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171.
Diurnal Cycle of Sound Scatterers and Measurements of Turbidity Using ADCP in Beppu Bay 总被引:2,自引:0,他引:2
Xiao-Hua Zhu Yoshio Takasugi Masayuki Nagao Eisuke Hashimoto 《Journal of Oceanography》2000,56(5):559-565
From September 20 to 22 in 1994, the vertical profiles of echo intensity and three-component velocities were measured with a bottom-mounted 300 kHz broadband acoustic Doppler current profiler (ADCP) in Beppu Bay in the Seto Inland Sea of Japan. A very strong thermocline was observed from 50 to 60 m. A pronounced diurnal cycle of backscatter strength (BS) was found above the thermocline. However, it was not found under the thermocline where there was a lack of dissolved oxygen. We suggest that the diurnal cycle of BS is caused by the vertical migration of zooplankton. The downward and upward migration occurred in early morning and late afternoon, respectively. The migration speeds estimated from BS isopleth displacements were about 1 cm s–1. Further, the contribution of turbidity (Tur) to BS was examined by separating out the effect of migrating zooplankton. There was a significant correlation between BS and turbidity under the thermocline. The maximum contributions of the Tur, migrating zooplankton and non-migrating plankton on BS were estimated at 3, 12, 25 dB, respectively. These data suggest that when using an ADCP to estimate Tur, it is very important to consider carefully the backscatter signal from zooplankton. 相似文献
172.
Jun Inoue Masayuki Kawashima Kay I. Ohshima Yasushi Fujiyoshi Ken-ichi Maruyama 《Journal of Oceanography》2000,56(5):507-515
Horizontal wind fields over Funka Bay during cold air outbreaks were simulated using a 3-D meso-scale atmospheric model. The simulated wind fields over the bay have a positive curl in the north and a negative curl in the south. These wind fields were used to simulate the current in Funka Bay using a barotropic ocean model. The simulated current pattern was composed of two vortices—one with anti-clockwise vorticity in the north and the other with clockwise vorticity in the south—and was in the opposite direction to that simulated by the uniform wind fields. This is because the wind stress curl effect on the vorticity production in Funka Bay opposes and overwhelms the bathymetry torque effect during cold air outbreaks. These results show that the non-uniformity of the wind fields caused by the land topography around a shallow lake or bay cannot be neglected in simulating its currents. 相似文献
173.
Ultrahigh‐temperature (UHT) granulite facies rocks from the Achankovil Shear Zone area and the southern domain of the Madurai Granulite Block in South India contain monazite useful for in situ microprobe U–Pb dating. The UHT rocks examined consist of garnet + cordierite (retrograde) + quartz + mesoperthite + biotite + plagioclase + Fe‐Ti oxides ± orthopyroxene ± sillimanite and accessory zircon and monazite. Sillimanite occurs only as inclusions in garnet. Microstructural observations suggest garnet, orthopyroxene, spinel and mesoperthite are products of peak metamorphism. Post‐peak formation of cordierite ± orthopyroxene ± quartz and cordierite + spinel + Fe‐Ti oxides assemblages is also observed. Geothermobarometry on orthopyroxene and garnet‐orthopyroxene bearing assemblages suggest peak UHT conditions of T = 940–1040°C and P = 8.5–9.5 kbar. This was followed by a retrograde stage of 3.5–4.5 kbar and 720 ± 60°C, estimated from garnet‐cordierite assemblages. A small population of rounded, probably detrital, monazites in these rocks yield ages from Meso‐ to Neoproterozoic indicating a heterogeneous source. The youngest associated spot ages are 660–600 Ma suggesting protolith deposition up to ca 600 Ma. In contrast, the vast majority of monazites that crystallized during the latest metamorphic event show late Neoproterozoic to Cambrian ages. Probability‐density plots of monazite age data show a ‘peak’ between 533 and 565 Ma, but this peak need not reflect a particular thermal event. Collating ages from homogenous metamorphic monazites associated with minerals stable at peak P‐T conditions suggests peak metamorphism in these rocks occurred at 580–600 Ma. Together with a re‐evaluation of available data from adjacent granulite blocks in southern India, these data suggest the main metamorphic event coinciding with the suturing of India with the Gondwana amalgam probably occurred 580–600 Ma. The 500–550 Ma ages commonly reported in previous studies might represent post‐peak thermal events. 相似文献
174.
Masa-Yuki Yamamoto Masayuki Toda Yoshihiro Higa Kouji Maeda Jun-Ichi Watanabe 《Earth, Moon, and Planets》2004,95(1-4):279-287
Observations of persistent meteor trains are limited because of the extreme rarity of the phenomenon. The altitudinal distribution
of persistent trains has previously been investigated via limited instances of simultaneous observation from multiple sites,
however, a statistical study of persistent trains has yet to be realized. The meteor train observation (METRO) campaign was
established in Japan in 1998 to obtain images of persistent trains. From 1998 to 2002, the METRO campaign, involving Japanese
amateur collaborators, captured more than 400 image sequences of persistent trains, resulting in 53 simultaneous multi-site
observations. Several Japanese observers were involved in imaging persistent trains prior to the METRO campaign, producing
6 simultaneous observations over the period 1988–1997. In this paper, simultaneous multi-site observations of high spatial
and temporal resolution are used to determine, via triangulation, the altitudinal distribution of persistent trains for 20
events. The altitudinal range of 2 Orionid trains was slightly higher than that of 18 Leonid trains. The Leonid train data
reveal no clear dependence of upper and lower altitude on the brightness of the associated fireball. The upper altitude of
the 18 observed Leonid trains were almost invariant with respect to local time (LT) of observation, however, a possible dependence
of lower altitude on LT of observation was also found, indicating a near-constant penetrating path-length in the upper atmosphere
for each train. The average upper altitude of persistent Leonid trains was 99.8 km, while the average central altitude was
93.0 km. These trends are probably determined by atmospheric conditions such as the abundance of O and O3. 相似文献
175.
