全文获取类型
收费全文 | 39931篇 |
免费 | 1957篇 |
国内免费 | 3132篇 |
专业分类
测绘学 | 1645篇 |
大气科学 | 4144篇 |
地球物理 | 6989篇 |
地质学 | 19718篇 |
海洋学 | 3720篇 |
天文学 | 5447篇 |
综合类 | 1152篇 |
自然地理 | 2205篇 |
出版年
2024年 | 115篇 |
2023年 | 322篇 |
2022年 | 739篇 |
2021年 | 966篇 |
2020年 | 857篇 |
2019年 | 891篇 |
2018年 | 4172篇 |
2017年 | 3837篇 |
2016年 | 2640篇 |
2015年 | 891篇 |
2014年 | 1022篇 |
2013年 | 1038篇 |
2012年 | 2093篇 |
2011年 | 3858篇 |
2010年 | 3510篇 |
2009年 | 3545篇 |
2008年 | 2891篇 |
2007年 | 3555篇 |
2006年 | 874篇 |
2005年 | 893篇 |
2004年 | 757篇 |
2003年 | 895篇 |
2002年 | 768篇 |
2001年 | 487篇 |
2000年 | 380篇 |
1999年 | 365篇 |
1998年 | 285篇 |
1997年 | 308篇 |
1996年 | 258篇 |
1995年 | 256篇 |
1994年 | 232篇 |
1993年 | 182篇 |
1992年 | 164篇 |
1991年 | 110篇 |
1990年 | 95篇 |
1989年 | 111篇 |
1988年 | 79篇 |
1987年 | 63篇 |
1986年 | 57篇 |
1985年 | 46篇 |
1984年 | 42篇 |
1983年 | 41篇 |
1982年 | 41篇 |
1981年 | 40篇 |
1980年 | 45篇 |
1979年 | 29篇 |
1977年 | 17篇 |
1976年 | 20篇 |
1975年 | 22篇 |
1973年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
9711号北上台风演变及暴雨过程的位涡诊断分析 总被引:6,自引:2,他引:6
通过对 971 1号台风登陆北上穿过山东造成山东特大暴雨过程的湿位涡的分析 ,并从湿位涡的角度研究了台风演变及山东特大暴雨的形成机制 ,揭示了冷空气在台风演变及暴雨过程中的重要作用。结果表明 :倾斜涡度发展是暴雨产生和台风加强的重要机制之一 ,暴雨产生在 θe线陡立密集区内 ;湿位涡在这次暴雨过程中对流层低层具有 MPV1 <0 ,MPV2 >0的特征 ,此次暴雨产生在负的MPV1等值线密集区中 ;对流层上部及平流层下部高位涡的下传使得低层斜压性增大 ,引起低层的对流稳定度减小 ,促使气旋性涡度发展 ,有利于位势不稳定能量的释放 ,使得暴雨增幅 ,导致台风的加强并演变为温带气旋。 相似文献
22.
Tiago M. Alves Vasilios Lykousis Dimitris Sakellariou Stamatina Alexandri Paraskevi Nomikou 《Geo-Marine Letters》2007,27(1):41-61
Bathymetric, 9.5-kHz long-range sidescan sonar (OKEAN), seismic reflection and sediment-core data are used in the analysis
of two tectonic troughs south of Crete, Eastern Mediterranean Sea. Here, up to 1.2 s two-way travel time (TWTT) of strata
have accumulated since the Middle Miocene in association with extension in the South Aegean region. The study area comprises
>100-km- long by >25-km-wide basins filled by sediments subdivided into two seismic units: (1) an upper Unit 1 deposited in
sub-basins which follow the present-day configuration of the southern Cretan margin; (2) a basal Unit 2, more than 500 ms
(TWTT) thick, accumulated in deeper half-graben/grabens distinct from the present-day depocentres. Both units overlap a locally
stratified Unit 3 comprising the pre-Neogene core complex of Crete and Gavdos. In this work, the interpreted seismic units
are correlated with the onshore stratigraphy, demonstrating that denudation processes occurring on Crete and Gavdos in response
to major tectonic events have been responsible for high sedimentation rates along the proximal southern Cretan margin. Consequently,
topographically confined sedimentary units have been deposited south of Crete in the last 12 Ma, including turbidites and
other mass-flow deposits fed by evolving transverse and axial channel systems. Surface processes controlling facies distribution
include the direct inflow of sediment from alluvial-fan systems and incising mountain rivers onto the Cretan slope, where
significant sediment instability processes occur at present. In this setting, seismic profiles reveal eight different types
of stratigraphic contacts on basin-margin highs, and basinal areas show evidence of halokinesis and/or fluid escape. The acquired
data also show that significant changes to the margin’s configuration occurred in association with the post-Alpine tectonic
and eustatic episodes affecting the Eastern Mediterranean. 相似文献
23.
