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231.
Rationalization of building micro-dams equipped with fish passages in West African savannas 总被引:1,自引:1,他引:0
Koichi Unami Macarius Yangyuoru Abul Hasan Md. Badiul Alam 《Stochastic Environmental Research and Risk Assessment (SERRA)》2012,26(1):115-126
Micro-dams in West African savannas are investigated in conjunction with aquatic fauna and human activities at a community
level. A study area is chosen in the Northern Region of Ghana. The micro-dams in the study area serve as habitats for fish,
providing food and job opportunities for inhabitants, but their construction has sacrificed rice fields and fragmented migration
routes of fish. A stochastic population dynamics model is developed to rigorously assess the effect of establishing fish passages
between the fragmented habitats containing the micro-dams on the ichthyological fauna. Values of the model parameters are
estimated from the literature and results of field surveys, in which ten fish species including cichlidae, clariidae, bagridae,
schilbeidae, cyprinidae, and alistidae are reported to be present. A sustainability criterion is proposed to judge whether
a set of model parameters realizes stationarity of the stochastic process representing the population dynamics. It is suggested
that ichthyological fauna can be sustainable provided that the fishing activity is restricted to upstream migrating and fast
growing species. More generally, building micro-dams in West African savannas will be much better justified when the dams
are equipped with appropriately designed fish passages. 相似文献
232.
Verifying optimality of rainfed agriculture using a stochastic model for drought occurrence 总被引:1,自引:1,他引:0
Erfaneh Sharifi Koichi Unami Macarius Yangyuoru Masayuki Fujihara 《Stochastic Environmental Research and Risk Assessment (SERRA)》2016,30(5):1503-1514
It may be paradoxical but subsistence rainfed agriculture is the predominant source of food in Sub-Saharan Africa where the production uncertainty is associated with the stochastic nature of rainfall. This paper attempts to comprehend the rationale of this situation by a mathematical approach. Considering the level of drought severity as the zero-reverting Ornstein–Uhlenbeck process, optimality of rainfed agriculture is investigated in the context of stochastic control theory. Occurrence of drought terminating growth of crops is modelled with the concept of first exit time. A stochastic control problem allowing for virtual cost of irrigation, water stress to crops, and benefits of farming is formulated with irrigation effort as the control variable. The Hamilton–Jacobi–Bellman equation governing the optimal control is studied to identify the set of cost functions optimizing rainfed agriculture in an inverse problem approach. Data and information were collected in the coastal savanna agro-ecological zone of Ghana, to identify model parameters, formulate the stochastic control problem, solve the inverse problem, and then verify optimality of rainfed agriculture. The results indicated that rainfed agriculture is not optimal when the crop is more tolerant to water stress. 相似文献
233.
Hiroyuki R. Takahashi Eiji Asano Ryoji Matsumoto 《Monthly notices of the Royal Astronomical Society》2009,394(1):547-568
We obtained self-similar solutions of relativistically expanding magnetic loops taking into account the azimuthal magnetic fields. We neglect stellar rotation and assume axisymmetry and a purely radial flow. As the magnetic loops expand, the initial dipole magnetic field is stretched into the radial direction. When the expansion speed approaches the light speed, the displacement current reduces the toroidal current and modifies the distribution of the plasma lifted up from the central star. Since these self-similar solutions describe the free expansion of the magnetic loops, i.e. d v /d t = 0 , the equations of motion are similar to those of the static relativistic magnetohydrodynamics. This allows us to estimate the total energy stored in the magnetic loops by applying the virial theorem. This energy is comparable to that of the giant flares observed in magnetars. 相似文献
234.