Local time asymmetries of the SSC-associated hydromagnetic variations at the geosynchronous altitude
167 SSC events have been studied by using the data observed at the multiple-satellites at the geosynchronous altitude. The strong local time asymmetry of the SSC amplitude which was found by Kokubun (1983) has been confirmed. The pronounced local time asymmetry has also been found with the direction of the initial movement of Psc magnetic pulsations. Those local time effects are interpreted by the intensification of the magnetopause surface current during a SSC event, and by the distance between the geosynchronous satellite and the surface current. It has also been clarified that the SSC signal propagates with a speed of 400–700 km s?1 across the field lines in the magnetosphere as suggested by Wilken et al. (1982). 相似文献
176.
Motomu Toda Masayuki Yokozawa Akihiro Sumida Tsutomu Watanabe Toshihiko Hara 《Carbon balance and management》2007,2(1):6
Background
Changes in the timing of phenological events may cause the annual carbon budget of deciduous forests to change. Therefore, one should take such events into account when evaluating the effects of global warming on deciduous forests. In this article, we report on the results of numerical experiments done with a model that includes a phenological module simulating the timing of bud burst and other phenological events and estimating maximum leaf area index. 相似文献177.
Partitioning Eddy-Covariance Methane Fluxes from a Shallow Lake into Diffusive and Ebullitive Fluxes 总被引:1,自引:0,他引:1
Hiroki Iwata Ryuichi Hirata Yoshiyuki Takahashi Yuichi Miyabara Masayuki Itoh Kotaro Iizuka 《Boundary-Layer Meteorology》2018,169(3):413-428
Methane (\(\mathrm {CH}_{4}\)) is known to be emitted from lakes to the atmosphere via processes such as diffusion and ebullition (i.e., bubble emission). We developed a practical method for partitioning eddy-covariance \(\mathrm {CH}_{4}\) fluxes from a shallow lake into diffusive and ebullitive fluxes using a wavelet analysis based on local scalar similarity between the \(\mathrm {CH}_{4}\) concentration and other reference scalars, such as the air temperature or water vapour concentration, in the wavelet time-scale domain, with the hypothesis that similar and dissimilar fluctuation components are related to diffusive and ebullitive \(\mathrm {CH}_{4}\) fluxes, respectively. Our method is applied to approximately two weeks of data obtained at a shallow mid-latitude lake. The partitioned diffusive flux has a physically sound relationship with wind speed, supporting the validity of the method. The ratio of the diffusive flux to the total flux is typically 0.11 with flow from an area of steady bubble emission, but otherwise 0.36. Further validation is required using a larger dataset and data from other lakes. The proposed method can be easily applied to historical data because it requires only 10-Hz data of \(\mathrm {CH}_{4}\) concentration and other reference scalars, along with an empirical parameter. 相似文献
178.
Tomoki Nakamura Aiko Nakato Hatsumi Ishida Shigeru Wakita Takaaki Noguchi Michael E. Zolensky Masahiko Tanaka Makoto Kimura Akira Tshuchiyama Toshihiro Ogami Takahito Hashimoto Mitsuru Konno Masayuki Uesugi Toru Yada Kei Shirai Akio Fujimura Ryuji Okazaki Scott. A. Sandford Yukihiro Ishibashi Masanao Abe Tatsuaki Okada Munetaka Ueno Junichiro Kawaguchi 《Meteoritics & planetary science》2014,49(2):215-227
The mineralogy and mineral chemistry of Itokawa dust particles captured during the first and second touchdowns on the MUSES‐C Regio were characterized by synchrotron‐radiation X‐ray diffraction and field‐emission electron microprobe analysis. Olivine and low‐ and high‐Ca pyroxene, plagioclase, and merrillite compositions of the first‐touchdown particles are similar to those of the second‐touchdown particles. The two touchdown sites are separated by approximately 100 meters and therefore the similarity suggests that MUSES‐C Regio is covered with dust particles of uniform mineral chemistry of LL chondrites. Quantitative compositional properties of 48 dust particles, including both first‐ and second‐touchdown samples, indicate that dust particles of MUSES‐C Regio have experienced prolonged thermal metamorphism, but they are not fully equilibrated in terms of chemical composition. This suggests that MUSES‐C particles were heated in a single asteroid at different temperatures. During slow cooling from a peak temperature of approximately 800 °C, chemical compositions of plagioclase and K‐feldspar seem to have been modified: Ab and Or contents changed during cooling, but An did not. This compositional modification is reproduced by a numerical simulation that modeled the cooling process of a 50 km sized Itokawa parent asteroid. After cooling, some particles have been heavily impacted and heated, which resulted in heterogeneous distributions of Na and K within plagioclase crystals. Impact‐induced chemical modification of plagioclase was verified by a comparison to a shock vein in the Kilabo LL6 ordinary chondrite where Na‐K distributions of plagioclase have been disturbed. 相似文献