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451.
This study deals with the assimilation of TOPEX altimeter-derived sea level variability in a reduced-gravity model of the northwestern Indian Ocean. The assimilation has been done using variational assimilation method with adjoint technique. A cost function representing the misfit between the model and the data is minimized with the model equations acting as constraints. The initial conditions of the model are used as control parameters and the best-fit initial conditions are determined as a result of minimization carried out using a variable-storage quasi-Newton method. Experiment has been done with 10 days' cycle-averaged data of TOPEX. Assimilation for 10 days and 20 days has been performed and it has been seen that 20 days' assimilation of satellite data provides better results. 相似文献
452.
453.
Recent observations of the rotation curves of large disk galaxies of all Hubble-types have shown that they possess flat or slowly rising rotation curves up to large distances from the centre. It has been suggested here that such rotation curves are understood under normal fluid dynamical considerations provided that viscous (and/or magnetic) transfer of mass and angular momentum from inner to outer regions of these galaxies is efficient. Flow of gas from halo to the disk in regions close to the axis of rotation is also suggested. The existence of rising rotation curves in some galaxies with varying gradients and flat rotation curves in others suggest that probably these galaxies are not coeval. The formers are probably of more recent origin. 相似文献
454.
S. K. Ghosh B. Mookerjea T. N. Rengarajan S. N. Tandon R. P. Verma 《Journal of Astrophysics and Astronomy》2001,22(2-3):173-185
Three Galactic star forming regions associated with W3(OH), S209 and S187 have been simultaneously mapped in two trans-IRAS
far infrared (FIR) bands centered at ≈140 and 200μm using the TIFR 100 cm balloon borne FIR telescope. These maps show extended
FIR emission with structures. The HIRES processed IRAS maps of these regions at 12, 25, 60 & 100 ìm have also been presented
for comparison. Point-like sources have been extracted from the longest waveband TIFR maps and searched for associations in
the other five bands. The diffuse emission from these regions have been quantified, which turns out to be a significant fraction
of the total emission. The spatial distribution of cold dust (T < 30 K) for two of these sources (W3(OH) & S209), has been
determined reliably from the maps in TIFR bands. The dust temperature and optical depth maps show complex morphology. In general
the dust around S209 has been found to be warmer than that in W3(OH) region. 相似文献
455.
456.
Prosenjit Ghosh S. K. Bhattacharya A. M. Dayal J. R. Trivedi M. Ebihara M. M. Sarin A. Chakrabarti 《Journal of Earth System Science》2002,111(2):87-93
Syngenetic carbonate nodules constitute an interesting feature of the glaciogene sediments of various Talchir basins in peninsular
India. Petrographic, cathodoluminescence and sedimentary results suggest that many of these nodules contain primary carbonate
precipitates whose geochemical signatures can be used for determining environment of deposition and provenance of the sediments
and drainage source. Several nodules were collected from Gondwana basins of east-central India and analyzed for stable carbon
and oxygen isotope ratios, REE and trace element composition, and Sr isotope ratio. The mean δ18O and δ13C values of the calcites in the nodules are — 19.5% and-9.7% (w.r.t. PDB) respectively suggesting a freshwater environment
(probably lacustrine) for formation of these objects. Trace element ratios (Eu/Eu * and La/Yb) of the nodule samples show
that the source of the sediments in the Damodar valley basin was the granites, gneisses and intrusives in the Chotanagpur
region. The sediments in the Mahanadi valley were derived from granulites, charnockites and granites of the eastern ghat region.
The Sr concentration of the carbonate phase of the nodules is low, ranging from 10–60 ng/g. The87Sr/86Sr ratios of the samples from the west Bokaro basin and Ramgarh basin vary from 0.735 to 0.748 (mean: 0.739) and from 0.726
to 0.733 (mean: 0.730) respectively. These values are consistent with our proposition that water of these basins drained through
the granitic rocks of the Chotanagpur region. In contrast, the87Sr/86Sr ratios of the samples from the Talchir basin (Type area) of Mahanadi valley vary from 0.718 to 0.723 (mean: 0.719). These87Sr/86Sr ratios are close to those of the granulites in the adjoining eastern ghat belt suggesting that area as the drainage source. 相似文献
457.
The progressive deformation of the Singhbhum Shear Zone (SSZ) involved the initiation of a mylonitic foliation, its deformation
by three generations of reclined folds and superposition of two later groups of folds, i.e., a group of asymmetric folds with
subhorizontal or gently plunging axes and a group of gentle and open, transverse and more or less upright folds. The occurrence
of sheath folds and U-shaped deformed lineations indicate that the reclined folds were produced by rotation of fold hinges
through large angles. The total displacement along the SSZ was compounded of displacements along numerous mesoscopic shear
zones. The cleavages in the shear lenses and the mesoscopic shear zones cannot be distinguished as C and S surfaces. They
have the same kinematic significance and were produced by ductile deformation, although there were localized discontinuous
displacements along both sets,-of cleavages. A mylonitic foliation had formed before the development of the earliest recognizable
folds. Its time of formation and folding could be synchronous, diachronous or partly overlapping in time in the different
domains of the SSZ. 相似文献
458.
