全文获取类型
收费全文 | 92049篇 |
免费 | 1423篇 |
国内免费 | 828篇 |
专业分类
测绘学 | 2271篇 |
大气科学 | 6619篇 |
地球物理 | 18351篇 |
地质学 | 32829篇 |
海洋学 | 7950篇 |
天文学 | 20536篇 |
综合类 | 255篇 |
自然地理 | 5489篇 |
出版年
2022年 | 483篇 |
2021年 | 875篇 |
2020年 | 993篇 |
2019年 | 1033篇 |
2018年 | 2360篇 |
2017年 | 2226篇 |
2016年 | 2786篇 |
2015年 | 1624篇 |
2014年 | 2709篇 |
2013年 | 4856篇 |
2012年 | 2871篇 |
2011年 | 3903篇 |
2010年 | 3325篇 |
2009年 | 4346篇 |
2008年 | 4034篇 |
2007年 | 3799篇 |
2006年 | 3617篇 |
2005年 | 2870篇 |
2004年 | 2792篇 |
2003年 | 2607篇 |
2002年 | 2458篇 |
2001年 | 2307篇 |
2000年 | 2204篇 |
1999年 | 1741篇 |
1998年 | 1828篇 |
1997年 | 1791篇 |
1996年 | 1437篇 |
1995年 | 1481篇 |
1994年 | 1302篇 |
1993年 | 1158篇 |
1992年 | 1163篇 |
1991年 | 1035篇 |
1990年 | 1147篇 |
1989年 | 986篇 |
1988年 | 927篇 |
1987年 | 1102篇 |
1986年 | 921篇 |
1985年 | 1178篇 |
1984年 | 1243篇 |
1983年 | 1214篇 |
1982年 | 1164篇 |
1981年 | 1004篇 |
1980年 | 988篇 |
1979年 | 870篇 |
1978年 | 853篇 |
1977年 | 788篇 |
1976年 | 754篇 |
1975年 | 720篇 |
1974年 | 731篇 |
1973年 | 687篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
821.
O. M. Makarova N. I. Korobova A. G. Kalmykov G. A. Kalmykov 《Moscow University Geology Bulletin》2018,73(2):213-217
The section structure was characterized according to the lithological and petrophysical studies of the core from the Bazhenov Formation that has been uncovered in the central part of the Tundrin Depression. The productive oil intervals where the reservoirs of the pore and fissure-pore types occur were identified. 相似文献
822.
The ultramafic rocks of the Kan block, East Sayan, are confined mainly to the Idar greenstone belt. In terms of formational
affiliation, they are subdivided into two groups: magmatic (Kingash Complex) and residual (Idar Complex) ones. The magmatic
ultramafic rocks compose hypabyssal and subvolcanic bodies, which are represented by rocks of dunite-wehrlite-picrite association
with cumulate textures. Uninterrupted chemical variations of the magmatic ultramafic rocks indicate subsequent magmatic differentiation
of parental picritic melt in the intermediate deep-seated chambers and emplacement of its derivatives in the crystallization
site. Differentiation leads to proportional increase of all rare-earth and other incompatible elements. The residual ultramafics
occur as boudined dunite-harzburgite bodies showing metamorphic granoblastic textures. They have more homogenous chemical
composition close to those of ophiolite complexes, which represent strongly depleted mantle rocks brought to the upper lithospheric
levels via deep-seated thrusts. Residual ultramafics differ from magmatic rocks in notably lower contents of some trace and
rare earth elements. 相似文献
823.
