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81.
The empirical bay shape model proposed by Hsu and Evans in 1989 for predicting the static planform of a pocket beach is expanded to enable the calculation of three-dimensional beach changes on a pocket beach with a seawall. The original formulation was developed on the basis of a second-order regression analysis. Unlike the one-line model of shoreline changes, the model of Hsu and Evans does not require repeated calculations of the wave field and shoreline position, because it was derived on the assumption of null sediment movement within a pocket beach in static equilibrium, hence without the need of applying the continuity condition of total sand volume in the calculation. The expanded model proposed by the present authors satisfies the total sand budget on a pocket beach, by taking into account the concept of depth change due to longshore sand transport. Model tests were carried out and the new model was further applied to the beach changes at Kemigawa on the northeast of Tokyo Bay in Chiba Prefecture, as well as at Oarai in Ibaraki Prefecture, Japan. On both locations, seawall has been installed as countermeasures against beach erosion, where wave sheltering effect of the main breakwater and beach changes in front of the seawall has also been observed. With this expansion, the present model can be applied to predict the three-dimensional beach changes on a coast with seawall on a pocket beach. 相似文献
82.
Characterization of Fe(III) (hydr)oxides in soils near the Ichinokawa mine was conducted using X-ray absorption fine structure (XAFS) and Mössbauer spectroscopies, and the structural changes were correlated with the release of As into pore-water. The Eh values decreased monotonically with depth. Iron is mainly present as poorly-ordered Fe(III) (hydr)oxides, such as ferrihydrite, over a wide redox range (from Eh = 360 to −140 mV). Structural details of the short-range order of these Fe(III) (hydr)oxides were examined using Mössbauer spectroscopy by comparing the soil phases with synthesized ferrihydrite samples having varying crystallinities. The crystallinity of the soil Fe (hydr)oxides decreased slightly with depth and Eh. Thus, within the redox range of this soil profile, ferrihydrite dominated, even under very reducing conditions, but the crystalline domain size, and, potentially, particle size, changed with the variation in Eh. In the soil–water system examined here, where As concentration and the As(III)/As(V) ratio in soil water increased with depth, ferrihydrite persisted and maintained or even enhanced its capacity for As retention with increased reducing conditions. Therefore, it is concluded that As release from these soils largely depends on the transformation of As(V) to As(III) rather than reductive dissolution of Fe(III) (hydr)oxide. 相似文献
83.
Shin'ichi Iida Kathryn I. Wheeler Kazuki Nanko Yoshinori Shinohara Xinchao Sun Naoki Sakai Delphis F. Levia 《水文研究》2021,35(8):e14294
An increasing number of studies have examined the effects of various biotic and abiotic factors on stemflow production. Of those that have ascribed the importance of canopy structure to stemflow production, there has been a bias towards field studies. Coupling Bayesian inference with the NIED (National Research Institute for Earth Science and Disaster Resilience, Tsukuba, Japan) large-scale rainfall simulator, this study leveraged a unique opportunity to control rainfall amounts and intensities to pinpoint the canopy structural metrics that differentially influence stemflow funnelling ratios for three common tree species between leafed and leafless canopy states. For the first time, we examined whether canopy structure metrics exert a static control on stemflow funnelling ratios or whether different elements of canopy structure are more or less important under leafed or leafless states, thereby allowing us to determine if tacit assumptions about the static influence of canopy structure on stemflow production (and funnelling) are valid (or not). Rainfall simulations were conducted at 15, 20, 30, 40, 50, and 100 mm h−1 under both leafed and leafless tree conditions (12 simulations in total) to detect any differential effects on the presence or absence of foliage on stemflow funnelling ratios. For leafed conditions, the highest percentages of best-fitting models (ΔDIC ≤2) indicated that stemflow funnelling ratios were mainly controlled by total dry aboveground biomass (Ball), diameter at breast height (DBH), total dry foliar biomass (Bf), tree height (H), and woody to foliar dry biomass ratio (BR). Whilst for the leafless state, the highest percentages of best-fitting models (ΔDIC ≤2) indicated that total dry branch biomass (Bbr) was relatively dominant as was the interaction effects between crown projection area and species (CPA:species). These results compel us to reject any assumption of a static effect of different elements of canopy structure on stemflow funnelling. 相似文献
84.
Abstract The linear stability of a non-divergent barotropic parallel shear flow in a zonal and a non-zonal channel on the β plane was examined numerically. When the channel is non-zonal, the governing equation is slightly modified from the Orr-Sommerfeld equation. Numerical solutions were obtained by solving the discretized linear perturbation equation as an eigenvalue problem of a matrix. When the channel is zonal and lateral viscosity is neglected the problem is reduced to the ordinary barotropic instability problem described by Kuo's (1949) equation. The discrepancy between the stability properties of westward and eastward flows, which have been indicated by earlier studies, was reconfirmed. It has also been suggested that the unstable modes are closely related to the continuous modes discretized by a finite differential approximation. When the channel is non-zonal, the properties of unstable modes were quite different from those of the zonal problem in that: (1) The phase speed of the unstable modes can exceed the maximum value of the basic flow speed; (2) The unstable modes are not accompanied by their conjugate mode; and (3) The basic flow without an inflection point can be unstable. The dispersion relation and the spatial structure of the unstable modes suggested that, irrespective of the orientation of the channel, they have close relation to the neutral modes (Rossby channel modes) which are the solutions in the absence of a basic shear flow. The features mentioned above are not dependent on whether or not the flow velocity at the boundary is zero. 相似文献
85.