Ya. A. Virolainen Yu. M. Timofeev A. V. Polyakov H. Steele M. Newchurch 《Izvestiya Atmospheric and Oceanic Physics》2006,42(6):752-764
A statistical ensemble of microphysical parameters of the background stratospheric aerosol at altitudes of 15 to 30 km is modeled on the basis of experimental data. The aerosol attenuation coefficients (AACs) in the wavelength range 0.38–16.3 μm are calculated for all realizations of the ensemble by algorithms of the Mie theory. Analysis of correlations between the AACs and the microphysical parameters indicate that the AAC correlates most strongly with the total volume V and area S of all particles. The errors of determining the microphysical parameters from AAC measurements are analyzed via the method of linear regression. It is shown that, if the AAC is measured with an error of 5%, the errors of determining both the particle size distribution (PSD) for particles with sizes of 0.4 to 4 μm and the parameter S are an order of magnitude smaller than the prior uncertainty, whereas the error of determining V is two orders of magnitude smaller than the prior uncertainty. Schemes of AAC measurements with the SAGE III, ISAMS, CLAES, HALOE instruments and an IR interferometer in the visible and IR regions are discussed. It is shown that combining the schemes makes it possible to extend the range of particle sizes for which the PSD is retrieved with a satisfactory accuracy and to increase the accuracy of determining S and V substantially and the accuracy of determining the total number of particles N opt to a lesser extent. Examples of interpreting AAC measurements carried out simultaneously with the SAGE III and HALOE instruments within the same spatial region are presented. A systematic discrepancy between vertical profiles of S and V obtained from SAGE III and HALOE measurements is revealed. 相似文献
24.
A. G. Matul T. A. Khusid V. V. Mukhina M. P. Chekhovskaya S. A. Safarova 《Oceanology》2007,47(1):80-90
The study of diatoms and benthic foraminifers from the southeastern shelf of the Laptev Sea shows that their most diverse and abundant recent assemblages populate the peripheral underwater part of the Lena River delta representing the marginal filter of the sea. This area is characterized by an intense interaction between the fresh waters of the Siberian rivers and the basin seawater, the Atlantic one included. Local Late Holocene (~last 2300 years) environments reflect the main regional and global paleoclimatic changes, the Medieval Warm Period (~600–1100 years B.P.) and the Little Ice Age (~100–600 years B.P.) inclusive. In addition, the composition and distribution of planktonic foraminifers implies a strong influence of the Atlantic water during the Holocene optimum ~5100–6200 years B.P. 相似文献
25.
In the food clods of the mass species of macrobenthos of the Gryaznaya Inlet, nonstructured matter plays a great role. We identify this matter as derivates from plant tissues, which are the products of their external metabolism and degradation, with associated microorganisms. This way, the near-shore community considered is supported by a detrital trophic web. This feature distinguishes it from the similar community of the near-Atlantic waters that is based on a pasture web, at least as far as the bivalve mass species are concerned. The groups of the near-shore species of Gryaznaya Inlet separated by a cluster analysis are identified as consortia, combined by the biogeochemical conditions (edifice factor), which can hardly be analyzed at present. 相似文献
26.
