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41.
Availability of weather data at finer timescales such as hourly is vital in the application of dynamic physical and biological models. In this study, we have examined the suitability of various approaches (deterministic periodic versus stochastic) of disaggregating daily weather data into hourly data in the Cedar Creek watershed, TX, USA. We found the cosine function suitable to disaggregate daily maximum and minimum temperatures and wind speed data into respective hourly data. We also used a common logarithmic equation to compute vapor pressures from temperature data, and hence relative humidity (the ratio between actual and saturated vapor pressures multiplied by 100). Disaggregation following uniform distribution of daily rainfall over 24 h did not reproduce most statistical parameters computed from observed hourly rainfall data onsite. Conversely, both stochastic models formulated based on univariate (Hyetos) and multivariate (MuDRain) processes mimicked the measured hourly rainfall distributions very well. Overall, we found the MuDRain model superior, compared to other models to disaggregate daily rainfall data into hourly data. 相似文献
42.
We use the recently introduced concept of a ‘window’ of magnetic field strengths in which pulsars can be active to explain
the variation in morphology of supernova remnants. The striking difference between shell-type and filled-type remnants is
attributed to differences in he magnetic field strengths of the neutron stars left by the respective Supernovae. Field strengths
of a value permitting pulsar activity result in particle production and Crab-like centrally concentrated remnants. Other field
values lead to strong magnetic dipole radiation and consequent shell formation (e.g. Cas A). Several apparent inconsistencies concerning pulsar-supernova associations appear to find a logical explanation on
the basis of this hypothesis. 相似文献
43.
N. Bhandari S. V. S. Murty P. N. Shukla A. D. Shukla R. R. Mahajan M. M. Sarin G. Srinivasan K. M. Suthar M. S. Sisodia S. Jha A. Bischoff 《Meteoritics & planetary science》2002,37(4):549-563
Abstract— A stony meteorite fell at Itawa Bhopji, Rajasthan, India on 2000 May 30. This is the fifth recorded fall in a small area of Rajasthan during the past decade. The meteorite is an ordinary chondrite with light clasts in a dark matrix, consisting of a mixture of equilibrated (mainly type 5) and unequilibrated components. Olivine is Fa24–26 and pyroxene Fs20–22 but, within the unequilibrated components, olivine (Fa5–29) and low calcium pyroxene (Fs5–37) are highly variable. Based on petrographic studies and chemical analyses, it is classified as L(3–5) regolith breccia. Studies of various cosmogenic records, including several gamma‐emitting radionuclides varying in half‐life from 5.6 day 52Mn to 0.73 Ma 26Al, tracks and rare gases have been carried out. The exposure age of the meteorite is estimated from cosmogenic components of rare gases to be 19.6 Ma. The track density varies by a factor of ?3 (from 4 to 12 times 106/cm2) within the meteorite, indicating a preatmospheric body of ?9 cm radius (corresponding to a meteoroid mass of ?11 kg) and small ablation (1.5 to 3.6 cm). Trapped components in various rare gases are high and the solar component is present in the dark portion of the meteorite. Large excess of neutron‐produced 82Kr and 128Xe in both the light and the dark lithology but very low 60Co, indicating low neutron fluxes received by the meteoroid in the interplanetary space, are clear signatures of an additional irradiation on the parent body. 相似文献
44.
The linearized analysis of Cess and Srinivasan (1971) for thermal emission from lunar and Mercurian surfaces following a sudden eclipse has been extended to include two additional factors. One is the separate influence of scattering upon the radiative transport process within the surface material. The second is the effect of thermal conduction as an additional energy transport mechainsm. 相似文献
45.
With the availability of spatially distributed data, distributed hydrologic models are increasingly used for simulation of spatially varied hydrologic processes to understand and manage natural and human activities that affect watershed systems. Multi‐objective optimization methods have been applied to calibrate distributed hydrologic models using observed data from multiple sites. As the time consumed by running these complex models is increasing substantially, selecting efficient and effective multi‐objective optimization algorithms is becoming a nontrivial issue. In this study, we evaluated a multi‐algorithm, genetically adaptive multi‐objective method (AMALGAM) for multi‐site calibration of a distributed hydrologic model—Soil and Water Assessment Tool (SWAT), and compared its performance with two widely used evolutionary multi‐objective optimization (EMO) algorithms (i.e. Strength Pareto Evolutionary Algorithm 2 (SPEA2) and Non‐dominated Sorted Genetic Algorithm II (NSGA‐II)). In order to provide insights into each method's overall performance, these three methods were tested in four watersheds with various characteristics. The test results indicate that the AMALGAM can consistently provide competitive or superior results compared with the other two methods. The multi‐method search framework of AMALGAM, which can flexibly and adaptively utilize multiple optimization algorithms, makes it a promising tool for multi‐site calibration of the distributed SWAT. For practical use of AMALGAM, it is suggested to implement this method in multiple trials with relatively small number of model runs rather than run it once with long iterations. In addition, incorporating different multi‐objective optimization algorithms and multi‐mode search operators into AMALGAM deserves further research. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
46.
Boby Ignatius Muthukumarasamy Srinivasan Srinivasan Balakrishnan 《Ocean Science Journal》2011,46(3):145-154
The sandbird octopus Amphioctopus aegina (Gray, 1849) is one of the important octopod species in trawl catches in Mandapam waters (Palk Bay). The reproductive biology
of this species from these waters was studied from October 2001 to September 2002. In the majority of months(Jan–June), the
sex ratio was biased towards males. The ratios of males to females increased consistently with respect to weight Total weight
at first maturity were 78.78g for females and 40.8 g for males. Four maturity stags were recognized for females and two for
males. Maturation and spawning occur all year round, with a peak during October and another peak during January–February.
