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91.
Sekiguchi T. Watanabe J. Fukushima H. Yamamoto T. Yamamoto N. 《Earth, Moon, and Planets》1997,78(1-3):143-148
In order to monitor the various phenomena of comets, we continuously made the near-nucleus imaging observations of comets
at National Astronomical Observatory, Mitaka. Here we report on the results of the observations of two spectacular comets.
One is the analysis of photometry of C2 emission images in the coma of comet Hyakutake (C/1996 B2). By comparing the production rates of C2 radicals with C2H2 molecules, we conclude that the most C2 radicals were originated from C2H2, while some of them might be produced from other parents. The second item is the analysis of the morphology of C2 emission images in the coma of comet Hale-Bopp(C/1995 O1). By applying a ring masking technique, we detected asymmetrical
distribution of the C2 molecules. The results of these two comets might suggest that a portion of C2 radicals were formed by the disintegration of the small organic dust grains, like the so-called CHON particles.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
92.
Blanco AC Watanabe A Nadaoka K Motooka S Herrera EC Yamamoto T 《Marine pollution bulletin》2011,62(4):770-785
Radon (222Rn) measurements were conducted in Shiraho Reef (Okinawa, Japan) to investigate nearshore submarine groundwater discharge (SGDnearshore) dynamics. Estimated average groundwater flux was 2-3 cm/h (maximum 7-8 cm/h). End-member radon concentration and gas transfer coefficient were identified as major factors influencing flux estimation accuracy. For the 7-km long reef, SGDnearshore was 0.39-0.58 m3/s, less than 30% of Todoroki River’s baseflow discharge. SGDnearshore was spatially and temporally variable, reflecting the strong influence of subsurface geology, tidal pumping, groundwater recharge, and hydraulic gradient. SGDnearshore elevated nearshore nitrate concentrations (0.8-2.2 mg/l) to half of Todoroki River’s baseflow -N (2-4 mg/L). This increased nearshore Chl-a from 0.5-2 μg/l compared to the typically low Chl-a (<0.1-0.4 μg/l) in the moat. Diatoms and cyanobacteria concentrations exhibited an increasing trend. However, the percentage contributions of diatoms and cyanobacteria significantly decreased and increased, respectively. SGD may significantly induce the proliferation of cyanobacteria in nearshore reef areas. 相似文献
93.
Tsunamis are high-impact disasters that can cause death and destruction locally within a few minutes of their occurrence and
across oceans hours, even up to a day, afterward. Efforts to establish tsunami warning systems to protect life and property
began in the Pacific after the 1946 Aleutian Islands tsunami caused casualties in Hawaii. Seismic and sea level data were
used by a central control center to evaluate tsunamigenic potential and then issue alerts and warnings. The ensuing events
of 1952, 1957, and 1960 tested the new system, which continued to expand and evolve from a United States system to an international
system in 1965. The Tsunami Warning System in the Pacific (ITSU) steadily improved through the decades as more stations became
available in real and near-real time through better communications technology and greater bandwidth. New analysis techniques,
coupled with more data of higher quality, resulted in better detection, greater solution accuracy, and more reliable warnings,
but limitations still exist in constraining the source and in accurately predicting propagation of the wave from source to
shore. Tsunami event data collected over the last two decades through international tsunami science surveys have led to more
realistic models for source generation and inundation, and within the warning centers, real-time tsunami wave forecasting
will become a reality in the near future. The tsunami warning system is an international cooperative effort amongst countries
supported by global and national monitoring networks and dedicated tsunami warning centers; the research community has contributed
to the system by advancing and improving its analysis tools. Lessons learned from the earliest tsunamis provided the backbone
for the present system, but despite 45 years of experience, the 2004 Indian Ocean tsunami reminded us that tsunamis strike
and kill everywhere, not just in the Pacific. Today, a global intergovernmental tsunami warning system is coordinated under
the United Nations. This paper reviews historical tsunamis, their warning activities, and their sea level records to highlight
lessons learned with the focus on how these insights have helped to drive further development of tsunami warning systems and
their tsunami warning centers. While the international systems do well for teletsunamis, faster detection, more accurate evaluations,
and widespread timely alerts are still the goals, and challenges still remain to achieving early warning against the more
frequent and destructive local tsunamis. 相似文献
94.