K. B. Broberg 《Pure and Applied Geophysics》2006,163(9):1867-1879
Although mode I and mode II crack propagation show many similarities, in particular when analysed by linear elastic fracture
mechanics, they differ significantly in the micro-structural behaviour. These differences, which are clearly noticeable in
the fracture surface morphology, lead to fundamental differences in the macroscopic behaviour. Thus, mode II crack expansion
under remote loading, appears to obey micro-structural scaling laws, implying that the dimensions of the process region stay
essentially constant during crack expansion, rather than increasing with crack length. Therefore, expanding mode II cracks
can almost reach the Rayleigh velocity, and actually also intersonic velocities. An expanding mode I crack, on the other hand,
seems to obey continuum scaling laws, implying that the dimensions of the process region increase in proportion to crack length,
leading to self-similar crack expansion at a velocity significantly below the Rayleigh speed and dependent on the remote load. 相似文献
824.
M. B. Fix J. A. Smith D. L. Tucker W. Wester J. Annis 《Astronomische Nachrichten》2015,336(6):614-618
We report the discovery of a bright blue quasar: SDSS J022218.03–062511.1. This object was discovered spectroscopically while searching for hot white dwarfs that may be used as calibration sources for large sky surveys such as the Dark Energy Survey or the Large Synoptic Survey Telescope project. We present the calibrated spectrum, spectral line shifts and report a redshift of z = 0.521±0.0015 and a rest‐frame g‐band luminosity of 8.71×1011 L⊙. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
825.
A series of hydraulic model tests has been carried out in a glass wave flume to investigate the influences of wave height, wave period, wave steepness, surf similarity parameter, roughness, layer thickness and porosity on wave run-up and overtopping of 1:2 sloped impermeable and permeable breakwaters fronted by a 1:10 gentle, smooth beach slope. The analysis of results involves the correlation between the overtopping energy transfer with the relative wall height and the relationship between wave run-up and overtopping rate. Further, measured wave run-up and overtopping rates are compared with the results given in the Shore Protection Manual (1984), Automated Coastal Engineering System (1992)and results of other investigators. 相似文献
826.
This communication is dedicated to the investigation history and naming of the undersea morphostructures of the Sea of Japan for the last 50 years. Many of them were first described and studied during long-term geological-geophysical investigations in this basin carried out by Russian scientists. The analysis of 60 names of its undersea feature names revealed that only approximately half of them are cited in the GEBCO Gazetteer some of the undersea morphostructures are known under two or more names, the origin of their names is unknown, or their names were chosen voluntarily. For maintaining the priority of Russian investigations, the nomenclature and names of the undersea features should be adjusted in accordance with the national and international principles and regulations. 相似文献
827.
The rate of wave overtopping of a barrier beach is measured and modeled. Unique rate of wave overtopping field data are obtained from the measure of the Carmel River, California, lagoon filling during a time when the lagoon is closed-off with no river inflow. Volume changes are based on measured lagoon height changes applied to a measured hypsometric curve. Wave heights and periods are obtained from directional wave spectra data in 15 m fronting the beach. Beach morphology was measured by GPS walking surveys. Three empirical overtopping models by Van der Meer and Janssen (1995), Hedges and Reis (1998) and Pullen et al. (2007) with differing parameterizations on wave height, period and beach slope and calibrated using extensive laboratory data obtained over plane, impermeable beaches are applied in a quasi-2D manner and compared with the field observations. Three overtopping events are considered when morphology data were available less than 2 weeks prior to the event. The models are tuned to fit the data using a reduction factor to account for beach permeability, berm characteristics, non-normal wave incidence and surface roughness influence. In addition, the run-up model by Stockdon et al. (2006) based on field data is examined and found to underestimate run-up as the calculated values were too small to predict any of the observed overtopping. The three overtopping models performed similarly well with values of 0.72–0.87 for the two narrow-banded wave cases, with an average reduction factor of 0.78. The European model (Pullen et. al., 2007) performed best overall and in particular for the case of the broad-banded, double peaked wave spectrum. 相似文献
828.