In males, no definite seasonal changes were observed in gonadosomatic index (GSI) values. In females there were two peaks
in GSI values during October and January–February. For individuals of a DML range of 67–85 mm fecundity varied between 2,962–8,820
oocytes. The average relative fecundity was estimated at 68 to 83 and the average number oocytes per gram of ovary were 488
to 539. 相似文献
47.
Abstract— The Rumuruti chondrites (R chondrites) constitute a new, well-established, chondrite group different from carbonaceous, ordinary, and enstatite chondrites. Most samples of this group are gas-rich regolith breccias showing the typical light/dark structure and consist of abundant fragments of various parent body lithologies embedded in a fine-grained, olivine-rich matrix. Most R chondrites contain the typical components of primitive chondrites including chondrules, chondrule and mineral fragments, sulfides, and rare calcium-aluminum-rich inclusions (CAIs). In Hughes 030, an interesting CAI consisting of abundant hibonite and spinel was found. Mg isotopic analyses revealed excess 26Mg in components of R chondrites for the first time. The hibonite grains with high Al/Mg values (∼1500 to 2600) show resolved 26Mg excess. The slope of the correlation line yields an initial 26Al/ 27Al = (1.4 ± 0.3) × 10−6, which is ∼40 times lower than the initial value measured in CAIs from primitive meteorites. The inferred difference in 26Al abundance implies a time difference of ∼4 million years for the closure of the Al-Mg system between CAIs from primitive chondrites and the Hughes 030 CAI. Based on mineralogy and the petrographic setting of the hibonite-rich CAI, it is suggested that 4 million years reflect the time interval between the formation of the CAI and the end of its secondary alteration. It is also suggested that most of this alteration may have occurred in the nebula (e.g. Zn- and Fe-incorporation in spinels). However, the CAI could not have survived in the nebula as a free floating object for a long period of time. Therefore, the possibility of storage in a precursor planetesimal for a few million years, resetting the magnesium-aluminum isotopic system, prior to impact brecciation, excavation, and accretion of the final R chondrite parent body cannot be ruled out. 相似文献
48.
A high galactic latitude HI 21 cm-line absorption survey using the GMRT: I. Observations and spectra
Rekhesh Mohan K. S. Dwarakanath G. Srinivasan 《Journal of Astrophysics and Astronomy》2004,25(3-4):143-183
We have used the Giant Meterwave Radio Telescope (GMRT) to measure the Galactic HI 21-cm line absorption towards 102 extragalactic
radio continuum sources, located at high (|b| > 15°) Galactic latitudes. The Declination coverage of the present survey is δ}> - 45°. With a mean rms optical depth of ∼ 0.003, this is the most sensitive Galactic HI 21-cm line absorption survey to
date. To supplement the absorption data, we have extracted the HI 21-cm line emission profiles towards these 102 lines of
sight from the Leiden Dwingeloo Survey of Galactic neutral hydrogen. We have carried out a Gaussian fitting analysis to identify
the discrete absorption and emission components in these profiles. In this paper, we present the spectra and the components.
A subsequent paper will discuss the interpretation of these results. 相似文献
49.
Rekhesh Mohan K. S. Dwarakanath G. Srinivasan 《Journal of Astrophysics and Astronomy》2004,25(3-4):185-201
We have carried out a sensitive high-latitude (|b| > 15°) HI 21 cm-line absorption survey towards 102 sources using the GMRT. With a 3σ detection limit in optical depth of
∼ 0.01, this is the most sensitive HI absorption survey. We detected 126 absorption features most of which also have corresponding
HI emission features in the Leiden Dwingeloo Survey of Galactic neutral Hydrogen. The histogram of random velocities of the
absorption features is well-fit by two Gaussians centered at V1sr ∼ 0 km s−1 with velocity dispersions of 7.6 ± 0.3 km s−1 and 21 ± 4 km s−1 respectively. About 20% of the HI absorption features form the larger velocity dispersion component. The HI absorption features
forming the narrow Gaussian have a mean optical depth of 0.20 ± 0.19, a mean HI column density of (1.46 ± 1.03) × 1020 cm−2, and a mean spin temperature of 121 ± 69 K. These HI concentrations can be identified with the standard HI clouds in the
cold neutral medium of the Galaxy. The HI absorption features forming the wider Gaussian have a mean optical depth of 0.04
± 0.02, a mean HI column density of (4.3 ± 3.4) × 1019 cm−2, and a mean spin temperature of 125 ± 82 K. The HI column densities of these fast clouds decrease with their increasing random
velocities. These fast clouds can be identified with a population of clouds detected so far only in optical absorption and
in HI emission lines with a similar velocity dispersion. This population of fast clouds is likely to be in the lower Galactic
Halo. 相似文献
50.
A 21 cm absorption measurement over a long path length free of the effects of differential galactic rotation indicates the
existence of two distinct cloud populations in the plane. One of them consisting of cold, dense clouds has been well studied
before. The newly found hot clouds appear to be at least five times more numerous. They have a spin temperature of ~ 300 K,
an rms velocity of ~ 35 km s-1, twice the total mass, and hundred times the kinetic energy of the cold clouds. Over long path lengths, the hot clouds haveN
H/kpc ~ 2 X 1021 cm-2 Kpc-1, and are estimated to have individual column densities ≤ 1020 cm-2. We propose that they are shocked clouds found only within supernova bubbles and that the cold clouds are found in the regions
in-between old remnants, immersed in an intercloud medium. We conclude that the solar neighbourhood must be located between
old supernova remnants rather than within one. 相似文献