possess Markov characteristic. This allowed coastline dynamics to be described using a Markov-chain model. A model is discussed that combines Markov characteristic and information about the composition and structure of the permafrost sediments to describe sediment flux dynamics. 相似文献