Purvee Joshi Sandip R. Oza Ujjwal K. Gupta Shailendra Saini D. Ram Rajak I. M. Bahuguna 《Marine Geodesy》2020,43(3):302-323
AbstractIntra and inter-annual variations in the sea ice thickness are highly sensitive indicators of climatic variations undergoing in the earth’s atmosphere and oceans. This paper describes the method of estimating sea ice thickness using radar waveforms data acquired by SARAL/Altika mission during its drifting orbit phase from July 2016 onwards yielding spatially dense data coverage. Based on statistical analysis of return echoes, classification of the surface has been carried out in three different types, viz. floe, lead and mixed. Time delay correction methods were suitably selected and implemented to make corrections in altimetric range measurements and thereby freeboard. By assuming hydrostatic equilibrium, freeboard data were converted into sea ice thickness. Results show that sea ice thickness varies from 4 to 5?m near ice shelves and 1 to 2.5?m in the marginal sea ice regions. Freeboard and sea ice thickness estimates were also validated using NASA’s Operation Ice Bridge (OIB) datasets. Freeboard measurements show very high correlation (0.97) having RMSE of 0.13. Overestimation of approximately 1–2?m observed in the sea ice thickness, which could be attributed to distance between AltiKa footprint and OIB locations. Moreover, sensitivity analysis shows that snow depth and snow density over sea ice play crucial role in the estimation of sea ice thickness. 相似文献
829.
J. Zahradník M. Antonini G. Grünthal J. Janský D. Procházková E. Schmedes A. Špičak J. Zedník 《Pure and Applied Geophysics》1990,133(1):53-71
The main shock of the West-Bohemian earthquake swarm, Czechoslovakia, (magnitudem=4.5, depthh=10 km) exhibits an irregular areal distribution of macroseismic intensities 6° to 7° MSK-64. Four lobes of the 6° isoseismal are found and the maximum observed intensity is located at a distance of 8 km from the instrumentally determined epicentre. This distribution can be explained by the energy flux of the directS wave generated by a circular source, the hypocentral location and focal mechanism of which are taken from independent instrumental studies. The theoretical intensity, which is assumed to be logarithmically proportional to the integrated squared ground-motion velocity (i.e.,I=const+log v
2
(t)dt), fits the observed intensity with an overall root-mean-square error less than 0.5°. It is important that the present intensity data can also be equally well explained by the isotropic source. The fit was attained by means of a horizontally layered model though large fault zones and an extended sedimentary basin suggest a significant lateral heterogeneity of the epicentral region. The results encourage a broader application of the simple modelling technique used. 相似文献
830.
Although the importance of sustainable soil management is recognized, there are many threats to soils including widespread soil structural degradation. This reduces infiltration through the soil surface and/or the percolation of water through the soil profile, with important consequences for crop yields, nutrient cycling and the hydrological response of catchments. This article describes a broad‐scale modelling approach to assess the potential effect that improved agricultural soil management, through reduced soil structural degradation, may have on the baseflow index (BFI) of catchments across England and Wales. A daily soil–water balance model was used to simulate the indicative BFI of 45 696 thirty‐year model runs for different combinations of soil type, soil/field condition, land cover class and climate which encapsulate the variability across England and Wales. The indicative BFI of catchments was then calculated by upscaling the results by spatial weighting. WaSim model outputs of indicative BFI were within the 95% confidence intervals of the national‐average BFI values given for the Hydrology of Soil Type (HOST ? ) classes for 26 of the 28 classes. At the catchment scale, the concordance correlation coefficient between the BFI from the WaSim model outputs and those derived from HOST was 0·83. Plausible improvements in agricultural soil/field condition produced modest simulated increases of up to 10% in the indicative BFI in most catchments across England and Wales, although for much of southern and northern England the increases were less than 5%. The results suggest that improved soil management might partially mitigate the expected adverse effects of climate change on baseflow to rivers. Healthy, well‐functioning soils produce many additional benefits such as better agricultural yields and reduced pollutant movement, so improved soil management should provide win‐win opportunities for society, agricultural systems and the environment and provide resilience to some of the expected environmental impacts of climate change. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献