95.
The pattern of the ionospheric electric field around the westward travelling surge (WTS) is theoretically studied. This is obtained by solving the current continuity equation at the ionospheric altitude for temporal and spatial development of the field-aligned current density modelled as the WTS phenomenon. The results show that the divergence of the ionospheric electric field is significantly changed depending on the dawn-to-dusk convection electric field E0 because of non-uniformity in the ionospheric conductivity: the ionospheric electric field diverges in the upward current region (around the head of the WTS) when a westward electric field E0 of 10 mV m−1 is uniformly applied. On the other hand, the ionospheric electric field converges without E0. From the observational inference that the ionospheric electric field converges around the head of the WTS, it is suggested that the WTS phenomenon may not be accounted for by the discharging process in the presence of the enhanced dawn-to-dusk convection electric field and non-uniform conductivity as was studied by previous authors. 相似文献
96.
Satoshi Yamamoto 《Journal of Oceanography》1979,35(2):91-99
Anisotropic detrital mineral grains were segregated microscopically from the suspended matter in surface waters of the Yellow Sea and East China Sea. Microscopic grain-size measurements of the anisotropic minerals were carried out for more than 80 slide specimens which are distributed homogeneously in the Yellow Sea and East China Sea. The distribution maps of mean grain size and sorting coefficients indicate that the mean size becomes coarser as one goes offshore, and the sorting coefficients are larger in the southern portion and smaller in the northern portion of this region. The clay-sized minerals in the suspended sediments carried out by the deltaic rivers of the continent were deposited in the nearshore area while coarser silt-sized minerals were suspended in offshore waters. The larger sorting coefficients (standard deviations) in the southern portion may imply that the silt-sized grains of offshore waters contain coarser sand-sized grains. The sand-sized grains may be supplied from offshore Taiwan and the Bashi Channel and transported by the main flow of the Kuroshio current. 相似文献
97.
Tetsuo Yamamoto 《Earth, Moon, and Planets》1981,24(2):175-188
Density distribution in cometary comae resulting from photodissociation, ionization and ion-molecule reaction of H2O is investigated in an analytic manner. It is assumed that particles expand isotropically around the nucleus, and that each species has its own constant radial velocity. Formulae for the density distribution of photochemical products are presented throught the coma, and approximate formulae are given for the distribution of ion-molecule reaction products in the inner coma. Characterictics of the density profile are discussed on the basis of these analytic formulae. 相似文献
98.
Tetsuo Yamamoto 《Earth, Moon, and Planets》1981,24(4):453-463
The formation of cometary CN, C2 and C3 radicals is investigated in a photochemical reaction scheme. From an analysis of the observed brightness profiles of these radicals, it is shown that CN is formed as a primary product in the photolysis of its parent molecules, whereas C2 and C3 are formed via two-step photodissociation of their parents. We suggest that major parent of C2 is different species from those of CN and C3 on the basis of the difference of the variation with heliocentric distance of the sublimation rate of the parents of these radicals. Parent molecules and reaction schemes for the formation of these radicals are discussed. 相似文献
99.
Takashi Yamamoto 《Planetary and Space Science》1976,24(11):1073-1080
Models of acceleration of auroral electrons by electrostatic shock waves are considered based on the model electron beam, calculated by Evans (1974), to account for the observed precipitating electron fluxes. Electron populations in our models include a primary accelerated beam, originating from the plasma sheet, the secondary electrons and the energy-degraded and backscattered primary electrons produced by precipitating electrons of that beam. We find a feasible electrostatic shock model with appropriate ion populations from considerations on the conditions for the existence of shock solutions. 相似文献
100.