The basic properties of the dynamic model of a turbulent jet formed by a deep-water sewage discharge into the stratified environment of coastal regions are considered. The model developed was used to estimate the parameters of a floating-up jet of deep wastewater discharge from Sand Island into the basin of Mamala Bay (Hawaii) depending on the season and discharge operation mode. The estimates of the float-up depths of the jet and the initial dilution of the jet were estimated on the basis of model calculations using experimental data on the vertical profiles of the water temperature and salinity under the actual conditions of stratification in the study region. It is shown that the further propagation of the wastewater jet depends on tidal events and internal waves generated by tides. The appearance of turbulent jets at the sea surface was recorded. The model estimates of the parameters of the wastewater discharge were compared with the results of experimental measurements. Good agreement was found, which indicates that the physical mechanisms of the propagation of turbulent jets in a stratified medium are adequately described by the model. 相似文献
27.
The analysis is performed on the basis of comparison of the hydrological characteristics of prestrait regions of the Sea of
Marmara. It is shown that, in summer, the Black-Sea waters are weakly mixed with the Mediterranean waters and the levels of
salinity in the prestrait regions differ by 0.6–0.9‰. In winter, the indicated difference increases and the level of salinity
near the entrance of Dardanelles reaches 29‰ and exceeds the level observed near the entrance of Bosporus by 5.5‰. In the
analyzed regions, we observe local temperature maxima and minima near the interface of two water masses. This is explained
by the presence of strong seasonal variations of temperature for the Black-Sea waters and their absence for the Mediterranean
waters. The physical mechanisms responsible for the seasonal variations of the intensity of transformations of the Black-Sea
waters are discussed.
__________
Translated from Morskoi Gidrofizicheskii Zhurnal, No. 2, pp. 49–55, March–April, 2007. 相似文献
28.
D. S. Drozdov F. M. Rivkin V. Rachold G. V. Ananjeva-Malkova N. V. Ivanova I. V. Chehina M. M. Koreisha Yu. V. Korostelev E. S. Melnikov 《Geo-Marine Letters》2005,25(2-3):81-88
A set of digital maps including geology, Quaternary sediments, landscapes, engineering-geological, vegetation, geocryological and the series of regional sources have been selected to characterize the Russian Arctic coast. Based on this data, new maps of engineering geocryological zoning and zoning of the coast with respect to the intensity of exogenous geological processes and risk of technogenic impacts have been generated at the scales of 1:4,000,000–1:8,000,000. These maps are a tool to assess the impact of industry on the Arctic coast of the country. 相似文献
29.
V. V. Knysh S. G. Demyshev G. K. Korotaev A. S. Sarkisyan 《Izvestiya Atmospheric and Oceanic Physics》2007,43(3):363-377
A method for combined assimilation of climatic hydrologic fields of temperature, salinity, and the climatic dynamic level of the Black Sea into a model of sea dynamics is proposed. The monthly mean fields of the dynamic sea level were obtained from the results of assimilation of satellite altimetry data into the model. The statistical characteristics of errors in the forecasts of the level, salinity, and temperature were assumed to be proportional to the statistical characteristics of the differences between monthly mean climatic fields of temperature, salinity, and sea level calculated by means of assimilating altimetry observations of the sea level and analogous climatic hydrologic fields. The climatic fields of currents are reconstructed and analyzed. The assimilation of the climatic altimetry level allows the reproduction (in current fields) of quasi-stationary synoptic anticyclonic eddies located along the periphery of the Black Sea Rim Current. 相似文献
30.
The nonlinear energy transfer through the wave spectrum is studied on the basis of the previously obtained explicit equation for matrix elements of a four-wave kinetic integral. The equation describes the evolution of a system of gravity waves at the surface of a sea of finite depth with a uniform distribution of broken ice over the sea surface. Particular attention is paid to the analytical part of the algorithm of the calculation of the kinetic integral. This part differs from the standard algorithm by a set of prominent features of the dispersion relation for wave oscillations in the ice-covered water. The kinetic integral for the system under consideration is calculated, and the results are compared with the results obtained for the ice-free water. 相似文献