Chiaki Hikage Kazuya Koyama Takahiko Matsubara Tomo Takahashi Masahide Yamaguchi 《Monthly notices of the Royal Astronomical Society》2009,398(4):2188-2198
We study the effect of primordial isocurvature perturbations on non-Gaussian properties of cosmic microwave background (CMB) temperature anisotropies. We consider generic forms of the non-linearity of isocurvature perturbations which can be applied to a wide range of theoretical models. We derive analytical expressions for the bispectrum and the Minkowski Functionals for CMB temperature fluctuations to describe the non-Gaussianity from isocurvature perturbations. We find that the isocurvature non-Gaussianity in the quadratic isocurvature model, where the isocurvature perturbation S is written as a quadratic function of the Gaussian variable σ, S =σ2 −〈σ2 〉 , can give the same signal-to-noise ratio as f NL = 30 even if we impose the current observational limit on the fraction of isocurvature perturbations contained in the primordial power spectrum α. We give constraints on isocurvature non-Gaussianity from Minkowski Functionals using the Wilkinson Microwave Anisotropy Probe ( WMAP ) 5-year data. We do not find a significant signal of isocurvature non-Gaussianity. For the quadratic isocurvature model, we obtain a stringent upper limit on the isocurvature fraction α < 0.070 (95 per cent CL) for a scale-invariant spectrum which is comparable to the limit obtained from the power spectrum. 相似文献
235.
Yuta Nishibe Kazutaka Takahashi Mitsuhide Sato Taketoshi Kodama Shigeho Kakehi Hiroaki Saito Ken Furuya 《Journal of Oceanography》2017,73(4):463-478
The relationships between the spatiotemporal variation in phytoplankton community structure and environmental variables were investigated in the Kuroshio Extension (KE) region from winter to spring by analysing biomarker pigments. In winter, when the mixed layer was deep, phytoplankton communities were characterised by low biomass and a relatively high dominance of cryptophytes, followed by chlorophytes and pelagophytes. In spring, phytoplankton biomass generally increased with shoaling of the mixed layer. In April, when nitrate was not exhausted, chlorophytes became the most dominant group throughout the KE region, followed by cryptophytes. In May, in the south of the KE, phytoplankton biomass decreased with the depletion of nitrate and cyanobacteria dominated, whereas at the northern edge of the KE, phytoplankton biomass remained high. A predominance of diatoms occurred sporadically at the northern edge of the first ridge with a shallow mixed layer and an elevated nutricline. In contrast, the contribution of diatoms was low at the northern edge of the second ridge, despite high levels of nitrate and silicic acid, suggesting that factors other than macronutrient depletion limited diatom production. In general, the contribution of diatoms to the total phytoplankton biomass in the KE region was small in both winter (2.9%) and spring (16%). This study showed that the phytoplankton communities in the KE region during the spring bloom were generally composed of non-diatom phytoplankton groups, chlorophytes, cryptophytes, and prasinophytes. It is necessary to identify the roles of non-diatoms in grazing food chains to more accurately evaluate the KE as a nursery area for pelagic fish. 相似文献
236.
Satoko Takahashi Masao Saito Shigehisa Takakuwa Ryohei Kawabe 《Astrophysics and Space Science》2008,313(1-3):165-168
We have performed millimeter- and submilli- meter-wave survey observations using the Nobeyama millimeter array (NMA) and the
Atacama Submillimeter Telescope Experiment (ASTE) in one of the nearest intermediate-mass (IM) star-forming regions: Orion
Molecular Cloud-2/3 (OMC-2/3). Using the high-resolution capabilities offered by the NMA (∼several arcsec), we observed dust
continuum and H13CO+(1–0) emission in 12 pre- and proto-stellar candidates identified previously in single-dish millimeter observations. We unveiled
the evolutionary changes with variations of the morphology and velocity structure of the dense envelopes traced by the H13CO+(1–0) emission. Furthermore, using the high-sensitivity capabilities offered by the ASTE, we searched for large-scale molecular
outflows associated with these pre- and proto-stellar candidates observed with the NMA. As a result of the CO(3–2) observations,
we detected six molecular outflows associated with the dense gas envelopes traced by H13CO+(1–0) and 3.3 mm continuum emission. The estimated CO outflow momentum increases with the evolutionary sequence from early
to late type of the protostellar cores. We also found that the 24 μm flux increases as the dense gas evolutionary sequence.
We propose that the enhancement of the 24 μm flux is caused by the growth of the cavity (i.e. the CO outflow destroys the
envelope) as the evolutionary sequence. Our results show that the dissipation of the dense gas envelope plays an essential
role in the evolution of the IM protostars. The extremely high-sensitivity and high-angular resolution offered by ALMA will
reveal unprecedented details of the inner ∼50 AU of these protostars, which will provide us a break through in the classic
scenario of IM star/disk formation. 相似文献
237.