The objective of the research was to undertake a quantitative comparison of spectral-reflectance measurements made slightly above the surface of water bodies with the measurements made slightly below the surface. The study is focused on three rivers; two in Georgia, USA and one in Japan. As expected, the differences in reflectance are not constant and vary with the wavelength. The contribution of surface-reflection effects to the surface reflectance measured slightly above the water is both pronounced and highly variable, but although they do alter the magnitude of the upwelling signal, they do not change the general shape of the spectral profiles. The correction of surface-reflection effects by assuming a proportionality factor (ρ) is not considered to be efficient for inland fresh water bodies. For in situ spectroscopy, the recommended approach is to measure upwelling radiance slightly below the water's surface as a means of minimizing extraneous noise. Researchers should be aware of the potential for diminishing the validity of findings because of measurement errors. 相似文献
86.
Masanao Shinohara Toshihiko Kanazawa Tomoaki Yamada Yuya Machida Takashi Shinbo Shin’ichi Sakai 《Marine Geophysical Researches》2014,35(3):231-242
The Japanese islands are positioned near the subduction zones, and large earthquakes have repeatedly occurred in marine areas around Japan. However, the number of permanent earthquake observatories in the oceans is quite limited. It is important for understanding generation of large earthquakes to observe seismic activities on the seafloor just above these seismogenic zones. An ocean bottom cabled seismometer (OBCS) is the best solution because data can be collected in real-time. We have developed a new compact OBCS system. A developed system is controlled by a microprocessor, and signals from accelerometers are 24-bit digitized. Clock is delivered from the global positioning system receiver on a landing station using a simple dedicated line. Data collected at each cabled seismometer (CS) are transmitted using standard Internet Protocol to landing stations. The network configuration of the system adopts two dual methods. We installed the first practical OBCS system in the Japan Sea, where large earthquakes occurred in past. The first OBCS system has a total length of 25 km and 4 stations with 5 km interval. Installation was carried out in August 2010. The CSs and single armored optical submarine cable were buried 1 m below the seafloor to avoid a conflict with fishing activity. The data are stored on a landing station and sent to Earthquake Research Institute, University of Tokyo by using the Internet. After the installation, data are being collected continuously. According to burial of the CSs, seismic ambient noises are smaller than those observed on seafloor. 相似文献
87.
Seiichiro Ioka Toshiaki Sakai Toshifumi Igarashi Yoji Ishijima 《Environmental Earth Sciences》2011,64(1):143-149
The in situ redox potential (Eh) in anoxic groundwater with high methane and iron contents (approximately 12.3 and 28.4 mg/L,
respectively) was potentiometrically measured to identify the processes that control Eh. The measured Eh ranged from −213
to −187 mV; it had an inverse correlation with the concentration of methane and no correlation with that of iron. The saturation
indices indicate that goethite and amorphous FeS were nearly at solubility equilibrium. A comparison of the measured Eh with
those calculated for the particular redox pairs indicates that either Fe2+/FeOOH or CH4/CO2, but not sulfur redox pairs, controlled the measured Eh. The inverse relationship between measured Eh and methane concentration
suggests possible control of the redox conditions by the CH4/CO2 redox pair. Furthermore, the equilibrium solubility state of goethite, which has higher crystallinity and lower solubility
than Fe(OH)3 indicates that the iron reaction was electrochemically irreversible. This further supports the contribution of the CH4/CO2 pair to controlling the measured Eh of groundwater. 相似文献
88.
The limb flare on August 2, 1993 08:30 UT, consisting of two crossed loops, shows evidence of partial X-type reconnection. The observations suggest that partial reconnection was an ongoing process during about 10 min until flare ignition.Visiting Fellow of the Japan Society for the Promotion of Science, on leave from SRON Laboratory for Space Research, Sorbonnelaan 2, Utrecht, The Netherlands. 相似文献
89.
We investigate how fast magnetosonic waves can be produced from a pinching current sheet, by using 3-D MHD code. We show that
after magnetic pinch of the current sheet due to pressure imbalance, the current sheet begins to expand by an excess of plasma
pressure at the center of the current sheet. During the expansion phase, strong fast magnetosonic waves can be created at
the steep region of the density gradient and propagate away from the current sheet. It is shown that the fast magnetosonic
waves become unstable against modulational instability, as found by Sakai (1983). After the emission of the fast magnetosonic
waves, the current sheet will relax to a new equilibrium state, where the current sheet can be heated by adiabatic compression.
The emission processes of the fast magnetosonic waves from the current sheet, as well as the modulational instability of these
waves that can lead to effective plasma heating through the Landau damping of the slow waves, are important for an understanding
of coronal heating and coronal transient brightening. 相似文献
90.
Jun-Ichi Sakai 《Solar physics》1996,169(2):367-376
It is shown by using a 3-D resistive MHD simulation code, taking into account the recombination effect, that magnetic reconnection during collision of two current loops can be enhanced by recombination. It is also shown that the temperature in the thin current sheet formed between two loops increases from few to about thirty times larger than a case of no recombination, depending on both the plasma beta and the strength of recombination. The simulation results obtained here may be applicable for a mechanism of chromospheric heating and as an explanation of X-ray bright points as well as solar flares observed in the chromosphere.Dedicated to Cornelis de Jager 相似文献