Dilip K. Mukhopadhyay Tamal K. Ghosh Bidyut K. Bhadra Deepak C. Srivastava 《Journal of Earth System Science》1997,106(4):197-207
The rocks of the Jutogh Group in the Himachal Himalayas and their equivalents elsewhere are now considered to represent a
several km thick crustal scale ductile shear zone, the so called Main Central Thrust Zone. In this article we present a summary
of structural and metamorphic evolution of the Jutogh Group of rocks in the Chur half-klippe and compare our results with
those of Naha and Ray (1972) who worked in the adjacent Simla klippe.
The deformational history of the Jutogh Group of rocks in the area around the Chur-peak, as deduced from small-scale structures,
can be segmented into: (1) an early event giving rise to two sets of very tight to isoclinal and coaxial folds with gentle
dip of axial planes and easterly or westerly trend of axes, (2) an event of superimposed progressive ductile shearing during
which a plethora of small-scale structures have developed which includes successive generations of strongly non-cylindrical
folds, several generations of mylonitic foliation, extensional structures and late-stage small-scale thrusts, and (3) a last
stage deformation during which a set of open and upright folds developed, but these are regionally unimportant. The structure
in the largest scale (tens of km) can be best described in terms of stacked up thin thrust sheets. Km-scale asymmetric recumbent
folds with strongly non-cylindrical hinge lines, developed as a consequence of ductile shearing, are present in one of these
thrust sheets. The ductile shearing, large-scale folding and thrusting can be related to the development of the Main Central
Thrust Zone. The microstructural relations show that the main phase of regional low-to medium-grade metamorphism (T ≈ 430–600°C andP ≈ 4.5–8.5 kbar) is pre-kinematic with respect to the formation of the Main Central Thrust Zone. Growth zoned garnets with
typical bell-shaped Mn profiles and compensating bowl-shaped Fe profiles are compatible with this phase of metamorphism. Some
of the larger garnet grains, however, show flat compositional profiles; if they represent homogenization of growth zoning,
it would be a possible evidence of a relict high-grade metamorphism. The ductile shearing was accompanied by a low-greenschist
facies metamorphism during which mainly chlorite and occasionally biotite porphyroblasts crystallized. 相似文献
459.
K. K. Ghosh 《Astrophysics and Space Science》1988,147(1):91-106
Rapid observations of H profiles of eight Be stars have been obtained and it is found that rapid (in a time-scale of 4 to 6 minutes) and irregular variations of total emission strength of H line are present in these stars. It has been suggested that these variations may be due to the material circulation in the envelope of Be stars. 相似文献
460.
R R Navalgund V Jayaraman A S Kiran Kumar Tara Sharma Kurien Mathews K K Mohanty V K Dadhwal M B Potdar T P Singh R Ghosh V Tamilarasan T T Medhavy 《Journal of the Indian Society of Remote Sensing》1996,24(4):207-237
Although data available from various earth observation systems have been routinely used in many resource applications, however there have been gaps, and data needs of applications at different levels of details have not been met. There is a growing demand for availability of data at higher repetivity, at higher spatial resolution, in more and narrower spectral bands etc. Some of the thrust areas of applications particularly in the Indian context are;
- Management of natural resources to ensure sustainable increase in agricultural production,
- Study the state of the environment, its monitoring and assessment of the impact of. various development actions on the environment,
- Updating and generation of large scale topographical maps.
- Exploration/exploitation of marine and mineral resources and
- Operational meteorology and studying various land and oceanic processes to understand/predict global climate changes.
- Moderate spatial resolution (l50-300m), high repetivity (2 Days), minimum set of spectral bands (VIS, NIR, MIR. TIR) full coverage.
- Moderate to high spatial resolution (20-40m), high repetivity (4-6 Days), spectral bands (VIS, MR, MIR, TIR) full coverage.
- High spatial resolution (5-10m) muitispectral data with provision for selecting specific narrow bands (VIS, N1R. MIR), viewing from different angles.
- Synthetic aperture radar operating in at least two frequencies (C, X, Ku), two incidence angles/polarizations, moderate to high spatial resolution (20-40m), high repetivity (4-6 Days).
- Very high spatial resolution (1-2m) data in panchromatic band to provide terrain details at cadastral level (1:10,000).
- Stereo capability (1-2m height resolution) to help planning/execution of development plans.
- Moderate resolution sensor operating in VIS, NIR, MIR on a geostationary platform for observations at different sun angles necessary for the development of canopy reflectance inversion models.
- Diurnal (at least two i.e. pre-dawn and noon) temperature measurements of the earth surface.
- Ocean colour monitor with daily coverage.
- Multi-frequency microwave radiometer, scatterometer. altimeter, atmospheric sounder, etc.