A dynamic method suitable for shipboard measurement of the partial pressure of CO2 exerted by a seawater sample has been developed. The system consists of a paddle-wheel-type gas-water equilibrator and an infrared gas analyzer. Since the system is open to the atmosphere at the in-take and the exhaust ends, it can be operated stably on shipboard conditions. A precision of ±2% has been obtained for shipboard measurement of pCO2. 相似文献
238.
Summary As a part of the Japanese earthquake prediction programme, deep borehole observation of the earth's crustal activities has been planned in and around Tokyo by the National Research Center for Disaster Prevention. The first place selected was in the city of Iwatsuki, about 30 km from the centre of Tokyo. Starting in 1970, the main construction was completed at the end of 1973. The tentative observation of micro-earthquakes and crustal movement by tiltmeters has been carried out since May, 1973. As expected, noise at the bottom of the hole (3500 m depth) is extremely small, about 1/1000–1/300 of that at the surface. We could, possibly, detect earthquakes with magnitudes greater than 2.0 within 50 km radius from the Iwatsuki observatory. 相似文献
239.
Afforestation in arid land is a promising method for carbon fixation, but the effective utili-zation of water is highly important and required. Thus, the evaluation of the amount of water perunit carbon fixed with the tree growth is required to minimize the amount of water supplied to theplants. In this research, a tree is regarded as a carbon fixation reactor with inflows of water andnutrients from roots, and CO2 as the carbon source from leaves with outflow of water vapor fromleaves and accumulation in the tree itself. In the process of photosynthesis and respiration nutri-tional elements are dissolved in water flow in trees. They do not flow out by these reactions, butare accumulated in trees. Thus, we have treated the behaviour of nutrients as a marker to evaluatethe water/carbon ratio. Assuming that nutrient concentration is constant in sap, and the differences in the ratios ofnutrient to carbon in living trees and dead (i.e. litter fall, etc.) are negiected, the ratio of the usedwater to fixed carbon is given as the ratio of nutrient to carbon in the tree body divided by the ratioof nutrient to water in sap. However, some nutrients are translocated and concentrated within thetree and some may be discarded through litter fall. Thus it is important to examine which nutrientelement is the most suitable as the tracer. In this paper, the results of the above method applied to Eucalyptus camaldulensis in semi-arid land of Western Australia are shown. The value of water requirement per unit carbon fixationdetermined from potassium balance is between 421 kg-H2O/kg-C for mature trees and 285kg-H2O/k9-C for young trees, while the values from calcium balance are much larger than these.The cause of the discrepancy between these values is discussed based on the measured elementconcentrations in sap and trees and the plant physiology. Finally, the actual average value throughthe life of a tree is suggested to fall between the two values. 相似文献
240.
H. Anawar K. Komaki J. Akai J. Takada T. Ishizuka T. Takahashi T. Yoshioka K. Kato 《Environmental Geology》2002,41(7):816-825
A stratigraphic profile of solid phase As was measured to investigate the diagenetic cycling of arsenic and related elements in fluvial sediments of the Meghna River delta plain. The distributions of Fe, Mn, and Al are typically characterized by surficial solid phase enrichment, and As is distributed down to 36.6 m showing similar alternate layers of maxima and minima with Fe, Mn and TOC, which reflects the diagenetic remobilization and periodical differences in source materials of As. Lithological characteristics and geochemical data suggest that elevated levels of As are found in organic-matter-rich clay and silty sand rather than sand samples, with occasionally enriched As content in iron-oxyhydroxide-coated sand grains. Arsenic demonstrates a positive and significant co-variation with total organic carbon in sediments, which suggests the important role of particulate and colloidal organic matter and biological activity in controlling the distribution of arsenic in the Bengal delta. However, the concentrations of Fe and Mn weakly correlate with As contents, whereas Al contents show no relationship with As. The results of this study suggest that reactive oxides or hydroxides of Fe and Mn, rather than Fe and Mn with other minerals, might control arsenic distribution. 相似文献